The Purkinje vascular entoptic test: a halogen light gives better results

The Purkinje vascular entoptic test is a test of macular function which employs a light directed through the sclera illuminating the fundus. This light casts shadows of retinal blood vessels on to posterior pole photoreceptors. When the light source is moved, a patient with a good macular function should be able to see a negative image of his or her retinal blood vessels. We evaluated the Purkinje test in eyes with clear ocular media. A bright 3.5 watt halogen rechargeable transilluminator was used instead of a pen torch as previously described. Sixty-eight patients (129 eyes) attending a diabetic eye clinic, were tested. The test correctly identified 91% of eyes with good macular function and 77% of eyes with poor macular function (visual acuity 6/24 or poorer). If a vascular pattern was seen, it was probable (0.89) that good macular function was present. If no vascular pattern was seen, it was probable (0.80) that the eye had poor macular function (chi 2 = 60.14, P = < 0.001). Our results were superior to those previously reported. We attribute the increased accuracy of our test to the brighter light source used.