November 30, 2018
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Study investigates dark adaptation changes in highly myopic patients

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Dark adaptation was found to be strongly correlated with axial length in highly myopic eyes, suggesting that globe elongation has an impact on dark adaptation.

Researchers aimed at investigating whether myopic eyes have a longer time of dark adaptation (DA) as compared with healthy eyes and, more specifically, if a correlation exists with axial length.

Data from 50 patients who consulted in the ophthalmology department of Strasbourg University Hospital between June and September 2016 were analyzed. Subjects were assigned to the group of high myopia over -6 D or the control group.

Dark adaptation tests were performed using the MacuLogix AdaptDx adaptometer, a technology that effectively measures DA with a short-duration protocol. Preliminary ophthalmologic examinations explored retinal status, including the presence or absence of atrophic retinal pigment epithelium (RPE) changes potentially related to high myopia.

DA time depends on rod functionality and rhodopsin regeneration. The AdaptDx adaptometer calculated for each patient an index called the rod intercept (RI), which corresponded to the time required to recover retinal sensitivity. The threshold for normal speed was established at less than 6.5 minutes.

Both highly myopic eyes and controls had a similar mean RI of slightly higher than 4 minutes. However, in the highly myopic group, a significant correlation was found between RI and AL.

“This observation suggests that myopic changes may have an impact on DA time,” the authors wrote.

Equally significant was the correlation in myopic patients between RI and RPE atrophy.

“This observation supports the hypothesis that DA impairment in high myopia may stem from RPE dysfunction,” they wrote.

The biochemical changes occurring during dark adaptation are located in the RPE, and slow DA might come as a consequence of slow rhodopsin regeneration, they said.

“This DA impairment in severely myopic patients could be explained by impaired photopigment regeneration, involved in scotopic retinal sensitivity recovery and may also be due to RPE alteration, which is frequently observed in high myopia,” the authors concluded. – by Michela Cimberle

Disclosure: The authors reported no relevant financial disclosures.