Distant Visual acuity tests:

Distant Visual acuity tests:

In all tests of V.A, one eye is tested & the other is covered.

1)-Distant vision acuity charts:(e.g. Landolet's chart or Snellen's chart)

Landolet's chart is formed of 7 rows of broken rings with their openings in different directions.(6/60, 6/36, 6/24, 6/18, 6/12, 6/9, 6/6)

Aim: Measure V.A from 6/6 up to 1/60

Steps:

*The patient is at 6 meters from the chart

*Ask the patient about the direction of the ring's opening starting from the upper most line (6/60)downwards up to (6/6)

*When the patient can not see the largest ring (6/60) at a distance of 6 meters, move him 1 meter nearer to the chartàif he can see it the V.A is 5/60 & so on (4/60, 3/60,2/60 1/60).

If he can not see the largest ring at 1 meter à CF test must be done

2)-Counting fingers(C.F):

Ask the patient to count the doctor's fingers at different distances( CF_75cm then CF_50cm then C.F_25cm). If he can notàHM test must be done

3)-Hand Movements(H.M):

*Explain the test to the patient at 1^st(when the hand moves & when stops),then

*Ask the patient to tell you about the movement of your hand which is present about 25cm from his face.

*The movement of the hand must be slow.

If the patient can not see the hand movementàP.L test must be done

4)-Perception of light(P.L):

*Must be done in dark room.

*The source of light must be held immediately in front of the eye

*Explain the test to the patient at 1^st(This is light & this is no light),then

*Ask the patient to tell you if he can perceive light(P.L) or not(No.P.L)when the source of light is in front of the eye or when withdrawn (No switch on or switch off of the torch)

Oral questions:

*V.A testing is a test of (Form sense)

*Also there are (near vision charts) at 33 cm(near point in normal persons)

*What is the meaning of (6/18 or 6/24 etc..) = patient / Normal person *The idea of the V.A Charts: is if the 2 ends of a broken ring are seen as 2 separate pointsàthis means that the rays passing through the 2 ends make a visual angle ≥ 1 minute at the nodal point of the eye & stimulate 2 cones with one unstimulated cone in between at the macula(if the angle is < 1minute the 2 ends can not be seen)