Table 1.

Comparison of the OHTS and EGPS Protocols¹⁵,¹⁶

	OHTS	EGPS
Design	Unmasked randomized clinical trial	Double-masked randomized, placebo controlled clinical trial
Hypothesis	To evaluate the safety and efficacy of topical ocular hypotensive medication in preventing or delaying the onset of POAG in individuals with ocular hypertension	To evaluate the safety and efficacy of dorzolamide in preventing or delaying POAG in individuals with ocular hypertension
Treatment Group	N=818 participants, treatment with any commercially available drug to achieve 20% IOP reduction from baseline and ≤ 24 mmHg	N=538 participants, treatment with dorzolamide
Control Group	Observation N=819	Placebo eye drops N=543
Median Follow-up	Every 6 months for 6.6 years	Every 6 months for 4.8 years
Eligibility
Age (Years)	40–80 inclusive	> 30
IOP	≥ 24 and ≤ 32 in one eye ≥ 21 and ≤ 32 fellow eye Mean of 4–6 IOPs in 2 Qualifying Visits Both eyes had to satisfy eye-specific eligibility criteria	≥ 22 and ≤ 29 in at least 1 eye Mean of 2–3 IOPs in 1 Eligibility Visit Both eyes had to satisfy eye-specific eligibility criteria except for IOP Some participants could have one eye entered into the study
Normal Optic Disc	Clinical exam and masked reading of stereophotographs, difference in cup/disc ratio between eyes not greater than 0.2	Similar
Visual Fields	Normal and reliable Humphrey 30-2 visual fields	Normal and reliable Humphrey 30-2 visual fields or Octopus 32-2 visual fields
Exclusions	Pigment dispersion or exfoliation syndrome	Not excluded
	Best corrected visual acuity worse than20/40 in either eye	Same
	Previous intraocular surgery except uncomplicated extracapsular cataract extraction with posterior chamber IOL	Same
	A life threatening or debilitating disease	Same
	Secondary causes of elevated IOP	Same except for pigment dispersion or exfoliation syndrome
	Angle closure glaucoma or anatomically narrow angles	Same
	Systemic or ocular conditions capable of causing visual field loss or optic disc abnormalities	Same
	Background diabetic retinopathy	Same
	Pregnant or nursing women	Same
Endpoint Ascertainment	Independent, masked readers	Same
Visual Fields	3 consecutive abnormal and reliable tests with defect in the same location and index	Same
Optic Discs	2 consecutive sets of photographs judged to have a clinically significant change	1 set of photographs judged to have changed by at least 2 of 3 masked readers
Attribution to POAG	Masked endpoint committee	Same

EGPS European Glaucoma Prevention Study

IOL Intraocular lens

IOP Intraocular pressure

OHTS Ocular Hypertension Treatment Study

POAG Primary open angle glaucoma