Romesh I. Angunawela

Early Corneal Wound Healing and Inflammatory Responses after Refractive Lenticule Extraction (ReLEx)

PURPOSE To compare the early corneal wound repair and inflammatory responses after refractive lenticule extraction (ReLEx) and LASIK. METHODS Eighteen rabbits underwent ReLEx and another 18 underwent LASIK. Each group was divided into three subgroups of six rabbits each and these were subjected to refractive corrections of -3.00 diopters (D), -6.00 D, and -9.00 D. Slit lamp photography, anterior segment optical coherence tomography (AS-OCT), corneal topography, and in vivo confocal microscopy were performed 1 day after surgery. After euthanatization, the corneas were subjected to immunofluorescent staining for fibronectin, CD11b, Ki-67, and TUNEL assay. RESULTS On slit lamp microscopy, all corneas appeared clear pre- and postoperatively in both ReLEx and LASIK eyes. Corneal topography showed a more significant corneal flattening after LASIK than after ReLEx as the degree of correction was increased (P = 0.916 after -3.00 D correction to P = 0.097 after -9.00 D correction). In vivo confocal microscopy showed less light-scattering particles at the flap interface after ReLEx compared with LASIK. Immunostaining of fibronectin showed a less abundant expression in corneas that underwent ReLEx than LASIK. The differences became more marked as the power of correction was increased. Similar trend was seen in the number of CD11b-positive cells (P = 0.476 after -3.00 D correction to P < 0.001 after -9.00D correction). There was no marked disparity observed in cell death and proliferation between post-ReLEx and -LASIK eyes. CONCLUSIONS This study has shown that the ReLEx procedure may result in less topographic changes, inflammation, and early extracellular matrix deposition than LASIK, especially at high refractive correction.

Femtosecond Lenticule Extraction (FLEx): Clinical Results, Interface Evaluation, and Intraocular Pressure Variation

PURPOSE To characterize the clinical profile of femtosecond lenticule extraction (FLEx) correlated with ultrastructural analysis of the corneal interface and in vivo real-time intraocular pressure (IOP). METHODS Prospective clinical case series with experimental studies; consecutive patients underwent FLEx at a single tertiary center over 10 months with postsurgical follow-up of 3 months. The patients were divided into three groups according to spherical equivalence (SE) (A, < -5.0 diopters [D]; B, ≥ -5.00 D and < -9.00 D; and C, ≥ -9.0 D). Twelve human cadaveric eyes analyzed using scanning electron microscopy after receiving FLEx; 40 rabbit eyes received FLEx with in vivo IOP measurements. The main outcome measures were refractive outcomes from study subjects; with corneal interface and IOP in experimental studies. RESULTS Thirty-three subjects (22 females, 66.7%) underwent FLEx in both eyes (66 eyes). Mean age was 32 years (range, 21 to 46 years). Preoperative mean SE was -5.77 ± 2.04 D with astigmatism of -1.03 ± 0.72 D. There was a slight hyperopic shift (mean SE 0.14 ± 0.53 D); 94% achieved uncorrected visual acuity ≥20/25 3 months postoperatively. Refractive stability was achieved within 1 month (P < 0.001). Ultrastructurally, the smoothness of the corneal interface was independent of ablation depth (mean irregularity scores A, B, C: 8.8 ± 0.6, 10.3 ± 0.4, 8.7 ± 0.6, respectively; P = 0.88). The increase in IOP during FLEx was similar to that in femtosecond (FS)-LASIK, albeit a twofold duration of raised IOP in FLEx (P < 0.001). CONCLUSIONS These results suggest that FLEx is predictable and effective in treating myopia and myopic astigmatism. Experimental studies support the early clinical results and safety of this procedure.

Peripheral sterile corneal infiltrates and melting after collagen crosslinking for keratoconus

Corneal collagen crosslinking (CCC)with riboflavin/ ultraviolet-A (UV-A) is a new therapeutic technique designed to strengthen the cornea and arrest progressive corneal ectasia. Few complications have been reported following this therapy. We report the case of a 40-year-old patient who had CCC for progressive keratectasia secondary to keratoconus. The patient had no medical history of systemic illness or ocular inflammatory disorders. Corneal collagen crosslinking was performed under topical anesthesia (proxymethacaine 0.5% without preservative). The central 8.0 mm of epithelium was mechanically debrided without trephination using a hockey stick blade. Riboflavin 0.1% in 20% dextran drops (Medio-Cross, IROC AG) were applied every 3 minutes for 30-minute exposure to UVA (365 nm, 3 mW/cm) using a dedicated UVA source (UV-X, IROC AG). Riboflavin 0.1% drops were applied every 5 minutes throughout the UV exposure period. A bandage contact lens was placed at the end of surgery. Postoperatively, chloramphenicol 0.3% 4 times daily, dexamethasone 0.1% drops 2 hourly (preservativefree), and cyclopentolate 1% drops twice daily were prescribed. Five days postoperatively, 3 peripheral areas of marginal infiltration without overlying epithelial ulceration were observed (Figure 1, A). The central epithelial defect had healed. A diagnosis of noninfective keratitis was made, and the patient was started on twice hourly preservative-free levofloxacin and dexamethasone 0.1%. Markers for rheumatoid factor, antineutrophilic cytoplasmic antibodies, immune complexes, erythrocyte sedimentation rate, and C-reactive protein were all negative. One week later, much of the marginal infiltration had disappeared leaving areas of peripheral stromal thinning, estimated at 40% to 50% of the total corneal thickness at the maximal point. A linear superior area of superficial infiltration remained (Figure 1, B). Topical steroids were increased to hourly prednisolone acetate 1%, and topical antibiotic agents were reduced to 4 times daily. In the subsequent weeks, there was complete resolution of infiltrates but with residual marginal thinning (maximum 30%) (Figure 1, B). The best corrected visual acuity had returned to 6/18 at the last examination, 2 months after the crosslinking procedure.

United Kingdom survey of antibiotic prophylaxis practice after publication of the ESCRS Endophthalmitis Study

&NA; The European Society of Cataract & Refractive Surgeons Endophthalmitis Study published preliminary results in 2006 showing a near 5‐fold decrease in the rates of postoperative endophthalmitis with the use of intracameral cefuroxime. The study findings have generated considerable controversy, and 1 year later its recommendations had been heeded by only 6% of American Society of Cataract and Refractive Surgery (ASCRS) members. This poll sought to gauge the uptake among surgeons in the United Kingdom and survey their response to its findings. Fifty‐five percent of respondents were using intracameral cefuroxime; 48% had switched after publication of the ESCRS study. Of those remaining, 68% reported their main concern was the risk for dilution errors in the absence of a commercially preformulated preparation, with 67% stating they would switch if such a product became available. Sixty‐eight percent considered the lack of a subconjunctival cefuroxime treatment arm within the study a major methodology flaw. Sixty‐seven percent said they do not consider penicillin allergy a contraindication to intracameral cefuroxime use, with the remaining 33% opting for alternative antibiotic prophylaxis. The majority of United Kingdom and Ireland Society of Cataract and Refractive Surgeons members have switched to intracameral cefuroxime, despite the absence of previously preferred practice in the study design. The major barrier to its further use appears to be the lack of a commercially available preformulated preparation.

Refractive lenticule re-implantation after myopic ReLEx: a feasibility study of stromal restoration after refractive surgery in a rabbit model.

PURPOSE To investigate the potential of refractive lenticule (RL) storage and re-implantation in vivo as a method for reversing RL extraction (ReLEx) and restoring corneal stromal volume. METHODS ReLEx [-6.00 diopter (D) correction] was performed on six New Zealand White rabbits in one eye. Each extracted RL was tagged and orientated before storage at -80°C for 28 days. Each RL was then re-implanted autologously in the correct orientation after flap relifting. All animals were monitored for 28 days before being euthanized for immunohistochemical analysis. Unoperated fellow eyes were used as controls. All animals had regular pre- and postoperative slit lamp photography, in vivo confocal microscopy, anterior segment optical coherence tomography (AS-OCT), keratometry, and topography. RESULTS No intra-operative complications occurred and RL re-implantation was performed without complication. A mild intrastromal haziness was noted on day 3 after re-implantation (corneal haze grade: 2.20 ± 0.45), but corneas were clear on day 28 (0.20 ± 0.27). RL re-implantation restored central corneal thickness, and keratometric and topographic indices to near pre-operative values. Wound healing processes, marked by fibronectin and tenascin, and a few inflammatory cells were present along the re-implanted lenticular interfaces. No myofibroblasts formation, and Ki67- and TUNEL-positive cells were observed in the corneal stroma on postoperative day 28. CONCLUSIONS RL storage and re-implantation is a feasible technique for restoring stromal volume after myopic ReLEx, and may provide a method for restoring tissue in ectatic corneas, or provide an opportunity for further refractive surgery and presbyopic treatment.

Reversible Femtosecond Laser-Assisted Myopia Correction: A Non-Human Primate Study of Lenticule Re-Implantation after Refractive Lenticule Extraction

LASIK (laser-assisted in situ keratomileusis) is a common laser refractive procedure for myopia and astigmatism, involving permanent removal of anterior corneal stromal tissue by excimer ablation beneath a hinged flap. Correction of refractive error is achieved by the resulting change in the curvature of the cornea and is limited by central corneal thickness, as a thin residual stromal bed may result in biomechanical instability of the cornea. A recently developed alternative to LASIK called Refractive Lenticule Extraction (ReLEx) utilizes solely a femtosecond laser (FSL) to incise an intrastromal refractive lenticule (RL), which results in reshaping the corneal curvature and correcting the myopia and/or astigmatism. As the RL is extracted intact in the ReLEx, we hypothesized that it could be cryopreserved and re-implanted at a later date to restore corneal stromal volume, in the event of keratectasia, making ReLEx a potentially reversible procedure, unlike LASIK. In this study, we re-implanted cryopreserved RLs in a non-human primate model of ReLEx. Mild intrastromal haze, noted during the first 2 weeks after re-implantation, subsided after 8 weeks. Refractive parameters including corneal thickness, anterior curvature and refractive error indices were restored to near pre-operative values after the re-implantation. Immunohistochemistry revealed no myofibroblast formation or abnormal collagen type I expression after 8 weeks, and a significant attenuation of fibronectin and tenascin expression from week 8 to 16 after re-implantation. In addition, keratocyte re-population could be found along the implanted RL interfaces. Our findings suggest that RL cryopreservation and re-implantation after ReLEx appears feasible, suggesting the possibility of potential reversibility of the procedure, and possible future uses of RLs in treating other corneal disorders and refractive errors.

Intraocular fluid dynamics and retinal shear stress after vitrectomy and gas tamponade.

PURPOSE To evaluate fluid dynamics and fluid shear stress on the retinal wall in a model eye after vitrectomy and gas tamponade in relation to saccadic eye movements and sudden head movements and to correlate the results with gas fill fraction (GF). Methods. Analyses was undertaken using high-resolution computational fluid dynamic software. The fluid volume within the eye was discretized using 6 × 10(5) elements and solved with a volume-of-fluid METHOD The eye was abstracted to a sphere. Vertical and horizontal saccades and sudden rectilinear displacement of the head were examined. GF was varied from 20% to 80% of the eye height filled with gas. RESULTS Maximum shear stress during horizontal and vertical saccades was 1.0 Pa (Pascal) and 2.5 Pa, respectively, and was dependent on GF. Rapid rectilinear acceleration of the head caused a maximum shear stress of 16 Pa, largely independent of GF. Fluid sloshing within the eye decayed within 0.1 second. Stresses were maximum at the contact line and equator of the eye and were parallel to the direction of motion. CONCLUSIONS This study predicts that saccadic eye movements and normal head movements after vitrectomy and gas tamponade generate only small fluid shear stresses on the retina that are below published norms for retinal adhesion strength. Sudden, jerking head movements generate fluid shear forces similar to retinal adhesion strength that localize to the area of gas-fluid interface. Fluid sloshing occurs after movement, but rapidly decays on cessation of movement. These results suggest that restrictive posturing after vitrectomy and gas tamponade may be unnecessary. Patients should avoid sudden head movements.

Reproducibility and age-related changes of ocular parametric measurements in rabbits

BackgroundThe rabbit is a common animal model for ophthalmic research, especially corneal research. Ocular structures grow rapidly during the early stages of life. It is unclear when the rabbit cornea becomes mature and stabilized. We investigated the changes of keratometry, refractive state and central corneal thickness (CCT) with age. In addition, we studied the intra- and inter-observer reproducibility of anterior chamber depth (ACD) and anterior chamber width (ACW) measurements in rabbits using anterior segment-optical coherence tomography (AS-OCT).ResultsThe growth of New Zealand White rabbits (n = 16) were monitored from age 1 to 12 months old. Corneal keratometric and refractive values were obtained using an autorefractor/keratometer, and CCT was measured using an AS-OCT. Keratometry and CCT changed rapidly from 1 to 7 months and appeared to be stabilizing after 8 months. The reduction of corneal curvature was approximately 1.36 diopter (D)/month from age 1 to 7 months, but the change decelerated to 0.30 D/month from age 8 to 12 months. An increase of 10 μm/month in CCT was observed from age 1 to 7 months, but the gain was reduced to less than 1 μm/month from age 8 to 12 months. There was a hyperopic shift over the span of 12 months, albeit the increase in spherical equivalent was slow and gradual. Rabbits of random age were then selected for 2 repeated ACD and ACW measurements by 2 independent and masked observers. Bland-Altman plots revealed a good agreement of ACD and ACW measurements inter- and intra-observer and the ranges of 95% limit of agreement were acceptable from a clinical perspective.ConclusionsCorneal keratometry, spherical equivalent refraction and CCT changed significantly during the first few months of life of rabbits. Young rabbits have been used in a large number of eye research studies. In certain settings, the ocular parametric changes are an important aspect to note as they may alter the findings made in a rabbit experimental model. In this study, we have also demonstrated for the first time a good between observer reproducibility of measurements of ocular parameters in an animal model by using an AS-OCT.

Ex-vivo ocular surface stem cell therapies: current techniques, applications, hurdles and future directions.

Engineered tissue derived from ocular surface stem cells (SCs) are a cutting edge biotechnology for repair and restoration of severely damaged eyes as a result of ocular surface dysfunction because of SC failure. Ex-vivo SC expansion techniques have advanced significantly since the first patients were treated in the late 1990s. The techniques and clinical reports reviewed here highlight the evolution and successes of these techniques, while also revealing gaps in our understanding of ocular surface and SC biology that drives further research and development in this field. Although hurdles still remain before stem-cell-based therapies are more widely available for patients with devastating ocular surface disease, recent discoveries in the field of mesenchymal SCs and the potential of induced pluripotent SCs heralds a promising future for clinicians and our patients.

Corneal transplantation: changing techniques.

We read with interest the article by Larkin et al. “Centre-specific variation in corneal transplant outcomes in the United Kingdom,” which was published in February 2011 (1). However, we felt that there were a few points that need clarification. The authors report that graft survival rates for corneal transplantation were not significantly different between those performed by highand low-volume centers (more than 50 and less than 10 procedures, respectively) and between highand low-volume surgeons (more than 30 and less than 10 procedures, respectively) at 5 years in patients with the diagnosis of keratoconus, Fuch’s endothelial disease, or pseudophakic corneal edema (1). Mean best-corrected visual acuity (BCVA) at 2 years was the same in highvs. low-volume centers or surgeons. However, a larger proportion of patients in high-volume centers or surgeons achieved BCVA of 6/12 or better at 2 years (1). The title of the article indicates a study in corneal transplant outcomes. However, corneal transplantation encompasses many techniques, and in 2011 corneal transplantation is not synonymous with penetrating keratoplasty (PK), the procedure that all the patients underwent in this study. PK is a technique where all layers of the cornea are replaced. However, there are many newer surgical corneal transplantation techniques that are designed to only replace the damaged layer of tissue and retain the unaffected healthy cornea. These techniques are called lamellar keratoplasty (LK) (2, 3). Hence, the title of the article should be “Centre-specific variation in penetrating keratoplasty outcomes in the United Kingdom.” The cornea is a highly organized, transparent tissue with five distinct layers: epithelium, Bowman’s membrane, stroma, Descemet’s membrane (DM), and endothelium (2). This layered structure allows selective replacement of only the diseased cornea a feasible option. LK is divided into two major types: (1) anterior lamellar keratoplasty (ALK) where the anterior part of the cornea is completely or partial replaced by donor allograft tissue while retaining the recipient unaffected DM and endothelium or (2) endothelial keratoplasty (EK) where there is allograft replacement of the diseased DM and endothelium but the recipients stroma is retained (2, 3). Over the past decade, there has been a shift to lamellar procedures by most progressive corneal surgeons. This pattern of shifting in techniques is clearly seen from our audit data at the Singapore National Eye Centre (Fig. 1). From 1991 to 2010, our data show a change in technique which clearly demonstrates a shift away from PK in direction to more selective lamellar procedures. From 2006 to 2010, the shift is more obviously seen mainly because of the emergence of the EK technique. The diagnoses reviewed in the article by Larkin et al., which underwent PK, would now undergo either an EK for Fuch’s endothelial disease/pseudophakic corneal edema or ALK for keratoconus in the majority of cases. Hence, the results in the article are really applicable to surgery per-