The goal of this randomised control trial is to learn about the effect of green tea consumption on patients with primary glaucoma.

The main questions to answer are:

1. Is there any difference of intraocular pressure (IOP) in patient with primary glaucoma after 1 month, 3 months and 6 months who is consuming green tea compared to patient not consuming green tea?
2. Is there any difference of retina nerve fibre layer in patient with primary glaucoma after 1 month, 3months and 6 months who is consuming green tea compared to patient not consuming green tea?

Researchers will compare patients with primary glaucoma who are consuming green tea and normal daily drinking to see if any affect to intraocular pressure and retina nerve fibre layer.

Glaucoma is a progressive optic neuropathy characterised by loss of retinal ganglion cells (RGCs) with corresponding visual field loss. The current established treatment of glaucoma is by reducing IOP, as one of neuroprotectant factor to prevent further loss RGCs. However, it is not always sufficient to fully prevent disease progression. Oxidative stress is one of biological insult contribute to etiology and progression of glaucoma. Antioxidants represent the first line of defence against oxidative stress and are obtained through the diet and produced internally has shown to be protective towards glaucoma. Green tea is one of the most antioxidant rich drink due to its high content of flavonoids commonly known as catechins.

The investigator would like to evaluate the effect of 6 months consumption of green tea on intraocular pressure (IOP) and retinal nerve fibre layer thickness (RNFL) in patients with primary glaucoma. This is a randomised controlled study involving primary glaucoma patients who are attending ophthalmology clinic at Hospital Universiti Sains Malaysia. Evaluation of study sample includes baseline ocular examination, IOP and Optical Coherence Tomography Retinal Nerve Fibre Layer (OCT RNFL). Subjects who fulfil the inclusion and exclusion criteria for the study will be selected.

Patients in Group A will consume two cups per day (250ml for each cup) of hot green tea, five days per week for 6 months while other Group B (control group) will not consume green tea. IOP and OCT RNFL measurement will be taken at baseline, first month, 3rd month and 6th month post recruitment of subjects. All patients will be given dietary diary to note down their daily drinks' consumption.

Inclusion Criteria:

• Patient with confirmed diagnosis of primary glaucoma (POAG/PACG/NTG) that achieve target IOP with medical therapy at least for 6 months.
• Never consume green tea as daily drinks.

Exclusion Criteria:

• Dense cataract with Lens Opacity Classification Sytem (LOCS II) of more than grade 2
• Any other ocular media opacity that may interfere with OCT imaging ( eg: cornea scar/vitreous haemorrhage)
• Any history of optic neuropathy
• History of glaucoma or retinal surgery
• Macular degeneration and retinal disorder
• Patient with caffein sensitive that causes unpleasant reaction (eg: palpitation, insomnia, nausea, constipation)
• Allergic to green tea