Sustained Plus Lens Defocus Alters Retinal Responses and Ciliary Muscle Morphology In Myopes and Near-emmetropes

The origin of myopia is multifactorial, with nearwork as one possible risk factor. Spectacles with peripheral positive defocus aim to inhibit further ocular elongation. However, myopic eyes of young adults were found to become longer with positive defocus. Additionally, they showed reduced ability to use chromatic cues for detecting the retinal defocus sign. Possible underlying retinal differences to non-myopes are yet to be determined.

The ciliary muscle (CM) was imaged in near-emmetropes and myopes (18-30 years of age) using optical coherence tomography after consecutively watching a movie for 30 min (i) in focus and (ii) with +3.00 D lenses, to assess possible interactions of defocus with accommodation. After a 2-h break, long flash electroretinograms (ERG) were measured after clear and defocused viewing. ERG b- and d-waves served as proxies to evaluate retinal ON- and OFF-responses. At a separate visit for a subgroup, the ERG experiment was exploratively repeated under red-light restriction.

B-wave amplitudes were reduced (-4.74 µV) and delayed (+0.30 ms, both p < 0.001) in both groups after experiencing defocus. The CM became significantly thinner in myopes only (-19.43 µm, p = 0.007). Exploratory outcomes with red filters revealed smaller b-wave amplitudes with defocus (Δ = -6.44 µV, p = 0.003), as well as delayed b-waves without (Δ = 1.03 ms) and with defocus (Δ = 0.67 ms, both p < 0.001) in both groups. OFF-response proxies of the myopic sub-group showed reduced i-waves after defocus, independent of light conditions.

Sustained positive defocus reduced physiological proxies for retinal ON activity irrespective of the refractive error. After defocus exposure, the CM of myopes reacted similarly to after sustained nearwork, as found previously. Altered OFF-response proxies in myopes after blur could point to modified retinal processing. Paediatric trials are required to assess whether these acute physiological responses following fixed-sequence defocus exposure relate to ocular growth signals, myopia progression or optical treatment response.