Manual small incision cataract surgery: An ergonomic solution to tackle cataract backlog and challenging situations

Abstract

Cataract surgery is still the most common surgery performed worldwide. It has evolved tremendously in terms of incision, from 12 mm to 1.8 mm, in terms of capsulotomy from envelope type to automated capsulorhexis, and from rigid intraocular lens to foldable intraocular lenses. Manual small incision cataract surgery (MSICS) remains a valuable technique, particularly in rural and underserved areas, due to its cost-effectiveness and simplicity. Its low logistics and favorable outcomes are particularly useful for managing the cataract backlog in developing countries. This review highlights the history and evolution of MSICS, and the reasons for the advent and popularity of this technique, especially in developing countries. It reviews the various recent modifications of the technique, for example, from a superior incision approach to temporal incision to customized MSICS, 2 mm MSICS, and astigmatism-correcting MSICS. It provides an overview of its applicability in complicated scenarios (viz., small pupil, compromised cornea, pseudoexfoliation, subluxated cataract, etc.). It briefly reviews the clinical trials on MSICS and its comparison with phacoemulsification. Finally, the review emphasizes why every ophthalmic surgeon must know MSICS, its relevance in postgraduate teaching, and the role of MSICS simulators for the same. Overall, the review presents a comprehensive picture of the present status of this technique in the surgical armamentarium of ophthalmology.

Key Words: Manual small incision cataract surgery; Astigmatism; Cataract; Complication; Cost-benefit; Efficiency; Teaching

Core Tip: Cataract surgery is the most common surgery performed worldwide. It has evolved tremendously in terms of incision, from 12 mm to 1.8 mm, in terms of capsulotomy from envelope type to automated capsulorhexis, and from rigid intraocular lens to foldable intraocular lenses. Manual small incision cataract surgery remains a valuable technique, particularly in rural and underserved areas, due to its cost-effectiveness and simplicity. Its low logistics and favorable outcomes are particularly useful for managing the cataract backlog in developing countries. This review provides a comprehensive picture of the current status of this technique in the surgical armamentarium of ophthalmology.

INTRODUCTION

Cataracts are responsible for the greatest share of the global burden of blindness and moderate-severe visual impairment. Approximately 50% of all blind eyes in low- and middle- income countries and about 5% in the first world are affected by cataracts[1,2]. Age-standardized pooled prevalence of cataract is about 17.2%, with a large proportion of these eyes suffering from poor visual acuity for distance and often for near, poor contrast, glare, colored haloes, photophobia, and discomfort in daily activities, often leading to psychosocial distress and impaired quality of life[3-5].

Globally, the disability adjusted life years (DALYs) due to cataracts have increased from 3.5 million (1990) to 6.7 million (2019). The age-standardized DALY rates due to cataract have decreased from 93.17 (1990) to 82.94 (2019), with an overall younger population now affected by cataract and opting for cataract surgeries[6]. The effects are compounded by various additional risk factors, including particulate matter pollution, smoking, a rising incidence of impaired glucose tolerance, and a higher body mass index of the younger population[7]. These problems, when presented in resource-deficient settings such as the developing world, pose significant challenges for ophthalmic care providers to deliver cost-effective options for visual recovery from cataracts while preserving the standards of safety and sterilization[8]. In addition, younger patients have more visual demands, leading to expectations of rapid visual recovery with reduced dependence on spectacles after cataract surgery[9]. The impact of these demands both on costs and carbon footprint have prompted the exploration of economically and environmentally sustainable alternatives to phacoemulsification surgery (“phaco”), which is currently the most commonly performed surgery for the management of visually significant cataract[10,11].

WHAT IS MSICS

Manual small incision cataract surgery (MSICS) is an alternative to phaco, involving a shelved trapezoidal corneoscleral incision for cataract lens removal, followed by intraocular lens (IOL) implantation to correct intraoperative aphakia. First described in the era of traditional extra- and intra-capsular cataract surgeries which were performed through large limbal incisions, MSICS has evolved to become the preferred option for extraction of the cataractous lens as a whole while retaining the capsular bag[12]. Even with increasing rates of phaco, MSICS continues to be relevant even today, and is advancing by leaps and bounds due to tremendous innovations in this technique[13]. Phaco and MSICS are regarded as complementary to each other in the repertoire of the modern cataract surgeon[14,15]. Experienced surgeons achieve comparable refractive outcomes and complication rates in their phaco and MSICS procedures, while exploiting the several advantages of MSICS in providing safe surgery in difficult situations, even in resource-scarce settings[16,17].

WHY MSICS

MSICS, with its proven track record of economic and environmental sustainability, may well be the answer to the woes of the modern era. MSICS has evolved over the years to become a fast, sutureless, convenient, resource-efficient, and carbon-neutral surgical procedure[18,19]. Whereas it was traditionally propagated to have limited application, modern MSICS can accommodate all of the requirements of cataract surgery as a true refractive surgery, from customized astigmatism correction to induced multifocality by manipulation of corneal incision morphology, and even multifocal IOL implantation without the need for any machine[20,21]. Similar to phaco, MSICS also has the potential to be combined with other medical and surgical procedures as well as alternative medical therapies[22,23].

The academic importance given to MSICS in recent published literature is miniscule compared to that given to phaco[15]. This review highlights the history and evolution of MSICS, and the reasons for the advent and popularity of this technique, especially in developing countries. It reviews the various recent modifications of the technique, for example, from a superior incision approach to temporal incision to customized MSICS, 2 mm MSICS and astigmatism correcting MSICS. It provides an overview of the applicability of MSICS in complicated scenarios (viz. small pupil, compromised cornea, pseudoexfoliation, subluxated cataract, coloboma, etc)[24]. It briefly reviews the clinical trials on MSICS. Finally, this review emphasizes why every ophthalmic surgeon must know MSICS, its relevance in post-graduate teaching and the role of MSICS simulators for the same.

SEARCH METHODOLOGY

The aim of this review is to put forth a comprehensive picture of the present status of the MSICS technique in the surgical armamentarium of ophthalmology. The objectives include an iterative review and analysis of literature to bring out the historical aspects of MSICS as well as various modifications and improvements achieved by surgeons worldwide, and how they have impacted the practice and outcomes of the MSICS technique as placed in perspective to phaco and other cataract extraction procedures, especially in the developing world. To achieve this, PubMed, EMBASE, Scopus, MEDLINE, Cochrane and Google Scholar were searched with the terms as mentioned in Table 1. These broad criteria amounted to a total of 12684 articles retrieved.

Table 1 Search terms for the present review.

Number	Search term
1	Manual small incision cataract surgery
2	Cataract surgery
3	Cataract extraction
4	Ocular anesthesia
5	Sclerocorneal tunnel
6	Capsulotomy
7	Hydrodissection
8	Hydroprolapse
9	Nuclear rotation
10	Viscoelastic substances
11	Viscoexpression
12	Snare
13	Nucleofractis
14	Nuclear bisection
15	Trisection
16	Cortex
17	Hydroimplantation
18	Irrigation
19	Aspiration
20	Posterior capsule rupture
21	Vitreous loss
22	Endophthalmitis

After removing duplicates, and excluding articles regarding only the intracapsular and conventional extracapsular cataract extraction (ECCE), and phaco, and considering only the articles with full texts available in the English language, 1566 articles were found to pertain to MSICS. Five independent reviewers went through the abstracts and full texts of all the articles, and shortlisted 116 articles for their relevance and uniqueness based on reference citation analysis and level of evidence. PRISMA flow diagram of the methodology is shown in Figure 1.

Figure 1 PRISMA of the methodology. ECCE: Extracapsular cataract extraction; ICCE: Intracapsular cataract extraction.

HISTORY OF MSICS

Prerequisites for a successful MSICS include a cooperative patient, a skilled surgeon, adequate anesthesia, full mydriasis, good instrumentation, and sterile environmental conditions[25]. The techniques described classically involved a combination of these in an inflexible manner. However, with experience, many modifications were made and the technique today is quite different from what it was in the last century.

CLASSICAL MSICS TECHNIQUES

In the initial days, a retrobulbar block was employed for anesthetizing the eye prior to any intraocular intervention. A combination of lignocaine 2%, bupivacaine 0.5%, and hyaluronidase 1:1500 was classically used, and 2-3 mL of the solution was injected into the retrobulbar space, i.e. within the cone of the rectus muscles. Considering the disadvantages of a retrobulbar block, like prolonged anesthesia, risk of retrobulbar hematoma and optic nerve injury, it was almost completely replaced by the peribulbar block, with injections at the junction of the medial and middle thirds of the eyelid in the upper fornix nasally, and the junction of the middle and lateral thirds of the eyelid in the lower fornix temporally[26].

For dissection of the superior limbus, the eye needs to be turned from the primary to a partially infraducted position. This used to be achieved using a superior rectus bridle suture (Figure 2A) with a monofilament nylon, sterilized braided cotton or silk thread, mounted on an eyed or eyeless needle, looped posterior to the superior rectus muscle blindly, and fixed onto the drape using a clamp (Figure 2A). This is especially useful in deep set eyes with prominent superior orbital ridges. Complications at this stage included subconjunctival hemorrhage, muscle hematoma or inadvertent injury to the eyeball. An increased incidence of post-cataract surgery blepharoptosis has also been attributed to the superior rectus bridle suture[27].

Figure 2 Steps of manual small incision cataract surgery. A: Superior rectus bridle suture; B: Superior conjunctival peritomy; C: Scleral groove (dashed lines estimate the extent of Koch’s Funnel); D: Sclerocorneal tunnel dissection; E: Keratome entry; F: Continuous curvilinear capsulorhexis; G: Hydrodissection; H: Nuclear rotation and prolapse; I: Nuclear delivery by viscoexpression; J: Irrigation and aspiration by simcoe cannula; K: Intraocular lens implantation; L: Cautery to repose the conjunctiva; M: Sideport hydration.

In the classically described MSICS technique, a superior fornix-based conjunctival flap is raised (“peritomy”, Figure 2B) and monopolar heat or bipolar electric cautery is applied to stop bleeding from the scleral bed[28]. The tunnel incision is made in the superior or superotemporal region. The sclerocorneal tunnel is a secure valvular incision that is well covered with the conjunctiva. It is a triplanar incision due to which the inner lip (shelf) becomes self-sealing[29]. Externally located on the mid-limbal line, it traverses the Schwalbe’s line internally, thus avoiding damage to the trabecular meshwork which lies more posteriorly[12]. It is regarded as that component of the MSICS technique which requires the most dexterity on the part of the surgeon, and several variations have been described. It consists of the following three subcomponents.

The external mid-limbal scleral groove or incision reaches almost a half-scleral depth in order to begin the plane for the sclerocorneal tunnel[14,30]. A straight linear incision or a smile shaped incision was initially described. A straight line with backward cuts on either side (after Blumenthal), or a chevron incision was also described for the same, the latter having least astigmatic effect (Figure 3). These incisions are made to lie in a zone called the Koch’s Funnel wherein they do not cause considerable astigmatism upon healing (Figure 2C)[31,32]. The incision length was described to be approximately 6-8mm for different grades of cataract, and to accommodate the rigid polymethylmethacrylate (PMMA) IOL with optic diameter of approximately 6 mm.

Figure 3 Various incision designs in manual small incision cataract surgery. A: Frown; B: Straight; C: Smile; D: Straight with Blumenthal back cuts; E: Chevron; F: W-shaped or M-shaped incision for manual small incision cataract surgery with trabeculectomy.

The sclerocorneal dissection is carried out parallel to the plane of the sclerocornea, at one-third to half-depth to create a 1-1.25 mm dissection in the sclera and a similar tunnel width in the clear cornea to achieve a valvular nature (Figure 2D). A crescent knife is classically described to be used for this purpose, cutting while coming outward, tilting the blade on either side of the lateral tunnel by 45 degrees to follow the contour of the globe. The dissection is advanced 1-1.25 mm into the corneosclera on both sides to form a funnel like configuration with side pockets[30]. This yields an external wound size of 6-8 mm but internal (corneal) entry wound about 2.5 mm larger to accommodate the full width of the nucleus[29,33,34].

The internal entry wound is made using a keratome (Figure 2E). The entry is initially made centrally with the sharp keratome tip pointing downwards to prevent Descemet’s membrane detachment. Then the entry is extended on either side, cutting while going inward to maintain the plane, the entire internal entry being approximately parallel to the limbus, thereby forming an overall trapezoidal section[29,34].

A 15-number Bard-Parker blade is classically used for the scleral incision, but a crescent knife, keratome or hockey-stick knife may also be used. In the earliest adaptation of the technique in resource-poor settings in India, a piece of sterilized shaving blade would be held firmly with forceps and broken using a blade-breaker, then bent and held in a blade-holder to be used for tunnel construction.

Anterior capsulotomy removes the central part of the anterior capsule, which is the barrier to access the lens material from the anterior chamber (AC). For this purpose, a side-port is made and the anterior capsule is stained with trypan blue dye under an intracameral air bubble. While a good capsular staining helps in good visualization of the same during intraocular procedures, the dye also changes the texture and fragility of the anterior capsule, making the capsulotomy more controlled. It can be performed before or after the opening of the internal entry wound.

Capsulotomy is traditionally performed under cover of a viscoelastic substance like 2% hydroxypropylmethyl cellulose, which maintains the AC, tamponades the anterior capsule and prevents uncontrolled fluttering or runaway of the capsular flaps and tags. Earlier reports showed the success of an envelope technique wherein approximately U- or V-shaped cuts on the anterior capsule were fashioned like the flap of an envelope, which gave sufficient access to extract the lens matter and implant the IOL, but showed complications like postoperative dyscoria, IOL tilt, and decentration. Can-opener capsulotomy was thus resorted to. An approximately circular opening with ragged edges is fashioned using a cystitome, but it could be performed in various shapes depending upon the preference of the surgeon (Figure 4). While suitable for most MSICS cases, it often results in several capsular tags which are at risk of runoff to the periphery if the AC is not maintained. Thus, can opener capsulotomy may be risky in the hands of beginners. The manual continuous curvilinear capsulorhexis is thus the preferred technique for anterior capsulotomy (Figure 2F). An adequately sized capsulorhexis is warranted, centered on the visual axis for optimum outcomes. Studies have found altered effective lens position in inadequately sized capsulotomies, dysphotopsias and compromised retinal images in decentered capsulotomies, and posterior capsule wrinkling and opacification (PCO) in large capsulotomies[35].

Figure 4 Various techniques and shapes of anterior capsulotomy in manual small incision cataract surgery. A: Envelop, B: Can opener; C: Christmas tree; D: Square; E: D-shaped; F: Continuous curvilinear capsulorhexis (preferred).

Hydrodissection is performed using a Rycroft cannula, injecting small aliquots of fluid below the anterior capsular rim, thereby causing anteroposterior waves of fluid free the cortico-capsular adhesions (Figure 2G). In dense nuclei, this may not be required as the cortical adhesions are flimsy, and are dissected easily on nuclear manipulation. With the combination of an adequate amount of fluid and an adequately sized anterior capsulotomy relative to the size of the nucleus, the nuclear mass can easily be prolapsed into the AC by this maneuver alone (“hydroprolapse”). In other cases, the nucleus can be “wheeled out” by lifting one pole with one or two blunt instruments such as Sinskey hooks, ball point manipulators or cannulas, and progressively rotating the nucleus while lifting anteriorly like a tire changer’s rolling tire technique (Figure 2H)[36]. In the earliest techniques, this step was often omitted if a can-opener capsulotomy was performed in selected cases, the nucleus being directly lifted in the AC by a Sinskey hook[37].

The AC is filled with viscoelastic substance to raise the intracameral pressure, push down the posterior capsule and coat the corneal endothelium. A dispersive viscoelastic like hydroxypropyl methylcellulose is most suitable for the purpose. Nuclear delivery is achieved in toto through the sclerocorneal tunnel, aided by viscoelastic pressure (Figure 2I), blunt irrigating instruments such as a cannula or vectis. A serrated wire vectis may also be equally effective. Early trends for smaller incisions in MSICS were matched with increasing adoption of nuclear fragmentation techniques. Nuclear bisection and trisection were described in the tunnel whereby remaining nuclear fragments were oriented with the long axis in the median of the tunnel length, allowing easy extraction using hydro- or viscoexpression or a vectis, aided by pressure on the posterior lip of the incision. Nuclear division inside the AC (“manual phacofragmentation”) had been described by Kelman in 1967 using Ringer forceps, and was further promoted by Kansas. Suture loops were described to bisect and trisect the nucleus in the AC-the early works of Keener and Shah made popular the snare-assisted technique for nucleofractis[38]. Other techniques included nucleosuction with a modified Simcoe cannula, phacosandwich technique (capturing the lens mass between a sinskey hook above and a vectis below), and various nuclear debulking techniques. The nuclear fragments are then removed in the usual manner.

Nuclear matter removal under fluid pressure has also been very popular. Various irrigating cannulas were described for pushing balanced salt solution (BSS) into the AC, thereby expressing the nucleus out[39]. Blumenthal introduced the use of AC maintainer (ACM) in his technique of MSICS for continuously maintaining the AC using gravity-fed fluid and aided nucleus delivery by pushing it out once the incision was held open by a sheet glide inserted beneath the nucleus and its outer end tapped[40]. ACM is a hollow sterile surgical steel tube (0.9 mm outer diameter and 0.65 mm inner diameter) inserted at one of the side ports, preferably on the temporal side. The steel tube is attached by a sterile pipe to a BSS bottle suspended 50-60 cm above eye level[41]. It is also possible to do manual phacofragmentation even under Blumenthal’s technique with ACM.

An irrigation-aspiration Simcoe cannula is used to clear the cortex, with a sterilized glass bottle containing BSS providing gravity-fed irrigation, and a 5 mL syringe connected to the aspiration channel (Figure 2J). If the ACM is used, irrigation need not be connected to the cannula, and a single port aspiration cannula may be used. Implantation of a rigid, monofocal PMMA IOL in the capsular bag completes the procedure (Figure 2K) followed by removal of the viscoelastic substance, optional closure of the conjunctiva by electrocautery (Figure 2L) and hydration of the side-port (Figure 2M). The self-sealing incision usually requires no sutures, but application of one or two sutures, if needed, may reduce the astigmatic effect of the incision.

EVOLUTION OF TECHNIQUES

Modern MSICS is fast, efficient and safe-only a few minutes in duration in the hands of experienced surgeons (Video). There have been several modifications and innovations described for each step of the procedure, that altered the complete scenario of cataract surgery making MSICS truly a surgical technique of the future[42].

Anesthesia

Prolonged anesthesia and full akinesia of the eye to be operated are no longer required. In the preoperative area, proparacaine (0.5%) is instilled once and supplemented with lignocaine jelly (2%) after a while. No sedation is employed. Constant surgeon–patient communication is maintained, allaying the patient’s apprehensions. A small piece of sterile gauze soaked in lignocaine may be applied to the area before scleral dissection. If the patient complains of pain, then 0.75 mL of 2% lignocaine is infused into the subtenon space using a blunt cannula[43]. Supplementation can be given at any stage of surgery if required. Intracameral 0.5 mL preservative-free lignocaine is irrigated into the AC[43]. Some cooperative patients are able to tolerate the procedure in topical anesthesia, while for some uncooperative ones, a peribulbar block is still used[44]. General anesthesia is still required for patients with psychological infirmities. Levobupivacaine and ropivacaine are other drugs recently introduced for infiltration, mainly for subtenon and peribulbar anesthesia.

Pupil dilation

While a full pupillary dilation is still ideal for all MSICS procedures, the advent of intracameral mydriatic pharmacologic agents as well as pupil dilation devices and speculums have diminished the mandate for prior pupillary dilation. For intracameral use, a commercially available combination of tropicamide, phenylephrine and lignocaine is commonly used[45]. Pupil dilation devices such as the B-Hex ring have been successfully used in various cases with small and rigid pupils[46].

No bridle suture

The superior rectus bridle suture has been done away with. Infraduction of the eye is now achieved by fixation of the eyeball using a forceps in the non-dominant hand. Sometimes, a partial-thickness posterior scleral groove is made posterior to the sclerocorneal tunnel to aid the grip of the forceps and prevent slippage of the fixation point. MSICS by a temporal approach does not require a rectus suture at all due to adequate exposure, avoiding the brow or nasal prominences. It is thus the preferred technique in deep set eyes[47].

Peritomy

Conjunctival peritomy is also not done by many surgeons who find it faster to approach the sclera transconjunctivally. In addition, the incision and tunnel are increasingly being made without the use of cautery on the scleral vessels, because the cells, growth factors, nutrients, and cytokines in the blood result in a theoretically more natural healing response.

Sclerocorneal tunnel

The frown incision for MSICS was described by Singer and is the most popular technique today[48]. It results in an approximately trapezoidal tunnel with side-pockets to accommodate large lens masses. Modifications of the incision are shown in Figure 3. For beginners, novel stamps have been developed to aid the visualization of the approximate limits of the incision or trapezoid to make a consistent tunnel[49,50]. Larger and wider tunnels have been described. For example, the extra-large temporal tunnel cataract extraction procedure consists of a 8-10 mm large modified MSICS sclerocorneal tunnel 4.5-5 mm from the limbus[51]. A combination of two adjoining frown-shaped incisions, a combined large sclerocorneal tunnel and an almost 6-clock hour internal keratome entry has been used in Mohanta’s double SICS technique, also called the large incision cataract surgery technique. After nuclear removal, the tunnels are apposed with only three 10-0 monofilament nylon sutures – one at the vertex of the two frown incisions, and one at the center of each tunnel. This allows an internal opening to accommodate the largest of lens masses, thereby making the technique effective to manage the most challenging nuclei of cataracta brunescens and nigra.

The sclerocorneal tunnel is now customized according to astigmatism of the patient, and a mix of factors are considered while predicting the astigmatic effect thus obtained - the incision location, size and shape, configuration of the tunnel, pre-existing ocular pathology, and whether sutures are used[30]. The term surgically-induced astigmatism (SIA) has now been transformed to surgically corrected astigmatism by custom designing of the incision according to the pre-existing corneal astigmatism (total keratometry) as measured on optical biometers, and intraoperative estimation of corneal distortion by keratometric software analyzing the shape of a ring projected onto the cornea[14,52]. The frown incision has been exaggerated to an inverted U-shape to enhance the delivery of nuclei through incisions of 2 mm chord length, combined with a phacofracture technique[42,53].

MSICS can be done through a 6 mm curvilinear clear corneal tunnel, but it was found that SIA is significantly higher in clear corneal MSICS than in sclero-corneal[33]. The astigmatic effect is far lesser when a postlimbal 2.2 mm or 2.8 mm keratome entry is used to make a small initial tunnel and enter the AC in one go, the entry later extended using a blunt 5.5mm keratome (“enlarger blade”). Good results in multifocal IOL implantation can also be achieved with the correct estimation of the surgically corrected astigmatism and efficient surgical technique[42]. A temporal approach to neutralize a steeper corneal curvature in the horizontal meridian (commonly seen in elderly patients) preserves the superior conjunctiva for future glaucoma filtration surgeries. In addition, it induces lesser astigmatism compared to a superior incision due to orientation of scleral fibers and more distance from center of the cornea[29].

Combination of MSICS with trabeculectomy entailed the innovation of a M or W-shaped incision (after Khurana et al[54]) or a Flying Eagle incision (after Malik et al[22]). The posterior extensions of the M/W or the flying eagle configuration allow the placement of sutures akin to standard trabeculectomy flaps, while the rest of the triplanar tunnels seal on their own like standard MSICS tunnels.

The paracentesis

The paracentesis can be created using a side port knife, lance tip (15 degree) knife, microvitreoretinal knife, partial entry of the keratome, and even a simple 21G needle puncture of the limbus. An initial small internal keratome entry in the sclerocorneal tunnel helps to maintain the AC while allowing a port to perform intracameral maneuvers like air bubble injection, anterior capsular staining, viscoelastic injection and anterior capsulotomy. This entry can later be enlarged to the full width of the tunnel. This has nearly eliminated the need for a separate paracentesis.

Anterior capsule

Maintaining the AC leads to better postoperative outcomes due to lesser mechanical stress on the cornea as well as preservation of corneal endothelial function[55]. Thus, various viscoelastic substances have been used in MSICS. Continuous viscoelastic infusion through an ACM has also been described[56]. Tunnel floor entry has been described to lessen the amount of fluid or viscoelastic loss through the large tunnel[42]. It has been found that ACM can help completely avoid the use of viscoelastic during surgery, which can be an effective technique for MSICS, or MSICS with trabeculectomy[57]. Thus, anterior capsulotomy can be performed under viscoelastic or under fluid. Manual techniques of anterior capsulorhexis remain essentially the same, except that for a continuous curvilinear capsulorhexis, a novel technique involves the use of an aspiration cannula to engage the leading edge of the capsular flap (Can-Vac technique)[58]. There are no contraindications to the use of modern automated techniques of anterior capsulotomy, utilizing femtosecond laser, CAPSUlaser^® (Excel-Lens inc., CA, USA), precision pulse capsulotomy technique, plasma blade etc. but they are neither required, nor cost effective in most settings.

Nuclear management

Nuclear rotation and prolapse in the AC using two instruments has been found to cause lesser stress on the zonules. This bimanual technique utilizes any combination of Sinskey hook, Kuglen hook, iris repositor, cyclodialysis spatula, ball-point manipulator and even phaco choppers of various designs, that are effective in the hands of skilled surgeons. Nuclear rotation in MSICS is safe even in posterior polar cataracts if the fluid dynamics are correctly understood[59]. Attempts for nuclear fragmentation into the smallest possible dimensions have paralleled the reducing size of the MSICS incision. Recently, nucleofractis in the AC has been made very popular by revival of the snare technique. The double nylon loop snare and Shah’s snare have been recently reintroduced and popularized[38,60]. Boramani et al[61] described an axe-shaped chopper wherein the dominant hand uses this instrument through the side port moving tangentially across, to an iris repositor which through the main port supports the prolapsed nucleus from behind.

Prechoppers can chop the nuclear mass in the bag, making it convenient to prolapse out and remove each piece sequentially. Bhatti utilized the Akahoshi prechop technique for in-the-bag nuclear fracture[62]. Various other forward-cutting prechoppers (Jacobovitz prechopper, Sohel Khan prechopper, Mohanta’s prechopper) have been utilized for in-the-bag nuclear fracture. The Mi-Loop, another modern in-the-bag nuclear fracturing device, may also be used for the purpose, but is expensive. Endoexpression of the nuclear material in whole or part has been described by Boramani et al[63], wherein the nuclear mass is mechanically pushed from its lower pole by a blunt instrument introduced through a paracentesis. Nuclear extraction has also been achieved by fluid pressure using modifications of irrigating cannulas and irrigating vectis. Various combinations of viscoexpression, endoexpression, phacosandwich and fishhook techniques are also in vogue[63-65].

Cortical aspiration

Simcoe, reverse simcoe, J-simcoe, and single port aspiration cannulas, with or without sandblasted tips, are all being used by various surgeons for cortical cleanup and polishing today. Another recent innovation in cortex aspiration is the use of a spring-assisted syringe for controlled aspiration pressure in order to make the procedure more predictable[66]. A fluid jet applied onto the posterior capsule removes fine adherent cortical fibers, while stubborn lens epithelial cells on the anterior capsular rim can be removed using a ring-shaped or olive-tipped capsule polisher.

IOL implantation

Modern day foldable IOL implantation is possible through the sclerocorneal tunnel of MSICS using a direct introduction using non-toothed forceps, or using the injector system similar to phacoemulsification depending upon the size of the tunnel incision. Some surgeons use the injector unaltered even through a larger incision, while some others prefer to slit the tip of the injector to lessen the stress on the IOL. Irrigation and aspiration of viscoelastic, followed by a final lavage of the AC after IOL implantation removes any remainder of viscoelastic. Hydroimplantation of the IOL using a continuous ACM infusion is also popular. Retained viscoelastic can raise intraocular pressure (IOP) postoperatively, and the latter technique completely avoids the need for viscoelastic removal, utilizing only fluid to form the AC while implanting and dialing the IOL. Even toric, presbyopia-correcting and advanced technology IOLs can be easily implanted using this technique.

Wound closure and patching

Intraoperative antibiotic prophylaxis against endophthalmitis is the recent trend, with intracameral moxifloxacin injection showing the best evidence towards prevention of this vision-threatening complication after MSICS[67]. A recent study has also shown addition of Amikacin in the BSS irrigating fluid to be beneficial in preventing endophthalmitis[68]. A recent innovation after hydration of the sideport is the Siep’s test - a novel test to check the wound integrity while forming the AC after completion of the IOL implantation procedure. It is the application of 2-3 drops of 5% povidone iodine to identify wound leaks, with the dual purpose of further sterilizing the ocular surface[69]. In modern MSICS, following the final hydration of the wounds, the eye may or may not be patched depending upon the surgeon’s preference and patient’s eyelid and ocular movements. If the postoperative status is satisfactory, the patient is provided a pair of clear polycarbonate protective goggles to wear, and discharged.

COMPLICATIONS OF MSICS

The profile of complications encountered in MSICS are similar to that of phaco and other cataract extraction procedures. Complications related to anesthesia include the adverse effects of anesthetic drugs as well as the technique of administration of the agents, with no significant differences observed in subtenon and peribulbar block techniques[70]. Some of the complications are similar to any other intraocular surgery, while others are unique to the MSICS procedure itself.

Intraoperative complications include bleeding, improper incision architecture leading to full thickness scleral penetration with uveal show, or too superficial a plane of scleral dissection leading to poor sealing of the incision[71]. The sclerocorneal tunnel may be too short leading to a premature entry or too long leading to high SIA. It may be jagged, multiplanar or irregular, leading to leaking and intraoperative shallowing of AC as well as postoperative hypotony[72]. Descemet’s membrane detachment at the incision sites is another complication, necessitating intraoperative or postoperative air or gas tamponade[73]. Intraoperative damage to the corneal endothelium or iris may occur due to various causes. The capsulorhexis may be inadequate or improperly shaped, leading to difficulties in handling of the nucleus. It may run off to the periphery or even trans-equatorially, thereby causing a posterior capsular rupture (PCR). A large PCR may lead to the whole nucleus unexpectedly dropping into the vitreous cavity, although it is infrequent in MSICS. A PCR may disrupt the vitreous face, leading to vitreous prolapse through it into the AC and out of the large MSICS wound, wherein meticulous limited anterior vitrectomy would be warranted. IOL may be implanted in the bag if the PCR is small, or in the ciliary sulcus if the latter is clearly visible. If there is doubt, the patient may be left aphakic. Larger anterior capsulotomies performed for harder nuclei may limit the ability to implant a standard PMMA IOL, in which case a PMMA IOL with a 6.5 mm optic may be preferred. There is risk of IOL decentration, given that the PMMA IOLs are 12.5 mm in size and the ciliary sulcus may be larger especially in myopes. A reverse optic capture may help in long-term centration of the IOL, however, there is limited evidence in its favor in MSICS procedures. Postoperatively, complications such as striate keratopathy, choroidal detachment, endophthalmitis, and hyphema may be encountered due to various causes, all of which are insufficiently discussed in literature as being attributable to the MSICS procedure per se[74]. However, the incidence of major complications is seen to be lesser in phaco than MSICS, making phaco an overall preferred choice of surgery today.

Postoperative corneal edema and AC inflammation usually resolve with medication and do not require additional procedures. However, surgical management of major complications after MSICS is challenging because of the resource constraints due to which the MSICS was performed in the first place. Many centers performing MSICS are not equipped with advanced operating microscopes, automated vitrectomy systems, or intraoperative visualization aids like endoilluminators or microscope-integrated optical coherence tomography systems. As usual, the surgeon’s discretion in the setting of a complication is the most important factor in determining the final outcome in these cases. With proper precautions and safe technique, MSICS results in early visual rehabilitation, return to work and restoration of quality of life similar to phaco.

MSICS IN SPECIAL SITUATIONS

Cataract subluxation

Subluxated cataract warrants special considerations, including the need for careful assessment and preservation of remaining zonular support, the possibility of trans-zonular vitreous in the AC, potentially difficult capsulorrhexis and nuclear prolapse as well as the risk of losing the bag. Goel et al[24] showed that in cases of subluxations less than 90°, MSICS can be easily done. But beyond this degree and in larger subluxations, a larger capsulorhexis is required which may be difficult to achieve with a larger incision. Manipulation during the prolapse of nucleus may lead to further zonular dialysis. There are rare conditions like lens coloboma associated with subluxation in which rotation of nucleus and prolapse is quite difficult. In these scenarios, the preferred choice is phacoemulsification. In a study, more than 76% of the MSICS eyes were successfully implanted with posterior chamber IOL along with the retention of capsular bag with subluxation. The modified Bluementhal technique is found to be effective in such subluxations of various degrees[75].

Phacomorphic glaucoma

MSICS is the preferred choice in phacomorphic glaucoma as per studies by Rajkumari et al[76] and Ramakrishanan et al[77] and has shown better results when post-operative visual acuity, intra-operative and post-operative safety were assessed. MSICS should be preferred due to preexisting short AC depth, large hard nucleus, zonular weakness and compromised cornea.

Pseudoexfoliation syndrome

In a study by Desinayak et al[78], MSICS was found to be a beneficial and convenient surgical technique for the patients of pseudoexfoliation syndrome and secondary glaucomas associated with it due to various co-existing morbidities like hazy cornea, poorly dilated pupil, low endothelial cell count and increased chances of zonular dialysis[78]. Proper precautions must be taken for anticipated difficulties during the surgery.

Intumescent white cataracts

There are three different vector forces coming into action in white intumescent cataracts, thereby making capsulorhexis the most exigent step during surgery. There are higher chances of Argentinian Flag Sign which may further leads to posterior capsular rupture and nucleus drop[79]. If a successful capsulorhexis is achieved, both MSICS and phacoemulsification can be performed, but in case of any extension it is safer to carry out MSICS to achieve better visual outcomes free of any complications[34].

Compromised corneas with low endothelial cell density

Mechanical distortion of the cornea, fluid turbulence in the AC, direct trauma by intraocular instruments, nuclear fragments, or IOLs, and reactive oxygen species, all have been implicated in causing corneal damage during cataract surgery, and these are theoretically more common in MSICS than phaco[80]. However, the study by Gajraj et al[81] and Kusumesh et al[82] had clearly shown that MSICS with posterior chamber IOL implantation is the only choice in compromised corneas with low endothelial cell count to provide the best possible functional vision. The authors were able to achieve good visual outcomes in such patients by doing MSICS[81,82]. The MSICS procedure causes endothelial cell depletion of approximately 16%, which is similar to other modalities of cataract surgery[80].

MSICS and premium IOL implantation

With the advent of the Boramani Nomogram for surgically corrected astigmatism, customized MSICS, smart small incision cataract surgery (SICS), and 2-mm incision Sahu’s MSICS, surgeons can implant all types of premium IOLs without any hesitation as the post-operative refractive surprises are reduced to bare minimum with excellent quality of vision. The success of these advanced techniques also proves that MSICS is no more the surgery of choice for the underprivileged but for the premium segment, too[14].

MSICS IN DEVELOPING COUNTRIES

MSICS is largely practiced in developing nations whereas phacoemulsification with its various technology-driven and commercially driven refinements is a more popular cataract surgery in the west[15]. MSICS is a boon and a logical solution for countries with limited resources with higher cataract morbidity. Multiple studies have suggested similar safety and efficacy for the two procedures with MSICS being more cost-effective with lesser surgical time[83,84]. As stated previously, it also scores over phacoemulsification in being more environment friendly with a smaller carbon footprint[19].

Burden of cataract in developing (middle- and low-income) countries

Cataract blindness continues to be one of the greatest public health challenges, with World Health Organization reporting it to be the main cause of preventable blindness[85,86]. A global study conducted in 2020 stated that 39.6% of overall 43.3 million blind (17.0 million) and 28.3% of 295 million with moderate or severe visual impairment (83.5 million) suffered from cataract as the cause of visual impairment[87]. Over the last three decades, the number of DALYs due to cataracts increased by 91.2% making it the second largest burden of eye disease[7]. Risk factors associated with higher cataract burden were female sex, aging, lower socio-economic status among others. The age-standardized DALYs of cataracts due to risk factors were highest in areas having low to middle sociodemographic indices. The prevalence of cataract-related blindness was higher than the global average only in nations of South Asia (62.9%) and Southeast Asia and Oceania (47.9%)[87].

In Asia, cataract is the most common cause of blindness and vision impairment followed by refractive error and near vision impairment in terms of the burden of DALYs[88]. India contributes almost 12 million of the total 22 million blind people worldwide. Of these, cataract has been reported to account for 50%-80% of the bilaterally blind (vision < 20/200 in the better eye). The incidence of cataract is 3.8 million/year with a backlog of approximately 6 million/year in India[89]. The high cataract burden in developing nations like India necessitates that a fast, economical yet effective cataract surgery like MSICS ought to be a well-utilized resource in the hands of many ophthalmic surgeons. High volume cataract surgery in resource-scarce settings can be accomplished by the majority of patients undergoing MSICS[90]. The overall complication rate is similar for MSICS and phaco. However, it has been shown that trainee surgeons have significantly more complications with phaco than with MSICS[91]. MSICS procedures have been shown to have short learning curves, thus, institutions training early-career surgeons must have MSICS as one of the preferred surgeries for their patients[92].

Cost considerations of phacoemulsification vs MSICS

In developing nations, phaco with the requirement of a permanent and reliable source of electricity, costly machinery needing regular maintenance and machine-specific consumables, may face limited use in resource-challenged situations. Also, safety may be compromised in extremely dense cataracts and compromised corneas, commonly encountered in patients of developing nations with delayed health-seeking behavior[18]. A study of the provider’s direct total annual costs using a “micro-costing approach” showed that phaco had higher direct costs (25.55 dollars) compared to MSICS (17.03 dollars) due to the cost of additional equipment and materials required in phaco. Also, a combined total of the costs incurred by the patient were studied and were found to be similar for MSICS and phaco (12.37 dollars)[93]. Another study comparing cost of cataract surgeries performed by residents found a higher total cost for phaco (416 dollars), vs ECCE (284 dollars)[94]. In a comparative study in India, phaco costed 42.10 dollars, whereas MSICS costed only 15.34 dollars. It was estimated that 10.65 dollars was the fixed-facility cost common to both MSICS and phaco[95]. Similar studies conducted in Nepal and Thailand have also demonstrated lower direct costs of MSICS compared to phaco (15-62.25 dollars for MSICS to 70-104.15 dollars for phaco)[96]. The use of locally manufactured viscoelastic devices, IOLs and pharmaceuticals dramatically lowers costs, with some surgeons reusing some consumables to further bring down the cost of the procedure[94].

A systematic survey showed that the cost utility analysis for MSICS shows savings of 79.57 dollars per unit gain in LogMAR best-corrected visual acuity, and 8.91 dollars per QALY gained in India with better incremental cost-effectiveness ratio vs phaco[96]. According to a study by Jongsareejit et al[97], cost-effectiveness ratio for MSICS was 13215.50 dollars compared to phaco which was 17561.70 dollars[97]. Improvement of QALY values - a surrogate marker for cost-benefit analysis - is better in treatments providing early rehabilitation like phaco traditionally. However 3-month data showed no statistical difference in visual gain or complication rate between phaco and MSICS[98]. Also, incision-related modifications in MSICS reduce spectacle dependence by inducing mild myopic astigmatic errors which may be very useful in resource-constrained environments. Thus, the cost-utility difference may be significantly better for MSICS compared to phaco[95,97].

A short turnover time for MSICS with a minimal cost per case makes it a prime candidate for high-volume surgery[90]. Hence, MSICS scores over other existing alternatives of cataract extraction from cost-effectiveness and cost-minimization approaches[94,96]. These findings are of relevance in formulating health care policies and in allocative decisions in public health and government-funded projects to combat cataract blindness especially in low to middle income or developing countries. Indeed, according to current evidence, MSICS is the procedure of choice in various humanitarian campaigns aimed to reduce cataract backlog in poor and underprivileged communities[92].

Instrumentation requirements of MSICS

The successful outcome of MSICS depends upon a surgeon’s skill rather than expensive machinery. The instrumentation requirements for MSICS are minimal and include consumables like disposable tunnel knives, irrigating solutions and ophthalmic viscoelastic devices. Newer methods of MSICS may also require the use of an ACM, phaco-fragmentation devices like a nylon loop, nuclear trisector, etc, which are reusable. These help in reducing the overall cost of this surgery and making it a popular choice for resource-constrained centers. Since most technological advancement is industry-driven, innovative instrumentation for MSICS has not gained global popularity. Newer advances in smaller incision construction, nuclear management, and astigmatic correction with smart incisions can herald a boost in utilization of MSICS worldwide[50,84]. Healthcare is a major contributor to greenhouse gas emissions and environmental pollution. With increasing focus on development of sustainable technology minimizing carbon imprint, MSICS is a beacon to more-environment friendly surgery that reduces the use of paper, plastic, and energy[19].

TRAINING OF MSICS

Simulation for training of MSICS has recently picked up a rapid pace on the global scale[99]. Wet lab and virtual reality-based training results in shorter surgical learning curve, better surgical outcomes, lesser complication rates, increased surgeon confidence, better tissue handling and reduced intra-operative time. Traditional methods of training include use of animal eyes like goats’ eyes, cadaveric eyes, artificial silicone eyes etc. The COVID era brought an increase in use of existing methods and newer innovative ideas for surgical training including use of simulators like EYESi (VRMagic, Haag-Streit, Switzerland), MicrovisTouch (ImmersiveTouch, Chicago, IL, United States), PhacoVision^® (Melerit Medical, Linkoping, Sweden), and the HelpMeSee Eye Surgery simulator (HelpMeSee, Inc., New York, United States)[99-103]. However, most of the simulators available in the market are for phaco. The HelpMeSee simulator is programmed for MSICS as well as phaco, and a study showed that surgeons trained with simulators may perform better than conventionally trained surgeons, as simulator scores also offer feedback to trainee surgeons[103].

Two- and three-dimensional videos have also gained traction over time as valuable addendum to training materials with studies showing greater reliance on e-learning by medical professionals and YouTube videos helping both senior and junior ophthalmic surgeons[104,105]. Also, MSICS and ECCE are seen as stepping stones in a surgeon’s journey towards mastery of phaco and are proven to ease the learning curve of phaco[18]. To standardize teaching and to objectively assess the proficiency of trainee surgeons, the International Council of Ophthalmology has developed the SICS Ophthalmic Simulated Surgical Competency Assessment Rubric. This is a validated surgical education and assessment tool and can guide young surgeons while progressing to live surgeries[106].

IMPORTANT RANDOMIZED CONTROLLED TRIALS FOR MSICS

Despite key differences in surgical techniques (Table 2), published studies have established comparable results and complication rates of MSICS and phaco, and both procedures have been shown to have similar efficacy and safety for visual rehabilitation[107]. A study conducted in Nepal on 108 patients showed that phaco and SICS had good visual outcomes with low complication rates with SICS being the faster and less expensive option[83]. Literature also supports MSICS as a preferred procedure for intumescent, mature and hard cataracts for resource-deficient settings[98,108]. Improvements in MSICS techniques like the use of ACM and viscoexpression results in earlier visual rehabilitation, with the phacosandwich being more effective in management of harder nuclear cataract[55]. Satisfactory outcomes are also noted in ocular inflammatory conditions like Fuch’s heterochromic uveitis[109].

Table 2 Key Differences between manual small incision cataract surgery and phacoemulsification.

Criterion	Manual small incision cataract surgery	Phacoemulsification
Anesthesia	Peribulbar, subtenon, topical augmented with subtenon	Topical, peribulbar, subtenon, topical augmented with intracameral
Superior rectus bridle suture	Optional	Not required
Conjunctival peritomy	Optional	Not required
Incision size	2-12 mm	Usually < 3 mm
Anterior capsulotomy	Can-opener, envelope, CCC	CCC
Viscoelastics	Usually low viscosity dispersive or cohesive	High viscosity dispersive required for harder cataracts
Nuclear removal	Wire vectis, Blumenthal, viscoexpression, hydroexpression, Fishhook, snare (nuclear fragmentation)	Ultrasonic emulsification and aspiration
Cortex removal	Simcoe cannula and modifications	Coaxial or bimanual automated, simcoe cannula less commonly
Machine dependence	No	Yes
Overall costs	Lower	Higher

CCC: Continuous curvilinear capsulorhexis.

A systematic review and meta-analysis by Gogate et al[84] included 11 comparative studies comparing the safety, efficacy, and expenses of MSICS vs phaco. The postoperative uncorrected (UCVA) and best-corrected visual acuity were comparable between techniques with no statistical difference in endothelial cell loss during surgery. The incidence of intraoperative and postoperative complications were also not significantly different. Time efficiency and comparable outcomes were confirmed by studies in Nepal and in India[95,110,111]. In comparison with ECCE, MSICS is shown to have comparatively better visual outcomes[112]. MSICS group achieved unaided visual acuity of 6/12 or 6/18 or better compared to conventional ECCE.

Although it is generally accepted that phaco has better short-term visual outcomes than MSICS, studies comparing short-term visual outcomes of phaco with MSICS are often affected by inadvertent case selection bias; hence, it is difficult to quantify the difference[113,114]. Phaco has the advantages of less mean corneal astigmatism, less AC inflammation, and better UCVA in the immediate postoperative period. A study conducted on 400 patients in India showed comparable efficacy between the two surgeries with better visual outcome at 6 weeks for phaco[115]. MSICS usually results in statistically greater astigmatism compared to phaco, and UCVA of 6/9 or worse, however, near UCVA may be better. Functional and anatomical outcomes at one month after surgery are comparable for both MSICS and phaco techniques[84,95].

As stated, astigmatism in MSICS has been countered by various maneuvers like a change of incision site, shape, size, architecture and placement of sutures[116]. On comparing various sites of surgery, the temporal approach for MSICS is reported to have less postoperative astigmatism and better UCVA than a superior approach[117]. X-pattern sutures were preferred to the horizontal sutures to reduce SIA[118,119]. Long-term data comparing the astigmatic outcomes of SICS and phaco are lacking, although the use of cautery in MSICS may not be associated with a higher post-operative SIA[28,107]. Similar astigmatism was seen irrespective of the mode used for nucleus delivery in MSICS[55].

Studies show that endothelial loss is greater in older patients with hard nuclear cataracts when the eyes undergo phaco, as compared to MSICS. In MSICS, the continued BSS infusion-assisted nuclear delivery technique is proven to reduce endothelial cell loss compared to viscoelastic-assisted nuclear delivery, as per studies by Morya et al[64] and Singh et al[120]. With regard to IOP, both phaco and MSICS led to significant and similar IOP reduction 6 months postoperatively (2.7 ± 2.9 mmHg vs 2.6 ± 2.6 mmHg, respectively) and caused comparable changes in the AC and angle parameters[121]. Mansoori et al[122] showed comparable IOP reduction at approximately 1.5 year follow up with phaco and MSICS combined with Mitomycin C-augmented trabeculectomy (13.9 ± 2.98 mmHg vs 14.1 ± 4.12 mmHg). An RCT again proved an IOP drop of 7.5% to 8.7% after MSICS[64].

Among the trials comparing phaco and SICS in terms of IOL implantation, phaco has shown proven advantages with ease in use of topical anesthesia, lower PCO rates, and lower SIA[107,112,115]. The recent use of square edge intra-ocular lens has shown considerable reduction in PCO rates in MSICS[123,124]. There are no randomized controlled trials describing the comparison in the rates of late-onset postoperative endophthalmitis. In addition, there is no evidence whether outcomes after the management of these cases favor one procedure over the other.

CONCLUSION

MSICS is a cost-effective and efficient procedure for cataract removal, especially in resource-limited settings. It involves creating a small, self-sealing scleral tunnel incision to remove the cataract and implant an IOL. Unlike phacoemulsification, MSICS does not rely on advanced machinery, making it accessible in rural and underserved areas. The incision is typically larger than that in phacoemulsification, but it is possible to perform MSICS through incisions as small as 2 mm as well. Surgeons use manual techniques to optionally fragment, and extract the cataractous lens through the scleral tunnel. MSICS provides excellent visual outcomes comparable to phacoemulsification when performed skillfully. The procedure has a short learning curve, making it ideal for simulation-aided training of ophthalmologists to meet the demands of high-volume settings. MSICS also minimizes surgical costs, benefiting patients in low-income regions. Postoperative recovery is generally quick, with minimal complications when proper aseptic techniques are observed, while controlling costs and carbon footprint. MSICS has a proven track record of success in the past, and is commonly performed even today in the era of machines. Recent improvements in the MSICS technique make it a true surgery for the future, with the potentially unlimited possibility of innovation. Overall, MSICS is a valuable technique for addressing the global burden of cataract blindness and a valuable resource for every ophthalmic surgeon to have in their armamentarium.