Definition of myopia :

Definition : Myopia also known as ‘short sight’ is that dioptric condition of the eye in which, with the accommodation at rest, incident parallel rays of light come to a focus anterior to the light – sensitive layer of the retina.

Symptoms of myopia :

1. Impaired distance vision.
2. Eye strain.
3. Black floaters.
4. Delayed dark adaptation.
5. Sudden loss of vision.
6. Prominent eyeball.
7. Large coma.
8. Deep anterior chamber.
9. Apparent convergent squint.
10. Posterior cortical cataract may be present.
11. Degeneration (liquefaction) of the vitreous may be present.
12. Ophthalmoscopic findings:
13. In simple myopia :

• Large disc.
• Temporal crescent may be seen.

Classification of myopia :

Aetiological classification:

1). Axial myopia : When the axial length of the eyeball is more.

2) Curvature myopia : When the curvature of the eye, cornea or lens is more.

• Keratoconus, keratoglobus. Lenticonus.

3) Index myopia:

• Index of the nucleus is more.
• Nuclear sclerosis and in diabetes

4) Forward displacement of the lens.

Clinical classification :

1. Congenital myopia.
2. Simple myopia.
3. Pathological myopia.

Treatment of myopia : 

Optical :

• Spectacle by spherical concave lens.
• Contact lens.

Surgery :

• Keratorefractive surgeries : Radial keratotomy (RK). & Keratomileusis.
• Fukala’s operation.
• Clear lens extraction (CLE).
• LASER: Photorefractive & keratoplasty, LASIK.

General :

• Good nutritional diet.
• Exercise.
• Fresh environment.
• Proper position of reading in good illumination.

Genetic counseling :

• A parent with degenerative myopia should be warned that any offspring may have same disability.
• Two highly myopic adults with degenerative changes should never, from the medical point of view, have children.

Pathological myopia / Progressive myopia :

Definition : Pathological myopia may be defined as a condition in which the myopic condition rapidly progresses so that in early adult life there may be myopia of 20D or more. It is also called progressive or degenerative myopia.

Types :

1. Pathological axial myopia.
2. Pathological curvature myopia.

Features of pathological myopia :

• Myopia appears in childhood (5-10 years of age) and increasing steadily with age up to 25 years or beyond.
• The final amount of myopia may be -15D to -25D or more.
• There are typical degenerative changes in the fundus.
• Strongly hereditary
• More common in female
• More in Japanese, Chinese or Jews
• Prognosis is usually poor.

Complication of pathological myopia :

1. Retinal tears → Vitreous haemorrhage.
2. Retinal detachment.
3. Degeneration of the vitreous
4. Posterior cortical & nuclear cataract.
5. Primary open angle glaucoma.

Pathological changes in left retina :

1. Retinal detachment.
2. Retinal tear→ Vitreous haemorrhage.
3. Retinal degenerations.

Simple myopia :

• Incidence : Commonest type of myopia.
• Age :Starts usually at school going age.
• progression : Progress slowly, maximum up to the age of 25 years.
• Changes : No pathological change in eye.
• Refractive error : Refractive error usually limited to-6D or less.
• Vision : Full vision can be achieved by spectacles, contact lens, or by surgical measures.

Causes of painless loss of vision :

1. Central retinal artery occlusion (CRAO).
2. Central retinal vein occlusion (CRVO)
3. Retinal detachment or hemorrhage.
4. Vitreous hemorrhage.
5. Optic or retrobulbar neuritis.
6. Internal carotid artery occlusion.