Q:
What are the 3 components of the fixation triad?

A:
* Accomodation (cilliary mm)
* Pupillary constriction (iris mm, intraocular mm)
* Convergence of ocular axes of eyes (extraocular mm)

Q:
What is the approximate refractive power of the lens system in the relaxed eye for viewing distant objects? 

A:
59 Dioptres.

Q:
How much can accomodation increase the refractive power of the lens of the eye in young adults?

A:
Approximately 10 dioptres.

Q:
What is strabismus?

A:
Failure of co-ordination of eye movements, with lack of fusion of the images from the 2 eyes. This commonly results in double vision (diplopia) or the suppression of one of the two images.


Q:
What is myopia?

A:
Nearsightedness. Image focussed in front of retina.

Q:
What is hyperopia (hypermetropia)?

A:
Long-sightedness. Image focusses behind of retina.

Q:
What is astigmatism?

A:
The cornea is not uniformly spherical in curvature. For example, curvature might be greater horizontally than vertically. This causes blurring of visual world in some visual planes.
A cylindrical lens with abnormal curvature may sometimes be used to correct this.

Q:
What is emmetropia?

A:
Normal focussing vision.

Q:
What is amblyopia?

A:
A central neural problem in which impairment of vision is retained after physical defect is repaired.

Q:
What is the normal range of intraocular pressure?

A:
~12-20mmHG (2-3 kPa).

Q:
What passage drains aqueous humour into the venous circulation?

A:
Canal of Schlemm.

Q:
What are 4 reasons for the higher visual accuity found in the fovea centralis?

A:
* Improved resolution (finer grain) due to greater density of slender cones.
* No major blod vessels cross the foveal region and inner layers of retina (e.g. ganglionic layer) are pushed aside and therefore do not interfere in the direct light path of foveal receptors.
* Convergence from foveal cones to associated retinal ganglion cells is much more restricted than convergence patterns in the periphery.
* Less light is reflected from the pigmented epithelium.

Q:
What is scotopic vision?

A:
Low light vision subserved by rod photoreceptors.

Q:
What is photopic vision?

A:
Cone photoreceptor vision.

Q:
What are the 3 cone pigments and what colours do they absorb maximally?

A:
* Cyanolabe - blue (445nm)
* Chlorolabe - green (535nm)
* Erythrolabe - red (570nm)