Week 2

Question 1

Four refracting surfaces of the eye

Answer 1

• anterior and posterior corneal surface
• anterior and posterior lens surface

Question 2

four optical media of the eye

Answer 2

• the corneal substrate
• aqueous humour
• the crystalline lens substrate
• the vitreous humour

Question 3

Optic Axis of the eye

Answer 3

the line joining the anterior and posterior poles of the eye through the centre of the pupil. The eye is rotationally symmetrical around the optic axis

Question 4

Visual Axis of the eye

Answer 4

The line joining the centre of the fovea to the object.
Visual axis is normally 3-5 degrees nasal and 2-3 degrees below the optic axis

Question 5

Pupillary axis of the eye

Answer 5

line perpendicular to the cornea and passing through the centre of the pupil.
It is easy to locate and therefore commonly used to asses binocular anomalies.

Question 6

Hirscberg Test

Answer 6

A test used to assess binocular anomalies
an optometrist will use shine a bright light onto both of the eye’s of a patient. The corneal reflection on the pupil of each eye is compared to assess ocular deviation or strabismus

Question 7

Angle Alpha

Answer 7

the angle between the visual and optic axis.
Angle alpha is positive if the visual axis is nasal to the optic axis

Question 8

Angle Kappa

Answer 8

the angle between the visual axis and the pupillary axis

Question 9

Optical properties of the cornea

Answer 9

• 80% of refractive power of the human eye occurs at the interface between air and the anterior corneal surface
• the cornea is aspheric and its power reduces from centre to periphery
• the cornea is transparent and slightly elliptical in shape

Question 10

Corneal Asphericity

Answer 10

• rate of corneal flattening from centre to periphery
• there is flattening both both surfaces however it is greater in the horizontal meridian
• corneal sphericity is best defined as a prolate ellipsoid

Question 11

corneal toricity

Answer 11

there is an unequal radius of curvature in two or more principle meridians. This is known as astigmatism

Question 12

important factors of corneal transparency

Answer 12

1. regular arrangement of collagen fibrils in the stroma ( causing destructive interference and reduced light scatter)
2. integrity of corneal endothelium