A comparison of the OKP visual field screening test with the humphrey field analyser

In order to determine the loss of retinal sensitivity detectable by oculokinetic perimetry (OKP), we tested 27 eyes of 27 persons with glaucoma and 32 eyes of 32 patients with ocular hypertension with the OKP screener and with a central threshold test on the Humphrey analyser. The threshold at eight locations on the OKP chart between 12.5° and 15° from fixation was compared with the corresponding Humphrey perimetric thresholds. Seventeen eyes from 17 patients with glaucoma failed the OKP screening test by not seeing the target at one or more locations. The mean light sensitivity threshold at points seen on OKP screening was −5.8 dB (SD 4.6 dB) from aged-matched normals (AMN), whereas points missed had a mean threshold −16.1 dB (SD 9.3 dB) from AMN. The sensitivity and specificity with which OKP testing differentiated normal points from abnormal ones in Humphrey testing was 82.5% and 80% respectively, with a threshold criterion of −12 dB from AMN. Ten eyes from 10 patients with glaucomatous defects and all of the ocular hypertensive eyes gave normal responses on the OKP screening test. The glaucomatous eyes that passed were characterised by less severe defects on the Humphrey than those who failed in terms of mean deviation (0.02<p<0.05) or corrected pattern standard deviation (0.01<p<0.02). Four of the glaucomatous eyes to pass had a nasal step as the primary field defect. None of those to fail failed only on points within 10° of fixation. We suggest further modification of the OKP screening chart to improve its efficiency.