Effect of Caffeine on Ocular Circulation in High Myopes
Condition: High Myopia; Choroid
MeSH terms: Myopia
Study type: Interventional

Summary: 
      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.
    

Detailed description: 
      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.
    

Intervention name(s): Caffeine; Vitamin E
Intervention type(s): Dietary Supplement; Dietary Supplement
Intervention description(s): As in group descriptions; As in group descriptions
Intervention MeSH terms: Vitamin E; Caffeine
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: 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.
Masking: Single (Participant)
Primary purpose: Diagnostic
Keywords: High Myopia; Caffeine; Choroidal Thickness; Choroidal Volume; Optical Coherence Tomography; Optical Coherence Tomography Angiography