Hypermetropia ,clinical feature and treatment Topic 18
Hypermetropia
Aka long-sightedness; can see in distance but not in the near
This is because the focal point is behind the retina so the retina produces blurred images due to lack of refraction. This is corrected by inserting a convex length which compensates as it bring the rays closer together so when they hit the eye lens, they converge enough to reach the retina.
Types
- a. Axial→ most common (total refractive power normal but the eyeball is shorter thus even though the refraction power are normal the distance is not sufficient thus focuses behind the retina→ blurry image)
- b. Curvatural →curvature of cornea/lens/both flattened thus decreasing refractive power thus → rays don’t converge on retina
- c. Index→ decrease in index thus convergence (refractive power) with age
- d. Positional → lens placed posteriorly thus convergence starts later than if it was more anteriorly placed
- e. Absence of crystalline lens→congenital or acquired
Clinical types
- 1. Simple/development→ normal biological variations in eyeball development
- 2. Pathological → index (cortical sclerosis) , Positional (posterior misalignment of lens) ,Aphakia
- 3. Functional → paralysing of accommodation third nerve paralysis and internal Ophthalmoplegia
Degree
Manifest hypermetropia→ facultative (can be corrected) + absolute (cannot be corrected by accommodative effort)
Symptoms:
- Asymptomatic ;
- Asthenopic= fully corrected by accommodative efforts but this is strenuous to the eye thus tiredness of eye, fronto-temporal headache, watering and mild photophobia especially in near (rather than distant vision) work & increase towards evening
- Defective vision with asthenopic→ not fully corrected thus complains of some defect
- Defective vision only→ hypermetropia too high , cant accommodate, near &distant bad