Myopia: the association between environmental factors and refractive error

Abstract

Background
The precise mechanism underpinning the protective effects of the outdoor environment against myopia is unclear. The release of the neurotransmitter, dopamine (DA), and the neurohormone, melatonin (Mel) is mediated by light exposure and circadian rhythm. Animal studies indicate that lower DA and higher Mel concentrations promote myopia. This relationship has yet to be explored in humans. A lower vitamin D status has also been associated with myopia but research disputes if vitamin D actively inhibits myopic growth. Conjunctival ultraviolet autofluorescence (CUVAF) has been used as a biomarker of sun exposure in Southern Hemisphere populations but its value in this role has not been investigated in the Northern Hemisphere.

Methods
A bespoke CUVAF photography system and image analysis method was created. The association between vitamin D and self-reported myopia was explored in adults (aged 18-64 years, n=52). The association between vitamin D, CUVAF, DA, Mel and myopia was determined in a prospective study in young adults (aged 18-20 years, n=54). To identify additional risk factors for myopia, prospective data from Northern Irish children (aged 6-7 and 12-13 years, n=387) were explored.

Results & conclusions
Higher Mel and lower DA serum concentrations were associated with myopia in humans for the first time. This finding will inform future myopia treatments and research into the myopic growth mechanism.Vitamin D does not appear to be actively involved in eye growth regulation.The association between average CUVAF measures and myopia was not significant. Analyses may have been confounded by individual inter-seasonal variation in measures and the limited sun exposure experienced in NorthernIreland.Children aged 6-7 years of age with a low level of hyperopia (cycloplegic spherical equivalent refraction (SER): ≤+0.75 dioptre sphere (DS)) are at a greater risk ofmyopia and may benefit from refractive monitoring.xviii

Date of Award	Sept 2016
Original language	English
Sponsors	Department for Employment and Learning (DEL)
Supervisor	Kathryn Saunders (Supervisor), Lisa O'Donoghue (Supervisor), Kirsty Pourshahidi (Supervisor) & Patrick Richardson (Supervisor)