Myopia, dry eye and Vitamin D – PhD 2017

VITAMIN D IN DRY EYE AND MYOPIA

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Chih Huang Yang, Bachelor of Optometry, Master of Optometry
Katrina L Schmid; Damien Harkin
Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy
School of Optometry and Vision Science, Faculty of Health, Queensland University of Technology
Keywords
Accommodation response
Amplitude of accommodation
Axial length Dopamine
Dry eye
Form deprivation myopia
Inflammation
Interleukin-6
Keratograph
Lenstar
Myopia
Ocular surface
Saliva
Tonic accommodation Vitamin D
Vitamin D binding protein

Abstract
Vitamin D has long been regarded as an essential daily nutrient of benefit to human health, particularly bone health. Studies have shown that low vitamin D levels may be related to ocular dryness. Vitamin D levels also impact dopamine controlled behaviours in animals. Dopamine, a neurotransmitter, may impact eye health and human eye accommodation. It has also been suggested that increased dopamine release can inhibit myopia development.

This study aimed to investigate whether there was an association between vitamin D levels and two eye conditions, dry eye and myopia, and whether an oral vitamin D supplement taken for 60 days could affect ocular dryness and accommodation/refraction in humans.

In Experiment 1, dry eye symptoms were assessed objectively using the keratograph 5 and subjectively using surveys, in 58 older adults aged between 43 and 69 years. Objective measurements included tear meniscus height, non-invasive tear break up time, ocular redness, oxford corneal staining grading, Schirmer’s test, and Phenol red thread tests of tear quantity. Subjective assessment included the dry eye symptoms survey and the Ocular Surface Disease Index (OSDI). There were two participant groups, one was recruited from AusSun study, and the other was from Optometry clinic of Queensland University of Technology. Blood samples were taken from each participant of Optometry clinic group for analysis of vitamin D levels and interleukin-6 analysis. The results showed dry eye was correlated with insufficient serum vitamin D levels (< 75 nmol/l).

In Experiment 2, 32 participants with insufficient vitamin D and/or dry eye from the participants of Experiment lwere included. They were provided with 1000 IU vitamin D supplements to take daily for 60 days. The assessments were identical as Experiment 1. The vitamin D supplement increased the vitamin D levels by 29.08 nmol/l after 60-day of treatment. The main finding was that OSDI significantly reduced in association with the rise of vitamin D levels. Also, Oxford grading score showed a significant reduction. Interleukin-6 levels did not show significant difference before and after the vitamin D treatment.

In Experiment 3, 55 young adults aged between 18 and 25 were recruited from QUT and UQ student populations. Saliva samples were collected from each participant for the analysis of dopamine and vitamin D levels, levels of vitamin D binding protein were measured in 40 participants. Ocular biometry including axial length, anterior chamber, lens thickness, anterior chamber depth, central cornea thickness, corneal astigmatism, and pupil diameter were measured using the Lenstar. Subchoroidal thickness was measured using Optical Coherence Tomography. Accommodation and binocular vision assessments included accommodation accuracy to near targets, tonic accommodation (TA), distance and near phoria, negative relative accommodation (NRA), positive relative accommodation, and near work induced transient myopia, and near work induced effect on TA. Main findings showed NRA was positively correlated with dopamine levels; people with poorer accommodation had lower dopamine levels. Pre-task TA was higher in high myopes. TA was quite stable when comparing pre-task and post-task in each refractive group. The near work induced TA shift in myopes was myopic whereas it was hyperopic in emmetropes. The levels of vitamin D binding protein were higher in emmetropes compared with myopes. People with lighter iris colour had higher levels of vitamin D binding protein.

In Experiment 4, 33 people with myopia/poor accommodation identified in Experiment 3 were recruited and provided with 1000IU vitamin D supplement to take daily for 60 days. Both the shifts in TA and accommodation accuracy at 25 cm were relatively stable after the vitamin D treatment. Choroidal thickness was greater following the vitamin D treatment. Early onset myopes showed higher central corneal thickness than late onset myopes.

In conclusion, dry eye score using OSDI was inversely correlated with serum vitamin D levels in people with vitamin D insufficiency. A 60 day 1000 IU vitamin D supplement was able to show improvement in dry eye symptoms assessed by OSDI and increases in tear meniscus height. Higher dopamine levels had effects on assisting relaxation of accommodation. A 60-day 1000IU vitamin D supplement in young adults stabilised TA and improved accommodation accuracy for higher accommodation stimulus. The results are suggestive of vitamin D being involved in the ocular surface and human accommodation.