Refraction Flashcards
Refractive errors arise from…
Disorders of size and shape of eye
Correct refraction depends on…
The distance between the cornea and the retina and curvatures of the lens and cornea
What is myopia?
Short sightedness
In those with myopia the eyeball is too…
Long
Describe myopia
In any eye, the nearer objects come to the eye, the further back their image falls. With myopia, only close objects focus on the retina - unless concave glasses used
What type of lenses correct myopia?
Concave
What causes myopia?
Genetic
Close work in early decades of life
Why does myopia in children worsen with age?
In normal growth, changes in eyeball and lens curvature compensate for the eye getting longer as it grows, but in myopic children such compensation may not be occurring so it worsens with age. Most do not become myopic until about 6 y/o
Myopia will usually worsen until late teens - changes stop below 6 dioptres
Why is it important for children with myopia to have eyes regularly checked?
Spectacle changes are to be expected, perhaps every 6 months
In later life, increasing myopia may indicate…
Cataracts
What are those with myopia at increased risk of due to the decreased longitudinal axis?
Posterior vitreous detachment
Retinal detachment
What is an astigmatism?
Irregular curvature of cornea or lens - the eye does not focus light evenly on the retina
Usually one half of the cornea is flatter or steeper than the other half
What symptoms occur with astigmatism?
Can be asymptomatic Blurred vision Double vision Squinting Eye strain headaches
Astigmatism can occur alone or be associated with…
Myopia or hypermetropia
How is an astigmatism managed?
Correcting lenses
