A 57-year-old woman with type 2 diabetes of 10 years reports wavy, blurred central vision in her right eye for two months. Vision is 6/18 right, 6/6 left. She wants to know whether laser or an injection is better.
Examination Findings
Right eye: a ring of hard exudates (circinate pattern) temporal to the fovea with visible leaking microaneurysms at its centre; the rest of the macula looks flat. Left eye: scattered microaneurysms only. No new vessels. Blood pressure is mildly elevated.
Investigations
OCT right macula: focal thickening temporal to the fovea with a cluster of hyperreflective microaneurysms and a small pocket of intraretinal fluid; central subfield thickness only mildly increased and the foveal centre is spared. Fluorescein angiography is not needed — the leaking points are clinically visible.
Questions to Think About
- How does OCT distinguish focal from diffuse DMO, and why does it change treatment?
- When is focal laser preferred, and when is anti-VEGF preferred?
Diagnosis
Focal (non-centre-involving) diabetic macular oedema, right eye.
Reasoning
Focal DMO shows thickening localised around identifiable leaking microaneurysms, often ringed by circinate exudates, while diffuse DMO shows widespread sponge-like thickening or cystoid change from generalised capillary leakage. OCT settles doubtful cases and detects centre involvement that the slit lamp can miss. Classical teaching: focal, non-centre-involving DMO is treated with focal laser to the leaking microaneurysms; centre-involving DMO is now usually treated first with anti-VEGF injections, which improve vision more reliably. Typical management here: focal laser to the leaking points, avoiding the foveal avascular zone, with OCT follow-up; counsel that laser stabilises more often than it sharpens vision, and that blood pressure and glycaemic control strongly influence the outcome. Diagnosis: focal diabetic macular oedema, non-centre-involving, right eye.
Differential Diagnosis
- Focal diabetic macular oedema — confirmed: circinate exudates around identifiable leaking microaneurysms with focal OCT thickening.
- Diffuse diabetic macular oedema — ruled out: no generalised sponge-like thickening or widespread cystoid changes on OCT.
- Centre-involving oedema needing injection — ruled out for now: the foveal centre is flat on OCT, so focal laser is the classical option; anti-VEGF is discussed if the centre becomes involved.
Management
Focal laser photocoagulation to the leaking microaneurysms, sparing the foveal centre; review with OCT in 2–3 months and re-treat leaking points if oedema persists. If the foveal centre becomes involved or vision drops, switch the plan to anti-VEGF injections. Optimise blood pressure, glycaemia and lipids with the diabetes team — systemic control is part of macular treatment. Warn about laser side effects near fixation (possible small paracentral scotoma).
Key Learning Points
- OCT is the arbiter in DMO: it separates focal leaks (treatable with focal laser) from diffuse swelling and, crucially, shows whether the foveal centre is involved.
- Treatment follows the centre: non-centre-involving focal DMO → focal laser; centre-involving DMO → anti-VEGF first in modern practice.
Red Flags
- Centre-involving oedema with vision loss — anti-VEGF pathway, not focal laser alone.
- Tractional thickening on OCT — vitreomacular traction needs surgical assessment, not laser.
- Macular ischaemia as the cause of poor vision — laser and injections will not restore ischaemic vision; angiography clarifies.
Educational content only — not medical advice. Clinical decisions must be made by a qualified professional for the individual patient.