Novel trocar assisted intraocular lens and capsular bag complex fixation.

PURPOSE: To describe the innovative technique of trocar-assisted intraocular lens (IOL) and capsular bag complex fixation. METHODS: In this technique, initial pupil dilatation is achieved either with intracameral adrenaline or with the help of iris hooks. Automated anterior vitrectomy is performed in cases with vitreous prolapse. A 25 G trocar cannula is placed at the limbus through a paracentesis opposite the zonular dialysis area. The cannula lumen act as a guide to pass the double-arm polypropylene suture attached to the needle. This prevents any inadvertent corneal injury and acts as a perpendicular tract to pass the needle through IOL capsular bag complex. RESULTS: We performed this technique in 9 cases with an excellent outcome with a minimum of 3 months of follow-up. All patients had well-centred IOL. There was no incidence of corneal injury, Descemet membrane detachment, iris trauma, IOL tilt, decentration, dislocation, vitreous prolapse or retinal detachment. All patients achieved excellent visual acuity ranging from 6/12-6/6 postoperatively. CONCLUSION: The novel trocar-assisted IOL bag complex fixation technique is very effective and allows smooth IOL fixation in technically challenging cases with IOL subluxation. The trocar acts as a guide to prevent injury to the surrounding tissue, and IOL fixation is achieved with minimal manipulations in the anterior chamber. It also prevents the need for IOL explantation in these cases.

Capsular phimosis with intraocular lens tilt and decentration.

A 34-year-old woman with quiescent bilateral intermediate uveitis maintained on once-daily dexamethasone 0.1% eyedrops, complicated by left cataract and glaucoma controlled with a single antiglaucoma medication, presented for cataract surgery. Her left corrected distance visual acuity (CDVA) was 20/40 because of a posterior subcapsular lens opacity. The anterior chamber angles appeared closed in all 4 quadrants on gonioscopy. Ultrasound biomicroscopy (UBM) confirmed the gonioscopy findings and, in addition, revealed a crystalline lens thickness of 5.53 mm, normal ciliary body structure, and multiple localized chorioretinal scars with membranes over the pars plana region. She underwent left phacoemulsification, goniosynechiolysis, and in-the-bag implantation of a single-piece monofocal hydrophobic acrylic intraocular lens (IOL). On the first postoperative day, she achieved pinhole vision of 20/70 (-6 diopters [D] myopia to balance with the fellow eye). There was mild anterior chamber cellular activity and flare, consistent with postoperative inflammation. Her intraocular pressure (IOP) was 16 mm Hg without antiglaucoma therapy. She was advised to continue the prednisolone acetate 1% eyedrops 6 times daily and to reduce it to 4 times daily after a week for the next 4 weeks. At 1 month, she was refracted to 20/40 N5, and the eye was quiescent. Optical coherence tomography showed that the macular was normal. The topical steroids were gradually tapered to the preoperative level. However, a month later, she returned complaining of deteriorating vision while using twice-daily steroid eyedrops. Her CDVA was 20/60. Slitlamp examination revealed anterior capsule fibrosis and capsular phimosis, resulting in partial obstruction of the visual axis and mild decentration of the IOL superior temporally (Figure 1JOURNAL/jcrs/04.03/02158034-202310000-00013/figure1/v/2023-09-28T161738Z/r/image-tiff). The anterior segment was quiescent. The pupil could only be dilated to 4.5 mm despite the absence of posterior synechiae. Fundus examination revealed a normal-looking quiescent posterior segment. Her IOP was 16 mm Hg. UBM showed a thickened anterior capsule, intact zonular fibers, and a posteriorly bowed and decentered IOL within the capsular bag (Figure 2JOURNAL/jcrs/04.03/02158034-202310000-00013/figure2/v/2023-09-28T161738Z/r/image-tiff). She was referred for further management. Discuss how you would manage this problem, explaining your decisions. How would you be able to avoid the same problem when operating on her fellow eye?

Management of corneal perforations in dry eye disease: Preferred practice pattern guidelines.

Corneal perforations in eyes with dry eye disease (DED) are difficult to manage due to the interplay of several factors such as the unstable tear film, surface inflammation, and the underlying systemic disease affecting the wound healing process, and the eventual outcome. A careful preoperative examination is required to identify the underlying pathology, and status of ocular surface and adnexa, rule out microbial keratitis, and order appropriate systemic workup in addition to assessing the perforation itself. Several surgical options are available, which include tissue adhesives, multilayered amniotic membrane grafting (AMT), tenon patch graft (TPG), corneal patch graft (CPG), and penetrating keratoplasty (PK). The choice of procedure depends upon the size, location, and configuration of the perforation. In eyes with smaller perforations, tissue adhesives are effective treatment modalities, whereas AMT, TPG, and CPG are viable options in moderate-sized perforations. AMT and TPG are also preferable in cases where the placement of a bandage contact lens may be a challenge. Large perforations require a PK, with additional procedures such as tarsorrhaphy to protect the eyes from the associated epithelial healing issues. Conjunctival flaps are considered in eyes with poor visual potential. The management of the acute condition is carried out in conjunction with measures to improve the tear volume bearing in mind the chances of delayed epithelialization and re-perforation in these cases. Administration of topical and systemic immunosuppression, when indicated, helps improve the outcome. This review aims to facilitate clinicians in instituting a synchronized multifaceted therapy for the successful management of corneal perforations in the setting of DED.

Graft rejection in component keratoplasty.

Among the various indications for keratoplasty, failed graft is one of the commonest indications in many published series. It is well known that the major cause of graft failure is endothelial rejection. In the last two decades, there has been a major paradigm shift in the surgical management of corneal diseases, and component keratoplasty has emerged from the concept of replacing the layer that is actually diseased, rather than replacing the full-thickness cornea with the traditional penetrating keratoplasty. This has resulted in improved outcomes and the risk of endothelial rejection has reduced drastically, thus expanding the survival time of the graft. In recent years, reports of graft rejection in component keratoplasty have emerged, with each having a different presentation and responding to a different line of treatment. This review aims to summarize the presentation, diagnosis, and management of graft rejections in component keratoplasty.

Novel nucleus management technique in hypermature morgagnian cataracts with liquified cortex during phacoemulsification.

PURPOSE: To describe a novel nucleus management technique of variable size mobile nucleus in Hypermature Morgagnian cataracts. METHODS: In this technique, under topical anesthesia, temporal tunnel incision and capsulorhexis were performed, and the capsular bag was inflated with 2% w/v hydroxypropylmethylcellulose. A chopper and phacoemulsification probe were used to consciously nudge the nucleus towards the capsular periphery (fornix) to immobilize the floating nucleus against the capsular bag recess. Firm nuclear impaling was achieved using longitudinal power in linear mode (range 0-70%), 650 mmHg vacuum, and aspiration flow rate of 42 ml/min. The nucleus was chopped by direct chop technique, total separation achieved, and fragments emulsified. Primary outcome measures included ease of nuclear holding, iatrogenic zonular stress/damage, posterior capsule tear, and endothelial cell loss. RESULTS: This technique was performed in 29 consecutive cases from June 2019 - December 2021, and no intraoperative or postoperative complications were noted. The average phacoemulsification time and cumulative dissipated energy (CDE) were nearly similar in all cases. CONCLUSION: This technique would make phacoemulsification much safer in eyes with hypermature cataract and liquified cortex with lower complication rates and maintenance of better endothelial integrity.

Infectious crystalline keratopathy following Descemet's stripping automated endothelial keratoplasty.

INTRODUCTION: We describe this first case of Staphylococcus epidermidis causing infectious crystalline keratopathy (ICK) following Descemet stripping endothelial keratoplasty (DSAEK), that resolved after 5 weeks of topical antibiotic and corticosteroid treatment. CASE DESCRIPTION: An 80-year-old woman presented with blurred vision, redness, and ocular pain 9 months after successful DSAEK. Slit lamp examination revealed the presence of white, non-suppurative, deep-branching stromal infiltrates, and a clinical diagnosis of ICK was made. Cultures of corneal scapings isolated multidrug-resistant Staphylococcus epidermidis. No subsequent surgical procedures were performed. Based on antibiotic sensitivity analysis, she was treated successfully with topical vancomycin and chloramphenicol for 5 weeks. Complete resolution of the infection with minor anterior stromal corneal scarring of the host cornea was noted after 5 weeks of treatment. This case report describes the diagnosis and management of ICK after DSAEK and reviews the relevant literature regarding the occurrence of ICK after DSAEK. CONCLUSION: In this case, vancomycin and chloramphenicol allowed for the uncomplicated resolution of infection with only minor visual impairment from baseline.

Prognostic significance of matrix metalloproteinase 9 in COMET operated chronic ocular Stevens-Johnson syndrome.

PURPOSE: Molecular pathogenesis underlying persistent ocular surface inflammation in chronic Stevens-Johnson syndrome (SJS) still remains largely unexplored. The present study investigates the expression of matrix metalloproteinase 2 (MMP2), MMP3, MMP9, MMP11 and TIMP1 (tissue inhibittor of matrix metalloproteinase 1) in pannus tissues of chronic ocular SJS undergoing cultivated oral mucosal epithelial transplantation (COMET) and their prognostic relevance. METHODS: In this prospective study, 45 eyes with chronic SJS underwent COMET for visual and anatomical rehabilitation. Preoperative and postoperative clinical parameters were documented. MMP2, MMP3, MMP9, MMP11 and TIMP1 expression were assessed using immunohistochemistry and quantitative real time PCR. Inflammadry MMP9 assay was performed at 1-year follow-up. Kaplan-Meier curves and Cox proportional hazard models were used to correlate protein expression with clinicopathological parameters and COMET graft survival outcomes. RESULTS: MMP9 and MMP11 positivity was seen in both pannus epithelia (48% and 55%, respectively) and in stromal layer (57% and 33%, respectively) while MMP2 and MMP3 showed only pannus epithelial positivity in 35% and 51% cases, respectively. High MMP9 stromal expression was significantly associated with preoperative corneal keratinisation (p=0.011), conjunctival hyperaemia (p=0.014), symblepharon (p=0.028). High MMP9 and MMP3 epithelial expression were found to be independent risk factors for poor best-corrected visual acuity (BCVA) outcomes post-COMET (p=0.022 and p=0.048). Multivariate analysis revealed MMP9 to be the best prognostic marker (p=0.050). CONCLUSION: Our findings suggest that differential expression of MMPs and TIMP1 is seen in SJS in chronic stage. Emergence of MMP9 as a poor prognostic predictor of BCVA post COMET and postoperative MMP9 immunoassay positivity could be a useful tool in further studies to understand the unresolved ocular surface inflammation seen in SJS.

Clinical, Biochemical, Genetic, and Therapeutic Profile of Patients with Epidermal Necrolysis: A Descriptive Study.

Background: Epidermal necrolysis (SJS/TEN) is a rare but acute severe drug reaction associated with high morbidity and mortality rates. Aims: To describe the clinical, molecular, biochemical, and therapeutic profile of these patients. Methods: A total of 24 acute SJS/TEN patients were recruited during their hospital stay and detailed clinical history and treatment course recorded. Blood samples collected were subjected to DNA and serum separation for molecular and biochemical analysis. Results: Of 24 patients, 18 (75%) were females and six (25%) were males with six SJS, six SJS-TEN overlap, and 12 TEN cases. The inciting drugs were non-steroidal anti-inflammatory (87.50%; n = 21) followed by antibiotics (66.67%; n = 16), antiepileptics (37.50%; n = 9), and others (37.50%; n = 9). Seventeen patients (77.2%) showed skin eruptions within 7 days after drug intake. Different co-morbidities were observed in 22 (91.6%) and 20 (83.3%) patients showed ocular manifestations. Length of hospital stay ranged from 8 to 55 days, 20 (83.3%) patients were treated with corticosteroids, and four (16.6%) received antimicrobial therapy. Interleukin polymorphisms revealed significantly low frequency of IL-4 in the patients, HLA-A locus typing revealed higher frequency of HLA-A*3301 (20.8%), HLA-A*02 (25%), HLA-A*2402 (14.6%), and sera showed raised levels of granulysin and sFas L in the patients compared to controls. Conclusions: The preliminary study illustrates the clinical, molecular, and biochemical features of acute SJS/TEN and provides a better understanding that helps to improve patient care at an earlier stage. It also highlights the use of corticosteroids and antimicrobial therapy for effective treatment of patients.

Volcano explosion in the eye: Expulsive choroidal haemorrhage.

BACKGROUND: This video shows the dreaded complication of expulsive suprachoroidal haemorrhage in a penetrating keratoplasty . It teaches the various measures that help in preventing and managing the challenge peri-operatively. PURPOSE: This video is intended to sensitize the corneal surgeons about this rare complication using real-time surgical video and prepare them to face this challenge by demonstrating the preventive and mitigating strategies. SYNOPSIS: A patient who was suitably taken up for an autokeratoplasty had expulsive choroidal haemorrhage in the non-seeing eye. This complication was managed using glycerin-preserved donor corneal button. Further, the video discusses various pre-operative and intra-operative optimizations to avoid such a complication and mitigate the damage caused by it, should it ever happen during a surgery. HIGHLIGHTS: Expulsive choroidal haemorrhage can be a traumatizing event and one must be mentally prepared to manage it. Pre-operative high-risk factors should always be managed and intra-operative maneuvers performed to prevent the complication, as shown in the video. VIDEO LINK: https://youtu.be/s_ImBugPELw.

Chronic ocular sequelae in Stevens-Johnson syndrome: a genetic association study.

Purpose: This study sought to investigate the association of molecular markers with chronic ocular sequelae in Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN). Methods: One hundred SJS/TEN patients (200 eyes) with confirmed diagnosis were enrolled between July 2011 and July 2015 from a tertiary eye-care hospital, and their clinical histories were noted. Each eye was scored for severity of manifestation on a scale of 0-5. Peripheral blood samples were collected for DNA followed by screening for interleukin (IL-4, IL-13, IL-4R) polymorphisms, HLA-A locus allele typing, and sera to detect levels of the apoptotic markers granulysin and sFas L. Results: Of the 100 enrolled patients (53 males/47 females; age range: 6-58 years), the incriminating drugs were non-steroidal anti-inflammatory (52%), antibiotics (10%), sulphonamides (8%), anti-epileptics (6%), and unknown (24%). Significant differences in the frequencies of IL-4R polymorphism, HLA-A*3301, HLA-A*02, and HLA-A*2402 alleles, and elevated levels of granulysin and sFas L were observed in patients compared to controls. The ocular complications of conjunctival keratinization (p=0.004) showed an association with IL-13 promoter region (IL-13a) genotypes. Conclusions: The study highlights the possible association of interleukin-13 with severity-graded chronic sequelae and the role of HLA-A alleles- HLA-A*3301, HLA-A*02, and HLA-A*2402 in SJS/TEN causation and manifestation. Screening of these alleles may help caregivers to identify markers associated with severe and lifelong ocular complications, and help in appropriate treatment and management of the condition.

Graft detachments in endothelial keratoplasty.

Graft detachment is the most common complication of endothelial keratoplasty. With the ongoing advancements in the field of endothelial keratoplasty, our understanding of risk factors of graft detachments and its management has been evolving. Various prevention measures have been described in literature including presoaking the donor graft, anterior chamber tamponade, venting incisions, sutures to prevent dislocation of graft. Management of a detached graft involves secondary interventions such as rebubbling, suturing and regrafts. In this review, we discuss graft detachment in different types of endothelial keratoplasty techniques including Descemet stripping endothelial keratoplasty, Descemet stripping automated endothelial keratoplasty and Descemet's membrane endothelial keratoplasty; with emphasis on incidence, risk factors, preventive measures and their management.

Post-penetrating keratoplasty astigmatism.

Postoperative astigmatism is one of the common complications affecting visual outcomes after a penetrating keratoplasty. It can result from various factors related to host, donor and surgical technique, resulting in suboptimal visual outcome. While some of the measures taken during preoperative planning and during actual surgery can reduce the magnitude of postoperative astigmatism, postoperative correction of astigmatism is often required in cases with high degrees of astigmatism. When spectacles and contact lenses fail to provide optimal visual outcomes, various surgical techniques that include astigmatic keratotomy, compression sutures, toric intraocular lens placement, and laser refractive procedures can be considered. When none of these techniques are able to achieve a desired result with in the acceptable optical range, a repeat keratoplasty is considered a last option. We discuss the various causes and management of complication of postoperative astigmatism occurring after a full thickness corneal transplantation surgery.

Complications of laser-assisted in situ keratomileusis.

Laser-assisted in situ keratomileusis (LASIK) is one of the most commonly performed kerato-refractive surgery globally. Since its introduction in 1990, there has been a constant evolution in its technology to improve the visual outcome. The safety, efficacy, and predictability of LASIK are well known, but complications with this procedure, although rare, are not unknown. Literature review suggests that intraoperative complications include suction loss, free cap, flap tear, buttonhole flap, decentered ablation, central island, interface debris, femtosecond laser-related complications, and others. The postoperative complications include flap striae, flap dislocation, residual refractive error, diffuse lamellar keratitis, microbial keratitis, epithelial ingrowth, refractive regression, corneal ectasia, and others. This review aims to provide a comprehensive knowledge of risk factors, clinical features, and management protocol of all the reported complications of LASIK. This knowledge will help in prevention as well as early identification and timely intervention with the appropriate strategy for achieving optimal visual outcome even in the face of complications.

A Comparison of Refractive Accuracy Between Conventional and Femtosecond Laser Cataract Surgery Techniques Using Modern IOL Formulas.

PURPOSE: To compare the refractive outcome prediction accuracy between conventional (CCS) and femtosecond laser assisted (FLACS) cataract surgery techniques using optimized lens constants for modern intraocular lens (IOL) formulas. PATIENTS AND METHODS: Our retrospective, comparative, interventional case series, compared data from 196 eyes undergoing CCS and 456 eyes undergoing FLACS with Acrysof IOL (Alcon laboratories, Inc) implantation. After optimizing IOL constants, the predicted refractive outcome was calculated for all formulas for each case. This was compared to the actual refractive outcome to provide the prediction error. The performance of CCS and FLACS was compared by the absolute prediction error and percentage of eyes within 0.25D, 0.5D and 1.0D of anticipated refractive outcome. RESULTS: There was no statistically significant difference in median absolute error between the CCS and LACS groups for the Kane (0.256, 0.236; p=0.389), SRK T (0.298, 0.302, p=0.910), Holladay (0.312, 0.275; p=0.090), Hoffer Q (0.314, 0.289; p=0.330), Haigis (0.309, 0.258; p=0.177), Barrett Universal 2(0.250, 0.250; p=0.866), Holladay 2 (0.250, 0.258; p=0.860) and Olsen (0.260, 0.255; p=0.570) formulas. Similarly, there was no consistent difference between the two techniques for percentage of patients within 0.25, 0.50 and 1.0D of predicted refractive outcome for each formula. CONCLUSION: There was no difference in refractive outcome prediction accuracy between the CCS and FLACS techniques.

Laser-assisted corneal transplantation surgery.

Corneal transplant surgeries have a broad range of indications with outcomes largely dependent on surgeon experience. Traditional manual techniques have certain limitations pertaining to the preparation of donor tissue and the recipient bed that might affect the predictability of visual outcomes. Use of lasers for keratoplasty procedures not only improves the repeatability and consistency of the technique, but also enables the surgeon to control the thickness and shape of the transplant tissue tailored to the specific condition. Despite the advantages, cost-effectiveness and technical know-how remain the major challenges. We discuss the various techniques of laser-assisted keratoplasties with respect to their methods, precision, and efficacy in various corneal indications.

Shaped corneal transplantation surgery.

Since its inception in 1905, keratoplasty techniques have continuously evolved. Shaped keratoplasty procedures have allowed corneal surgeons to use complex graft-host junctions and non-circular graft designs to optimise wound strength and healing, facilitate early suture removal and expedite visual rehabilitation. While this was initially limited to penetrating procedures, shaped lamellar keratoplasty techniques have since emerged. Furthermore, the arrival of femtosecond laser has dramatically increased the range of graft designs available to surgeons, due to the technology's ability to precisely cut complex wound edges. This review describes the broad range of shaped keratoplasty grafts currently available and elaborates on their respective advantages and disadvantages in relation to conventional keratoplasty.

Outcomes of Cultivated Oral Mucosal Epithelial Transplantation in Eyes With Chronic Stevens-Johnson Syndrome Sequelae.

PURPOSE: To study the outcomes of cultivated oral mucosal epithelial transplantation (COMET) in eyes with chronic Stevens-Johnson syndrome (SJS) sequelae. DESIGN: Prospective interventional case series. METHODS: Forty-five eyes of 41 patients with chronic SJS sequelae were recruited and evaluated from 2013 to 2017 in an institutional setting. All patients underwent COMET, with an aim of fornix reconstruction and visual rehabilitation. Change in corrected distance visual acuity (CDVA), severity scores of various ocular surface parameters, and the occurrence of complications were documented during a follow up period of 2 years. Attainment and maintenance of a stable ocular surface, as assessed by change in the ocular surface severity scores was the primary outcome measure, while change in CDVA was the secondary outcome measure. RESULTS: The mean preoperative CDVA was 2.7± 0.5 logMAR, which improved to 1.5± 0.7 logMAR and 1.49± 0.98 postoperatively, at 1- and 2-year follow-up visit. Overall, 82.2% eyes (37/45) had improvement in visual acuity, 13.3% (6/45) experienced no change, whereas 2 eyes (4.4%) had worsening of visual acuity. The total ocular surface severity scores improved from a mean preoperative value of 29.1± 9.7 to 18.7± 7.2 postoperatively, at 2-year follow-up. Two eyes developed persistent epithelial defects, with progression to corneal melting requiring keratoplasty. CONCLUSIONS: COMET allows successful and sustained restoration of ocular surface anatomy with functional improvement, in eyes with chronic sequelae of SJS.

Impact of corneal refractive surgery on the precorneal tear film.

Corneal refractive surgeries are one of the commonly performed procedures for correction of refractive errors. Tear film abnormality is the most common postoperative complication of corneal refractive surgeries. Consequently, these procedures represent a clinically significant cause of dry eye disease. The mechanisms which lead to dry eye disease include corneal sensory nerve dysfunction, ocular surface desiccation, glandular apoptosis and ocular surface inflammation. Although transient tear film abnormalities occur in almost all patients following surgery, patients with pre-existing dry eye symptoms or dry eye disease are at significant risk of developing more severe or long-term ocular surface disease. As such, careful patient selection and preoperative evaluation is essential to ensuring successful surgical outcomes. This is particularly important with LASIK which has the strongest association with dry eye disease. Appropriate surface lubrication and anti-inflammatory therapy remains the cornerstone treatment. Timely and effective management is important to facilitate visual rehabilitation and reduce the risk of secondary complications. In this review we describe the causes, pathophysiology, risk factors, manifestations, and management of tear film dysfunction and dry eye disease following corneal refractive surgery.

Techniques of noncircular corneal transplantation.

PURPOSE OF REVIEW: The management of peripheral corneal diseases, including Mooren's ulcer, Terrien's marginal degeneration, peripheral ulcerative keratitis and pellucid marginal degeneration is challenging. Circular grafts must either be very large, resulting in the excision of healthy tissue, or eccentric, leading to high levels of astigmatism. This review summarizes the range of noncircular keratoplasty procedures available to surgeons, in addition to their indications, and surgical techniques. RECENT FINDINGS: Noncircular grafts have been demonstrated to be useful in the management of peripheral corneal diseases. They are effective at providing tectonic support and also facilitate visual rehabilitation. Specifically, they produce favourable postoperative visual and astigmatic outcomes. The evidence relating to these procedures is largely limited to case reports and case series, with no large-scale studies available. SUMMARY: Noncircular keratoplasty procedures are useful in the management of peripheral corneal diseases, which is typically difficult. There is a need for larger studies to investigate the relative advantages and disadvantages of these procedures and further characterize their outcomes.

Phototherapeutic keratectomy.

Phototherapeutic keratectomy is an excimer laser-based surgical procedure widely performed by corneal surgeons for treating anterior corneal stromal pathologies. Phototherapeutic keratectomy helps by ablating the corneal stroma, thereby improving corneal clarity and smoothening the surface. Transient discomfort and induced hyperopia from corneal flattening are the immediate postoperative concerns. The long-term course is often marked by the recurrence of original corneal pathology and corneal haze formation. Phototherapeutic keratectomy, however, allows for repeat stromal ablation for managing recurrences, as the corneal thickness permits, without affecting the outcome of future keratoplasty. Adjunctive methods such as topical mitomycin-C may be additionally used to reduce recurrence rates. Also, various masking agents such as carboxymethyl cellulose, sodium hyaluronate, and dextran are used in eyes with irregular corneal surface to allow for uniform stromal ablation. Overall, phototherapeutic keratectomy has provided corneal surgeons an additional surgical tool, particularly those residing in developing nations where the availability of donor corneal tissue is an important limiting factor.