Digital Gonioscopy Based on Three-dimensional Anterior-Segment OCT: An International Multicenter Study.

PURPOSE: To develop and evaluate the performance of a 3-dimensional (3D) deep-learning-based automated digital gonioscopy system (DGS) in detecting 2 major characteristics in eyes with suspected primary angle-closure glaucoma (PACG): (1) narrow iridocorneal angles (static gonioscopy, Task I) and (2) peripheral anterior synechiae (PAS) (dynamic gonioscopy, Task II) on OCT scans. DESIGN: International, cross-sectional, multicenter study. PARTICIPANTS: A total of 1.112 million images of 8694 volume scans (2294 patients) from 3 centers were included in this study (Task I, training/internal validation/external testing: 4515, 1101, and 2222 volume scans, respectively; Task II, training/internal validation/external testing: 378, 376, and 102 volume scans, respectively). METHODS: For Task I, a narrow angle was defined as an eye in which the posterior pigmented trabecular meshwork was not visible in more than 180° without indentation in the primary position captured in the dark room from the scans. For Task II, PAS was defined as the adhesion of the iris to the trabecular meshwork. The diagnostic performance of the 3D DGS was evaluated in both tasks with gonioscopic records as reference. MAIN OUTCOME MEASURES: The area under the curve (AUC), sensitivity, and specificity of the 3D DGS were calculated. RESULTS: In Task I, 29.4% of patients had a narrow angle. The AUC, sensitivity, and specificity of 3D DGS on the external testing datasets were 0.943 (0.933-0.953), 0.867 (0.838-0.895), and 0.878 (0.859-0.896), respectively. For Task II, 13.8% of patients had PAS. The AUC, sensitivity, and specificity of 3D DGS were 0.902 (0.818-0.985), 0.900 (0.714-1.000), and 0.890 (0.841-0.938), respectively, on the external testing set at quadrant level following normal clinical practice; and 0.885 (0.836-0.933), 0.912 (0.816-1.000), and 0.700 (0.660-0.741), respectively, on the external testing set at clock-hour level. CONCLUSIONS: The 3D DGS is effective in detecting eyes with suspected PACG. It has the potential to be used widely in the primary eye care community for screening of subjects at high risk of developing PACG.

Asian-specific vertical cup-to-disc ratio cut-off for glaucoma screening: An evidence-based recommendation from a multi-ethnic Asian population.

IMPORTANCE: Evidence-based guidelines are essential for glaucoma screening to work effectively. BACKGROUND: To derive a vertical cup-to-disc ratio (VCDR) cut-off for glaucoma screening in a multi-ethnic Asian population. DESIGN: The Singapore Epidemiology of Eye Diseases (SEED) study is a population-based study conducted from 2004 to 2011 in a single tertiary care research institute. PARTICIPANTS: SEED comprised of 10 033 Chinese, Malay and Indian adults aged ≥40 (response rate 75.6%). After excluding participants with a history of glaucoma medication or surgery, 9673 participants were included for analysis. METHODS: A systematic eye examination, which included applanation tonometry, visual field testing, gonioscopy and dilated fundus examination was conducted. MAIN OUTCOME MEASURE: Diagnosis of glaucoma. RESULTS: The distribution of VCDR and VCDR asymmetry were relatively homogenous in this multi-ethnic Asian population, with a 97.5th percentile value of 0.67 and 0.17, respectively. In the absence of more definite signs of glaucoma, VCDR ≥0.60 and VCDR asymmetry ≥0.20 provided the best balance between sensitivity (95.1%) and specificity (90.9%) in detecting glaucoma. For larger optic disc (≥2.0 mm), VCDR ≥0.65 with VCDR asymmetry ≥0.20 provided the best balance between sensitivity (84.8%) and specificity (93.2%). CONCLUSION AND RELEVANCE: Overall, VCDR ≥0.60 with VCDR ≥0.20 asymmetry provides a good balance between sensitivity and specificity in detecting glaucoma. For larger optic disc, VCDR ≥0.65 should be considered instead to mitigate against false-referrals due to larger physiological disc cupping. Our findings may act as a reference to populations with similar VCDR distribution.

A common variant near TGFBR3 is associated with primary open angle glaucoma.

Primary open angle glaucoma (POAG), a major cause of blindness worldwide, is a complex disease with a significant genetic contribution. We performed Exome Array (Illumina) analysis on 3504 POAG cases and 9746 controls with replication of the most significant findings in 9173 POAG cases and 26 780 controls across 18 collections of Asian, African and European descent. Apart from confirming strong evidence of association at CDKN2B-AS1 (rs2157719 [G], odds ratio [OR] = 0.71, P = 2.81 × 10(-33)), we observed one SNP showing significant association to POAG (CDC7-TGFBR3 rs1192415, ORG-allele = 1.13, Pmeta = 1.60 × 10(-8)). This particular SNP has previously been shown to be strongly associated with optic disc area and vertical cup-to-disc ratio, which are regarded as glaucoma-related quantitative traits. Our study now extends this by directly implicating it in POAG disease pathogenesis.

Handheld chromatic pupillometry can accurately and rapidly reveal functional loss in glaucoma.

BACKGROUND/AIMS: Early detection and treatment of glaucoma can delay vision loss. In this study, we evaluate the performance of handheld chromatic pupillometry (HCP) for the objective and rapid detection of functional loss in glaucoma. METHODS: In this clinic-based, prospective study, we enrolled 149 patients (median (IQR) years: 68.5 (13.6) years) with confirmed glaucoma and 173 healthy controls (55.2 (26.7) years). Changes in pupil size in response to 9 s of exponentially increasing blue (469 nm) and red (640 nm) light-stimuli were assessed monocularly using a custom-built handheld pupillometer. Pupillometric features were extracted from individual traces and compared between groups. Features with the highest classification potential, selected using a gradient boosting machine technique, were incorporated into a generalised linear model for glaucoma classification. Receiver operating characteristic curve analyses (ROC) were used to compare the performance of HCP, optical coherence tomography (OCT) and Humphrey Visual Field (HVF). RESULTS: Pupillary light responses were altered in glaucoma compared with controls. For glaucoma classification, HCP yielded an area under the ROC curve (AUC) of 0.94 (95% CI 0.91 to 0.96), a sensitivity of 87.9% and specificity of 88.4%. The classification performance of HCP in early-moderate glaucoma (visual field mean deviation (VFMD) > -12 dB; AUC=0.91 (95% CI 0.87 to 0.95)) was similar to HVF (AUC=0.91) and reduced compared with OCT (AUC=0.97; p=0.01). For severe glaucoma (VFMD ≤ -12 dB), HCP had an excellent classification performance (AUC=0.98, 95% CI 0.97 to 1) that was similar to HVF and OCT. CONCLUSION: HCP allows for an accurate, objective and rapid detection of functional loss in glaucomatous eyes of different severities.

Change in iris parameters with physiological mydriasis.

PURPOSE: A pilot study to analyze the association of change in iris parameters with physiological mydriasis in angle closure eyes compared with normal control eyes among south Indian participants. METHODS: Sixteen eyes diagnosed with primary angle closure and 14 age, gender-matched open-angle control eyes were selected. All participants underwent anterior segment imaging using anterior segment optical coherence tomography in dim and bright illumination. The iris area (IA), iris volume (IV), and pupillary diameter were calculated using customized image processing software. RESULTS: The IA and IV were found to be lesser in angle closure compared with normal controls. Average IA (dim and bright) was found to be 3.4 and 3.7 mm(2) in normals and 3.03 and 3.35 mm(2) in angle closure, and average IV (dim and bright) was found to be 24.28 and 26.09 mm(2) in normals and 21.38 and 22.6 mm(2) in angle closure. The IA and IV decreased significantly with pupillary dilation in normals and in angle closures. However, decrease in the IA (slope = 0.52 and 0.42; p = 0.012) and IV (slope = 1.97 and 1.41; p = 0.014) with pupillary dilation was significantly higher in normals compared with angle closures, respectively. CONCLUSIONS: IA and IV were found to decrease as pupil dilates in normal and angle closure eyes among South Indians. Loss in the IV was found to be lower in angle closure eyes.

Effect of immediate shallow anterior chamber after Ahmed glaucoma valve implantation on intermediate-term intraocular pressure control.

Purpose: To evaluate the incidence of shallow anterior chamber in the early postoperative period following Ahmed glaucoma valve (AGV) implantation and its effect on the hypertensive phase (HP), intermediate-term intraocular pressure (IOP) control, and success rate. Methods: A retrospective analysis of 369 eyes of 360 patients who underwent AGV implantation between January 2005 and January 2020 with a minimum follow-up of 2 months was performed. Twenty-six patients developed shallow anterior chamber (AC) within 8 weeks following surgery (cases). They were compared with 39 randomly selected controls (no shallow AC post AGV). HP (IOP spike >21 mmHg), use of ocular hypotensive medications, and other associations were compared. Results: Incidence of shallow AC post AGV was 7% (95% confidence interval [CI] 4, 9). The onset of shallow AC was 3 ± 2.1 days and resolved within 6 ± 4.7 days. Hypotony (12 [47%] vs. 1 [2.5%], P 0.0001) and choroidal detachment (CD; 7 [27%] vs. 3 [8%], P 0.03) were more common in cases compared to controls. The HP occurred in 11 (43%) cases versus 13 (34%) controls (P 0.4). Cases required more ocular hypotensive medications than controls at the end of 8 weeks (1.1 ± 1 vs. 0.5 ± 0.5, P 0.01). There was no significant difference in the qualified success between the groups at 1 year. Conclusion: The development of postoperative shallow AC post AGV implantation was not detrimental to IOP control at 1 year. However, there is a need to monitor the occurrence of HP in these eyes.

Diagnostic accuracy of swept source optical coherence tomography classification algorithms for detection of gonioscopic angle closure.

PURPOSE: To evaluate the performance of swept source optical coherence tomography (SS-OCT) to detect gonioscopic angle closure using different classification algorithms. METHODS: This was a cross-sectional study of 2028 subjects without ophthalmic symptoms recruited from a community-based clinic. All subjects underwent gonioscopy and SS-OCT (Casia, Tomey Corporation, Nagoya, Japan) under dark room conditions. For each eye, 8 out of 128 frames (22.5° interval) were selected to measure anterior chamber parameters namely anterior chamber width, depth, area and volume (ACW, ACD, ACA, and ACV), lens vault (LV), iris curvature (IC), iris thickness (IT) from 750 µm and 2000 µm from the scleral spur, iris area and iris volume. Five diagnostic algorithms-stepwise logistic regression, random forest, multivariate adaptive regression splines, recursive partitioning and Naïve Bayes were evaluated for detection of gonioscopic angle closure (defined as ≥2 closed quadrants). The performance of the horizontal frame was compared with that of other meridians. RESULTS: Data from 1988 subjects, including 143 (7.2%) with gonioscopic angle closure, were available for analysis. They were divided into two groups: training (1391, 70%) and validation (597, 30%). The best algorithm for detecting gonioscopic angle closure was stepwise logistic regression with an area under the curve of 0.91 (95% CI 0.88 to 0.93) using all parameters, and 0.88 (95% CI 0.82 to 0.93) using only ACA, LV and IC of the horizontal meridian scan. CONCLUSIONS: A stepwise logistic regression model incorporating SS-OCT measurements has a high diagnostic ability to detect gonioscopic angle closure.

Six-Year Incidence and Risk Factors of Primary Glaucoma in the Singapore Indian Eye Study.

PURPOSE: To determine the 6-year incidence of primary glaucoma and its risk factors in an Indian population in Singapore. DESIGN: Cohort population-based study. PARTICIPANTS: Indian adults between 40 and 80 years of age living in Singapore. A total of 3400 participants underwent the baseline examination between 2007 and 2009. Of them, 2200 (response rate, 75.5% of those eligible) participated in the 6-year follow-up visit between 2013 and 2015. METHODS: Standardized examination and investigations were performed, including indentation gonioscopy, intraocular pressure (IOP) measurement, optic disc examination, and static automated perimetry. Glaucoma was defined according to the International Society Geographical and Epidemiological Ophthalmology criteria. MAIN OUTCOME MEASURES: Incidences of primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG). RESULTS: The age-standardized incidences of primary glaucoma, POAG, and PACG were 1.68% (95% confidence interval [CI], 1.21%-2.32%), 1.37% (95% CI, 0.94%-1.96%), and 0.32% (95% CI, 0.15%-0.66%), respectively. For eyes with ocular hypertension (n = 45) at baseline, the incidence of POAG was 4.83% (95% CI, 1.24%-17.21%) and for eyes with primary angle closure (n = 14) or suspected primary angle closure (n = 101), the incidence of PACG developing was 1.82% (95% CI, 0.37%-9.68%). Baseline factors associated significantly with risk of primary glaucoma developing included older age (per decade; odds ratio [OR], 1.84; 95% CI, 1.44-2.36; P < 0.001), larger vertical cup-to-disc ratio (per 0.1 unit; OR, 2.78; 95% CI, 2.12-3.64; P < 0.001), and higher IOP (per millimeter of mercury; OR, 1.25; 95% CI, 1.13-1.38; P < 0.001). However, 71 of 85 eyes (84.5%) diagnosed with incident glaucoma had IOP of less than 21 mmHg at the time of examination. CONCLUSIONS: Our study showed that the overall age-standardized incidence of primary glaucoma was 1.68% in an Indian population in Singapore. In our population, the incidence of POAG was only half and the incidence of PACG was similar to the incidence reported by the Chennai Eye Disease Study.

Diagnostic accuracy of macular ganglion cell-inner plexiform layer thickness for glaucoma detection in a population-based study: Comparison with optic nerve head imaging parameters.

AIMS: To determine the diagnostic performance of macular ganglion cell-inner plexiform layer (GCIPL) thickness measured by spectral-domain optical coherence tomography (SD-OCT) for glaucoma detection in a Chinese population in comparison with optic nerve head (ONH) and retinal nerve fiber layer (RNFL) parameters measured by both SD-OCT and Heidelberg Retina Tomography 3 (HRT-3). METHODS: Adults aged 40 to 80 years were recruited from the population-based study (n = 3353, response rate 72.8%). Macular cube 200x200 scan was performed with Cirrus SD-OCT (version 6.0, Carl Zeiss Meditec Inc, Dublin, CA) for GCIPL thickness measurement. ONH and RNFL imaging was performed with Cirrus SD-OCT and HRT-3 (Heidelberg Engineering, Heidelberg, Germany). Glaucoma was defined according to International Society for Geographical and Epidemiological Ophthalmology criteria. RESULTS: In total, 86 eyes of 60 subjects with glaucoma and 1709 eyes of 1001 non-glaucoma participants were included. The best performing parameters for Cirrus SD-OCT GCIPL, Cirrus SD-OCT ONH and HRT-3 were minimum GCIPL thickness (Area under receiver-operating curve [AUC] = 0.89, 95% CI 0.83-0.95), vertical cup-disc ratio (CDR) (AUC = 0.94, 0.91-0.98) and vertical CDR (AUC = 0.86, 0.81-0.92), respectively. At 85% specificity, vertical CDR measured using Cirrus OCT ONH scan showed the highest sensitivity (88.64%, 95% CI 75.4-96.2) compared to minimum GCIPL thickness with sensitivity of 60.53% (95% CI 46.4-73.0) (p<0.001). Inferior RNFL thickness (AUC = 0.84, 95% CI 0.91-0.97) measured by Cirrus SD-OCT was also superior to Cirrus SD-OCT GCIPL (p<0.007). CONCLUSIONS: The diagnostic performance of macular GCIPL scan is inferior compared to vertical CDR measured by Cirrus OCT ONH scan. Cirrus OCT ONH scan showed the best ability in detecting glaucoma in a Chinese population, suggesting it could be a good glaucoma screening tool in an Asian population.

Gender variation in ocular biometry and ultrasound biomicroscopy of primary angle closure suspects and normal eyes.

PURPOSE: To compare A-scan biometry and ultrasound biomicroscopy of primary angle closure suspects (PACS) with age-matched normal Indian eyes. PATIENTS AND METHODS: Subjects with primary angle closure suspects (n=57 eyes) and normal eyes (n=57 eyes) underwent A-scan biometry and ultrasound biomicroscopy. Anterior chamber depth (ACD), anterior chamber angle (ACA), axial length (AXL), lens thickness, relative lens position (RLP), central corneal thickness (CCT), angle opening distance 500, trabecular-ciliary process distance (TCPD), iris-ciliary process distance, iris thickness, and scleral-ciliary process angle were measured. The subjects were divided into males, females, and combined groups for analysis. The parameters were compared using independent sample t test with Bonferroni correction for multiple comparisons. RESULTS: In the combined group, the PACS subjects presented a significantly low ACD, AXL, CCT, AOD500, TCPD, ACA (P<0.001), and RLP (P=0.04). In males, RLP was anterior (P=0.002) and in females, the lens thickness (P<0.001) was significantly thicker among the PACS group. CONCLUSIONS: ACD, AXL, CCT, TCPD, ACA, and angle opening distance 500 of the PACS group were significantly lower than in normals. In females, the lens in PACS was thicker than in normals. Lens in males was more anterior-placed in PACS group than in normals.

Common variants near ABCA1 and in PMM2 are associated with primary open-angle glaucoma.

We performed a genome-wide association study for primary open-angle glaucoma (POAG) in 1,007 cases with high-pressure glaucoma (HPG) and 1,009 controls from southern China. We observed genome-wide significant association at multiple SNPs near ABCA1 at 9q31.1 (rs2487032; P = 1.66 × 10(-8)) and suggestive evidence of association in PMM2 at 16p13.2 (rs3785176; P = 3.18 × 10(-6)). We replicated these findings in a set of 525 HPG cases and 912 controls from Singapore and a further set of 1,374 POAG cases and 4,053 controls from China. We observed genome-wide significant association with more than one SNP at the two loci (P = 2.79 × 10(-19) for rs2487032 representing ABCA1 and P = 5.77 × 10(-10) for rs3785176 representing PMM2). Both ABCA1 and PMM2 are expressed in the trabecular meshwork, optic nerve and other ocular tissues. In addition, ABCA1 is highly expressed in the ganglion cell layer of the retina, a finding consistent with it having a role in the development of glaucoma.

Optic disc dimensions and cup-disc ratios among healthy South Indians: The Chennai Glaucoma Study.

PURPOSE: To present optic disc and cup dimensions, cup-disc ratios (CDRs) and asymmetry among healthy South Indians, and their associations with ocular and systemic variables. METHODS: A total of 623 healthy phakic participants of the Chennai Glaucoma Study underwent complete eye examinations including optic disc stereo-photography. Planimetry was performed under stereo-viewing conditions. The morphological type of cupping (no cups, steep cups, partly sloping and fully sloping cups) was identified based on a modification of the classification by Jonas et al.( 11 ) The associations of planimetric measures (optic disc area, cup area and vertical cup-disc ratio [VCDR]) with age, gender, height, intraocular pressure, refraction, astigmatism, axial length and corneal thickness as explanatory variables were examined. The associations of asymmetries in the above planimetric measures with age, gender and asymmetries of the above explanatory variables were examined. RESULTS: Mean optic disc and cup areas were 2.82 ± 0.52 mm(2) and 0.53 ± 0.39 mm(2). Mean CDR was 0.36 ± 0.18. Men had larger discs (P = 0.03). Cup area and VCDR revealed significant associations with disc area (P <0.0001) and type of cupping (P < 0.0001). Mean disc and cup area asymmetries were 0.19 ± 0.16 mm(2) and 0.15 ± 0.15 mm(2). Mean VCDR asymmetry was 0.07 ± 0.08 mm(2). Cup area and VCDR asymmetries showed significant associations with disc area asymmetry (P < 0.0001, both) and asymmetry in the presence or absence of physiological cupping, i.e. subjects with physiological cupping in one eye and no cupping in the other (P < 0.0001, both). CONCLUSIONS: We present normative optic disc, cup and VCDR measures and asymmetries among healthy South Indians. We demonstrated the dependence of VCDR on the morphological type of cupping.

Pupil constriction can alter the accuracy of dark room provocative test.

BACKGROUND: Primary angle-closure glaucoma (PACG) is a major cause of visual morbidity in East Asia. Dark-room provocative test (DRPT) has been used to determine which narrow angles have the risk to develop angle closure. However, the accuracy of DRPT might be altered because that after emerging from the dark room, the configuration of the angle is affected by the light of the slit-lamp and the appositionally closed angle reopens. The aim of this study was to examine the pupillary diameter in different light conditions and use it as a parameter to assess the accuracy of dark-room provocative test. METHODS: Patients with suspected primary angle-closure glaucoma undergoing DRPT were recruited. The anterior chamber angle was examined by anterior segment optical coherence tomography under the following conditions: (1) in standard room illumination; (2) after short-term dark-adaptation and (3) after DRPT. Mean values of pupil size and numbers of appositionally closed angle under different conditions were compared. RESULTS: A total of 47 eyes of 47 patients were analyzed. The pupil size after DRPT was smaller than that after short-term dark-adaptation (P < 0.001) and smaller than that in standard room illumination (P = 0.026). The numbers of appositionally closed angles after short-term dark-adaptation were significantly larger than those after DRPT (P < 0.001). There was no significant difference between the numbers of appositionally closed angles in standard room illumination and after DRPT (P = 0.157). CONCLUSIONS: Constriction of pupil size immediately after prolonged dark room provocative test may lead to change in the angle configuration, which may lead to false negative results. We suggest a modified protocol of recording intraocular pressure immediately after DRPT and performing gonioscopy following short-term dark adaptation to improve the accuracy of angle closure assessment.

Follow-up of primary angle closure suspects after laser peripheral iridotomy using ultrasound biomicroscopy and A-scan biometry for a period of 2 years.

AIM: To determine the morphologic changes in the anterior segment of primary angle closure suspects (PACS) who underwent laser peripheral iridotomy (LPI) for a period of 2 years. METHODS: PACS (n=82 eyes) of Asian Indian origin who attended the Glaucoma clinic of tertiary eye hospital underwent A-scan biometry and ultrasound biomicroscopy. Anterior chamber depth, anterior chamber angle (ACA), axial length, lens thickness, relative lens position, central corneal thickness, angle opening distance 500, trabecular-ciliary process distance, iris-ciliary process distance, and iris thickness were measured before LPI and after LPI at 1 week, 6 months, 1 year, 1.5 years, and 2 years. Variation in the parameters measured over a period of 2 years was analyzed. RESULTS: Fifteen eyes out of 52 eyes developed into primary angle closure (PAC) with synechial changes. Univariate analysis for the predictive factors of PAC showed no significant association for age, sex, narrow angle, ultrasound biomicroscopy parameters, and vertical cup-disc ratio. When analyzed as continuous variables, decreasing ACA was significant risk factor (95% confidence interval: 0.703, 0.989, P=0.037). Iris-ciliary process distance, ACA, lens thickness, and angle opening distance 500 were the parameters that varied significantly (P<0.05) between "before LPI group" and "after LPI groups." None of the subjects developed increased intraocular pressure after laser iridotomy. CONCLUSIONS: In this hospital-based study on the course of PACS subjects after LPI, as many as 28% progressed to PAC. Decreasing ACA was the predictive factor for the progression of PACS to PAC. There was no increase in intraocular pressure, history, or symptoms of acute attack of glaucoma among the study subjects after LPI.

Neural rim characteristics of healthy South Indians: the Chennai Glaucoma Study.

PURPOSE: To report neural rim dimensions for South Indians and examine rim shape with relevance to clinical evaluation. METHODS: Healthy phakic participants (n = 623) of the Chennai Glaucoma Study with normal frequency-doubling perimetry underwent complete eye examinations including optic disc digital stereophotography. Planimetry was performed under stereoviewing conditions using custom software. Rim area, shape, and associations were examined. Rim area asymmetry was studied in a subgroup of 565 subjects. RESULTS: Mean neuroretinal rim area was 2.29 +/- 0.39 mm(2). Disc area (P < 0.001) and type of cupping (P < 0.001) were associated with rim area. Mean rim area asymmetry was 0.18 +/- 0.15 mm(2); 95% of subjects had asymmetry < 0.5 mm(2). Disc area asymmetry (0.359, P < 0.0001) and intraocular pressure (IOP) asymmetry (P = 0.004) were related to rim area asymmetry. On average, the inferior rim was thickest and the temporal was thinnest. Mean inferior by superior rim width was 1.18 +/- 0.17; 2.5 percentile, 0.9. Thirty-eight (7.1%) subjects had the superior rim thicker than the inferior rim, the occurrence of which was associated with disc torsion (P = 0.002) and male sex (P = 0.04). Of the clinically relevant rim width measures in glaucoma (i.e., inferior, superior, and temporal) the temporal rim was thinnest in 469 (87.8%) eyes. Horizontally oval disc shape (P < 0.0001), type of cupping (P = 0.006), and astigmatism (P = 0.001) were associated with the presence of thicker temporal than superior/inferior rims. CONCLUSIONS: The report provides hitherto unreported neural rim measurements among healthy South Indians. The ISNT rule (inferior rim thicker than superior rim, thicker than nasal rim, thicker than temporal rim) was violated in a significant minority. Physiological associations with such violations are described.