Interocular Contrast Balancing Partially Improves Stereoacuity in Keratoconus.

SIGNIFICANCE: Partial improvement in stereoacuity may be achieved by balancing the contrast input to the two eyes of patients with bilaterally asymmetric keratoconus. PURPOSE: Interocular differences in image quality, characterized by dissimilar contrast loss and phase shifts, are implicated in stereoacuity loss in keratoconus. This study determined whether contrast balancing improves stereoacuity in this disease condition and, if so, whether it is dependent on the baseline interocular contrast imbalance. METHODS: Interocular contrast imbalance and stereoacuity of 43 subjects (16 to 33 years) with bilaterally asymmetric keratoconus were tested with spectacle correction as baseline using a binocular rivalry paradigm and random-dot stereograms, respectively. Stereoacuity measurements were repeated in a subset of 33 subjects at their contrast balance point (i.e., contrast level in stronger eye allowing balanced rivalry with 100% contrast in weaker eye) and with contrast levels biased in favor of stronger or weaker eye, all conditions in randomized order. RESULTS: Contrast imbalance level was significantly correlated with the subject's stereoacuity at baseline ( r = -0.47, P = .002). The median (25th to 75th interquartile range) stereoacuity improved by 34.6% (19.0 to 65.1%) from baseline (748.8 arc sec [261.3 to 1257.3 arc sec]) to the contrast balanced condition (419.0 arc sec [86.6 to 868.9 arc sec]) ( P < .001), independent of their baseline stereoacuity or contrast imbalance levels ( r < 0.2, P > .26 for both). Contrast bias in favor of the weaker eye (881.3 arc sec [239.6 to 1707.6 arc sec]) worsened stereoacuity more than a bias toward the stronger eye (502.6 arc sec [181.9 to 1161.4 arc sec]), both relative to the contrast balanced condition ( P < .002). CONCLUSIONS: Interocular contrast balancing partially improves stereoacuity in bilaterally asymmetric keratoconus, independent of their baseline contrast imbalance level. Cyclopean viewing may be inherently biased toward the input from the stronger eye in keratoconus.

Differences in Image Quality after Three Laser Keratorefractive Procedures for Myopia.

SIGNIFICANCE: Psychophysical estimates of spatial and depth vision have been shown to be better after bilateral ReLEx small-incision lenticule extraction (SMILE) refractive surgery for myopia, relative to photorefractive keratectomy (PRK) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). The present study provides the optical basis for these findings using computational image quality analysis. PURPOSE: This study aimed to compare longitudinal changes in higher-order wavefront aberrations and image quality before and after bilateral PRK, FS-LASIK, and SMILE refractive procedures for correcting myopia. METHODS: Wavefront aberrations and image quality of both the eyes of 106 subjects (n = 40 for FS-LASIK and SMILE and n = 26 for PRK) were determined pre-operatively and at 1-week, 1-month, 3-month, and 6-month post-operative intervals using computational through-focus analysis for a 6-mm pupil diameter. Image quality was quantified in terms of its peak value and its interocular difference, residual defocus that was needed to achieve peak image quality (best focus), and the depth of focus. RESULTS: The increase in root mean squared deviations of higher-order aberrations post-operatively was lesser after SMILE (1-month visit median [25th to 75th interquartile range], 0.34 µm (0.28 to 0.39 µm]) than after PRK (0.80 µm [0.74 to 0.87 µm]) and FS-LASIK (0.74 µm [0.59 to 0.83 µm]; P ≤ .001), all relative to pre-operative values (0.20 µm [0.15 to 0.30 µm]). The peak image quality dropped and its interocular difference increased, best focus shifted myopically by 0.5 to 0.75 D, and depth of focus widened significantly after PRK and FS-LASIK surgeries, all relative to pre-operative values (P < .001). All these changes were negligible but statistically significant in a minority of instances after SMILE surgery (P ≥ .01). CONCLUSIONS: Although all three refractive surgeries correct myopia, the image quality and its similarity between eyes are better and closer to pre-operative values after SMILE, compared with FS-LASIK and PRK. These results can be explained from the underlying increase in higher-order wavefront aberrations experienced by the eye post-operatively.

The Value of Eccentric Infrared Photorefraction in Evaluating Keratoconus.

SIGNIFICANCE: Nonlinearity in the luminance profile of eccentric, infrared photorefraction may be used to differentiate corneal diseases such as keratoconus that distort the cornea, relative to regular refractive errors. PURPOSE: This study aimed to determine the profile of eccentric, infrared photorefraction in keratoconus as a prototypical disease model for distorted corneas and identify a parameter in this profile for differentiating such disease conditions from healthy controls. METHODS: Photorefraction reflex of 75 eyes with forme fruste to advanced keratoconic cases and that of 75 eyes of controls with regular refractive errors (spherical equivalent, +0.50 to -11.75 D; astigmatism, -0.50 to -4.50 D across 0 to 180° axes) were obtained over their natural pupils under unaided viewing using a custom-designed photorefractor placed at 1 m from the subject. The test was repeated in 10 controls with 4 and 6 D of trial-lens-induced myopia and myopic astigmatism at 0, 90, 45, and 135°. Linear regression was performed on the luminance profile across the pupil, and the departure of the data from linearity was estimated using the average residual error of the fit (Res avg ). RESULTS: Photorefraction profiles varied linearly across the pupil in controls, with slopes increasing with refractive error ( r = 0.87; P < .001) and Res avg remaining invariant of refractive error ( r = -0.29; P > .4). Corresponding profiles in keratoconus significantly departed from linearity, with Res avg progressively increasing with disease severity ( r = 0.66; P < .001). Res avg of 0.03 gray-scale units/pixel distinguished keratoconus from controls with sensitivity increasing from 66.7 to 100% for mild to advanced keratoconus and specificity remaining ≥97.1% across disease severity. Induced myopia and myopic astigmatism produced predictable changes in luminance profile slopes but with no change in Res avg values. CONCLUSIONS: Unlike regular myopia and astigmatism, the photorefraction reflex is significantly nonlinear in keratoconus because of the distorted cornea. Measures of nonlinearity in luminance profile may be incorporated in commercial photorefractors for differentiating such disease conditions from regular refractive errors.

Visual photosensitivity threshold and objective photosensitivity luminance in healthy human eyes assessed using an automated ocular photosensitivity analyser: a step towards translation of a clinical tool for assessing photophobia.

PURPOSE: To evaluate the visual photosensitivity threshold and objective photosensitivity luminance in healthy eyes, thereby providing a normative dataset that will lead to a better understanding of diseases causing photophobia. METHODS: This was a prospective cross-sectional study. Emmetropes whose visual acuity was better than 0.18 logMAR (6/9) with no other ocular abnormality were included. Headache Impact Test-6 and visual light sensitivity questionnaires were administered. Visual photosensitivity threshold was measured subjectively using the ocular photosensitivity analyser. Objective photosensitivity luminance was assessed manually by evaluating videos recorded using an infrared camera and noting the intensity of light at the first squeezing reflex. RESULTS: Seventy five normal subjects (age range, 7-71 years) were included. Median age was 32.7 years (inter-quartile range, 20.3-47.9 years). Forty (53.3%) were males. Median Headache Impact Test score was 38 (inter-quartile range, 36-42) and visual light sensitivity questionnaire score was 11 (inter-quartile range, 8-15). Mean (standard deviation) right eye, left eye and binocular visual photosensitivity threshold was 3.34 (0.78), 3.33 (0.81) and 3.37 (0.78) loglux, respectively. There was a significant negative correlation of visual light sensitivity questionnaire scores with right eye, left eye and binocular visual photosensitivity thresholds, and positive correlation of age with binocular visual photosensitivity thresholds. Mean (standard deviation) right eye, left eye and binocular objective photosensitivity luminance was 3.25 (0.55), 3.35 (0.47) and 3.15 (0.52) loglux, respectively. Age was only positively correlated with binocular objective photosensitivity luminance, and there was no correlation between age and right eye or left eye objective photosensitivity luminance. CONCLUSIONS: The study characterised, for the first time, objective photosensitivity luminance and established normative data for both visual photosensitivity threshold and objective photosensitivity luminance. The data will help in understanding the pathophysiology of diseases causing photophobia, monitoring the disease progression and evaluating treatment modalities.

Complications and visual outcomes of cataract surgery in patients with pseudoexfoliation.

PURPOSE: To compare outcomes of cataract surgery performed by ophthalmic trainees and consultants in patients associated with pseudoexfoliation (PXF) METHODS: Retrospective review of medical records of all patients with PXF who had undergone cataract surgery from January 2016 to December 2018 at L V Prasad Eye Institute, Hyderabad, India, were analysed RESULTS: A total of 914 eyes were included in the study; surgeries on 501 (54.8%) eyes with PXF were performed by trainees, while 413 (45.2%) were performed by consultants. Posterior capsule rupture (PCR) with vitreous loss (VL) occurred in significantly fewer eyes operated on by consultants (n = 8, 1.9%) than those operated on by trainees (n = 23, 4.5%) (p = 0.002). Eyes that underwent small incision cataract surgery (n = 100, 21.2%) had a significantly greater number of complications than those that underwent phacoemulsification (n = 31, 7.1%) (p = 0.00001). Multivariate logistic regression analysis shows that chances of a complication are higher when operated on by a trainee (OR = 1.59, 95% CI: 1.09-2.34, p = 0.02).The mean logMAR corrected distance visual acuity of patients one month post-surgery was significantly higher for patients in the consultant group (0.15 ± 0.3) than for those in the trainee group (0.2 ± 0.4) (p = 0.003). CONCLUSION: Patients with PXF operated on by trainees for cataract had a relatively higher risk of developing PCR with VL and had poorer visual outcomes than those operated on by consultants.

Longitudinal Changes in Optical Quality, Spatial Vision, and Depth Vision after Laser Refractive Surgery for Myopia.

SIGNIFICANCE: Laser refractive surgery procedures are efficacious at correcting myopia, but they result in long-term deterioration of optical quality that affects monocular and binocular visual performance. The study shows that the optical quality of the two eyes needs to be similar to optimize binocular visual performance after surgery. PURPOSE: This study aimed to systematically analyze longitudinal changes in optical quality, high- and low-contrast logMAR acuity and random-dot stereoacuity before and after three refractive surgery procedures for correcting myopia. METHODS: A total of 106 subjects (laser-assisted in situ keratomileusis, 40; photorefractive keratectomy, 26; small-incision lenticule extraction, 40) with myopia and astigmatism ≤1.5 D participated in this prospective cohort-based study. All aforementioned outcome variables were measured in both eyes pre-operatively and 1 week and 1, 3, and 6 months post-operatively. RESULTS: Pre-operative myopic spherical equivalent of refraction (median [25th to 75th interquartile range], -6.4 D [-8.0 to -4.2 D] for laser-assisted in situ keratomileusis, -4.3 D [-5.0 to -3.5 D] for photorefractive keratectomy, -5.5 D [-6.5 to -4.3 D] for small-incision lenticule extraction) was corrected to within ±0.75 D of emmetropia in all cohorts up to 6 months post-operatively (P < .001). Higher-order wavefront aberrations, uncorrected high- and low-contrast logMAR acuity, and stereoacuity all worsened and remained so up to 6 months post-operatively, relative to pre-operative values (P < .001). Stereoacuity worsened with both interocular average and difference in the magnitude of higher-order aberrations, whereas logMAR acuities worsened only with interocular average of these aberrations (r ≥ 0.40; P < .01 for all). CONCLUSIONS: Although the refractive surgery procedures tested here correct myopia, they result in a sustained (up to 6 months) loss of optical quality and spatial and depth-related visual functions post-operatively. Both interocular average and difference in the eye's optical quality seem to impair binocular visual functions after refractive surgery for myopia.

Treatment Practices and Outcomes of Meibomian Gland Dysfunction at a Tertiary Center in Southern India.

OBJECTIVE: To describe the current treatment practices for meibomian gland dysfunction (MGD) at a tertiary eye center, together with the subjective outcomes and compliance behaviors of patients. METHODS: This retrospective cohort study reviewed medical records for MGD severity grading, treatment prescribed, and follow-up schedule. In addition, participants were surveyed to gauge subjective outcomes and treatment adherence. RESULTS: Eight hundred ten patients were diagnosed with "MGD" or "meibomitis" and had a total of 14 different treatment combinations prescribed. In 3.0% of cases, there was no treatment specified. As MGD severity increased, it became more likely that management would be applied and this was also associated with significantly longer treatment durations (P=0.02) and shorter follow-up periods (P<0.001). Posttreatment subjective outcomes and treatment adherence surveys had a response rate of 36.7% and 24.1% respectively. Overall, 53.5% reported sustained improvement, 40.7% no improvement, and 5.7% experienced temporary relief. Although no treatment regimen seemed to be more efficacious than others, patients showed greater adherence when using topical reagents compared with lid hygiene measures (P≤0.002). CONCLUSION: Clinicians, in this large tertiary eye center, use a wide range of treatment regimens to manage MGD. This suggests the need for development of standard management protocols. Whether alone, or in combination, no MGD treatment significantly improved subjective symptoms, a result that may be influenced by compliance behaviors. Use of topical reagents (eye drops or ointment) seemed to be associated with the best compliance. Future focus on more effective MGD treatments is needed to improve practical outcomes.

The use of Bowman's layer vertical topographic thickness map in the diagnosis of keratoconus.

PURPOSE: To evaluate the use of Bowman's layer (BL) vertical topographic thickness maps in diagnosing keratoconus (KC). DESIGN: Prospective, case control, interventional case series. PARTICIPANTS: A total of 42 eyes: 22 eyes of 15 normal subjects and 20 eyes of 15 patients with KC. INTERVENTION: Bowman's layer 2-dimensional 9-mm vertical topographic thickness maps were created using custom-made ultra high-resolution optical coherence tomography. MAIN OUTCOME MEASURES: Bowman's layer average and minimum thicknesses of the inferior half of the cornea, Bowman's ectasia index (BEI; defined as BL minimum thickness of the inferior half of the cornea divided by BL average thickness of the superior half of the cornea multiplied by 100), BEI-Max (defined as BL minimum thickness of the inferior half of the cornea divided by BL maximum thickness of the superior half of the cornea multiplied by 100), keratometric astigmatism (Ast-K) of patients with KC, and average keratometric (Avg-K) readings. RESULTS: In patients with KC, BL vertical thickness maps disclosed localized relative inferior thinning of the BL. Inferior BL average thickness (normal = 15±2, KC = 12±3 µm), inferior BL minimum thickness (normal = 13±2, KC = 7±3 µm), BEI (normal = 91±7, KC = 48±14), and BEI-Max (normal = 75±8; KC = 40±13) all showed highly significant differences in KC compared with normal subjects (P< 0.001). Receiver operating characteristic (ROC) curve analysis showed excellent predictive accuracy for BEI and BEI-Max with 100% sensitivity and specificity (area under the curve [AUC] of 1) with cutoff values of 80 and 60, respectively. The AUC of inferior BL average thickness and minimum thickness were 0.87 and 0.96 with a sensitivity of 80% and 93%, respectively, and a specificity of 93% and 93%, respectively. Inferior BL average thickness, inferior BL minimum thickness, BEI, and BEI-Max correlated highly to Ast-K (R = -0.72, -0.82, -0.84, and -0.82, respectively; P< 0.001) and to Avg-K (R = -0.62, P< 0.001; R = -0.59, P = 0.001; R = -0.60, P< 0.001; and R = -0.59, P = 0.001, respectively). CONCLUSIONS: Bowman's layer vertical topographic thickness maps of patients with KC disclose characteristic localized relative inferior thinning. Inferior BL average thickness, inferior BL minimum thickness, BEI, and BEI-Max are qualitative and quantitative indices for the diagnosis of KC that accurately correlate with the severity of KC. In our pilot study, BEI and BEI-Max showed excellent accuracy, sensitivity, and specificity in the diagnosis of KC.

Central Toxic Keratopathy After Collagen Cross-Linking: A Case Series.

PURPOSE: The aim of this study was to report a case series of central toxic keratopathy (CTK) after collagen cross-linking (CXL) in keratoconus. METHODS: This is a retrospective case series between January 2020 and September 2021. In this period, CXL was performed for progressive keratoconus in 964 eyes. CXL was performed using the epithelium-off accelerated protocol in all patients with a riboflavin soak time of 20 minutes and a UVA light exposure of 9 mW for 10 minutes using the Avedro KXL (Glaukos Inc, Aliso Viejo, CA) cross-linking system. RESULTS: Twelve of 964 eyes (1.2%) developed CTK within 1 week of CXL. All patients presented with well-circumscribed, central disciform haze that was broader in the anterior stroma and narrower in the posterior stroma. We noted initial flattening in keratometry up to 3 months post-CXL in these patients, which gradually steepened over 12 months, but did not reach preoperative levels. We also noted exuberant flattening in pachymetry in the first 3 months, which improved over 12 months. There was a statistically significant decrease in pachymetry in patients who developed CTK at 3 and 12 months postoperatively when compared to patients who underwent CXL but did not develop CTK. CONCLUSIONS: Several reports of CTK postrefractive surgery have been described previously. However, the association of CXL in the development of CTK has not been described previously. Here, we elucidated the clinical features of CTK after CXL and how it differs from corneal scarring or haze that occurs post-CXL.

Central toxic keratopathy leading to epithelial ingrowth following femtosecond LASIK.

We report a case of a woman in her 30s who underwent femtosecond LASIK (laser-assisted in situ keratomileusis) in both eyes to correct her simple myopic astigmatism. After the surgery, both eyes developed diffuse lamellar keratitis, and intensive topical steroids were initiated to control the same. Subsequently, central toxic keratopathy (CTK) developed bilaterally. Three weeks after the surgery, the right eye showed signs of progressive epithelial ingrowth involving the pupillary area. Surgical intervention in the form of flap relift followed by debridement of the epithelial cells and an alcohol interface wash were performed to treat the same. This is the first report of an epithelial ingrowth following CTK after femtosecond LASIK.

Evolving Trends in the Diagnosis and Management of Keratoconus Over 3 Decades.

PURPOSE: To report the trends in the clinical presentation, diagnosis, and management of keratoconus (KC) in patients presenting to a multitier hospital network over 33 years. METHODS: This retrospective study included patients with KC presenting from 1987 to 2020. Patients with KC in at least 1 eye were included. The data of 20,576 patients included in this study were retrieved from the electronic medical record database. Data on patient demographics, ocular diagnosis, contact lens usage, and surgical history were collected and exported for analysis. Descriptive statistics and chi square test were used for statistical analysis. RESULTS: A total of 20,576 KC cases were seen from 1987 to 2020. Mean age at diagnosis reduced from 29.3 years (1987-1991) to 22.2 years (2016-2020). Adults (76.64%) were commonly affected with a majority being male (61.25%). Use of contact lenses increased from 4.34% (2002-2006) to 11.23% (2016-2020). Of the total number of surgical interventions, collagen crosslinking (CXL) constituted more than 1/5th (22.28%) between 2007 and 2011, which increased to more than half between 2012 and 2016 (53.61%) and almost 3/4th (72.53%) between 2017 and 2020. Advances in lamellar surgery have led to more patients undergoing deep anterior lamellar keratoplasty (DALK) as compared with penetrating keratoplasty. In the last 8 years, 17.2% patients underwent surgery and the most common was CXL (14.77%) followed by DALK (1.72%) and penetrating keratoplasty (1.04%). CONCLUSIONS: We report the trends in the clinical presentation and management of KC over 3 decades. In the last 33 years, advances in diagnostics have helped diagnose KC earlier. Contact lenses and advances in CXL have reduced the number of keratoplasties in KC, DALK being more common.

Investigation of mechanical strength and structure of corneal graft-host junction.

Dehiscence is a common complication of corneal transplant surgery involving separating the graft from the host eye. The present article aims to investigate fundamental insights into the mechanical and structural aspects of the graft-host junction (GHJ) of a graft that survived in a patient for 13 years after penetrating keratoplasty (PK). Additionally, it adopts the sutur retention strength (SRS) test procedure defined in ISO:7198-2016 and aims to provide a comprehensive test protocol to study the biomechanics of the GHJ in extracted PK buttons. A 9 mm corneal button with GHJ was extracted from a 46-year-old patient who underwent PK 13 years back. The strength of the GHJ was quantified using the SRS test. Corresponding control results were obtained from the SRS tests of a corneoscleral button with no history of any refractive procedure. Birefringence, histological, and scanning electron microscopy (SEM) imaging were used to visualize the microstructural details of the GHJ. The strength of the GHJ was observed to be ten times lower than the native cornea. Histopathological features, such as fragmented Bowman's layer, and fibrosis with a clear demarcation line between host and graft tissue, were observed at the GHJ, suggesting a weak bond across the GHJ. The low strength of the GHJ in PK indicates the high susceptibility of the GHJ towards wound dehiscence.

RiTe conjugate mediated corneal collagen crosslinking, a novel therapeutic intervention for keratoconus - in vitro and in vivo study.

Corneal collagen crosslinking (CXL) is an effective method to halt the disease progression of keratoconus, a progressive corneal dystrophy leading to cone shaped cornea. Despite the efficacy of standard protocol, the concerning step of this procedure is epithelial debridement performed to facilitate the entry of riboflavin drug. Riboflavin, a key molecule in CXL protocol, is a sparsely permeable hydrophilic drug in corneal tissues. The present study has employed cell penetrating peptide (CPP), Tat2, to enhance the penetration of riboflavin molecule, and thereby improve currently followed CXL protocol. This study demonstrates approximately two-fold enhanced uptake of CPP riboflavin conjugate, Tat2riboflavin-5'Phosphate (RiTe conjugate), both in vitro and in vivo. Two different CXL protocols (Epi ON and Epi OFF) have been introduced and implemented in rabbit corneas using RiTe conjugate in the present study. The standard and RiTe conjugate mediated CXL procedures exhibited an equivalent extent of crosslinking in both the methods. Reduced keratocyte loss and no endothelial damage in RiTe conjugate mediated CXL further ascertains the safety of the proposed CXL protocols. Therefore, RiTe conjugate mediated CXL protocols present as potential alternatives to the standard keratoconus treatment in providing equally effective, less invasive and patient compliant treatment modality.

Keratoconus in India: Clinical presentation and demographic distribution based on big data analytics.

PURPOSE: This paper aims to describe the clinical presentation and demographic distribution of keratoconus (KCN) in India by analyzing the electronic medical records (EMR) of patients presenting at a multitier ophthalmology hospital network. METHODS: This cross-sectional hospital-based study included the data of 2,384,523 patients presenting between January 2012 and March 2020. Data were collected from an EMR system. Patients with a clinical diagnosis of KCN in at least one eye were included in this study. Univariate analysis was performed to identify the prevalence of KCN. A multiple logistic regression analysis was performed using R software (version 3.5.1), and the odds ratios are reported. RESULTS: Data were obtained for 14,749 (0.62%) patients with 27,703 eyes diagnosed with KCN and used for the analysis. The median age of the patients was 22 (inter-quartile range (IQR): 17-27). In total, 76.64% of adults (odds ratio = 8.77; P = <0.001) were affected the most. The majority of patients were male (61.25%), and bilateral (87.83%) affliction was the most common presentation. A significant proportion of the patients were students (63.98%). Most eyes had mild or no visual impairment (<20/70; 61.42%). Corneal signs included ectasia (41.35%), Fleischer ring (44.52%), prominent corneal nerves (45.75%), corneal scarring (13.60%), Vogts striae (18.97%), and hydrops (0.71%). Only 7.85% showed an association with allergic conjunctivitis. A contact lens clinic assessment was administered to 47.87% of patients. Overall, 10.23% of the eyes affected with KCN underwent a surgical procedure. the most common surgery was collagen cross-linking (8.05%), followed by deep anterior lamellar keratoplasty (1.13%) and penetrating keratoplasty (0.88%). CONCLUSION: KCN is usually bilateral and predominantly affects males. It commonly presents in the second and third decade of life, and only a tenth of the affected eyes require surgical treatment.

Teleophthalmology at a primary and tertiary eye care network from India: environmental and economic impact.

OBJECTIVE: To evaluate the environmental and economic impact of teleophthalmological services provided by a primary (rural) and tertiary (urban) eyecare network in India. METHODS: This prospective study utilised a random sampling method, and administered an environmental and economic impact assessment questionnaire. The study included 324 (primary: 173; tertiary: 151) patients who received teleconsultations from July to September 2022. The primary network (rural) used a colour-coded triage system (Green: eye conditions managed by teleconsult alone; yellow: semi-urgent referral within 1 week to a month, red: urgent referral within a day to a week). The tertiary network (urban) included new and follow-up patients. The environmental impact was assessed by estimating the potential CO2 emissions saved by avoiding travel for various transport modes. Economic impact measured by the potential cost savings from direct (travel) and indirect (food and wages lost) expenses spent by yellow and red referrals (primary) and the first-visit expenses of follow-up (tertiary) patients. RESULTS: The primary rural network saved 2.89 kg CO2/person and 80 km/person. The tertiary urban network saved 176.6 kg CO2/person and 1666 km/person. The potential cost savings on travel expenses were INR 19,970 (USD 250) for the primary (average: INR 370 (USD 4.6) per patient) and INR 758,870 (USD 9486) for the tertiary network (average: INR 8339 (USD 104) per patient). Indirect cost savings (food and wages) were of INR 29,100 (USD 364) for the primary and INR 347,800 (USD 4347) for the tertiary network. CONCLUSION: Teleophthalmology offers substantial environmental and economic benefits in rural and urban eyecare systems.

Corneal thickness in keratoconus: comparing optical, ultrasound, and optical coherence tomography pachymetry.

PURPOSE: To compare the central and peripheral pachymetry measurements determined using Orbscan IIz (Bausch & Lomb, Rochester, NY), Visante optical coherence tomography (OCT; Carl Zeiss Meditec, Dublin, CA), and RTVue OCT (Oculus Technologies, Wynwood, WA) with ultrasound pachymetry in eyes with established keratoconus and to evaluate the agreement between them. DESIGN: Evaluation of diagnostic technologies. PARTICIPANTS: One hundred six eyes of 67 consecutive patients with a clinical diagnosis of keratoconus ranging in age from 12 to 40 years. METHODS: Central corneal thickness (CCT) was determined by all the 4 techniques. Peripheral corneal thicknesses were determined using Orbscan IIz, Visante OCT, and RTVue at 8 points (superior, inferior, temporal, nasal, superior-temporal, inferior-temporal, superior-nasal, and inferior-nasal) all in the 5.0- to 7.0-mm arcuate zone. MAIN OUTCOME MEASURES: Central and peripheral keratoconus thickness. RESULTS: Ultrasound pachymetry determined significantly higher CCT values than Orbscan IIz (P<0.001), Visante (P<0.001), and RTVue (P = 0.037), with a mean ± standard deviation difference of 14±3 µm, 13±2 µm, and 5±3 µm, respectively. The mean CCT difference was minimal (1±3 µm; P = 0.69) between the Orbscan IIz and Visante. A strong correlation was found (r>0.80) between all the CCT measurement techniques. Orbscan IIz significantly overestimated the peripheral thickness compared with the rest, and the mean differences ranged between 21 and 60 µm. Mean peripheral thickness differences between RTVue and Visante OCT always remained less than 20 µm. Weak correlations and larger limits of agreement were found between the techniques in thinner and peripheral zones. CONCLUSIONS: Orbscan IIz, Visante, RTVue, and ultrasound pachymetry show high correlation, although Orbscan IIz and Visante significantly underestimated CCT measurements compared with ultrasound pachymetry in keratoconus. Orbscan IIz significantly overestimated peripheral corneal thickness compared with RTVue and Visante.

Implications and management of suction loss during refractive lenticule extraction (ReLEx).

PURPOSE: To describe a case in which the ReLEx procedure was abandoned following suction loss on two occasions due to an uncooperative patient. METHODS: Case report with anterior segment optical coherence tomography and aberrometry changes before and after surgery. RESULTS: Lamellar haze was present but diminished in the early postoperative period. The patient successfully underwent a femtosecond LASIK procedure in the same eye 2 months later. CONCLUSIONS: This case demonstrates the possibility of performing femtosecond LASIK after failed ReLEx, with good visual outcomes.

Agreement between Pentacam and IOL master in patients undergoing toric IOL implantation.

PURPOSE: To investigate inter-device agreement between the Pentacam (Optikgerate GmbH, Wetzlar, Germany) and IOLMaster (Carl Zeiss Meditec, Jena, Germany) in measuring corneal power, cylinder, and axis of astigmatism. METHODS: Retrospective case series reviewing the status of eyes after toric IOL implantation to evaluate inter-device agreement in measuring corneal power, cylinder, and axis of astigmatism. RESULTS: Forty-nine eyes from 41 patients were evaluated. Agreement for corneal power and cylinder were deemed good and moderate, with 95% limits of agreement of -1.02 to +1.13 and -1.37 to +1.09 diopters (D), respectively. Agreement for axis of astigmatism was only fair, with a mean absolute difference of 8.9 degrees (range: 0.3 to 37.7 degrees, standard deviation: 8.79 degrees). Thirty percent of eyes had a 10-degree or greater difference in axis measurements, and 13% of eyes had a 20-degree or greater difference in measurements. Analysis by multivariate logistic regression showed higher cylinder powers associated with discrepant corneal power measurements (odds ratio: 3.46, P = .02), and increasing age was associated with discrepant axis measurements (odds ratio: 1.09, P = .03). Overall, there was no significant difference in accuracy predicting postoperative spherical equivalent refraction. CONCLUSIONS: Pentacam and IOLMaster agree well for corneal power but less so for cylinder and axis of astigmatism and thus cannot be used interchangeably.