Visual Field Progression in Treated Glaucoma Patients.

Abstract

As soon as the diagnosis of glaucoma has been made, the most important remaining question for all diagnostic efforts in glaucoma patients is whether the disease is stable or progressive. If the situation is stable, the therapy including the compliance of the patient has been sufficient, independent of the height of intraocular pressure, and if the disease is detected to be progressing, the therapy (which is lowering of intraocular pressure) has to be intensified independently of the present intraocular pressure. Paradoxically, it is clinically better if at that time the intraocular pressure is high instead of being low, because it is easier to lower the intraocular pressure from a high level than from an already low level. The question is how to detect a progression of glaucomatous optic neuropathy. For the primary diagnosis of glaucomatous optic nerve damage, morphological techniques and psychophysical methods have been scientifically tested and clinically applied. Studies have suggested that morphological tests may be better than functional tests for the detection of early glaucomatous optic nerve damage. These morphological tests include simple ophthalmoscopy, assessment of photographs of the optic nerve head and retinal nerve fiber layer, and confocal laser scanning tomography and optical coherence tomography of the optic nerve head and peripapillary retinal nerve fiber layer. 1,2 Functional tests are methods to measure the differential light threshold in a static or kinetic manner (perimetry). 3Y5 Other functional tests such as measurement of color vision and of critical flicker fusion frequency and electrophysiological methods have not been widely applied. In analogy to the superiority of morphological tests over functional tests in the early detection of glaucomatous abnormalities, one may infer that, for the detection of progression in an early stage of the disease, morphologic tests may be superior to functional methods. In an advanced stage of glaucoma, however, one may assume that functional tests such as perimetry are more useful, because in advanced glaucoma, only a relatively small part of the neuroretinal rim as the main morphological parameter remains and can show further, relatively small, change, whereas the visual field often can still be almost normal and can therefore show more marked changes. Analysis of changes in the visual field can be performed by an event analysis or a trend analysis. 3Y6 Event-based techniques compare a set of recent perimetric tests and define progression as a binary outcome of a difference (ie, progression) or no difference (ie, stable) between the baseline examination and the follow-up examination. Results of examinations performed in the interval between the baseline examination and the last follow-up examination are usually not taken into account. Trend analysis of changes in the visual field applies a pointwise linear regression analysis that provides an automated calculation of slopes of progression for individual perimetric test points (‘‘localized progression’’) and for the average of all test points (‘‘global progression’’). In this issue of the journal, Carlos Gustavo de Moraes and his colleagues from the New York Eye and Ear Infirmary examined the diagnostic capabilities of both approaches, with the new version of the Glaucoma Progression Analysis (GPA2) as event-based technique and PROGRESSOR analysis as trend-based method. 7 Including a relatively large group of well-examined patients with a large series of visual field examinations, they found that the PROGRESSOR analysis tended to detect more progressing eyes than GPA2, with both techniques showing a moderate agreement with respect to the progression criteria and a good spatial consistency regarding the location of the progressing points in the visual field. Although one has to take into account that there are different ways to define progression of glaucoma by using the GPA2 method and the PROGRESSOR technique, the results of the study indicate that, first, detection of glaucoma progression of course depends on the techniques applied; second, that also within the same type of examinations, in the study perimetry of Gustavo de Moraes et al, variations in the results of different technologies are common; third, that as anywhere in clinical medicine, a synopsis of all available clinical data should be performed to finally decide whether the patient was stable or progressive in his/her glaucoma; and fourth, that the PROGRESSOR analysis is without doubt an additional help or more in the detection of glaucoma progression.