Variations in the shape of the cornea or the length of the eye result in refractive errors that require correction by glasses or contact lenses for the sharpest vision. These variations from normal occur as the result of poorly understood complex developmental processes in most cases. However, in rare instances, such as in this condition, single gene changes (mutations) have been identified.
Several Chinese families have been reported in which a mutation (change in DNA) results in extreme nearsightedness (myopia) in females. This condition is clinically evident by the age of 7 years but may actually occur in utero. The retina and associated structures have a characteristic appearance such as a tigroid pattern of pigmentation and an unusual 'crescent' around the optic nerve. The eye is several millimeters longer than average.
There are no associated abnormalities in other parts of the body. No males were found to be affected in these families.
Mutations (changes) in the DNA of the X-chromosome have been found in females who have this form of nearsightedness. For reasons that are not understood, males with the DNA changes are not nearsighted.
Both males and females can transmit the changed X-chromosome to the next generation. However, since males have only one X-chromosome, all their female offspring will inherit the mutation whereas females with two X-chromosomes will pass along their mutant X-chromosome only 50% of the time.
The diagnosis can be made by eye doctors most likely at birth but this has not been reported. The signs are present by age 7 according to published reports in several Chinese families.
Corrective lenses should improve vision dramatically.
Periodic examinations are important to detect and treat certain complications of nearsightedness such as retinal disease, glaucoma, and cataracts that may develop. Published reports, however, have not noted such associated conditions in this disorder.