blue field entoptoscope
entoptoscope, blue field
An instrument enabling the visualization, especially by patients with a dense cataract, of the shadows of leucocytes flowing in the retinal capillaries and therefore providing a test of macular function. It consists of a very bright light source, an interference filter with a maximum transmission in the blue end of the spectrum, and a diffuser. The instrument is held close to the eye of the patient who is asked to describe his or her observations. The leucocytes appear as flying corpuscles and if many corpuscles (at least 15) are seen moving in the entire field the test is considered positive whereas if none or only a few corpuscles are seen the test is considered negative. Positive responses usually indicate that the patient has good macular function and negative responses usually indicate that the patient has poor macular function. This test is very useful in predicting central vision before cataract extraction. See angioscotoma; clinical maxwellian view system.