Myopia or Shortsightedness:
Myopia meaning:
A condition in which a person can see near objects clearly,but not the far objects.
Definition:
Myopia (Shortsightedness) is a type of refractive error, where the parallel rays of light from infinity are focused in front of the retina, with accommodation at rest.
Etiological Classification:
1. Axial:
- due to increase in antero-posterior length of the eyeball. It is the most commonest type.
2. Curvatural:
- due to increase in curvature of the lens, cornea or both.
3. Positional:
- caused by anterior displacement of lens.
4. Index:
- caused by increased refractive index of the crystalline lens.
5. Myopia also occurs in excessive accomodation due to spasm of accommodation.
Grading of Myopia:
≤ -3D - Low myopia
-3D to -6D - Moderate myopia
≥ -6D - High myopia
Clinical varieties:
1. Congenital :
- High degree of error, even upto 10D
- Present since birth
- Convergent squint may also develop
- Anisometropia
- Early correction is desirable.
2. Simple :
- most common type
- it is due to physiological changes not due any diseases of the eye
- it is also called ‘school myopia'.
Causes:
- it is due to normal physiological changes in the development of eye.
- Precocious neurological growth during childhood.
- underdevelopment of eyeball.
- poor nutrition.
- inheritance.
- excessive near work.
Clinical features:
Symptoms:
- diminished far vision
- asthenopia symptoms
Signs:
- prominent eyeball
- deepened anterior chamber
- larger, sluggish pupils
- fundus is normal
3.Pathological myopia:
It is an degenerative and progressive condition which manifests in early childhood.
It results in high myopia (>-6D) and it is less common.
Etiology:
Pathological myopia results from a rapid axial growth of the eye ball. It is also linked with heredity and general growth process.
The condition has strong hereditary tendancy and it is more common in women than men.
The elongation of eyeball occurs primarily due to degeneration of the posterior half of sclera and is often accompanied with an outward scleral bulge at the posterior pole.
Clinical features:
Symptoms:
- Defective vision
- Muscae volitantes (floating black opacities in front of the eye)
- Night blindness
Signs:
- Prominent eyeball
- large cornea
- deep anterior chamber
- pupils are large
- fundus examination
- myopic crescent
- chorioretinal atrophic patches
- foster fuch's spot
- cystoid and lattice degenerations
- retinal atrophy
- posterior staphyloma
- degenerative changes.
Complications:
1. Retinal detachment
2. Vitreous Haemorrhage
3. Cataract
4. Choroidal haemorrhage
5. Strabismus
Treatment:
1. Optical treatment:
Prescription of appropriate concave lenses.
2.surgical treatment:
- radial keratotomy(RK)
- photorefractive keratectomy (PRK)
- laser in-situ keratomileusis (LASIK)
5. General measures
6. Low vision aids
7. Genetic counseling.
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