Analysis of foveal characteristics and their asymmetries in the normal population.

The advance of optical coherence tomography (OCT) enables a detailed examination of the human retina in-vivo for clinical routine and experimental eye research. Only few investigations to date captured human foveal morphology in a large subject group on the basis of a detailed analysis employing mathematical models. However, even for important foveal characteristics unified terminology and clear definitions were not implemented so far. This might be a reason, why to this day the human fovea is considered to be a mostly symmetric and round structure. Therefore, the most important finding of this work is the detailed analysis of the asymmetric structure of the human fovea. We employed five clinically highly relevant foveal characteristics, which are derived from a previously published fovea model. For each, an accurate mathematical description is given. The presented properties include (1) mean retinal thickness inside a defined radius, (2) foveal bowl area, (3) a new, exact definition of foveal radius, (4) maximum foveal slope, and (5) the maximum height of the foveal rim. Furthermore, minimum retinal thickness was derived and analyzed. 220 strictly controlled healthy Caucasian subjects of European decent with an even distribution of age and gender were imaged with an Heidelberg Spectralis OCT. Detailed analysis demonstrated the following general results: (1) significant gender difference regarding the central foveal subfield thickness (CFST) but no significant differences for the minimum central retinal thickness, (2) a strong correlation between right and left eye of the same subject, and, as essential finding, (3) strong structural differences of the fovea form in the different anatomical directions (nasal, temporal, inferior and superior). In the analysis of the foveal asymmetry, it will be demonstrated that the foveal radius is larger in nasal and temporal direction compared to inferior and superior position. Furthermore, it will be shown that the circular fovea rather has an elliptic form with the larger axis along the nasal to temporal direction. Interestingly, the foveal slope shows a divergent behavior as the temporal direction has the smallest slope angle and both, inferior and superior angles are clearly larger than the others. The findings in this work can be used for an exact quantification of changes in early stages of various retinal diseases and as a marker for initial diagnosis.

Biometry and visual function of a healthy cohort in Leipzig, Germany.

BACKGROUND: Cross-sectional survey of ocular biometry and visual function in healthy eyes across the life span of a German population aged 20 to 69 years (n = 218). Subject number in percent per age category reflected the percentage within the respective age band of the population of Leipzig, Germany. METHODS: Measurements obtained: subjective and objective refraction, best-corrected visual acuity, accommodation, contrast sensitivity, topography and pachymetry with Scheimpflug camera, axial length with non-contact partial coherence interferometry, and spectral-domain optical coherence tomography of the retina. Pearson correlation coefficients with corresponding p-values were given to present interrelationships between stature, biometric and refractive parameters or their associations with age. Two-sample T-tests were used to calculate gender differences. The area under the logarithmic contrast sensitivity function (AULCSF) was calculated for the analysis of contrast sensitivity as a single figure across a range of spatial frequencies. RESULTS: The results of axial length (AL), anterior chamber depth (ACD) and anterior chamber volume (ACV) differed as a function of the age of the participants (rho (p value): AL -0.19 (0.006), ACD -0.56 (< 0.001), ACV-0.52 (< 0.001)). Longer eyes had deeper ACD (AL:ACD 0.62 (< 0.001), greater ACV (AL:ACV 0.65 (< 0.001) and steeper corneal radii (AL:R1ant; R2ant; R1post; R2post 0.40; 0.35; 0.36; 0.36 (all with (< 0.001)). Spherical equivalent was associated with age (towards hyperopia: 0.34 (< 0.001)), AL (-0.66 (< 0.001)), ACD (-0.52 (< 0.001)) and ACV (-0.46 (< 0.001)). Accommodation was found lower for older subjects (negative association with age, r = -0.82 (< 0.001)) and contrast sensitivity presented with smaller values for older ages (AULCSF -0.38, (< 0.001)), no change of retinal thickness with age. 58 % of the study cohort presented with a change of refractive correction above ±0.50 D in one or both eyes (64 % of these were habitual spectacle wearers), need for improvement was present in the young age-group and for older subjects with increasing age. CONCLUSION: Biometrical data of healthy German eyes, stratified by age, gender and refractive status, enabled cross-comparison of all parameters, providing an important reference database for future patient-based research and specific in-depth investigations of biometric data in epidemiological research. TRIAL REGISTRATION: ClinicalTrials.gov # NCT01173614 July 28, 2010.