Background: Studies on glaucoma therapy were analyzed with regard to study design, diagnostic parameters and success criteria.
Materials and methods: In 11 frequently read peer-reviewed periodicals, 101 studies published between 1996 and 1999 were chosen according to specific criteria. Design parameters, diagnostic measures and success criteria were investigated.
Results: Thirty-seven studies were retrospective and 64 prospective. Twenty-five studies were multicenter studies. Thirty-seven studies dealt with drug therapy, 12 with laser therapy, and 52 with surgical therapy. The study duration in 51% of the studies (n=52) was up to 1 year, in 28% (n=28) from 1 to 2 years, in 17% (n=17) over 2 years, and in 5% (n=5) in excess of 4 years. Four studies gave insufficient data. Forty-one studies recruited less than 50 patients and 57 studies recruited less than 75 patients. Thirty-four studies included more than 100 patients and 11 studies more than 250 patients. Sixty-one studies included race as a parameter. All 101 studies measured intraocular pressure (IOP). Forty-five studies explicitly described the method of tonometry. Thirteen studies measured a diurnal IOP. Forty-one studies examined the visual field, of which 30 named the method of perimetry. Only 28 studies examined the optic disc morphology. They all employed ophthalmoscopy, and two additionally employed optic disc photography. Sixty-three studies explicitly defined success criteria, establishing 95 different definitions: 74 definitions (78%) used a specified value for IOP as a success criterion. Out of the 70 definitions that gave an absolute value for IOP, 12 definitions (17%) used IOP values between 14 and 16 mmHg as the upper limit, 4 definitions (6%) used IOP values between 17 and 19 mmHg, and 54 definitions (77%) used IOP values between 20 and 22 mmHg. Out of the 26 definitions that specified a percentage IOP reduction, it was judged to be a success when the IOP was lowered by 20% or more from the starting value in ten definitions (38%), by 25% or more in three definitions (12%), and by 30% or more in 13 definitions (50%).
Conclusions: Examples of prestigious studies show the necessity of observation periods of several years and demonstrate the need for a high number of participants, necessitating the cooperation of many study centers. Beside a more precise characterization of the patient collectives, clinical studies should always specify the measurement method clearly. Investigating a diurnal IOP profile to recognize changes in IOP and IOP peaks, as well as the routine determination of central corneal thickness, would be desirable. New diagnostic techniques for improved assessment of the functional and morphologic damage will gain in relevance in the future. The lack of a common definition of success reveals the complexity of the disease. However, an IOP reduction based on the degree of damage and ascertaining the target pressure seems sensible.