Optic tracts quiz (revis W/B 15/08)

Which artery supplies the eye, orbit and surrounding structures?

• Optic artery

• Internal carotid artery

• Opthalamic artery

• Lacrimal artery

Answer explanation

The opthalamic artery supplies the eye, orbit and surrounding structures including parts of the nose and face.

The opthalamic is a branch of the internal carotid artery.

The lacrimal artery is branch of the opthalamic artery (supplies the lacrimal glands)

What visual defect would a lesion at the optic chiasm cause?

• Loss of vision in one eye

• Enlarged blind spot

• Bitemporal hemianopia

• Homonymous hemianopia

Answer explanation

A lesion at the optic chiasm will cause bitemoral hemianopia. The nasal fibres carrying visual information from the peripheal aspect of the visual field cross here.

Which structure occupies the normal 'blind spot' area on the retina?

• Retinal haemorrhage

• Ophthalamic artery

• Fovea

• Optic disc

Answer explanation

The area of the retina occupied by the optic disc. This is where axons of sensory cells leave the eye.

The fovea is the area of retina responsible for sharp central vision.

Retinal haemorrhages are a pathology causing visual problems but not the normal blind spot.

How would the eye accommodate for a hear object (vs an object further away)?

• Ciliary muscles contract + lens becomes more convex

• Ciliary muscles relax + lens becomes more convex

• Ciliary muscles contact + lens becomes less convex

• Ciliary muscles relax + lens becomes less convex

Answer explanation

As objects move closer, reflected light becomes more divergent.

The accomodation reflex results in contraction of the ciliary muscle and the lens becoming more convex (increasing the refractive power and allowing the eye to focus light rays onto the retina). The pupils also constrict and the eyes converge.

This is what a patient sees. Where is the most likely location of the lesion?

• Optic chiasm

• RIGHT retina

• LEFT occipital lobe

• RIGHT occipital lobe

Answer explanation

The photos shows a RIGHT homonymous hemianopia (loss of the RIGHT side of the visual field for both eyes).

Of the options, only a lesion of the LEFT occipital lobe would give this defect.

A lesion at the optic chiasm would give a bitemporal hemianopia

A lesion at the retina would result in loss of vision in one eye only.

A lesion of the RIGHT occipital lobe would a LEFT honomymous hemianopia

Which answer is true?

• Rod cells are concentrated towards the centre of the retina

• Cone cells function better than rods in lower light

• The fovea is an area of the retina comprising only cones

• Rod cells permit colour vision

Answer explanation

The fovea (centralis) is an area of the retina containing only cone cells responsible for sharp central vision.

Cone cells are primarily responsible for colour vision

Rod cells function better in lower light than cone cells

Rod cells function better at lower light levels (and hence colour vision is worse at lower light levels)

Rod cells are concentrated towards the periphery

Which description most closely matches myopia?

• The refractive power of the eye is too high so the image is focussed in front of the retina

• The refractive power of the eye is too high so the image is focussed behind the retina

• The refractive power of the eye is too low so the image is focussed in front of the retina

• The refractive power of the eye is too low so the image is focussed behind the retina

Answer explanation

Myopia of 'short sightedness' is a refractive error

The refractive power of the eye is too great so the image is focussed in front of the retina. This can be because the refractive power of the lens is too great or the axial length of the eye is too long.

Which statement is true regarding bipolar cells?

• Bipolar cells transmit signals from photoreceptors to ganglion cells

• Bipolar cells are a type of cone cell

• Bipolar cells never receive input from interneurones

• Bipolar cells are found in the lateral geniculate nucleus

Answer explanation

Bipolar cells are found in the retina. They transmit signals from photoreceptors (rods and cones) to ganglion cells.

They also have input from interneurones (e.g. horizontal cells) which combine information from multiple rod/ cell cells.

The majority of ganglion cells terminate in the lateral geniculate nucleus (part of the thalamus)

A patient is unable to move their right eye towards the right hand side. All other eye movements are normal. Which nerve has most likely been damaged?

• Trocheal nerve (IV)

• Optic nerve (II)

• Abducens nerve (VI)

• Oculomotor nerve (III)

Answer explanation

The patient is unable to abduct their right eye. This corresponds to a defect in the lateral rectus of the right eye.

This muscle is supplied by the abducens nerve.

The trochlea nerve supplies the superior oblique which depresses, abducts and internally rotates the eye.

The oculomotor nerve supplies all other eye muscles.

What is presbyopia?

• Progressive long sightedness with age

• Progressive short sightedness with age

• Strabismus with age

• Long sightedness amongst younger people

Answer explanation

Presbyopia is the tendency to develop long sightedness with age

Age related changes to the lens and ciliary mucles result in a fall in the refractive power of the lens so rays from closer objects are brough to focus behind the trisn