Effect of Caffeine on Ocular Circulation in High Myopes

To investigate the effect of caffeine on ocular circulation by using Optical Coherence Tomography and Optical Coherence Tomography Angiography. This study will evaluate blood supply to the inner and outer retina after consumption of 200mg caffeine capsule, in particular its effect in high myopes.

Caffeine could cause vasoconstriction. Previous studies revealed a reduction of retinal blood vessels diameter, a decrease in macular blood flow, and a decrease in blood velocity of optic nerve. Research devices, such as laser speckle tissue circulation analyzer and blue field simulation technique, were used in previous studies. With an advancement of technology such as optical coherence tomography (OCT), choroidal thickness can be measured, which indicates blood supply to outer retina. In addition, superficial retinal vasculature can be measured using optical coherence tomography angiography (OCTA). Previous studies found that subfoveal choroidal thickness declined with increase in myopia. A negative association between subfoveal choroidal thickness and axial length was also found. A recent study found a negative association between retinal vessel density with axial length in Chinese myopes using OCTA. Therefore, caffeine consumption may further make high myopes prone to ocular diseases development due to poor ocular circulation. The current study will use OCTA to measure the superficial retinal vasculature and OCT to measure choroidal thickness and choroidal volume of high myopes after consumption of caffeine capsule. Statistical analysis Normality of data will be assessed. The effect of caffeine on choroidal thickness, choroidal volume, vessel density, and perfusion density of superficial retinal layers will be analysed using repeated-measures ANOVA (co-variates) to compare baseline data and that after caffeine consumption at various time points. If significant difference is obtained, post hoc tests will be conducted to compare results from various time points with the baseline data. Difference between different age groups will be compared using unpaired t-test or Mann Whitney test, as appropriate.

High Myopia, Caffeine, Choroidal Thickness, Choroidal Volume, Optical Coherence Tomography, Optical Coherence Tomography Angiography

This will be a crossover study. Each subject is required to consume 200mg caffeine capsule and 200IU vitamin E control capsule, as control, in two different visits. The two visits will be randomized, with a washout period of at least one week.

To determine the effect of caffeine on ocular circulation in high myopes by consuming 200 mg caffeine capsule

To determine the effect of caffeine on ocular circulation in high myopes by consuming and 200 International Unit vitamin E control capsule, as control

Inclusion Criteria: Refractive error should be at least -6 Diopters or lower (spherical equivalent) Best corrected visual acuity of at least 6/6 Non-smoker Exclusion Criteria: - Diagnosed with any ocular diseases and systemic diseases