FOVEA: a new program to standardize the measurement of foveal pit morphology

Gender- and age-related differences in foveal pit morphology

AIMS

To measure the foveal pit morphology parameters and evaluate their correlations with age and sex.

SETTINGS AND DESIGN

A retrospective cross-sectional matched comparison study in a tertiary center.

METHODS AND MATERIALS

Forty men and 40 age-matched women who had normal macular structures and foveal contours were enrolled. Foveal pit parameters including top width, base width, nasal width, temporal width, minimal thickness, nasal thickness, temporal thickness, nasal height, temporal height, nasal slope, and temporal slope were measured on horizontal B-scan macular optical coherence tomography and compared between men and women.

STATISTICAL ANALYSIS USED

Paired t-tests and Pearson's correlation analysis.

RESULTS

The average patient age was 51.4 ± 17.5 (21-84) years. Women had a wider base width (313.1 ± 68.0 μm vs 266.8 ± 70.9 μm, P = 0.006), wider temporal width (1043.1 ± 245.6 μm vs 968.9 ± 261.0 μm, P = 0.006), thinner nasal thickness (345.6 ± 36.2 μm vs 359.7 ± 35.8 μm, P = 0.048), and flatter temporal slope (11.60 ± 2.52° vs 12.98 ± 2.68°, P = 0.016) than men. With age, the base width (r = 0.35, P = 0.025) and temporal width (r = 0.54, P = 0.0003) tended to be wider and the temporal slope was flatter (r = -0.45, P = 0.003) in women but not men. The minimal thickness tended to be thinner in the elderly group (r = 0.038, P = 0.015).

CONCLUSIONS

Women had a significantly wider base width, wider temporal width, thinner nasal thickness, and flatter temporal slope of the foveal pit than age-matched men. The base width and temporal width were wider and the temporal slope was flatter with age in women but not men.

FOVEAL SPARING INTERNAL LIMITING MEMBRANE PEELING FOR IDIOPATHIC MACULAR HOLES: EFFECTS ON ANATOMICAL RESTORATION OF THE FOVEA AND VISUAL FUNCTION

PURPOSE

Muller cells seem to be important in maintaining foveal morphology through connections between their foot processes and the internal limiting membrane (ILM). Internal limiting membrane peeling causes Muller cell trauma. We hypothesized that leaving a rim of unpeeled ILM around idiopathic macular holes undergoing vitrectomy surgery would improve postoperative foveal morphology and vision.

METHODS

Prospective pilot study of fovea-sparing ILM peeling in a consecutive cohort of patients with macular holes over a 12-month period. Spectral-domain optical coherence tomography and Early Treatment Diabetic Retinopathy Study letters best-corrected visual acuity were assessed preoperatively and postoperatively, and foveal morphology and metamorphopsia postoperatively. The foveal sparing group was compared with a second consecutive cohort who received standard ILM peeling (control group).

RESULTS

Thirty-four eyes of 34 patients were included in each group. Groups showed no significant preoperative differences. 34/34 holes were successfully closed with surgery in the foveal sparing group and 32/34 in the control group. The foveal sparing group showed better postoperative best-corrected visual acuity (67.7 vs. 63.8, P = 0.003) and best-corrected visual acuity improvement (25.1 vs. 20.2, P = 0.03). The foveal sparing group demonstrated thicker minimum foveal thickness (211 vs. 173 μm, P = 0.002) and less steep foveal depression (158 vs. 149, P = 0.002).

CONCLUSION

Preserving nonpeeled ILM around macular holes resulted in a high closure rate, improved foveal morphology, and better postoperative best-corrected visual acuity. An appropriately powered randomized controlled study is warranted.

Wide-based foveal pit: a predisposition to idiopathic epiretinal membrane

PURPOSE

To report the anatomical characteristics of wide-based foveal pit and its possible associations with macular diseases.

METHODS

Wide-based foveal pit was defined as a foveal base width (FBW) larger than the mean value plus one standard deviation of the normal population. Eyes with a wide-based foveal pit were retrospectively collected as the study group, and age- and sex-matched subjects with a normal FBW were recruited as the control group. FBW, area of foveal avascular zone (FAZ), and retinal artery trajectory (RAT) were compared between the two groups. The characteristics of the fellow eyes in the study group were also described.

RESULTS

Fifty-two eyes from 52 patients were identified as having a wide-based foveal pit; 43 (82.7%) were female. Both their FBW (474.7 ± 84.6 μm) and area of FAZ (0.50 ± 0.11 mm²) were significantly larger than in the control group (297.6 ± 42.3 μm and 0.29 ± 0.10 mm², respectively; p < 0.001 for both), and they also had a wider RAT than the control group (p < 0.001). During follow-up, three eyes had developed idiopathic epiretinal membrane. As for their fellow eyes, they either also had a wide-based foveal pit (11 eyes) or had various macular diseases including idiopathic epiretinal membrane (27 eyes), macular hole (5 eyes), and others (16 eyes).

CONCLUSIONS

Eyes with a wide-based foveal pit had a large FAZ and a wide RAT, and they might have a predisposition to idiopathic epiretinal membrane formation. Their fellow eyes also had a predisposition to epiretinal membrane and macular hole.

Inter-individual differences in foveal shape in a scavenging raptor, the black kite Milvus migrans

Birds, and especially raptors, are believed to forage mainly using visual cues. Indeed, raptors (scavengers and predators) have the highest visual acuity known to date. However, scavengers and predators differ in their visual systems such as in their foveal configuration. While the function of the foveal shape remains unknown, individual variation has never been quantified in birds. In this study, we examined whether foveal shape differs among individuals in relation to eye size, sex, age, eye (left or right) and genetic proximity in a scavenging raptor, the black kite Milvus migrans. We assessed foveal shape in 47 individuals using spectral domain optical coherence tomography (OCT) and geometric morphometric analysis. We found that foveal depth was significantly related to eye size. While foveal width also increased with eye size, it was strongly related to age; younger individuals had a wider fovea with a more pronounced rim. We found no relationship between foveal shape and genetic proximity, suggesting that foveal shape is not a hereditary trait. Our study revealed that the shape of the fovea is directly linked to eye size and that the physical structure of the fovea may develop during the entire life of black kites.

Spectral-domain optical coherence tomography imaging of normal foveae: A pilot study in 17 diurnal birds of prey

OBJECTIVE

To describe and to establish normative data for the foveae of diurnal birds of prey using spectral-domain optical coherence tomography (SD-OCT).

METHODS

All animals (9 red-tailed hawks, 3 Cooper's hawks, 3 American kestrels, 1 sharp-shinned hawk, and 1 broad-winged hawk) had an ophthalmic examination performed with slit lamp biomicroscopy and indirect ophthalmoscopy. Following ophthalmic examination, SD-OCT was performed in each eye that had a visible fundus and normal fovea on SD-OCT. Temporal foveae depth, central foveae depth, pecten-temporal foveae distance, and pecten-central foveae distance (PCFD) were measured using SD-OCT. Differences in measured outcomes between species were determined using generalized linear mixed effects models.

RESULTS

The central foveae (mean ± SD) displayed a small but significant depth variation between species (P = .002) and was deepest in red-tailed hawks (293 ± 16 µm), followed by American kestrels (260 ± 12 µm), broad-winged hawks (256 ± 16 µm), Cooper's hawks (250 ± 9 µm), and sharp-shinned hawks (239 ± 16 µm). The temporal foveae were shallower than the central foveae in all species tested, and there was a significant variation between species (P < .001). The temporal foveae (mean ± SD) were deepest in American kestrels (137 ± 8 µm), followed by red-tailed hawks (129 ± 3 µm), broad-winged hawks (59.5 ± 3.5 µm), Cooper's hawks (20.3 ± 6.4 µm), and sharp-shinned hawks (17.5 ± 0.7 µm). Pecten-temporal foveae distance was approximately 30% shorter than PCFD in all species. There were no differences in the parameters tested between the eyes within each species (P ≥ .47).

CONCLUSION

Normative foveae SD-OCT data were obtained in four species of diurnal birds of prey. Further studies are warranted to provide structural and functional information regarding normal and pathologic changes that can affect the foveae.

Shape Decomposition of Foveal Pit Morphology using Scan Geometry Corrected OCT

The fovea is an important structure that allows for the high acuity at the center of our visual system. While the fovea has been well studied, the role of the foveal pit in the human retina is still largely unknown. In this study we analyze the shape morphology of the foveal pit using a statistical shape model to find the principal shape variations in a cohort of 50 healthy subjects. Our analysis includes the use of scan geometry correction to reduce the error from inherent distortions in OCT images, and a method for aligning foveal pit surfaces to remove translational and rotational variability between the subjects. Our results show that foveal pit morphology can be represented using less than five principal modes of variation. And we find that the shape variations discovered through our analysis are closely related to the main metrics (depth and diameter) used to study the foveal pit in current literature. Lastly, we evaluated the relationship between the first principal mode of variation in the cohort and the axial length from each subject. Our findings showed a modest inverse relationship between axial length and foveal pit depth that can be confirmed independently by existing studies.

Direct modeling of foveal pit morphology from distortion-corrected OCT images

Inherent distortions affect the spatial geometry of optical coherence tomography (OCT) images and consequently the foveal pit dimensions. Distortion correction provides an accurate anatomical representation of the retinal shape. A novel approach that automatically extracts foveal pit metrics from distortion-corrected OCT images using a sum of Gaussian function is presented. Foveal width, depth and slope were determined in 292 eyes with low fitting errors and high repeatability. Comparisons to undistorted scans revealed significant differences. To conclude, the internal OCT distortions affect the measurements of the foveal pit with their correction providing further insights into the role of foveal morphology in retinal pathologies and refractive development.

The organization of tyrosine hydroxylase-immunopositive cells in the sparrow retina

The purpose of this study was to identify tyrosine hydroxylase-immunopositive (TH+) cells in the sparrow retina using immunocytochemistry and quantitative analysis. All TH+ cells were conventional amacrine cells. Based on dendritic morphology, at least two types were observed. The first type had a single thick primary process that descended from the cell body and many densely beaded processes in substrata (s) 1, less beaded processes in s3, and spiny processes in s4/5 of the inner plexiform layer. The dendrites of the second type appeared similar in each layer, but it displayed several primary processes that spread laterally away from the soma before descending to the inner plexiform layer. The average density of TH+ cells was 37.48 ± 1.97 cells/mm² (mean ± standard deviation; n = 4), and the estimated total number of TH+ cells was 3,061.25 ± 192.79. The highest and lowest densities of TH+ cells were located in the central dorsotemporal retina and periphery of the ventronasal retina, respectively. TH+ cells did not express calbindin-D28 K, calretinin, or parvalbumin. These results suggest that all TH+ cells in specific amacrine cell subpopulations are involved in retinal information processing in both the ON and OFF sublaminae in sparrow retina.

A sloped piecemeal Gaussian model for characterising foveal pit shape

PURPOSE

High-quality optical coherence tomography (OCT) macular scans make it possible to distinguish a range of normal and diseased states by characterising foveal pit shape. Existing mathematical models lack the flexibility to capture all known pit variations and thus characterise the pit with limited accuracy. This study aimed to develop a new model that provides a more robust characterisation of individual foveal pit variations.

METHODS

A Sloped Piecemeal Gaussian (SPG) model, consisting of a linear combination of a tilted line and a piecemeal Gaussian function (two halves of a Gaussian connected by a separate straight line), was developed to fit retinal thickness data with the flexibility to characterise different degrees of pit asymmetry and pit bottom flatness. It fitted the raw pit data between the two rims of the fovea to improve accuracy. The model was tested on 3488 macular scans from both eyes of 581 young adults (376 myopes and 206 non-myopes, mean (S.D.) age 21.9 (1.4) years). Estimates for retinal thickness, wall height and slope, pit depth and width were derived from the best-fitting model curve. Ten variations of Gaussian and Difference of Gaussian models were fitted to the same scans and compared with the SPG model for goodness of fit (by Root mean square error, RMSE), model complexity (by the Bayesian Information Criteria) and model fidelity.

RESULTS

The SPG model produced excellent goodness of fit (mean RMSE = 4.25 and 3.89 μm; 95% CI: 4.20, 4.30 and 3.86, 3.93 for fitting horizontal and vertical profiles respectively). The SPG model showed pit asymmetry, with average nasal walls 17.6 (11.6) μm higher and 0.96 (0.61)^° steeper than temporal walls and average superior walls 7.0 (12.2) μm higher and 0.41 (0.65)^° steeper than the inferior walls. The SPG model also revealed a continuum of human foveal shapes, from round bottoms to extended flat bottoms (up to 563 μm). 49.1% of foveal profiles were best fitted with a flat bottom >30 μm wide. Compared with the other tested models, the SPG was the preferred model overall based on the Bayesian Information Criteria.

CONCLUSIONS

The SPG is a new parsimonious mathematical model that improves upon other models by accounting for wall asymmetry and flat pit bottoms, providing an excellent fit and more faithful characterisation of typical foveal pit shapes and their known variations. This new model may be helpful in distinguishing normal foveal shape variations by refractive status as well by other characteristics such as sex, ethnicity and age.