Retinal Responses to Short- and Longer-Term Predominant ON or OFF Stimulation in Emmetropes and Myopes

The link between nearwork and myopia is controversially discussed. Features of the viewing target may stimulate eye growth, for example, black-on-white text was found to stimulate retinal OFF pathways and promote choroidal thinning, whereas inverted text led to ON pathway stimulation and thicker choroids. We used electroretinograms (ERGs) to compare retinal activity for both stimuli in the parafovea in emmetropes and myopes and studied the effects of adaptation.

ERGs were recorded in 42 subjects (18-30 years) during 200 ms-flashes on a CRT monitor, superimposed with an annulus or circles filled with gray or inverted or standard text. Ganzfeld ERGs (500 ms) were taken before and after 30 minutes of reading standard or inverted text at 25 cm to determine adaptation effects. The ON- (b-wave) and OFF-responses (d-wave) were analyzed using linear mixed effects models and pointwise t-testing.

(1) Stimulus size affected retinal ON-responses of both groups (p < 0.001), with larger responses to a 6 to 12 degrees annulus than to a 12-degree circle. (2) Myopes displayed larger ON-responses to inverted text contrast than emmetropes within 6 to 12 degrees. (3) After adaptation to text, ON-responses were reduced (p = 0.010) irrespective of refraction and contrast. (4) Emmetropes showed reduced ON- and OFF-responses to inverted text contrast. (5) Only emmetropes had reduced ON- and larger OFF-responses after adapting to standard text.

Myopes had largest ON-responses with inverted contrast in the perifovea. Emmetropes displayed larger adaptive changes after ON/OFF stimulation. In both groups, inverted contrast still reduced ON-responses, suggesting that efficient activation of retinal ON channels to inhibit myopia might require additional OFF channel suppression.