Cornea and ocular surface · 07
Conjunctivitis
Red itchy eye · do not self-buy steroids for heavier allergy; needs a doctor's assessment
Last reviewed: 2026-10-06 · 潘家健醫生
Key points
- Conjunctivitis is inflammation of the white of the eye; red itchy eyes are common; causes include infection and allergy.
- Do not self-buy steroid eye drops for heavier allergy — a doctor must assess.
- Severe pain with headache and vomiting, or sudden vision drop / sudden blindness: go to A&E now.
- Severe photophobia and pain, or contact-lens-related pain and light sensitivity that persists after lens removal: same-day ophthalmic assessment.
What it is
Inflammation of the conjunctiva. Teaching buckets below: infectious, allergic (including heavier VKC / AKC), and medication-related — not every red eye belongs in the same leftover drop bottle.
Infectious
Viral disease is often watery and spreads readily by hand–eye contact and shared towels (public-health education in the spirit of CDC / AAO guidance). Bacterial discharge tends to be stickier. In adults with sexually transmitted infection risk, a doctor may educate about and work up chlamydia- or gonococcus-associated conjunctivitis (public references such as the MSD Manual) — not a DIY purchase. Do not self-buy steroid eye drops.
Allergic (including VKC / AKC)
Itch is usually prominent. Vernal keratoconjunctivitis (VKC) and atopic keratoconjunctivitis (AKC) are heavier chronic allergy and can risk shield ulcer — not ordinary red eye; do not self-buy steroids. Drug classes and principles: allergic-conjunctivitis treatment page; Hong Kong environment triggers: allergy and the Hong Kong environment page.
Medication-related
Benzalkonium chloride (BAK), a common preservative in multi-dose drops, can irritate the ocular surface (Goldstein et al., Eye 2022). Long-term topical therapy (especially glaucoma drops) is also discussed in the literature as drug-induced cicatrizing / pseudopemphigoid-like conjunctivitis (Singh et al., Ocul Surf 2022) — for ophthalmologist assessment, not a DIY stop-or-swap handbook.
When it is urgent
- Pain with headache and vomiting: go to A&E now (rule out acute angle-closure glaucoma). Sudden vision drop or sudden blindness: go to A&E now. Severe photophobia and pain without those red flags: same-day ophthalmic assessment to rule out keratitis. Contact-lens-related pain and light sensitivity: if it still hurts after lens removal, same-day assessment — do not delay.
What a doctor may discuss
- Hygiene, cool compresses, allergy strategies
- Prescription drops if needed — never long-term steroid drops on your own
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.
- Goldstein MH, Silva FQ, Blender N, et al. Ocular benzalkonium chloride exposure: problems and solutions. Eye (Lond). 2022;36(2):361-368. https://doi.org/10.1038/s41433-021-01668-x. PMID 34262161BAK 防腐劑對眼表影響的綜述。教育用途；不作商品比較或自行換藥手冊。
- Singh S, Donthineni PR, Shanbhag SS, et al. Drug induced cicatrizing conjunctivitis: A case series with review of etiopathogenesis, diagnosis and management. Ocul Surf. 2022;24:83-92. PMID 35247582藥物誘發瘢痕性／擬類天疱瘡樣結膜炎教育文獻。須專科評估；不是自行停藥或換藥指引。
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.