Course: Visual Assessment of Children: The Orthoptist Role
Presented on Wednesday 9 February 2005
The Visual Pathway
Claire Gilmour Orthoptist Ninewells Hospital
There are 3 parts to the visual system
- Optic Nerve
- Conjunctiva and Sclera
- Protect the eye from injury and excessive light by closing.
- Assist in distributing tears over the front of the eye for lubrication.
- Contain meibomian glands and glands of Zeis and Moll which secrete oils into the tear film.
Conjunctiva and Sclera
- Conjunctiva is the thin mucous membrane that lines the eye lids
- Sclera forms 5/6th of the posterior eye and is opaque, white
- The sclera is continuous with the cornea anteriorly and covered by the conjunctiva posteriorly
- 1/6th of the anterior eye
- It is the transparent ?window? of the eye
- Convex and elliptical in shape
- It is responsible for the refraction of light entering the eye
- Is a thin pigmented diaphragm with a central aperture ? pupil
- Varies in colour light blue to dark brown
- Controls the amount of light entering the eye ? miosis/mydriasis of pupil
- Transparent, biconvex structure sitting behind the iris in front of the vitreous
- Kept in position by suspensory ligaments
- Flexible ? accommodation - until older age
- The vitreous fills the eye ball and keeps its shape.
- It is a colourless transparent gel (98% H2O)
- It allows transmission of light to retina.
- Supports the lens in place and pushes the layers of retina together.
- Is the internal layer of the eye
- Images are formed here and transmitted to the brain via the optic nerve.
- It consists of many layers with different cells absorbing light and transmitting information.
Rods ? No colour Poor acuity; Work well in dark; Movement
Cones ? Colour Fine detail Daylight
Still Fovea - This is the area of macula gives the most distinct visual acuity.
The optic nerve is a continuation of the retinal nerve fibres (approx 1,200,000)
Visual information is transmitted along the optic nerve to the brain.
Optic nerve pathway
- Optic nerves meet at the optic chiasm
- Here the nasal retinal fibres from each eye cross to the opposite side.
- The fibres then form the optic tract
- Lateral Geniculate Nucleus relays information to the optic radiations
which terminate in
the visual cortex of the occipital lobe
- Important note
- The left visual cortex receives the nerve fibres from the right half
of the visual field and
- Therefore damage to the left visual cortex results in a right homonymous hemianopia
Visual cortex processes the picture and passes on the information to
other areas of brain for -
recognition - movement (cognitive functions)
Binocular vision develops from birth providing both eyes have the ability
to see and the eye
muscles all work normally allowing the eyes to maintain straight ahead position in the orbit.
- This results in stereopsis (3D vision) which is demonstrable by 6/12.
- Any barrier such as poor vision caused by refractive error, ocular
pathology or CVI will
prevent binocular vision.
Normal visual development
- Newborn 6/240
- 2-3 mths 6/180 ? 6/90
- 6 mths 6/60 ? 6/24
- 12 mths 6/18 ? 6/12
- 18 mths 6/9
- 24 mths 6/6 singles
- 4 yrs 6/6 test type