Long-term retinal imaging of a case of suspected congenital rubella infection

Cone Density Is Correlated to Outer Segment Length and Retinal Thickness in the Human Foveola

Purpose

Assessment of the relationship between in vivo foveolar cone density, cone outer segment length (OSL), and foveal retinal thickness (RT).

Methods

Foveolar cone density maps covering the central ±300 µm of the retina were derived from adaptive optics scanning laser ophthalmoscopy images. The corresponding maps of foveal cone OSL and RT were derived from high-resolution optical coherence tomography volume scans. Alignment of the two-dimensional maps containing OSL and RT with the cone density map was achieved by placing the location of maximum OSL on the cone density centroid (CDC).

Results

Across 10 participants (27 ± 9 years; 6 female), cone density at the CDC was found to be between 147,038 and 215,681 cones/mm². The maximum OSL and minimum RT were found to lie between 31 and 40, and 193 and 226 µm, respectively. A significant correlation was observed between cone density at the CDC and maximum OSL (P = 0.001), as well as the minimal RT (P < 0.05). Across all participants, the best fit for the relationship between normalized cone density and normalized OSL within the central 300 µm was given by a quadratic function.

Conclusions

Using optical coherence tomography-derived measurements of OSL enables to estimate CDC cone density and two-dimensional foveal cone density maps for example in patient eyes unsuitable for adaptive optics imaging. Furthermore, the observation of a fixed relationship between the normalized OSL and cone density points to a conserved mechanism shaping the foveal pit.

Foveal Hypoplasia Related to Congenital Rubella

Normal development of the fovea begins before midgestation and continues for several years after birth. Foveal hypoplasia is a condition in which the foveal pit and the foveal avascular zone do not fully develop. Several diseases are known to be associated with foveal hypoplasia; however, a direct association between foveal hypoplasia and congenital rubella has not been stated so far. This report describes a case of foveal hypoplasia detected during adulthood in a patient with known fetal exposure to maternal rubella infection and several ocular features of congenital rubella syndrome, including microphthalmia, congenital cataract, and pigmentary retinopathy. During follow-up, the visual acuity and ocular fundus changes remained stable.