Refractive errors Flashcards
When does a refractive error occur?
When the shape of the eye prevents light from focusing directly on the retina to form a clear image
Define emmetropia.
The power of the eye to focus light on the retina
What are the 3 types of refractive errors (ametropia)?
Myopia, Hyperopia, Astigmatism
Define myopia.
Difficulty in seeing distant objects clearly (Nearsightedness)
What causes myopia?
- Increase in axial length of the eyeball
- Increased curvature of the cornea
- Increased refractive index of the eye
Give 2 risk factors of myopia.
- A family history of myopia
- Prolonged near work activities( e.g. reading, screen time)
- Low outdoor activity(especially in childhood
What was the 3 types of myopia?
Congenital, Simple, Degenerative
What kind of lenses is given to myopic patients?
Concave lenses
Define hypertropia.
Blurred near vision and clear far vision (farsightedness)
What causes hypertropia?
- Smaller axial length of the eye
- Flatter cornea
- Decreased refractive index
Give 2 risk factors for hypertropia.
- Genetic predisposition
- Prematurity and low birth weight
- Maternal smoking during pregnancy
What kind of lenses are given to hyertropic patients?
Convex lenses
Mention 2 complications of hypertropia.
- Closed angle glaucoma
- Early onset of presbyopia
- Amblyopia
Define astigmatism.
Refraction varies in different meridian of the eye
Ray of light entering the eye can not converge to a point focus but form focal lines
Which lenses correct astigmatism?
Toric lenses
Define presbyopia.
Loss of accommodative ability
Usually in older patients, from age of 40
Which lenses can correct presbyopia?
Concave lenses
Give 3 other manifestations of refractive errors.
- Pain in the eyes
- Headache
- Strabismus
