Refers to any abnormality in the focusing mechanism of the eye
Definitions
- Emmetropia: no refractive error, light focussed onto retina
- Ametrophia: retractive error present, light focussed in front of retina or behind retina
- Anisometrophia: significant difference between right and left ametropia
Myopia (short-sightedness)
Pathophysiology
- Abnormally increased axial length of eye or, less commonly, increased refraction means light focuses in front of the retina
Clinical features
- Clear near vision, blurred far vision
Management
- Glasses with concave (negative) lenses
Complications
- Complications related to larger eyeball size
- Retinal detachment
- Primary open-angle glaucoma
Hyperophia (far-sightedness)
Pathophysiology
- Abnormally decreased axial length of eye means light focuses in behind the retina
Clinical features
- Blurred near vision, clear far vision
Management
- Glasses with convex (positive) lenses
Complications
- Complications related to smaller eyeball size
Astigmatism
Pathophysiology
- Eye has unequal refractive powers at different meridians of curvature
Clinical features
- Causes distorted vision at all distances
Management
- Correction with cylindrical lenses
Presbyopia
Pathophysiology
- Age-related degeneration of structures responsible for accomodation of the lens
Clinical features
- Preexisting myopia may temporarily compensate presbyopia, leading to better near vision
Management
- This requires a supplementary convex or positive lens (i.e. reading glasses) in order to focus light from a near object onto the retina
Management of low vision
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