Photostress test

Photostress recovery time (PSRT) is the time taken for visual acuity to return to normal levels after the retina has been bleached by a bright light source. Photostress recovery time measurement procedure is known as photostress test. Normal recovery time is about 15-30 seconds.[1]

The photostress test is a simple, easy and quick clinical technique that can differentiate between retinal (macular) and postretinal (e.g.optic nerve) disease.[2]

Clinical significance

The photo stress test is clinically useful in diabetes,[3] glaucoma,[3] macular degeneration[4] etc. Diabetic retinopathy affects the microvasculature of the inner retina and causes neurodegeneration. Several studies reported that PSRT is elevated in people with diabetes.[3] Recovery time is more in macular diseases (50 seconds or more) than postretinal (e.g.optic nerve) diseases.[1] Elevated PSRT has also been found in primary open angle glaucoma (POAG) which is characterized by progressive death of the retinal ganglion cells.[3] Amblyopic eyes with normal fundus also have normal recovery time.[5]

Materials needed

Ophthalmoscope or alternative source of light (e.g.penlight),[2] stop watch, distance vision charts like snellen's chart.

Procedure
  • Testing is done monocularly.
  • Patient is asked to sit in front of an illuminated vision chart, at 6 meter distance.
  • Initial measurement of best corrected visual acuity should be done.
  • Locate fovea using ophthalmoscope.
  • Ask the patient to look at the bright light of the ophthalmoscope for 10 seconds.[1]
  • Time taken to read any three letters of the pre-test visual acuity is noted.
  • Normal recovery time is 15-30 seconds.[1]

Disadvantages

The main disadvantage of the test is that there is no standardization of the procedure.[6] The effect of aging on recovery time is also thought as a disadvantage, but it is still under discussion since some studies found increased PSRT with age, and others did not find any significant effect.[3]

Reference
  1. "Examination techniques". Kanski's clinical ophthalmology : a systematic approach (9th ed.). pp. 6–7. ISBN 978-0-7020-7711-1.
  2. "PHOTOSTRESS TEST" (PDF).
  3. "The macular photostress test in diabetes, glaucoma and cataract".
  4. Wu, G.; Weiter, J. J.; Santos, S.; Ginsburg, L.; Villalobos, R. (November 1990). "The macular photostress test in diabetic retinopathy and age-related macular degeneration". Archives of Ophthalmology (Chicago, Ill.: 1960). 108 (11): 1556–1558. doi:10.1001/archopht.1990.01070130058030. ISSN 0003-9950.
  5. Lavingia, Bharti (1 May 1983). "Photostress test". Indian Journal of Ophthalmology. 31 (3): 183. ISSN 0301-4738.
  6. David B., Elliott. "Assessment of visual function". Clinical procedures in primary eye care (3rd ed.). Elsevier/Butterworth Heinemann. ISBN 9780750688963.
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