A hand-held OKP chart for the screening of glaucoma: preliminary evaluation

Oculo-kinetic perimetry (OKP) uses controlled movements of the patient's eye to position a static test stimulus in the visual field. The test chart consists of a white tangent screen with 23 numbered fixation points located eccentrically at strategic points in relation to a central black spot, which is the test stimulus. As the patient looks at each number in turn, the spot stimulates the retinal areas that are most likely to show early glaucomatous damage. The result is positive if one or more numbers make the spot disappear. Ninety-eight eyes of 54 patients attending a hospital glaucoma clinic were tested with a prototype OKP glaucoma screener and by conventional perimetry. Visual fields plotted conventionally were independently categorised as normal, equivocal and glaucomatous by the perimetrist and the ophthalmologist and these results were further categorised as normal, equivocal or glaucomatous according to whether they were considered abnormal by none, one or both of the observers respectively. The OKP test was positive in (i) 93% of 27 eyes with glaucomatous defects, (ii) 69% of 32 eyes with equivocal loss, (iii) 41% of 39 eyes without previously recognised field loss but having ocular hypertension, a suspicious disc, or contralateral glaucoma, (iv) 9% of 116 eyes from 60 age matched persons accompanying the patients to hospital. If the results were considered in terms of patients not eyes, the OKP test was positive in 85% individuals with glaucomatous field loss in their worse eye and in 12% of the controls. A hand-held OKP chart testing a small set of points and using a constantly exposed stimulus could be a useful tool for the detection of glaucoma in the community.