Vision assesment

VISION ASSESSMENT TYPES OF VISION CHARTS

1. Vision assessment Mahantesh.B HOD of optometry

2. What is vision ? Resolving power of the eye or the ability to see two separate objects as separate.

3. Vision Assessment of visual function visual perception Visual Acuity Dark adaptation Contrast sensitivity

4. V isual perception Forms of visual perception are form sense , the field of vision, the light sense and the colour sense .

5. Visual Acuity Definition- It is defined as the measure of the smallest retinal image which can be appreciated with reference to its shape and size .it is actually measure of form sense. Distance vision Near vision Pin hole vision Colour vision

6. Distance vision DISTANCE VISION Two distance point can be visible as separate only when they subtend an angle of 1 minute at the nodal point of eye.

7. Distance vision charts types Snellen Tumbling E Landolt C ETDRS Picture chart

8. Snellen charts The original eye chart designed in the 1860’s by the Dutch eye doctor Hermann Snellen. The first line on this chart is a giant letter E. You read the chart from top to bottom, left to right covering one eye at a time.

9. Tumbling E charts his type of eye chart is used for children that are too small to read or adults with reading or speaking difficulties. The patient is asked to lift their hand up, down, to the left or right depending on the image orientation of the letter E they see on the chart.

10. Landolt C charts Edmund Landolt, a Swiss ophthalmologist, created this visual acuity chart. This eye chart, which is similar to the Tumbling E chart, uses a Landolt broken ring symbol in various orientations. The Landolt C chart is a way to check vision for illiterate or mute patients.

11. ETDRS charts The Early Treatment Diabetic Retinopathy Study helped develop standardization for both visual acuity testing and eye chart design. The ETDRS is accepted by The National Eye Institute and the FDA as the mandated standard for clinical eye test trials worldwide.

12. Picture chart Picture chart. Used to test visual acuity in preliterate children 2 to 4 years of age and in moderately mentally impaired adults. Available for both distance and near testing.

13. Snellen chart Principle Each individual letter subtends an angle of 5 minutes and each component of letter subtends an angle of 1 minute at the nodal point of eye from the distance in meters written as numerical.

14. Principal Snellen chart is having different number of letters in different rows and the letter at top line should be read clearly at distance of 60 m Similarly the letters ar36, 24,18,12,9,6, respectively the numerator is the distance at which the patient is sitting from chart and the denominator is the distance at which person (with normal vision) should be able to read the last line that person is able to read

15. Procedure of testing Distance of 6 mts is taken as at this distance it is assumed that the rays are almost parallel and patient exert minimum accommodation

16. Continue The chart should be properly illuminated Patient made to wear trial frame. It is adjusted according to patient inter pupillary distance Ask the patient to read with one eye from the top letter while the contra lateral eye is closed with occlude in the trial frame the patient can read from distance of 6mts his vision is recorded as 6/6, 6/9 ,6/12,6/18, 6/24, 6/36, 6/60.

17. Continue If patient is not able to see the top line from 6mts he is asked to come towards Snellen’s charts step by step and vision recorded at 5,4, 3, 2, 1 mts and noted as 5/60,4/60,3/60, respectively If patient is not able to read top line even at the distance of 3 mts he is asked to count fingers of examiner and his vision is recorded as CF3mtr, CF 2mtr, CF1mtr OR CFCF

18. Continue If patient not able to count examiner finger close to face then examiner moves his hand and asks patient whether he is able to see hand movement or not. Visual acuity then recorded as HM+/HM- IF NOT the examiner notes whether the patient can perceive light (PL) or not . If he perceive light it is noted as PL + ve PL- ve . Also examiner then throw the light from four directions (nasal, superior, temporal, inferior) • and record accordingly. if present patient perceive light from all directions it is marked as PR (Projection of rays ) present or else mark as absent or defective. The test is repeated for the other eye in similar

19. Pin Hole Test If patient vision is improved with pin hole it means the poor acuity is due to refractive error. If not improve means may be due to structural or organic cause. If reduced the poor visual acuity may be due to corneal opacity or Lanticular opacity occupying papillary area or macular pathology.

20. Near vision Snellen near vision chart Jaeger near chart Roman near test type

21. Procedure of testing Ask the patient to sit with his back to the light If the patient is using glasses for distance the same number will be put on the trial frame. Occlude one eye with an occulder Ask the patient to hold the near vision by his right hand at a distance of 25 to 33 cms Note the near vision as per the letter read Repeat the test for the other eye.

22. Dark adaptation Threshold (DAT) is a vision test that measures the adjustment of the eye occurring under low levels of illumination measurement of least luminance required to produce a visual sensation

23. Contrast sensitivity Ability of eye to perceive slight changes in luminance between regions not separated by definite borders