Information about eye conditions
Refractive eye condition is the general term for conditions caused by the structure of the eye affecting the light entering the eye.
Myopia is short-sightedness. This means that distant objects are blurred but close objects are in focus. It is caused by the eye being too long which means the focal point is in front of the retina.
Hypermetropia (or hyperopia) is long-sightedness. This means that distant objects are in focus while close objects are blurred. It is caused by the eye being too short which means the focal point is behind the retina.
Astigmatism causes blurred vision. It is caused by the cornea not being a perfectly curved shape.
Strabismus is commonly known as a squint where the eyes look in different directions.
Amblyopia is commonly known as “lazy eye”. It is usually due to an untreated squint when the brain suppresses the image from the squinting eye.
Focal point is the point at which the light passing through the eye, converges to create a sharp image on the retina.
Visual acuity is the ability to discriminate high contrast fine detail at a distance. This is expressed as two numbers separated by / which is known as the Snellen index. The first figure is the distance from the chart and the second figure is the distance at which a “normal” eye can see the letters. The higher the second figure, the worse the vision.
For example, 6/6 is normal acuity. A person can see at 6 metres what they are expected to see at 6 metres.
6/60 is severely reduced vision. A person can see at 6 metres what a fully sighted person would see at 60 metres.
Health professionals more commonly use the LogMAR chart to assess visual acuity. This is a decimal starting at 0 for normal acuity. 6/60 on the Snellen chart is 1.0 in LogMAR.
Nystagmus is the involuntary movement of the eyes.
Cataracts are the clouding of the lens which causes blurred or misty vision.
Ocular albinism is the loss of pigment in the eyes causing extreme sensitivity to light.
Retinitis Pigmentosa (RP) is a disease affecting the retina. It is usually progressive. It initially affects peripheral vision and ability to see in the dark.
Retinopathy of Prematurity (ROP) can occur when the blood vessels of the retina have not completely developed in the womb. This is a process which starts at 16 weeks and is completed by 36 weeks gestation. In premature babies, abnormal vessels can develop which leads to bleeding and scar tissue forming. This can cause vision loss.
Retinoblastoma is a malignant tumour of the retina. It is rare and usually affects children under the age of 5.
Macular degeneration causes the loss of fine central vision. Peripheral vision is unaffected. It may be progressive.
Optic atrophy is the damage to or degeneration of, the cable of nerve fibres that transmits the signals from the retina to the visual centre of the brain.