Abstract
Purpose :
Dynamic changes in ocular shape during embryonic development have been observed in foveated vertebrates including humans, other primates and recently lizards. Areas that develop a fovea elongate shortly after retinal differentiation and then undergo ocular retraction or a return to ocular symmetry, during which time retinal remodeling occurs (pit formation, photoreceptor cell packing). We propose that fovea development is a protracted process that begins early in embryonic development and that ocular elongation followed by retraction are necessary steps for fovea formation. To better understand this, we investigated the role of morphological changes in eye shape in the foveated chameleon, Chamaeleo calyptratus, and the bifoveated brown anole lizard, Anolis sagrei, before examining albino anoles with tyrosinase mutations. Wildtype chameleons have a central fovea while anoles have both a central and temporal fovea. Albino lizards with tyrosinase mutations fail to develop their temporal fovea.
Methods :
Embryonic eyes were dissected and then measured along 3 different anatomical planes in chameleons as well as wildtype and albino anoles. Albino (tyr -/-) lizards were created using a CRISPR gene editing approach.
Results :
Between early and mid-embryonic development, the central and temporal regions of the wildtype anole eye elongate. Later, both regions retract, returning the eye to its’ spherical shape, at which point the fovea develops. A similar process occurs in chameleons but only the central region undergoes ocular elongation, retraction, and fovea formation. Preliminary results of the albino anoles, which exhibit temporal fovea hypoplasia, suggest embryonic albino eyes exhibit a reduction in temporal ocular elongation but not in central elongation during development.
Conclusions :
These results support the premise that ocular elongation and retraction are necessary steps in fovea formation and the idea that the onset of fovea development may occur much earlier than previously believed. Together these findings indicate that the anole lizard is a promising model system for studies investigating human ocular developmental disorders.
This is a 2021 ARVO Annual Meeting abstract.