Contrast Features in Ophthalmology: 20 Look-Alike Pairs
Last updated: October 2026
Pages on this topic
- This page: 20 look-alike disease pairs compared
- 17 look-alike terms explained
"In contrast to..." statements are a favourite in exams. Here they are as side-by-side pairs, grouped by subspecialty.
Lids, orbit and anterior segment
| Condition | In contrast to | Key difference |
|---|---|---|
| Preseptal cellulitis | Orbital cellulitis | No proptosis or chemosis; vision, pupils and eye movements are normal |
| Chronic canaliculitis | Dacryocystitis | No duct obstruction, sac swelling or sac inflammation; pouting punctum with concretions |
| Simple congenital ptosis | Acquired (aponeurotic) ptosis | On downgaze the ptotic lid sits higher (poor levator relaxation); in acquired ptosis it is level or lower |
| Sebaceous gland carcinoma | Basal and squamous cell carcinoma | More common on the upper lid (more meibomian glands) |
| Papillae | Follicles | Papillae have a central vascular core; follicles are avascular centrally with vessels around them |
| Vernal keratoconjunctivitis | Atopic keratoconjunctivitis | Lid disease is mild in VKC; AKC affects older patients with eczematous lids and scarring |
| Rosacea | Acne vulgaris | No comedones in rosacea |
| Peripheral ulcerative keratitis | Mooren ulcer | PUK may spread into the sclera and is usually linked to systemic disease (RA, GPA) |
| Pellucid marginal degeneration | Keratoconus | Inferior band of thinning below the steepening; no Fleischer ring or Vogt striae; hydrops is rare |
| Tyrosinaemia type 2 (Richner–Hanhart) | Herpes simplex keratitis | Bilateral, pseudodendritic; normal sensation, no terminal bulbs, little staining, no response to antivirals |
| Pigment dispersion syndrome | POAG | Dense, homogeneous trabecular pigment in PDS; heavier inferiorly in POAG |
Retina, uvea and oncology
| Condition | In contrast to | Key difference |
|---|---|---|
| Non-ischaemic CRVO | Ischaemic CRVO | RAPD absent or mild; better vision; fewer haemorrhages and cotton wool spots |
| Sarcoid retinal vasculitis | Behçet vasculitis | Sarcoid: segmental periphlebitis, rarely occlusive, little vitritis. Behçet: arteries and veins, diffuse, often occlusive, marked vitritis |
| Posterior scleritis | Choroidal melanoma | Painful; T-sign on B-scan |
| Melanocytoma | Choroidal melanoma | Jet-black, usually on the disc, more common in darker-skinned people and women, nearly always stationary |
| Choroideremia | Primary retinal dystrophies (RP) | Fovea spared until late; female carriers show patchy pigment |
| Macular disease | Optic neuropathy | Positive scotoma (something in the way), metamorphopsia; optic nerve disease gives a negative scotoma, colour loss and RAPD |
Neuro-ophthalmology and strabismus
| Condition | In contrast to | Key difference |
|---|---|---|
| NAION | Optic neuritis | Colour loss is proportional to acuity loss in NAION; in optic neuritis colour is badly affected even when acuity is fair. NAION is painless, older patients, disc swollen with a crowded fellow disc |
| Constant early-onset exotropia | Infantile esotropia | Neurological problems are frequently present in early-onset exotropia |
| GPA-associated PUK | RA-associated PUK | In GPA, eye disease is the first presentation in about half of cases |
Related: Confusers in ophthalmology, Triads, Pathognomonic signs.
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Key sources
- Bowling B. Kanski's Clinical Ophthalmology, 9th ed. Elsevier; 2020
- American Academy of Ophthalmology. Basic and Clinical Science Course (current editions)
📘 Want the exam-ready deep dive? This topic, and much more is covered in Ophthalmology Explorer (A High-Yield Clinical Reference for Ophthalmology Residents, Fellows & Board Exams) — available on Kindle. See all my books.
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