Optometry Flashcards
Refractive status:
What is meant by the clinical term emmetropia?
An eye which has no refractive error or visual defect
The light which enters the eye focuses perfectly on the fovea in the retina
Refractive status:
What is meant by the clinical term ametropia?
An eye which has one or more refractive errors
The light which enters the eye does not focus correctly on the fovea in the retina
Refractive status:
What is meant by the clinical term anisometropia?
When a person has a significant difference between their left and right ametropia (refractive errors)
Give 3 examples of refractive errors
Myopia
Hyperopia/hypermetropia
Astigmatism
What is myopia?
Short-sightedness i.e., distance vision is blurred
What abnormality of the eye causes myopia?
The light is focused too far in front of the retina, usually due to the eye being too long or the refractive power of the lens being too strong
What sort of lenses are used to treat myopia?
Why?
-ve / concave lenses
The concave shape (thicker around periphery than in centre) of the lens causes light to pass through and diverge (spread) so that it can reach further back to the retina
What is hyperopia?
Long-sightedness i.e., near vision is blurred
What abnormality of the eye causes hyperopia?
The light is focused too far behind the retina, usually due to the eye being too short or the refractive power of the lens being too weak
What sort of lenses are used in hyperopia?
Why?
+ve / convex lenses
The convex shape (thicker in the centre than around the periphery) of the lens causes light to pass through and converge so that it focuses earlier than its current position behind the retina
What is a ‘diopter’?
A measurement of refractive power e.g., a -1.5 diopter prescription
What is astigmatism?
‘Rugby-ball shaped eye’ causing blurring of distant and near vision
What abnormality of the eye causes astigmatism?
Due to rotational asymmetry of the eye’s refractive power
i.e., refractive power is different depending on the meridian (longitudinal axis) the eye is lying in
What sort of lenses are used to treat astigmatism?
Cylindrical shaped lenses
If astigmatism in early life is left untreated, what may the child develop?
Amblyopia
i.e., lazy eye - brain develops to process inputs from the good eye and vision becomes worse in the affected eye
What is presbyopia?
Age-related hyperopia (long-sightedness)
What abnormality of the eye causes presbyopia?
The lens loses its ability to accommodate for close up vision
How does the lens normally accommodate for close up vision?
The ciliary muscles tense to relax the suspensory ligaments and cause the lens to become more rounded
How is presbyopia managed?
+ve / convex lenses
The convex shape (thicker in the centre than around the periphery) of the lens causes light to pass through and converge so that it focuses onto the retina
When testing a patients vision, what is meant by the testing of…
- Vision
- Visual acuity
- Pinhole acuity
- Vision: smallest letter on the chart that can be read without the aid of glasses or contact lenses i.e., uncorrected vision
- Visual acuity: smallest letter on the chart that can be read with the best glasses or contact lenses i.e., corrected vision
- Pinhole acuity: smallest letter on the chart that can be read through a pinhole
Why is pinhole acuity measured?
It gives an indication of the best visual acuity that is likely to be achieved with corrected vision
Name two letter charts used to test a patient’s vision
What is the difference between them?
Snellen chart
LogMAR
Snellen: number of letters in each row increases with decreasing letter size down the chart
LogMAR: number of letters in each row decreases with decreasing letter size down the chart
What do the line numbers on the Snellen chart indicate?
How far away the patient should be to be able to read the letters
e.g., line 16 - should be readable from 16m, line 5 - should be readable from 5m
What is meant by Snellen notation 6/24
The patient was 6m away and could only read letters up to line 24
