Lesson · ABO / NCLE
Refractive conditions and eye disease
Presbyopia, anisometropia and the binocular conditions, then the common eye diseases an optician must recognise and refer.
After this lesson you can
About 10 minutes- Tell anisometropia, antimetropia and aniseikonia apart
- Explain why presbyopia starts and how it is corrected
- Tell a phoria from a tropia
- Recognise cataract, glaucoma, conjunctivitis and keratoconus and know when to refer
Refractive conditions
| Condition | What it is | Correction |
|---|---|---|
| Myopia | Light focuses in front of the retina; distance is blurred | Minus lens |
| Hyperopia | Light focuses behind the retina; near is harder than distance | Plus lens |
| Astigmatism | The eye has two different powers 90° apart (regular) | Cylinder, or a rigid lens for irregular |
| Presbyopia | Loss of focusing range with age, noticed around 40 | Plus add: readers or multifocals |
| Anisometropia | Same type of error in both eyes, very different amounts (usually over 2.00 D) | Glasses or contact lenses |
| Antimetropia | One eye myopic, the other hyperopic | Glasses or contact lenses |
| Aniseikonia | The two eyes see images of different size or shape | Iseikonic lenses |
| Aphakia | No crystalline lens, most often after cataract removal | High plus or an implant |
Presbyopia has two causes: the crystalline lens stiffens, and the ciliary muscle can no longer help it round up. When the ciliary muscle contracts it relaxes the zonules, the lens bulges and gains plus power; that is accommodation.
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Binocular and lid conditions
| Condition | What it is |
|---|---|
| Phoria | A hidden tendency for an eye to drift, which shows only when fusion is broken (for example by covering one eye) |
| Tropia | An eye that is turned all the time; the brain cannot fuse |
| Strabismus | Any eye turn that prevents normal binocular vision; helped by prism, therapy or surgery |
| Diplopia | Double vision; may be helped with prism. Sudden onset in an adult needs the doctor now |
| Amblyopia | “Lazy eye”: vision that no lens corrects to normal |
| Nystagmus | Involuntary, rapid eye movement; contact lenses help because they move with the eye |
| Ptosis | A drooping upper lid; a ptosis crutch on the frame can lift it |
| Photophobia | Abnormal sensitivity to light |
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Common eye diseases
| Disease | What happens | What it means for you |
|---|---|---|
| Cataract | Clouding of the crystalline lens, mostly with age | Removed surgically; the patient is then aphakic or has an implant |
| Glaucoma | Raised eye pressure damages the optic nerve; usually no symptoms | Routine screening matters; treated with drops or surgery |
| Conjunctivitis | “Pink eye”: bacterial, viral, allergic or contact-lens related | Possibly contagious: disinfect equipment after a red-eye patient |
| Keratoconus | The cornea thins and bulges into a cone, giving irregular astigmatism | Needs specialty contact lens fitting, usually rigid lenses |
Opticians do not diagnose. Your job is to notice the signs, keep equipment clean and send the patient to the doctor. Sudden double vision, a painful red eye in a contact lens wearer or a sudden loss of vision are same-day referrals.
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