High myopia (shortsightedness) is 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 not be low. High myopia is associated with some ocular complications which cause irreversible visual impairment and they will be discussed as follows:
Pathologic Myopia
The eyeball length of high myopic patients is far longer than those without myopia. The stretching pressure from eyeball elongation causes the retina, macula (centre part of the retina) and choroid (back part of the retina) being susceptible to pathological changes. A recent research from Singapore found that out of 100 high myopic young adults, 8 of them had pathologic myopia. 2 Myopic choroidal neovascularization (myopic CNV) is one of the types of pathologic myopia that causes rapid vision loss. Patients with myopic CNV will be referred to ophthalmologists immediately for intraocular Anti-Vascular Endothelial Growth Factor (Anti-VEGF) 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.
Glaucoma
Elongation of the eyeball can also cause stretching pressure to the optic nerve head, which in make the high myopic eyes more prone 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 myopia. 3 There is no obvious symptom of early glaucoma, retinal examination is necessary to detect early changes.
Retinal Detachment
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,4 which makes the high myopic eyes 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 myopia.5 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.
Cataract
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 than for patients with high myopia than general population (2.2% for high myopia vs 0.93% for general population). 7,8
Chan Ka Ho, Paco
Registered Optometrist (Part I)
References:
- Wong YL, Saw SM. Epidemiology of Pathologic Myopia in Asia and Worldwide. Asia-Pacific journal of ophthalmology (Philadelphia, Pa) 2016; 5(6): 394-402.
- Koh V, Tan C, Tan PT, et al. Myopic Maculopathy and Optic Disc Changes in Highly Myopic Young Asian Eyes and Impact on Visual Acuity. American journal of ophthalmology 2016; 164: 69-79.
- Akiba J. Prevalence of posterior vitreous detachment in high myopia. Ophthalmology 1993; 100(9): 1384-8.
- Pierro L, Camesasca FI, Mischi M, Brancato R. Peripheral retinal changes and axial myopia. Retina (Philadelphia, Pa) 1992; 12(1): 12-7.
- Xu L, Wang Y, Wang S, Wang Y, Jonas JB. High myopia and glaucoma susceptibility the Beijing Eye Study. Ophthalmology 2007; 114(2): 216-20.
- Pan CW, Cheng CY, Saw SM, Wang JJ, Wong TY. Myopia and age-related cataract: a systematic review and meta-analysis. American journal of ophthalmology 2013; 156(5): 1021-33.e1.
- Neuhann IM, Neuhann TF, Heimann H, Schmickler S, Gerl RH, Foerster MH. Retinal detachment after phacoemulsification in high myopia: analysis of 2356 cases. Journal of cataract and refractive surgery 2008; 34(10): 1644-57.
- Norregaard JC, Thoning H, Andersen TF, Bernth-Petersen P, Javitt JC, Anderson GF. Risk of retinal detachment following cataract extraction: results from the International Cataract Surgery Outcomes Study. The British journal of ophthalmology 1996; 80(8): 689-93.