Fundus Examination
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Direct answer
Fifteen times magnification, upright, monocular — the direct ophthalmoscope trades field for detail, showing about a 10-degree upright virtual image of the disc and macula through an undilated or dilated pupil, ideal for neurological screening and disc assessment. The indirect ophthalmoscope inverts the bargain: a +20 dioptre lens held at arm's length forms a real, inverted image magnified three to five times but spanning 37 degrees (eight times the area), stereoscopic, viewable through media haze, and — with scleral indentation — reaching the ora serrata, which is why it is the instrument of retinal detachment surgery and of every paediatric screening under anaesthesia. Between them sits slit-lamp biomicroscopy with +78 or +90 dioptre lenses, the working ophthalmologist's routine. Mydriasis with tropicamide alone or with phenylephrine 2.5 per cent opens the view in 20 to 30 minutes, with the one caution of provoking angle closure in a shallow anterior chamber — assess the angle or history before dilating.
What you must remember
- Direct ophthalmoscopy: monocular, about 15 times magnification, upright virtual image, 10-degree field; strong on disc, vessels and macular detail, weak on the periphery and through hazy media.
- Indirect ophthalmoscopy: binocular stereopsis, inverted real image, about 3 to 5 times magnification with a +20 dioptre lens, wide 37-degree field; scleral indentation visualises the peripheral retina to the ora serrata; the standard for retinal detachment surgery, ROP screening and examination under anaesthesia.
- Slit-lamp biomicroscopy with +78D/+90D lenses: the everyday view — stereoscopic, magnified, adjustable slit beam; the +90D gives a wider field in a small pupil, the +78D more magnification.
- Dilatation protocol: tropicamide 0.5 to 1 per cent, with phenylephrine 2.5 per cent added for stronger mydriasis; effect in 20 to 30 minutes; caution in shallow anterior chambers, occludable angles (check by van Herick or history) and in patients on systemic sympathomimetics.
- Examination routine to recite: red reflex first (media), then optic disc (colour, cup-to-disc ratio, margins, vessels), vascular arcades (calibre, crossings, haemorrhages), macula and foveal reflex (patient fixates the light), then the four peripheral quadrants.
- Fluorescein angiography essentials: 5 mL of 10 per cent sodium fluorescein intravenously; phases — arm-to-choroid (pre-arterial) at about 10 to 12 seconds, arterial, arteriovenous, venous, late recirculation; interpretation by hypofluorescence (blocked fluorescence or filling defect) versus hyperfluorescence (window defect, leakage, pooling, staining).
- Angiography cautions: transient nausea and yellow urine are common, anaphylaxis rare but resuscitation ready; indocyanine green serves the choroidal circulation when fluorescein is limited.
- Photography and screening: fundus photography powers diabetic retinopathy screening and tele-ophthalmology — the model Indian programmes use to reach rural populations.
Choosing the instrument for the question
Let the clinical question choose the instrument. A neurologist's headache patient needs the disc: direct ophthalmoscopy answers in a minute — cup-to-disc ratio and margins are the deliverable. A diabetic needs grading: slit-lamp biomicroscopy with a +78D lens covers the posterior pole, but suspected peripheral neovascularisation switches to indirect ophthalmoscopy with indentation — the periphery hides the answer. A detachment case in theatre needs a retinal map with breaks drawn: indirect ophthalmoscopy, patient supine, with indentation — breaks live at the periphery. A premature baby needs zone and stage: indirect ophthalmoscopy with a 28-dioptre lens, under sedation, documented by drawing. And whenever an undilated view frustrates the question, dilate — after confirming the angle is safe — provided a driver is arranged for the blurred near vision after.
Where the exam frames it
The instrument-comparison stem is the most reliable: image upright or inverted, magnification numbers (15 times direct, 3 to 5 times indirect with +20D), field (10 versus 37 degrees), stereopsis present or absent, and which instrument sees the periphery. The second favourite is dilatation safety — the shallow anterior chamber, the mechanism of provoking acute angle closure, and the van Herick screen as the pre-dilatation check. Third, fluorescein angiography is tested on phases and the hyper- versus hypofluorescence logic, with timings as tie-breakers. A viva favourite asks why indirect ophthalmoscopy rules in hazy media: brighter coaxial illumination scattered less by opacity — plus children examined properly only under anaesthesia.
Frequently asked questions
What are the key differences between direct and indirect ophthalmoscopy?
Direct gives an upright, virtual, monocular image at about 15 times magnification over a 10-degree field; indirect gives an inverted, real, stereoscopic image at 3 to 5 times magnification over a 37-degree field, extendable to the far periphery with scleral indentation.
Which patients need caution before dilatation?
Shallow anterior chambers or occludable angles — angle closure can be provoked; assess by van Herick technique or history before instilling mydriatics.
What are the phases of fluorescein angiography?
Pre-arterial (choroidal) at about 10 to 12 seconds after injection, then arterial, arteriovenous, venous and late recirculation phases, each read for hypo- and hyperfluorescent patterns.
Why is indirect ophthalmoscopy the standard for retinal detachment surgery?
Stereopsis, a wide field, performance through hazy media, and scleral indentation to inspect the peripheral retina where breaks originate — the operative retinal map depends on it.
How is the macula best examined at the slit lamp?
With a +78D or +90D non-contact lens through a dilated pupil, patient fixating on the light, using the slit beam for stereoscopic detail of the foveal reflex and any exudate or fluid.