Exposure to Sunlight Reduces the Risk of Myopia in Rhesus Monkeys

Abstract

Exposure to sunlight has recently been postulated as responsible for the effect that more time spent outdoors protects children from myopia, while early life exposure to natural light was reported to be possibly related to onset of myopia during childhood. In this study, we had two aims: to determine whether increasing natural light exposure has a protective effect on hyperopic defocus-induced myopia, and to observe whether early postnatal exposure to natural light causes increased risk of refractive error in adolescence. Eight rhesus monkeys (aged 20-30 days) were treated monocularly with hyperopic-defocus (-3.0D lens) and divided randomly into two groups: AL group (n=4), reared under Artificial (indoor) Lighting (08:00-20:00); and NL group (n=4), exposed to Natural (outdoor) Light for 3 hours per day (11:00-14:00), and to indoor lighting for the rest of the light phase. After being reared with lenses for ca. 190 days, all monkeys were returned to unrestricted vision until the age of 3 years. Another eight age-matched monkeys, reared with unrestricted vision under artificial lighting since birth, were employed as controls. The ocular refraction, corneal curvature and axial dimensions were measured before lens-wearing (at 23±3 days of age), monthly during the light phase, and at the age of puberty (at 1185+3 days of age). During the lens-wearing treatment, infant monkeys in the NL group were more hyperopic than those in the AL group (F=5.726, P=0.032). Furthermore, the two eyes of most NL monkeys remained isometropic, whereas 3 of 4 AL monkeys developed myopic anisometropia more than -2.0D. At adolescence, eyes of AL monkeys showed significant myopic anisometropia compared with eyes of NL monkeys (AL vs NL: -1.66±0.87D vs -0.22±0.44D; P=0.002) and controls (AL vs Control: -1.66±0.87D vs -0.05±0.85D; P<0.0001). All differences in refraction were associated with parallel changes in axial dimensions. Our results suggest that exposure to natural outdoor light might have an effect to reduced hyperopic defocus-induced myopia. Also, the data imply that early life exposure to sunlight may help to maintain normal development of emmetropization later in life, and thus lower the risk of myopic anisometropia in adolescent monkey.

Bright Light Suppresses Form-Deprivation Myopia Development With Activation of Dopamine D1 Receptor Signaling in the ON Pathway in Retina

“…It is noteworthy that the light intensity in this study was lower (1500-3300 lux) than in the other studies (10,000-40,000 lux), but similar to the intensity employed in the current study (i.e., 2500-5000 lux). 9,15,42,45 This difference may be a critical factor because there are numerous reports indicating that laboratory light intensity and duration are in fact contributing factors because they do affect FDM progression in animal studies. 6,8,[36][37][38] Our results agree other reports indicating that the intensity and duration of light exposure are contributing factors to FDM in mice.…”

“…Other animal studies further indicated that laboratory bright light (BL) is a factor contributing to myopia inhibition in chicks, [10][11][12] guinea pigs, 13 and primates. 14,15 However, the underlying receptor-linked signaling mechanisms mediating such suppression require clarification. Dopamine (DA) is a retinal neurotransmitter released by dopaminergic amacrine cells (ACs).…”

Dopamine signaling and myopia development: What are the key challenges

“…Furthermore, the light hypothesis, i.e. light-stimulated DA antagonizes myopia development (Rose et al, 2008) has been supported by a number of studies that show outdoor activity and/or bright light inhibits myopia, potentially through DA-mediated mechanisms (Ashby et al, 2009; Chen et al, 2017; Cohen et al, 2011; Cohen et al, 2012; Li et al, 2014; Morgan et al, 2012; Smith et al, 2012; Wang et al, 2015; Wu et al, 2013). The evidence from pharmacological and genetic studies has provided more details regarding how light or visual input controls retinal DA signaling and contributes to refractive development (for a recent review, see (Feldkaemper and Schaeffel, 2013)).…”

Prevention and Management of Myopia and Myopic Pathology

“…[50][51][52][53][54] In animal studies, experiments in chicken and nonhuman primate animal models have shown that high illuminance levels of light (>15,000 Lux) can slow or even stop the development of experimentally induced myopia. [65][66][67][68] Another hypothesis is that the pupillary miosis that occurs while viewing distant objects outdoors results in less image blur and peripheral hyperopic defocus. 69 Evidence from both animal and human studies has shown that ambient light exposure plays an important role in controlling eye growth.…”