Visual acuity.ppt
- 2. ◉ Visual acuity is measurement of the ability to discriminate and recognize the smallest differences between tow objects . This may be thought of as the ability of the eye to see fine detail. ◉ The ability to identify minimal separation between tow targets
- 3. Visual acuity should be done on all patients as the first procedure following the case history. indications
- 4. purpose ◉ To measure the clarity of vision or the ability of the visual system to resolve detail. A patient ,s visual acuity depends on the accuracy of the retinal focus , the integrity of the eye's neural elements ,and the interpretive faculty of the brain
- 5. To assess the adequacy of spectacle correction and as a key indicator to the ocular health . To assess person's fitness to drive or enter to the some professions such as police. what are objectives of measuring visual acuities?
- 6. Cont :
- 9. Projector with visual acuity slide or wall mounted acuity chart Occluder lamp Equipment
- 10. Set- up ◉ The patient wear his hapitual correction for the distance being tested. When the examiner wants to measure the patient,s VA both with (cc) and without (sc) correction, the acuity should be measure wihout correction first . ◉ The patient hold the occluder ◉ An acuity chart , with lines from 6/60 to 6/5 exposed, is shown
- 15. Step –by- step procedure 1. always observe the patient , not the chart. 2. Instruct the patient to cover his left eye and not to squint. 3. Instruct the patient to read the smallest line of letters he can. 4. Encourage the patient to read the letters on the next smallest line ,even he has to guess. stop the patient when more than half have been missed.
- 17. 5. Have the patient cover the right eye and repeat the above steps. 6. Sometimes the patient will be unable to read even the largest letter on chart in this event the patient walk towards the chart until he can read the largest letter . 7. If the patient cannot see the letter at any distance ,initiate the following:
- 18. a. counting fingers b. Hand motion (HM) c. Light projection(L Proj) d. Light perception (LP)
- 19. ◉ Testing distance / distance at which optotype would subtend 5 min of arc at retina Snellen fraction
- 22. THANK YOU