Physiology Lab - Vision

Question 1

What is visual acuity?

Answer 1

The ability of the eye to see sharply and clearly

Resolving power of the eye

Question 2

What do clinical tests of visual acuity indicate?

Answer 2

Function of the fovea

Assume remainder of the visual system is normal

Question 3

What is a standard test of visual acuity?

Answer 3

Ability to read small letters (Snellen chart) at a distance of 4 or 6 metres

Question 4

What does 6/6 visual acuity mean?

Answer 4

Can see at 6m the letters visible to a normal eye

Question 5

What does a 6/9 vision mean?

Answer 5

At 6m, an individual can see only those letters that should still be visible at 9m

Question 6

What does the numerator in the Snellen chart exam denote?

Answer 6

Distance in metres at which the test is conducted

Question 7

What does the denominator of a vision test describe.

Answer 7

Distance at which the smallest letters can be seen

The greater the denominator the poorer the vision

Question 8

What test is used to test vision in young children and how does it work?

Answer 8

Illiterate E test
Series of Es randomly orientated in one of 4 directions - child is asked to point the fingers of his or her hand in the same direction as the E

Question 9

Is visual acuity better tested with isolated or many symbols?

Answer 9

Isolated symbols

Question 10

How do we overcome the defect of isolated symbols?

Answer 10

Surrounding the symbol on all four sides with an adjacent black bar (confusion bar)

Question 11

What is a useful test for infants and how is it done?

Answer 11

Letter matching test
Able to recognise the shape of a letter shown individually on a card by pointing to the same letter on a key card bearing all five or seven letters used in the test

Question 12

What do we call lazy eyes and how is this condition fixed?

Answer 12

Amblyopia

If detected early in life, it can be corrected/treated with occlusion (patching)

Question 13

What is near vision testing used for?

Answer 13

Test the power of accommodation

Question 14

How do we test near vision?

Answer 14

Examples of print of different sizes is used
Patient is asked to read the text and the smallest text which is able to be read is noted
Documented as N followed by the number of print size e.g. N5 to N48

Question 15

What is emmetropia?

Answer 15

Normal condition of the eye in which with no accommodation, parallel light is focused on the retina

Question 16

What is refractive error/ametropia?

Answer 16

Any optical departure from emmetropia

Question 17

Name the three major types of refractive error.

Answer 17

Myopia
Hypermetropia
Astigmatism

Question 18

What is myopia?

Answer 18

Eye is too long for its refracting system or the refracting system is too powerful for its length
Rays of light come to focus in front of the retina when the eye is at rest

Question 19

What is hypermetropia?

Answer 19

Eye is too short or the refraction is too weak

Rays of light come to focus behind the retina

Question 20

What is astigmatism?

Answer 20

Curvature of some component of the optical system of the eye is not spherical.
Refraction in different meridians of the eye is not the same = preventing light rays from coming to a single focus (point focus) on the retina

Question 21

What is the most common form of colour blindness?

Answer 21

Red-green

More common in males

Question 22

What causes congenital colour vision defects?

Answer 22

Deficiency/absence of one or more of the cone pigments

Question 23

What chart is used to test colour vision?

Answer 23

Ishihara chart - consists of numbers/symbols on a slightly different background
The numbers/symbols are made up of differently coloured spots

Question 24

What is perimetry?

Answer 24

Assessed by confrontation - patient’s fields are compared to those of the examiner
Accurate instrumental measure of visual fields

Question 25

What is the Bjerrum Screen?

Answer 25

Perimetry measurement
Subject sits in front of screen with one eye occluded. Focus on a white spot in the centre of the screen - target brought in from peripheral field until they can see it.
Entire mid peripheral field can be mapped out

Question 26

What is the Goldmann Perimeter test?

Answer 26

Equipment
Subject to detect light flashes shone randomly around their visual field
Entire visual field can be mapped