Positive relative accommodation
Positive relative accommodation (PRA) in biology, is a measure of the maximum ability to stimulate eye accommodation while maintaining clear, single binocular vision.[1] This measurement is typically obtained by an orthoptist, ophthalmologist or optometrist during an eye examination using a phoropter. After the patient's distance correction is established, she or he is instructed to view small letters on a card 40 cm from the eyes. The examiner adds lenses in −0.25 diopter increments until the patient first reports that they become blurry. The total value of the lenses added to reach this point is the PRA value.
High PRA values (>= 3.50 diopters) are considered to be diagnostic of disorders involving accommodative excess.[2] Those with accommodative insufficiency typically have PRA values below −1.50 diopters.[3]
See also
- Accommodation in fish
- Adaptation (eye)
- Amplitude of accommodation
- Convergence insufficiency
- Mandelbaum effect
- Negative relative accommodation
References
- ^ www.vision-therapy.com Archived December 8, 2005, at the Wayback Machine
- ^ Garcia A, Cacho P, Lara F (Dec 2002). "Evaluating relative accommodations in general binocular dysfunctions". Optom. Vis. Sci. 79 (12): 779–87. doi:10.1097/00006324-200212000-00010. hdl:10045/9622. PMID 12512686. S2CID 31075351.
- ^ "Care of the Patient with Accommodative and Vergence Dysfunction" (PDF). Archived from the original (PDF) on May 10, 2006. Retrieved May 8, 2006.