Causes of hyperopia
There are different causes for hyperopia, as there are multiple types of hyperopia with different etiologies. Hyperopia is classified according to its etiology into:
1- Axial hyperopia
It is the most common type of hyperopia; it is a simple hyperopia. Axial hyperopia usually results from shortening of the axial length of the eye. In this type genetics plays significant role in the developing of simple hyperopia. A study by Strang et al. founded that shortening of the axial length of the eye by 1mm leads to +6 diopters refractive error.
2- Index hyperopia
It occurs in patients with diabetes or in old age. In this type there is a change in the power of the crystalline length, which causes progression to hyperopia.
3- Curvature hyperopia
In this type, hyperopia may result from flattening of the cornea, or flattening of the crystalline lens, or both.
4- Positional hyperopia
In positional hyperopia, it results from
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- changing the position of the crystalline lens in the eye
- absence of the crystalline lens due to genetic or acquired diseases
- Post- traumatic
- Post-surgical loss of the crystalline lens
5- Functional hyperopia
Malfunction of accommodations which may appear since birth causes functional hyperopia. Other causes of accommodation disfunction includes using cycloplegic drugs, or in cases of third nerve palsy.
6- Miscellaneous
A few conditions can be associated with hyperopia such as microphthalmos, Anophthalmus, and aniridia. There are multiple diseases and environmental factors that could be linked to hyperopia, from these factors:
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- Family history
- Excessive smoking during pregnancy
- Diabetes mellitus
- Optic nerve edema
- Retinal edema
- Heimler syndrome
