Finite Element Analysis of Cornea and Lid Wiper during Blink, with and without Contact Lens.

Ocular surface disorders such as Lid Wiper Epitheliopathy (LWE), Superior Epithelial Arcuate Lesion (SEAL), and contact lens-induced Limbal Stem Cell Deficiency (LSCD) as well as Superior Limbic Keratoconjunctivitis (SLK) affect one's quality of life. Hence, it is imperative to investigate the underlying causes of these ocular surface disorders. During blink, the undersurface of the eyelid tends to interact with the cornea and the conjunctiva. The presence of a contact lens can add to the biomechanical frictional changes on these surfaces. To estimate these changes with and without a contact lens, a finite element model (FEM) of the eyelid wiper, eyeball, and contact lens was developed using COMSOL Multiphysics. Biomechanical properties such as von Mises stress (VMS) and displacement were calculated. Our study concluded that (a) maximum VMS was observed in the lid wiper in the absence of contact lens in the eye and (b) maximum VMS was observed in the superior 1.3 mm of the cornea in the presence of the contact lens in the eye. Thus, the development of friction-induced ocular surface disorders such as LWE, SLK, SEAL, and LSCD could be attributed to increased VMS. FEA is a useful simulation tool that helps us to understand the effect of blink on a normal eye with and without CL.

Impact of living with a bilateral central vision loss due to geographic atrophy-qualitative study.

OBJECTIVE: Geographic atrophy (GA), a type of dry age-related macular degeneration, affects vision as central vision loss (CVL). The challenges faced due to bilateral CVL in activities of daily living and strategies taken to overcome those challenges are not very well understood in the Indian population. This qualitative study aims to understand the impact on everyday life activities and related adaptive and coping strategies in people with long-standing bilateral CVL due to GA in India. DESIGN, PARTICIPANTS, SETTING AND METHODS: A qualitative study using a semistructured face-to-face interview was conducted on 10 people with bilateral CVL after obtaining written informed consent. The interviews were audio-recorded, and were transcribed verbatim. Thematic analysis was carried out to understand the challenges faced and adaptive methods due to the impact of CVL. RESULTS: Ten participants (50% male) with a median age (IQR) of 72 (70, 74) years were interviewed. All the participants had best-corrected visual acuity of ≤6/60 in the better eye and reported an absolute central scotoma with the home Amsler chart. Qualitative thematic analysis identified four main themes: challenges in everyday living (difficulty in face identification, reading), challenges with lifestyle and socialisation (driving, cooking, reading for a longer duration, watching TV, socially inactive), psychological implications (depression, poor self-esteem, fear due to poor vision) and strategies to overcome the challenges (voice identification, technology support). CONCLUSION: GA has a severe negative impact on the quality of life in people with CVL. Inability to recognise faces was the main reason for dependency on others and being socially disconnected. The findings will help clinicians in providing improved rehabilitative care.

Virtually controlled computerised visual acuity screening in a multilingual Indian population.

INTRODUCTION: The efficacy of tele-based (virtually monitored) visual acuity (VA) examination in a hospital-based multilingual population was assessed based on subjects from the Outpatient Department of Optometry, School of Allied Health Sciences, Manipal University and Department of Ophthalmology, Kasturba Medical College, Manipal, India. METHODS: Visual acuity measurement using a computerized VA chart (COMPlog) was done using a telemethod and face-to-face method in a randomized fashion for all subjects. Virtual (remotely operated) control of examination procedure and video-conferencing helped the optometrist positioned elsewhere (different physical location) to remotely operate the COMPlog VA chart and also interact with the subjects. The connection was facilitated using Lync software connected through local area network connections. During tele-examination, instructions were given on subject's language preference (Kannada, Malayalam or English). RESULTS: Mean age of 96 subjects (three language groups) was 40.3±14.1 years and a Bland-Altman plot showed good agreement with clinically acceptable limits of agreement. The mean difference in VA between the telemethod and face-to-face method was 0.00 logMAR (±0.16), p=0.844. Two methods had good intra-class correlation (0.912, 95% confidence interval 0.868-0.941) and had good agreement across the language groups (kappa>0.7). CONCLUSIONS: Visual acuity measurements using the telemethod along with native dialect was comparable to conventional face-to-face method in a hospital-based multilingual population. Digital VA testing systems along with communication in native dialect can be effectively integrated into a tele-eyecare model.

Efficacy of a remote based computerised visual acuity measurement.

AIM: To determine the efficacy of a remotely operated computer-based logarithmic (logMAR) visual acuity chart. METHODS: Visual acuity was tested using a laptop or computer-based logMAR chart (COMPlog) for all subjects by two different methods. The methods differed by the physical presence and absence (remote) of an optometrist and in the mode of instructions provided. Remote access was obtained through the internet, using Teamviewer software to control the system linked to COMPlog and instructions were provided by telephone. The order of measurements and the eye to be tested was randomised. logMAR visual acuity and time taken were recorded. A questionnaire was used to assess the participant's feedback. RESULTS: Intraclass correlation for visual acuity between the two methods (α=0.964, 95% CI 0.937 to 0.979). There was no statistically significant difference (p=0.648) in the median visual acuity measurement between the two methods (median difference 0.00, IQR 0.20 logMAR). The time taken between the two methods was not statistically significant (p=0.457). There was no significant difference in the responses to the questionnaire between the study methods (p=0.119). CONCLUSIONS: Tele (remotely controlled) visual acuity measurement is as reliable as that measured with the physical presence of an optometrist.

Perimetric severity in hospital-based and population-based glaucoma patients.

BACKGROUND: The aim was to compare the severity of glaucoma among newly diagnosed patients presenting to a hospital-based glaucoma care centre (HBGS: Sankara Nethralaya, Medical Research Foundation) with that of age matched subjects from the population-based Chennai Glaucoma Follow-up Study (CGFS). METHODS: Newly diagnosed subjects with primary glaucoma from HBGS and age- and gender-matched subjects from the urban arm of CGFS examined during the same time period were included. All subjects underwent comprehensive ocular examinations including Humphrey visual field (HVF: 24-2 SITA Standard). Glaucoma was defined as: an intraocular pressure (IOP) of 22 or greater mmHg in either eye; vertical cup-to-disc ratio (VCDR) of 0.7 or greater or asymmetry 0.2 or more or the presence of focal thinning, notching or a splinter haemorrhage. All subjects had a minimum of three follow-up visits and reliable visual fields. The IOP, vertical cup-to-disc ratio, mean deviation (MD) and pattern standard deviation (PSD) of the Humphrey field measurements at the third follow-up visit of CGFS were compared for assessing the severity of glaucoma with the HBGS group. RESULTS: Forty-seven age-matched subjects from both the study populations were selected. Significantly higher (p = 0.04) IOP was noted in the HBGS population than the CGFS, with a difference in mean IOP of 2.80 mmHg (95% CI of diff: 0.14 to 5.46). The mean ± SD of the mean deviation and pattern standard deviation were -6.92 ± 6.53 dB and 6.05 ± 4.20 dB among the HBGS and -4.47 ± 4.19 dB and 3.26 ± 2.69 dB among the CGFS population, respectively, the difference in the mean deviation (p = 0.036) and pattern standard deviation (p = 0.0001) were statistically significant. The mean vertical cup-to-disc ratio did not vary between populations (p = 0.14). CONCLUSION: Patients from the HBGS group had higher IOP and more severe visual field defects than the CGFS group. Hence, results from hospital-based studies on severity and the rates of progression should be interpreted with caution.

The Chennai glaucoma study: prevalence and risk factors for glaucoma in cataract operated eyes in urban Chennai.

We report the prevalence and risk factors for glaucoma among aphakes and pseudophakes in 3850 subjects who participated in a population-based study in urban south India. The subjects underwent an ophthalmic examination including applanation tonometry, gonioscopy, optic disc evaluation and frequency doubling perimetry. Glaucoma was diagnosed using the International Society of Geographical and Epidemiological Ophthalmology (ISGEO) criteria. Thirty eight, 15 aphakes and 23 pseudophakes (0.99% of 3850 subjects) of the 406 persons who had undergone cataract surgery were diagnosed with glaucoma. Aphakes/pseudophakes were at higher risk of glaucoma as compared to the phakic population (Odds Ratio: 2.71, 95% CI: 1. 94, 3.38, p=0.001). On multivariate analysis, older age and higher intra ocular pressure were risk factors for glaucoma. Blindness attributable to glaucoma was detected in 20% of aphakic and 4.3% of pseudophakic eyes. Glaucoma was a significant cause of morbidity in those who had undergone cataract surgery in this urban population.

Agreement between two Goldmann type applanation tonometers.

The aim of the study was to assess agreement between two commercially available applanation tonometers for the measurement of intraocular pressure (IOP). Forty subjects underwent IOP measurement on two accurately calibrated Goldmann type applanation tonometers (Zeiss AT 030 (GATZ) and Inami L-5110(GATI)). The order of examination was randomized and observers were masked to the IOP recorded. The mean of two consecutive readings, from a randomly selected eye for each subject, was used for analysis. Agreement was assessed using the Altman and Bland plot. The mean (SD) IOP readings on GATZ was 15.32 (+/-6.80) mm Hg and on GATI was 13.52 (+/-5.65) mm Hg (p< 0.001, 95% CI of the difference: -2.48 to -1.11). The 95% limits of agreement on the Altman and Bland plot were:-2.47 to 6.16 mm Hg). There was significant inter-instrument variability between the two accurately calibrated Goldmann type applanation tonometers studied.

Prevalence of primary open-angle glaucoma in an urban south Indian population and comparison with a rural population. The Chennai Glaucoma Study.

OBJECTIVE: To estimate the prevalence and risk factors of primary open-angle glaucoma (POAG) in an urban population and compare the same with that of our published rural population data in southern India. DESIGN: Population-based cross-sectional study. PARTICIPANTS: Four thousand eight hundred subjects 40 years or older were selected using a multistage random cluster sampling procedure in Chennai city. INTERVENTION: Three thousand eight hundred fifty (80.2%) subjects underwent a complete ophthalmic examination, including applanation tonometry, gonioscopy, pachymetry, optic disc photography, and automated perimetry. MAIN OUTCOME MEASURES: Glaucoma was diagnosed using the International Society of Geographical and Epidemiological Ophthalmology Classification. RESULTS: The distribution of intraocular pressure (IOP) and vertical cup-to-disc ratio (VCDR) was obtained from the right eye of the 2532 subjects with normal suprathreshold visual fields. Mean IOP was 16.17+/-3.74 mmHg (97.5th and 99.5th percentiles, 24 mmHg and 30 mmHg). The mean VCDR was 0.43+/-0.17 (97.5th and 99.5th percentiles, 0.7 and 0.8). One hundred thirty-five (64 men, 71 women) subjects had POAG (3.51%; 95% confidence interval [CI], 3.04-4.0). Primary open-angle glaucoma subjects (58.4+/-11.3 years) were older (P<0.0001) than the study population (54.8+/-10.6 years). One hundred twenty-seven (94%) subjects were diagnosed to have POAG for the first time. Two subjects (1.5%) were bilaterally blind, and 3 (3.3%) were unilaterally blind due to POAG. The urban population prevalence was more than that of the rural population (1.62%; 95% CI, 1.4%-1.8%; P<0.0001). In both populations, increasing IOP (per millimeter of mercury) and older age were associated with the disease. There was no association with gender, myopia, systemic hypertension, diabetes, or central corneal thickness. CONCLUSIONS: The prevalence of POAG in a > or =40-year-old south Indian urban population was 3.51%, higher than that of the rural population. The prevalence increased with age, and >90% were not aware of the disease.

Prevalence of angle-closure disease in a rural southern Indian population.

OBJECTIVE: To estimate the prevalence of primary angle-closure glaucoma, primary angle closure (PAC), and primary angle-closure suspect (PACS) and its associated risk factors in a rural population in southern India. METHODS: Three thousand and nine hundred thirty-four (81.95%) of 4800 enumerated subjects aged 40 years or older underwent a complete ophthalmic examination, including compression gonioscopy. Glaucoma was diagnosed using International Society of Geographical and Epidemiological Ophthalmology classification. RESULTS: Data were analyzed for 3924 subjects (81.75%). Primary angle-closure glaucoma was diagnosed in 34 subjects (0.87%; 95% confidence interval [CI], 0.58 to 1.16) (27 women, 7 men). The mean intraocular pressure was 20.71 +/- 9.24 mm Hg. One subject (2.94%) was blind. Twenty-eight subjects (0.71%; 95% CI, 0.45 to 0.98) were diagnosed to have PAC (21 women, 7 men). Eleven subjects (39.3%) had an intraocular pressure greater than 21 mm Hg, 13 subjects (46.43%) had peripheral anterior synechiae, and 4 subjects (14.29%) had both. Two hundred forty-six subjects (6.27%; 95% CI, 5.51 to 7.03) had PACS (168 women, 78 men). Primary angle closure and primary angle-closure glaucoma were more common in women (age-adjusted odds ratio, 3.02; 95% CI, 1.66 to 5.51) with an increasing prevalence with age. Increasing intraocular pressure was associated with the disease (odds ratio, 1.14; 95% CI, 1.09 to 1.19). There was no association with hypertension and hyperopia. Axial length and anterior chamber depth were longer in the normal group than in the 3 groups with angle closure (P<.05). Women had shorter axial lengths than men (P<.001) in the angle closure groups. CONCLUSIONS: The overall prevalence of primary angle closures (PAC and primary angle-closure glaucoma) in a rural population of southern India was 1.58%. There was a female preponderance, and the disease tends to be asymptomatic.

Prevalence of open-angle glaucoma in a rural south Indian population.

PURPOSE: To determine the prevalence of primary open-angle glaucoma (POAG) and the associated risk factors in a rural population in southern India. METHODS: Subjects aged 40 years or more (n = 3934) underwent a complete ophthalmic examination. Glaucoma was diagnosed according to the International Society of Geographical and Epidemiologic Ophthalmology classification. RESULTS: Complete data were available for 3924 subjects (response rate, 81.75%). In eyes with normal suprathreshold visual fields, the mean intraocular pressure was 14.29 +/- 3.32 mm Hg (97.5th and 99.5th percentiles, 21 and 25 mm Hg, respectively). The mean vertical cup-to-disc ratio was 0.39 +/- 0.17 (97.5th and 99.5th percentiles, 0.7 and 0.8, respectively). Sixty-four subjects had definite POAG (1.62%, 9.5% CI 1.42-1.82); 30 were men and 34 were women. Subjects with POAG (59.85 +/- 10.43 years) were older (P < 0.001) than the study population (53.78 +/- 10.71 years). In only one (1.5%) person was POAG diagnosed before the study. Two (3.12%) subjects were blind due to POAG; 21 (32.81%) subjects had a presenting IOP >21 mm Hg, and 43 (67.19%) had an IOP <21 mm Hg. The mean central corneal thickness in subjects with POAG (502.82 +/- 35.29 microm) was not different from that of the normal study population (505.93 +/- 31.11 microm). No association was found with diabetes mellitus, systemic hypertension, gender, and myopia. Increasing IOP (per mm Hg) was associated with the disease (OR 1.12; 95% CI, 1.08-1.16). The odds for POAG increased with advancing age after adjustment for gender. CONCLUSIONS: The prevalence of POAG in this population was 1.62%. The prevalence increased with age, and 98.5% were not aware of the disease.

A comparison of participants and non-participants in the Chennai Glaucoma Study-rural population.

PURPOSE: To study whether the difference in the demographic characteristics of participants and non participants could result in biased prevalence estimates and associations. AIM: To compare the non-participant and participant characteristics, and to ascertain if non-response bias is present in the rural population of the Chennai Glaucoma Study (CGS). METHODS: Rural participants and non-participants were compared with regard to socio-demographic variables (age, gender, religion, mother tongue, literacy and employment). RESULTS: 4800 subjects aged 40 years or over were enumerated, 82% (3934: 45% male and 55% female) responded. Gender did not influence participation (adjusted OR-1.11, CI: .91-1.36). Subjects in the 70-79 year age group were more likely to respond (OR-1.76; CI-1.31-2.38). Hindus had a higher participation rate than Christians or Muslims (adjusted OR-2.63, CI: 1.80-3.84). The other predictors of participation were illiteracy (adjusted OR-1.44, CI: 1.22-1.70), unemployment (OR-1.28, CI: 1.04-1.58), place of residence (main villages) (OR-6.66, 95% CI: 4.6-9.64). CONCLUSION: Based on our study findings, it does not seem likely that participation bias will affect the study results.

Effect of cataract surgery with intraocular lens implant on frequency doubling perimetry.

PURPOSE: To study the effect of cataract surgery with intraocular lens (IOL) on frequency doubling perimetry (FDP). METHODS: Patients aged 40 years or above seen at our outpatient clinic with no ocular pathology except for visually significant cataract and visual acuity 6/24 or better were eligible. They underwent FDP before and 4 to 6 weeks after cataract surgery with IOL. RESULTS: Screening test: Mean scores by three different scoring methods were 1.82 (3.21), 2.80 (5.54), 4.18 (9.18) before and 0.22 (0.51), 0.26 (0.63), 0.26 (0.69) after surgery (p = 0.002 0.001, < 0.0001). Threshold test: Mean deviation (MD) and pattern standard deviation (PSD) were -5.23 (3.08) and 5.15 (2.78) before and -2.94 [corrected] (2.49) (p < 0.0001) and 5.21 (1.780) (p = 0.63) after surgery. CONCLUSIONS: The screening test should be interpreted cautiously in the presence of cataract. On threshold testing, cataract surgery causes significant decrease in MD but no change in PSD.

Prevalence of refractive errors in a rural South Indian population.

PURPOSE: To report the prevalence of refractive errors in a rural south Indian population. METHODS: Four thousand eight hundred subjects (age, >39 years) from rural south India were enumerated for a population-based study. All participants underwent complete ophthalmic evaluation. Subjects who were phakic in the right eye with best corrected visual acuity of 20/40 or better were included for analysis. Association of refractive errors with age, sex, cataract, and diabetes mellitus were analyzed. RESULTS: Of the 3924 responders, 2508 were eligible. The unadjusted prevalence of emmetropia (spherical equivalent [SE], -0.50 to +0.50 diopter sphere [DS]), myopia (SE < -0.50 DS), high myopia (SE < -5.00 DS), and hyperopia (SE > 0.50 DS) were 50.60%, 26.99%, 3.71%, and 18.70% and age and gender adjusted for the rural Tamil Nadu population were 46.77%, 30.97%, 4.32%, and 17.94%, respectively. The prevalence of emmetropia decreased significantly with age (P < 0.0001), and the prevalence of myopia and high myopia increased significantly with age (P < 0.001) and were significantly associated with nuclear sclerosis (P < 0.001). The prevalence of hyperopia increased until 60 years of age and then decreased. Hyperopia was more common among women than men (P < 0.001) and was negatively associated with nuclear sclerosis (P < 0.001) and positively with diabetes mellitus (P = 0.008). Of the participants with astigmatism (cylindrical error greater than 0.50 DC), 9.80% had with-the-rule (WTR) and 77.44% against-the-rule (ATR) astigmatism. The prevalence of WTR and ATR astigmatism significantly decreased (P < 0.001) and increased (P = 0.006) with age, respectively. CONCLUSIONS: The pattern of refractive errors in this rural south Indian population is similar to those reported in other tropical regions of the world.

Pseudoexfoliation in South India.

AIM: To study the profile of pseudoexfoliation in a population based study. METHOD: 2850 consecutive subjects aged 40 years or older from a population based survey in a rural area of southern India underwent complete ophthalmic evaluation including history, visual acuity testing, refraction, slit lamp examination, applanation tonometry, gonioscopy, and dilated examination of the lens (including LOCS II grading of cataract), fundus, and optic disc. Patients with pseudoexfoliation syndrome were identified and their data were analysed with respect to age, sex, intraocular pressure, gonioscopic grading, cataract, and optic neuropathy. RESULTS: 108 subjects had pseudoexfoliation syndrome (3.8 %). There was a significant increase in prevalence with age but no sex predilection. The condition was unilateral in 53 cases (49.1%) and bilateral in 55 cases (50.9%). 18 cases with pseudoexfoliation (16.7%) had high intraocular pressure (>21 mm Hg), 16 cases (14.8%) had occludable angles, and 14 cases (13%) had pseudoexfoliation glaucoma. There was a significantly higher prevalence of cataract among people with pseudoexfoliation compared to those without pseudoexfoliation (p = 0.014). CONCLUSION: The prevalence of pseudoexfoliation syndrome in the rural population of south India was 3.8%. Raised intraocular pressure was seen in 16.7% of people with pseudoexfoliation and glaucoma was present in 13%.

Methods and design of the Chennai Glaucoma Study.

PURPOSE: To describe the methodology of a population-based study to estimate the prevalence of glaucoma in a rural and urban South Indian population and to study the genetics of glaucoma in this population. METHODS: A sample size of 4758 each for rural and urban populations in the Indian state of Tamil Nadu was calculated. Eligible subjects aged 40 years and above from the rural study area covering 32 contiguous villages and the urban area comprising five random clusters in Chennai city are enumerated. Demographic data are collected in the field. A detailed clinical examination, including glaucoma diagnostic procedures, is conducted at the examination centre. Pedigree ascertainment and genetic studies are performed for subjects with occludable angles or glaucoma. Data are recorded in a computerised database. CONCLUSIONS: This study is expected to result in an estimation of the prevalence and a better understanding of the genetics of glaucoma in this region.

Ocular biometry in occludable angles and angle closure glaucoma: a population based survey.

AIM: To compare ocular biometric values in a population based sample of eyes with occludable angles, angle closure glaucoma, and normal subjects. METHOD: 2850 subjects from a population based glaucoma prevalence study underwent complete ocular examination including indentation gonioscopy. Ocular biometry was performed in all subjects classified to have occludable angles (n = 143); angle closure glaucoma (n = 22), and a random subgroup of 419 normal subjects. Ocular biometry readings between the groups were compared and statistically analysed using "t," "z," and Mann-Whitney U tests. RESULTS: The mean age among subjects with occludable angles (54.43 (SD 9.53) years) and angle closure glaucoma (57.45 (8.5) years) was significantly higher (p<0.001) than normal subjects (49.95 (9.95) years). Axial length was shorter (p<0.001) in the occludable angle group (22.07 (0.69) mm) compared to the normal group (22.76 (0.78) mm). Anterior chamber depth (ACD) was shallower (p<0.001) among subjects with occludable angles (2.53 (0.26) mm) than normal subjects (3.00 (0.30) mm). Lens thickness (LT) was greater (p<0.001) in people with occludable angles (4.40 (0.53) mm) compared to normal subjects (4.31 (0.31) mm). No significant difference was noted in axial length, ACD (p = 0.451), and LT (p = 0.302) between angle closure glaucoma and occludable eyes. CONCLUSION: South Indian eyes with angle closure glaucoma and occludable angles seem to have significantly shorter axial lengths, shallower anterior chambers and greater lens thickness compared to the normal group.