Emmetropes, but not myopes exhibit reduced retinal ON-responses in ERG after prolonged reading of standard contrast text

Abstract

Purpose : The myopic retina has presumably undergone changes that inhibit a successful emmetropization (Swiatczak & Schaeffel, 2022). Animal research revealed an association between myopia and defects in the visual ON pathway (Pardue, 2008). This pathway is overstimulated with reading material of inverted contrast, while standard contrast text stimulates the retinal OFF pathway (Aleman, 2018). We aimed to assess how longer periods of reading text with both contrast polarities affect the ERG ON/OFF responses in young adults with emmetropia vs. myopia.

Methods : Retinal activity was assessed before and after 30min of reading text of standard or inverted contrast (isoluminant 34cd/m², Michelson contrast 86%) presented at 25cm at separate dates in random order. On-Off ERGs (Ganzfeld, 500ms length, 30cd/m² vs. 330cd/m²) of one eye were recorded using a DTL electrode while myopes were corrected with soft contact lenses. Recordings were compared between refractive groups and conditions using the 95% confidence interval of mean differences (pre/post; contrast) or differences of means (groups).

Results : ERGs were recorded from 21 emmetropic (age 25.3±2.4yrs; SER OD -0.1±0.2D) and 21 myopic (age 25.1±3.2yrs; SER OD -2.5±1.1D) subjects. Emmetropes showed significantly reduced b-wave amplitudes (ON-response) after reading text with standard contrast (-4.2µV; Fig.1). Their d-wave amplitudes (OFF-response) were significantly larger after the stimulation with standard compared to inverted contrast text (+2.5µV; Fig.2). ERG ON/OFF responses in myopes did not change significantly after reading text of either polarity, nor differ between stimulation conditions. Pairwise comparison between refractive groups did not reveal any significant differences.

Conclusions : Longer reading periods of standard contrast text with 4D accommodation demand, providing an enhanced OFF stimulus, result in reduced retinal ON-responses in emmetropes only. After reading, emmetropes exhibit smaller OFF-responses when using text with inverted than with standard contrast. The latter, causing choroidal thinning, was previously suggested to trigger myopia. Our results indicate text contrast polarity to only affect retinal processing before myopia onset. The study thus reveals novel information concerning the link between myopia and reading and sheds light on the retinal changes occurring with myopia.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.