15. Central vision. Methods for evaluation. Visual acuity testing

Question 1

what is the visual field ?

Answer 1

portion of area which objects are visible in a steady fixation of gaze in one direction

Question 2

what are the normal limits to the visual field ?

Answer 2

60 degrees superiorly - inferior retina

60 degress nasally - goes to the temporal retina

75 degree inferiorly - superior retina

100 degrees temporally - nasal retina

Question 3

what is the visual field limited by ?

Answer 3

size of the retina

margins of the orbit

Question 4

what is central field ?

Answer 4

the area in which there is a fixation point and the radial diameter of 30 degrees away from it
physiological blind spot on temporal side

Question 5

what is the method for detection of central field ?

Answer 5

amsler grid

berkley central visual field test - detect loss of sensitivity and maculopathy

tangents screen

Question 6

the amsler grid is screening done for ?

Answer 6

macular function

easiest way to screen for age related macular degeneration

Question 7

what is visual acuity ?

Answer 7

clarity , abilty to distinguish

Question 8

what is visual acuity dependant on ?

Answer 8

optic and neuronal factors
sharpness, health and function of retina
sensitivity of the interpretative faculty of brain

Question 9

what is the reference value of visual acuity ?

Answer 9

6/6
means that patient at 6m away is able to separate contours that are 1.75mm apart

first number means the metre
second number the distance at which a person with 6/6 would discern the same optotype

Question 10

what visual acuity is better performance ?

Answer 10

6/3

Question 11

what visual acuity is lower performance ?

Answer 11

6/12

means the person with 6/6 would see the same 12 m away

Question 12

at the edge of our vision or periphery of the retina we can see what type of cone cells ?

Answer 12

blue sensitive cone cells -blue light seen more in the

we can see tiny darting bright spots against smooth blue background= white cells moving in the blood vessel over retina

we don’t see much colour vision outside the centre or our vision
the colour receptor density increases towards the centre of our vision

Question 13

red and green cones are are mainly limited to which part of our vision ?

Answer 13

centre of our vision

Question 14

where do we see high resolution ?

Answer 14

we only see high resolution of a small area at the centre of our vision where the retinal cells are the densest - the fovea

Question 15

what type of chromatic does rods have ?

Answer 15

monochromic

Question 16

visual acuity is tested when one eye is blinded ?

Answer 16

yes