Lens and refraction · 01
Refractive error
Myopia · hyperopia · astigmatism · presbyopia
Last reviewed: 2026-10-06 · 潘家健醫生
Key points
- Myopia, hyperopia, astigmatism and presbyopia are refractive / accommodative problems; high myopia usually means ≥ 600 degrees.
- High myopia raises risks such as retinal detachment (relative risk, not personal absolute probability).
- New flashes or a clear increase in floaters: prompt dilated assessment; a curtain or sudden vision drop: go to A&E now.
- Childhood myopia management aims to slow progression — not to shorten the eye axis or “cure” the degree.
What it is
Light does not focus on the retina. Myopia blurs distance; hyperopia makes near work effortful; astigmatism distorts. Presbyopia is loss of lens focusing with age — strictly a decline in accommodation, not a classic refractive error, grouped here because the optical approaches overlap. In Hong Kong, 100 degrees = 1.00 D; high myopia is usually ≥ 600 degrees (−6.00 D). Myopia is often axial. About 1 mm of extra axial length is roughly 2.5–3.00 D. Myopia is very common in local schoolchildren. Earlier school screening reports could exceed 80% in secondary school; more recent larger questionnaire surveys are about 60–70%. Figures differ by method (dilated refraction screening ≠ self-report questionnaire); the two sets cannot be compared directly, and neither is your child’s personal prognosis.
Long-term risks of high myopia (≥ 600 degrees)
| Related eye disease | Literature report (education ballpark) |
|---|---|
| Retinal detachment | About 10–20× vs emmetropia (relative risk; not personal absolute probability) |
| Open-angle glaucoma | About 2–3× (relative risk) |
| Nuclear cataract | About 2–5×; may start earlier (relative risk) |
| Myopic maculopathy | Structural / degenerative change; can permanently damage central vision (not a fold comparison) |
| Posterior staphyloma | Posterior-segment structural expansion (structural change, not a relative-risk multiple) |
If you have high myopia and new flashes or a clear increase in floaters: same-day dilated fundus exam. A curtain or sudden vision drop: go to A&E now. For a deeper explanation of pathologic myopia, myopic maculopathy and retinal breaks, see the dedicated high-myopia risks page.
What a doctor may discuss
- Spectacles or contact lenses after refraction; high myopia needs regular dilated fundus exams by an ophthalmologist
- If you have high myopia and new flashes or a clear increase in floaters: same-day dilated fundus exam. A curtain or sudden vision drop: go to A&E now.
- Childhood myopia: outdoor daylight is associated with slower onset (shade and corridors count). How long per day is a public-health suggestion, not a personal prescription and not the “most important / most effective” treatment. See the childhood-myopia page.
- Classes a doctor may discuss for slowing childhood progression are on the childhood-myopia education page — not a product pitch
- Presbyopia: reading glasses, progressive lenses, or, after cataract assessment, lens options
Related public education video (HKOS)
Video source: Hong Kong Ophthalmological Society (HKOS) “Eyes Decoded” YouTube (public education)
This site is not affiliated with, and is not the same organisation as, the Hong Kong Ophthalmological Society (HKOS).
Selected public references (not a full bibliography)
These are the public studies this page draws on. PMID links go to PubMed (US National Library of Medicine) so you can check them. Figures are from those studies — not your prognosis and not a clinic success rate. Links are not a shop.
- Lam CS, Goldschmidt E, Edwards MH Prevalence of myopia in local and international schools in Hong Kong. Optom Vis Sci. 2004;81(5):317-322. PMID 15181356本地中學篩查近視約 85–88%；國際學校約 60–66%。用來對應「中學階段可超過八成」。
- CUHK EdDataX Research Centre Pupils' eyesight survey (questionnaire). The Chinese University of Hong Kong, June 2021 (press briefing 20 Dec 2022). 中三問卷約 66%。問卷不是散瞳驗光，與學校篩查八成不可直接比較。無 PubMed 條目。
- Haarman AEG, Enthoven CA, Tideman JWL, et al. The Complications of Myopia: A Review and Meta-Analysis. Invest Ophthalmol Vis Sci. 2020;61(4):49. PMID 32347918近視併發症綜述與統合分析。本頁正文採定性表述，不羅列個人終生風險百分比。
This is general medical information, not a diagnosis, and cannot replace an in-person consultation with a registered ophthalmologist, refraction, or a dilated fundus exam. It is not advice to use any medicine or undergo any procedure. Medicines (including off-label use), laser or surgery must be decided by a registered doctor after examination, according to indications and Hong Kong registration. Figures from the literature are published averages, not any clinic’s results. This site does not book, prescribe or refer. Do not change treatment on your own.