What Can Go Wrong With Vision

1. What Can Go Wrong With Vision

2. Visual Acuity • The clarity with which a person is able to see. • How well the eye can focus.

3. Measuring Visual Acuity • Optical Infinity • distance at which the eye can focus without action by the suspensory ligaments on the lens. • the light is perfectly focused on the retina. • 20 feet

4. Optical Infinity 20 feet

5. How is refraction measured? The amount that the light is bent is measured in diopters. Normal eye generates approximately 60 diopters.

6. Refraction and Acuity • Each of the clear surfaces of the eye contribute at least some refraction. • Tears 1-2 diopters • Conjunctiva 3-4 diopters • Cornea 40 diopters

7. Acqueous humor 4-5 diopters • Lens 5-8 diopters • Viterous humor 5 diopters

8. Snellen Acuities • Based on Optical Infinity • Snellen chart is placed 20 feet away from the person to be assessed. • The chart has gradually diminishing visual targets (letters, numbers, symbols, etc.) • The person is asked to read progressively smaller targets.

10. Simplified Definition of Snellen Acuities • “If a person with normal vision was standing the number of feet below the slash mark (/) they would be able to see the chart like a person with impaired acuity (less than 20/20) could see the chart from 20 feet.”

11. When the person can no longer read the chart, the acuity is 20 over the number next to the line on the chart. • Example: normal = 20/20

12. Example of Snellen Acuity • 20/50 • 20/120 • 20/80 • 20/400 • 20/2400

13. Acuity Left, Right, and Both • Left = OS • Right = OD • Both = OU

14. Acuity at Distance Ranges • Near acuity -- 18 inches or less • Intermediate acuity -- 19 to 36 inches • Distance acuity -- more than 3 feet

15. Legal Blindness Based on Acuity 20/200 in the best eye with the best correction.

16. Causes of Acuity Loss • Myopia • Nearsightedness • Too much refraction • Light comes to its focal point “behind the retina.” • Corrected with a minus lens.

17. The Normal Eye 20 feet Optical Infinity

19. Correcting Myopia • There is too much “bending power” (diaopters) in the eye. • We “reduce” the bending power with a concave lens.

20. Causes of Acuity Loss • Hyperopia • Farsightedness • Too little refraction of the light • Treated by prescribing a plus lens

22. Causes of Acuity Loss • Astigmatism • Blurry vision due to misshapen cornea • Measured

23. Field Loss • Loss of the ability to see the whole picture.

24. Conditions that Cause Field Loss • All of the “RETINO…” conditions. • Retinopathy of prematurity • Retinitis pigmentosa • Diabetic retinopathy • Anything that has “cone/rod” in it. • Ex: cone rod dystrophy

25. Anything that has to do with the visual cortex (CVI) • Any thing that has to do with damage to the optic nerve.

26. Central (macular) Loss

27. Peripheral Loss

28. Random Field Loss

29. Binocularity • The ability to use both eyes together. • Stereopsis • Produces depth perception (a 3 D picture)

30. Causes of Loss of Binocular Vision • Muscle Imbalance • Normally balanced eyes

31. Esotropia Esotropia – turning inward toward the nose.

32. Exotropia • Exotropia is a turning out of one eye toward the temple.