High myopia (shortsightedness) is usually defined as having myopia of -6.00D or stronger. The prevalence of young adults with high myopia in Asia was found to be 6.8% to 21.6%.1 The prevalence is far higher in urban than in rural area, it could be inferred that the amount of high myopic population in Hong Kong should be not less than 15%. Vision of high myopic patients can be easily corrected by glasses, however, there are some complications of high myopia that can cause irreversible visual impairment. The following entry will discuss some of the common complications of high myopia.
The eyeball length of high myopic patients is far longer than those without myopia. Due to such elongation, the retina, macula (centre part of the retina) and choroid (back part of the retina) are susceptible to pathological changes. A recent research from Singapore found that out of 100 high myopic young adults, there were about 8 of them had pathologic myopia. 2 Such figure indicated that the incidence of pathologic myopia is not low. Pathologic myopia can be classified into 5 categories based on different clinical characteristics, among them “myopic choroidal neovascularization” (myopic CNV) is the one that can cause fast vision loss. Patients with myopic CNV will be referred to ophthalmologists immediately for intraocular Anti-Vascular Endothelial Growth Factor injections in a bid to preserve vision and regain some vision loss. High myopic patients should also pay attention to sudden drop of vision and seeing distorted straight lines, and perform annual eye check for ruling out are any early pathological changes.
The vitreous gel inside the eyeball of high myopic patients becomes liquefied and detaches from the retina at a younger age than those without myopia,3 this should be the most probable cause that makes the patients with high myopia more prone to retinal breaks and detachment. A research showed that the risk of high myopic patients to have retinal detachment was 20-fold higher than those without.4 Therefore, if there is any sudden onset of flashes and floaters (which are the classical symptoms of retinal detachment), dilated fundus examination must be performed immediately to rule out retinal detachment.
Elongation of the eyeball not only causes higher risk of macular degeneration, but also causes stretching effect to the optic nerve head, which in turn may lead to higher risk of glaucoma. A recent research from Beijing found that under similar intraocular pressure, high myopic eyes are with about 7.5 times more risk of developing glaucoma than those without any prescription.5 There is no obvious symptom of early glaucoma, retinal examination is necessary to detect early changes.
It is still controversial of whether there is an association between high myopia and age-related cataract, some research did find an association, but some did not.6 However, it should be noted that the incidence of retinal detachment after cataract surgery is slightly higher for patients with high myopia than general population (2.2% for high myopia vs 0.93% for general population). 7,8
By Paco Chan, Registered (Part I) Optometrist
Eyecare information by SWISSCOAT Vision Centre
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