The purpose of this study is to investigate the effect of trabeculectomy, glaucoma drainage devices, cyclophotocoagulation and ocular hypotensive eye-drops on IOP elevation with postural change from the sitting to supine positions in eyes with open-angle glaucoma.

Patients will be assigned to the different study groups according to their past ocular history. Interventions are similar to all study group and no medical therapy alteration will be made.

Visual impairment and blindness due to chronic progressive optic neuropathy developing from glaucoma are major health problems worldwide.

Glaucoma is a progressive, potentially blinding disease, in which the only modifiable risk factor in intraocular pressure. In a significant proportion of patients, the disease progresses despite apparent IOP control(1-3).

One factor which may explain some of this discrepancy is a fluctuation of the IOP during the day, which may be missed in a single visit to the ophthalmologist(4). Although this fluctuation depends to some degree on daily biologic rhythms and the specific type of glaucoma, a constant significant factor responsible for this effect is the IOP-dependent changes of body posture, from sitting or standing to lying down(5). Older studies have shown IOP postural changes in the range of 4-6 mmHg(6-8). Seeing how a typical patient may spend as much as a third of his life in the supine position, knowledge of IOP in this position, and its control, are of great importance in decreasing the chance for irreversible optic nerve damage.

Several studies of Liu JH(9-11) have investigated the effect of hypotensive drops on nocturnal IOP. While prostaglandin analogues (PGA) and carbonic anhydrase inhibitors (CAI) seemed to have a significant nocturnal IOP lowering effect, the effect seen with beta blockers and alpha agonists was minimal. Mansouri et al.(12) recently showed that PGA seem to flatten the IOP-related increase when moving from the sitting to the supine position at nocturnal period, without effecting other circadian IOP-related patterns.

Hirooka Kazuyuki investigated the effect of trabeculectomy on the IOP fluctuations caused by postural changes(13-14). He showed that successful trabeculectomy, which didn't require needling, have significantly decreased the posture-induced IOP changes to less than 3 mmHg.

To the best of our knowledge there is no data regarding the effect of glaucoma drainage devices and cyclophotocoagulation on supine IOP.

The purpose of this study is to investigate the effect of different IOP lowering methods, including trabeculectomy, glaucoma drainage devices, cyclophotocoagulation and ocular hypotensive eye-drops on IOP with postural change from the sitting to supine positions in eyes with open-angle glaucoma.

Inclusion Criteria:

• OAG patients
• Ocular Hypertension (OHT) patients
• Healthy subjects, without any ocular pathology (except for refraction errors, past cataract surgery, strabismus or amblyopia).

Exclusion Criteria:

• Other intraocular surgeries within the past 3 months
• Illness effecting episcleral venous pressure, such as superior vena cava syndrome, thyroid eye disease, orbital masses
• Patients who are unable to maintain supine position for 15 minutes
• Corneal abnormalities: epithelial pathologies, corneal infection, corneal erosions, corneal scars, keratoconus, S/P corneal transplantation (lamellar/full thickness)
• Hypersensitivity to oxybuprocaine hydrochloride

subjects with open angle glaucoma with past ocular history of surgical treatment (trabeculectomy, implantation of an Ahmed glaucoma drainage device or cyclophotocoagulation) or are using ocular hypotensive eye drops and subjects with ocular hypertension.