Functional Maturation of Scotopic and Photopic Retinal Function in the Swine

Abstract

Purpose: : The swine provides an attractive model of normal retina function because of the anatomic and functional similarity of their eye and retina to that of humans. The possibility of creating transgenic swine makes them even more useful as potential models of retinal disease. While precocial animals such as swine are born with a retina which appears morphologically mature, postnatal development of retinal function has not been documented. For animal models of disease, like retinitis pigmentosa (RP), determining normative function is crucial because photoreceptor degeneration may overlap with changes due to postnatal maturation. We followed and correlated the morphological and functional maturation of swine retinal function, using the full field electroretinogram (ERG).

Methods: : Full field ERGs were recorded under scotopic and photopic conditions following an International Society for Clinical Electrophysiology of Vision protocol. The age at evaluation ranged from postnatal day (P)3 to P120 with an average of 6 pigs in each of 6 age groups. The amplitudes of the a- and b-waves of scotopic and photopic ERGs were measured in both eyes of each pig and means computed for each age group. Mean responses were compared across age groups. Eyes were harvested and retinal morphology was assessed histologically.

Results: : The mean scoptopic full field ERG b-wave amplitude at P3 was 17% of the adult response and increased systematically through P60. No further changes were observed through P120. The same developmental sequence was observed for the photopic full field ERG b-wave response. The mean photopic 30 Hz flicker response at P3 was 10% of the adult response. In contrast to photopic full field ERG response, the flicker response continued to increase systematically through P90. Overall retinal morphology and lamination pattern was similar from P3 onward.

Conclusions: : Although overall retina morphology appears mature at P3, both rod and cone initiated function develops over the first two to three months of life in swine. In particular, the ability of the cone pathway to encode temporal variation requires even longer. This development in retinal function is an important consideration when assessing and treating models with early disease onset, such as RP.

Keywords: retinal development • electrophysiology: non-clinical • electroretinography: non-clinical