Clinical varieties of myopia
1. Congenital myopia
2. Simple or developmental myopia
3. Pathological or degenerative myopia
4. Acquired myopia which may be: (i) post-traumatic; (ii) post-keratitic; (iii) drug-induced, (iv)
pseudomyopia; (v) space myopia; (vii) night myopia; and (viii) consecutive myopia.
1. Congenital myopia
Congenital myopia is present since birth, however, it is usually diagnosed by the age of 2-3 years. Most of the time the error is unilateral and manifests as anisometropia. Rarely, it may be bilateral. Usually the error is of about 8 to 10 which mostly remains constant. The child may develop convergent squint in order to preferentially see clear at its far point
(which is about 10-12 cms). Congenital myopia may sometimes be associated with other congenital anomalies such as cataract, microphthalmos, aniridia, megalocornea, and congenital separation of retina. Early correction of congenital myopia is desirable.
2. Simple myopia
Simple or developmental myopia is the commonest variety. It is considered as a physiological error not associated with any disease of the eye. Its prevalence increases from 2% at 5 years to 14% at 15 years of age. Since the sharpest rise occurs at school going age i.e., between 8 year to 12 years so, it is also called school myopia.
Etiology. It results from normal biological variation in the development of eye which may or may not be genetically determined. Some factors associated with
simple myopia are as follows:
Symptoms
3. Pathological myopia
Pathological/degenerative/progressive myopia, as the name indicates, is a rapidly progressive error which starts in childhood at 5-10 years of age and results in high myopia during early adult life which is usually associated with degenerative changes in the eye.
Etiology. It is unequivocal that the pathological myopia results from a rapid axial growth of the eyeball which is outside the normal biological variations of development. To explain this spurt in axial growth various theories have been put forward. So far no satisfactory hypothesis has emerged to explain the etiology of pathological myopia. However, it is
definitely linked with (i) heredity and (ii) general
growth process.
1. Role of heredity. It is now confirmed that genetic factors play a major role in the etiology, as the progressive myopia is (i) familial; (ii) more common in certain races like Chinese, Japanese, Arabs and Jews, and (iii) uncommon among Negroes, Nubians and
Sudanese. It is presumed that heredity-linked growth of retina is the determinant in the development of myopia. The sclera due to its distensibility follows the retinal growth but the choroid undergoes degeneration due to stretching, which in turn causes degeneration of retina.
2. Role of general growth process, though minor, cannot be denied on the progress of myopia.
Lengthening of the posterior segment of the globe commences only during the period of active growth and probably ends with the termination of the active growth. Therefore, the factors (such as nutritional deficiency, debilitating diseases, endocrinal disturbances and indifferent general health) which affect the general growth process will also influence the progress of myopia.
1. Congenital myopia
2. Simple or developmental myopia
3. Pathological or degenerative myopia
4. Acquired myopia which may be: (i) post-traumatic; (ii) post-keratitic; (iii) drug-induced, (iv)
pseudomyopia; (v) space myopia; (vii) night myopia; and (viii) consecutive myopia.
1. Congenital myopia
Congenital myopia is present since birth, however, it is usually diagnosed by the age of 2-3 years. Most of the time the error is unilateral and manifests as anisometropia. Rarely, it may be bilateral. Usually the error is of about 8 to 10 which mostly remains constant. The child may develop convergent squint in order to preferentially see clear at its far point
(which is about 10-12 cms). Congenital myopia may sometimes be associated with other congenital anomalies such as cataract, microphthalmos, aniridia, megalocornea, and congenital separation of retina. Early correction of congenital myopia is desirable.
2. Simple myopia
Simple or developmental myopia is the commonest variety. It is considered as a physiological error not associated with any disease of the eye. Its prevalence increases from 2% at 5 years to 14% at 15 years of age. Since the sharpest rise occurs at school going age i.e., between 8 year to 12 years so, it is also called school myopia.
Etiology. It results from normal biological variation in the development of eye which may or may not be genetically determined. Some factors associated with
simple myopia are as follows:
- Axial type of simple myopia may signify just a physiological variation in the length of the eyeball or it may be associated with precocious neurological growth during childhood.
- Curvatural type of simple myopia is considered to be due to underdevelopment of the eyeball.
- Role of diet in early childhood has also been reported without any conclusive results.
- Role of genetics. Genetics plays some role in the biological variation of the development of eye, as prevelance of myopia is more in children with both parents myopic (20%) than the children with one parent myopic (10%) and children with no parent myopic (5%).
- Theory of excessive near work in childhood was also put forward, but did not gain much importance. In fact, there is no truth in the folklore that myopia is aggravated by close work, watching television and by not using glasses.
Symptoms
- Poor vision for distance (short-sightedness) is the main symptom of myopia.
- Asthenopic symptoms may occur in patients with small degree of myopia.
- Half shutting of the eyes may be complained by parents of the child. The child does so to achieve the greater clarity of stenopaeic vision.
- Prominent eyeballs. The myopic eyes typically are large and somewhat prominent.
- Anterior chamber is slightly deeper than normal.
- Pupils are somewhat large and a bit sluggishly reacting.
- Fundus is normal; rarely temporal myopic crescent may be seen.
- Magnitude of refractive error. Simple myopia usually occur between 5 and 10 year of age and it keeps on increasing till about 18-20 years of age at a rate of about –0.5 ± 0.30 every year. In simple myopia, usually the error does not exceed 6 to 8.
3. Pathological myopia
Pathological/degenerative/progressive myopia, as the name indicates, is a rapidly progressive error which starts in childhood at 5-10 years of age and results in high myopia during early adult life which is usually associated with degenerative changes in the eye.
Etiology. It is unequivocal that the pathological myopia results from a rapid axial growth of the eyeball which is outside the normal biological variations of development. To explain this spurt in axial growth various theories have been put forward. So far no satisfactory hypothesis has emerged to explain the etiology of pathological myopia. However, it is
definitely linked with (i) heredity and (ii) general
growth process.
1. Role of heredity. It is now confirmed that genetic factors play a major role in the etiology, as the progressive myopia is (i) familial; (ii) more common in certain races like Chinese, Japanese, Arabs and Jews, and (iii) uncommon among Negroes, Nubians and
Sudanese. It is presumed that heredity-linked growth of retina is the determinant in the development of myopia. The sclera due to its distensibility follows the retinal growth but the choroid undergoes degeneration due to stretching, which in turn causes degeneration of retina.
2. Role of general growth process, though minor, cannot be denied on the progress of myopia.
Lengthening of the posterior segment of the globe commences only during the period of active growth and probably ends with the termination of the active growth. Therefore, the factors (such as nutritional deficiency, debilitating diseases, endocrinal disturbances and indifferent general health) which affect the general growth process will also influence the progress of myopia.
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