Ophthalmoscopy Technique
On this page
Direct answer
The red reflex comes first, from about a metre out: approach through it and the direct ophthalmoscope delivers an erect, virtual, 15-times magnified monocular view of disc and posterior pole — perfect for detail, hopeless for extent. Indirect ophthalmoscopy is its mirror image: a +20 D condensing lens before a dilated pupil produces a real, inverted image at roughly 3× (the eye's 60 D divided by the lens's 20 D), with stereopsis, a field near 37 degrees and far-periphery access by scleral depression. Dilate when the view demands it (tropicamide with or without phenylephrine), but never before judging the anterior chamber — and examine the fundus as a sequence: red reflex, vessels, disc, macula, periphery.
What you must remember
- Direct ophthalmoscopy: erect, virtual, about 15× magnification, monocular, roughly 10-degree field (about two disc diameters) — the tool of disc detail and macular pathology.
- Indirect: real, inverted, about 3× with +20 D (magnification = eye power ÷ condensing lens power), stereoscopic, 37-degree field, brighter through media opacities; +28/+30 D trades magnification for wider field.
- Dilation: tropicamide 0.5–1 per cent (about 20 minutes onset, 4–6 hours), phenylephrine 2.5 per cent added when needed; warn drivers about glare.
- Never dilate without assessing peripheral anterior chamber depth (Van Herick) in eyes at risk of angle closure — an attack precipitated by dilation is the classic iatrogenic emergency.
- Direct technique: start at a metre on the red reflex (an opacity shows as a dark shadow whose movement with gaze localises it fore or aft), close to about 2 cm, patient fixing a distant target.
- Find the disc by following a vessel nasally — about 15 degrees nasal to the fovea; arteries narrower than veins (about 2:3) with a bright reflex.
- Disc assessment: vertical cup-to-disc ratio, the ISNT rule (Inferior rim thickest, then Superior, Nasal, Temporal), pallor, haemorrhages, peripapillary atrophy.
- Macula: two disc diameters temporal and slightly below the disc; the patient looks directly at the light to bring it into view.
- Indirect technique: headset binoculars with the condensing lens, patient's gaze to eight positions, scleral depression for the periphery.
A diabetic fundus exam, walked through
The task: grade diabetic retinopathy in a 54-year-old. Dilation follows a Van Herick check showing a safe angle. The direct scope starts at one metre — the red reflex is uniform, so no significant media opacity. Closing in on the right eye, sweep systematically: superior arcades, temporal macula, inferior arcades, nasal field, back to the disc — microaneurysms as tiny red dots, dot-and-blot haemorrhages darker, hard exudates as yellow circinate rings.
The macula is examined last with the patient staring at the light: foveal reflex intact, no exudates within a disc diameter — no clinically significant macular oedema on this view, though OCT has the final word. The disc is judged for new vessels — a red-flag escalation. Indirect ophthalmoscopy then completes what direct cannot: peripheral sweeps in all eight gazes reveal a patch of pre-retinal haemorrhage — new vessels somewhere. The drawing afterwards uses standard conventions so the surgeon reads a map, not a memory. Direct for character, indirect for extent — the two are complements.
Where students slip
The comparison is the exam, and the swaps are predictable: direct gives about 15× with a small field; indirect gives less magnification with a wide stereoscopic field — candidates who write "indirect magnifies more because the machine is bigger" have learned only the machine's price. On the direct scope, the beginner's classic is searching temporal for the disc — follow a large vessel nasally and the disc arrives. ISNT gets quoted without order; "which rim is thickest?" wants "inferior", and its violation by notching is a glaucoma sign. Finally the safety question: dilating an unchecked elderly hyperope risks acute angle closure — Van Herick first, dilation second, with the patient warned.
Frequently asked questions
Compare the images of direct and indirect ophthalmoscopy.
Direct: erect, virtual, about 15×, monocular, roughly 10-degree field. Indirect: inverted, real, about 3× with a +20 D lens, stereoscopic, field near 37 degrees with peripheral access.
Why is the indirect image inverted?
The convex condensing lens forms a real, inverted aerial image of the illuminated retina between lens and observer; the headset restores binocular viewing, not orientation.
Which condensing lens is routine for indirect ophthalmoscopy?
The +20 D lens, balancing about 3× magnification with a wide field and workable distance; +28 or +30 D widens the field at lower magnification.
What is scleral depression and when is it used?
Gentle indentation of the peripheral sclera through the lids to bring the extreme periphery, including the ora serrata, into view — essential in detachment and peripheral lesion searches.
What is the ISNT rule?
In the normal disc the neuroretinal rim is thickest Inferiorly, then Superior, then Nasal, then Temporal; thinning or notching that violates the order suggests glaucomatous damage.
What precautions precede pharmacological dilation?
Assess peripheral anterior chamber depth (Van Herick) in at-risk eyes — shallow chambers may precipitate acute angle closure — and warn drivers.