What Constitutes Progression of Glaucomatous Visual Field Defects?

Glaucoma studies from 1996 to 1999 in peer-reviewed journals

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.

How often do patients need visual field tests?

BACKGROUND

This study was undertaken to determine whether the interval between visual field tests affects the ability to detect progressive glaucomatous field loss.

METHODS

One hundred and nineteen retinal locations which were deteriorating significantly by > or = 1 dB/ year (untreated normal tension glaucoma patients: 6 eyes) were studied. Analysis was repeated using 'thinned' visual field tests: one test per year instead of the complete three per year over a period of 4 years.

RESULTS

The 'thinned' tests identified only 45.4% of the deteriorating points over the 4-year period. Furthermore, there was a mean delay of 1.10 years in detection (P < 0.01).

CONCLUSIONS

Less frequent visual field testing detects fewer progressing locations and detects them later.

Improving the prediction of visual field progression in glaucoma using spatial processing

PURPOSE

The authors show how the predictive performance of a method for determining glaucomatous progression in a series of visual fields can be improved by first subjecting the data to a spatial processing technique.

METHOD

Thirty patients with normal-tension glaucoma, each with at least ten Humphrey fields and 3.5 years of follow-up, were included. A linear regression model of sensitivity against time of follow-up determined rates of change at individual test locations over the first five fields (mean follow-up 1.46 years; standard deviation = 0.08) in each field series. Predictions of sensitivity at each location of the field nearest to 1 and 2 years after the fifth field were generated using these rates of change. Predictive performance was evaluated by the difference between the predicted and measured sensitivity values. The analysis was repeated using the same field data subjected to a spatial filtering technique used in image processing.

RESULTS

Using linear modeling of the unprocessed field series, at 1 year after the fifth field, 72% of all predicted values were within +/- 5 dB of the corresponding measured threshold. This prediction precision improved to 83% using the processed data. At the 2-year follow-up field, the predictive performance improved from 56% to 73% with respect to the +/- 5 dB criterion.

CONCLUSIONS

Predictions of visual field progression using a pointwise linear model can be improved by spatial processing without increased cost or patient time. These methods have clinical potential for accurately detecting and forecasting visual field deterioration in the follow-up of glaucoma.