Abstract
Purpose :
We had previously found two visual stimuli that can make the human eye shorter and potentially inhibit myopia: (1) watching movies with the blue channel spatially low pass filtered and (2) reading text with inverted contrast. To learn more about the underlying retinal mechanisms, we tested whether a combination of both stimuli may have additive effects. Observation (1) was explained by longitudinal chromatic aberration (LCA) which indicates to the retina that the eye is too long when blue is out of focus, triggering eye growth inhibition. Observation (2) was explained by over-stimulation of retinal ON bipolar cells which triggers enhanced release of dopamine, a known inhibitor of axial eye growth.
Methods :
Fifteen emmetropic (average refraction: -0.6±0.7D) and fifteen myopic (average refraction: -3.7±1.8D, range -6 to -1.5D) young subjects (average age: 26±4 years) read text from a large screen (65'') in a dark room at 2 m distance. Text with inverted contrast (bright text on dark background, average luminance 86±7 cd/m2, letter height 0.5 deg) was presented, either unfiltered or low-pass filtered in the blue. Text was filtered in real-time by custom-developed software written in Visual C++. Axial length changes were measured using low coherence interferometry with autopositioning system (Lenstar LS-900) before and after 30 minutes of reading.
Results :
Unexpectedly, significant eye elongation was found in emmetropes after 30 minutes when they read text with inverted contrast that was also low pass filtered in the blue (+5.7±15.3 μm). Unfiltered text with inverted contrast made eyes shorter (-7.9±14.7 μm, p<0.05). Strinkingly, no such changes were observed in myopic eyes, neither when text was low pass filtered in the blue, nor when text with inverted contrast remained unfiltered.
Conclusions :
In emmetropes, the two stimuli had no additive effect but rather seemed to cancel each other out. The explanation may. be simpler than expected: low pass filtering the text in the blue may remove spatial information that is needed by the retina to detect defocus in the blue. In fact, subjects could not read the text in the blue channel after spatial filtering. Therefore, our finding is in line with the hypothesis that the emmetropic retina needs spatial information in the blue to generate growth inhibiting signals. As found before, the myopic retina was not responsive to stimulated LCA.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.