Optic Disc-Fovea Distance, Axial Length and Parapapillary Zones. The Beijing Eye Study 2011.

PURPOSE: To measure the distance between the optic disc center and the fovea (DFD) and to assess its associations. METHODS: The population-based cross-sectional Beijing Eye Study 2011 included 3468 individuals aged 50+ years. The DFD was measured on fundus photographs. RESULTS: Readable fundus photographs were available for 2836 (81.8%) individuals. Mean DFD was 4.76 ± 0.34 mm (median: 4.74 mm; range: 3.76-6.53 mm). In multivariate analysis, longer DFD was associated with longer axial length (P<0.001; standardized correlation coefficient beta: 0.62), higher prevalence of axially high myopia (P<0.001; beta:0.06), shallower anterior chamber depth (P<0.001; beta:-0.18), thinner lens thickness (P = 0.004; beta: -0.06), smaller optic disc-fovea angle (P = 0.02; beta: -0.04), larger parapapillary alpha zone (P = 0.008; beta: 0.05), larger parapapillary beta/gamma zone (P<0.001; beta: 0.11), larger optic disc area (P<0.001; beta: 0.08), lower degree of cortical cataract (P = 0.002; beta: -0.08), and lower prevalence of age-related macular degeneration (P = 0.001; beta: -0.06). Bruch´s membrane opening-fovea distance (DFD minus disc radius minus parapapillary beta/gamma zone width) in non-glaucomatous eyes was not significantly (P = 0.60) related with axial length in emmetropic or axially myopic eyes (axial length ≥23.5 mm), while it increased significantly (P<0.001; r: 0.32) with longer axial length in eyes with an axial length of <23.5 mm. Ratio of mean DFD to disc diameter was 2.65 ± 0.30. If the ratio of disc-fovea distance to disc diameter was considered constant and if the individual disc diameter was calculated as the individual disc-fovea distance divided by the constant factor of 2.65, the resulting calculated disc diameter differed from the directly measured disc diameter by 0.16 ±0.13 mm (median: 0.13 mm, range: 0.00-0.89 mm) or 8.9 ± 7.3% (median: 7.4%; range: 0.00-70%) of the measured disc diameter. CONCLUSIONS: DFD (mean: 4.76 mm) increases with longer axial length, larger parapapillary alpha zone and parapapillary beta/gamma zone, and larger disc area. The axial elongation associated increase in DFD was due to an enlargement of parapapillary beta/gamma zone while the Bruch's membrane opening-fovea distance did not enlarge with longer axial length. This finding may be of interest for the process of emmetropization and myopization. Due to its variability, the disc-fovea distance has only limited clinical value as a relative size unit for structures at the posterior pole.

Corneal arcus and its associations with ocular and general parameters: the Central India Eye and Medical Study.

PURPOSE: To investigate the prevalence of corneal arcus and its associations. METHODS: The Central India Eye and Medical Study was a population-based study performed in rural Central India on 4711 subjects (age, 30+ years). Corneal arcus was assessed in corneal photographs. RESULTS: The study included 952 randomly selected participants. Mean body mass index (BMI) was 19.8 ± 3.6 kg/m(2), with 786 (41.3%) subjects being underweight (BMI < 18.5 kg/m(2)). Corneal arcus of any degree was detected in 102 (10.7% ± 1.0%; 95% CI, 8.8-12.7) subjects. Corneal arcus was significantly associated with increasing age (P < 0.001). It was not significantly (all P > 0.10) associated with serum concentrations of high-density lipoproteins, cholesterol, creatinine, glucose, and glycosylated hemoglobin; with prevalence of arterial hypertension and diabetes mellitus; with body height, weight, and BMI; or with level of education, daily activities, nutrition, alcohol consumption, smoking, and blood pressure. In an intereye comparison, corneal arcus was significantly more marked in the eye with lower intraocular pressure (P = 0.006), thinner central cornea (P = 0.005), and more hyperopic refractive error (P = 0.003). CONCLUSIONS: In this adult rural Central Indian population with low mean BMI, the prevalence of corneal arcus was 10.7% ± 1.0%. The only systemic parameter associated with corneal arcus was increasing age (P < 0.001). Corneal arcus was not associated with dyslipidemia, diabetes mellitus, arterial hypertension, alcohol consumption, or smoking. In this population with low BMI, corneal arcus was not a clinical biomarker for major metabolic disorders. The intereye associations between corneal arcus and low intraocular pressure, thin central cornea, and hyperopia may be of importance in the ophthalmic examination.