Slit Lamp Examination Viva: Every Question Examiners Actually Ask

The reliable slit-lamp viva answer has three parts: name the illumination method, say what plane or interface it shows, then describe the finding before diagnosing it. A slit lamp combines binocular magnified observation with a controllable beam; the value is not the instrument name but the way you alter beam width, angle, height, magnification and filters to make a sign visible.¹

Exam-education boundary: this is a practical-viva framework for ophthalmology PGs. It is not a substitute for supervised examination, diagnosis, local infection-control procedures or patient-specific management.

Start the station without making the patient a prop

Examiners notice handling before they begin asking optics. Introduce yourself, confirm the patient and side where the station requires it, explain that you will examine the front of the eye with a bright light and microscope, and ask the patient to sit comfortably with forehead and chin supported. Set your own chair height first. Then adjust the patient so both can maintain position without strain.

Before looking through the oculars, set a low magnification, a broad beam and comfortable illumination. Align the interpupillary distance and focus the eyepieces for your refractive correction. If the model has an eyepiece dioptre scale, neutralise and focus it according to the instrument’s operating method rather than guessing at the setting. Ask the patient to look where needed, and warn before increasing brightness.

The opening spoken answer can be short:

“I will begin with low magnification and diffuse illumination for an external survey, then examine both eyes systematically from lids and conjunctiva through cornea, anterior chamber, iris, pupil and lens. I will narrow and angle the beam to localise any abnormality by depth, comparing sides before I interpret a sign.”

That answer gives the examiner a sequence and a safety boundary. It does not pretend that every station requires every manoeuvre.

The examination sequence that prevents wandering

A repeatable sequence is more useful than a long list of techniques. Start broad; then make the beam narrow only when a structure or sign needs depth localisation.

For any abnormality, use a record-like description: site, size, shape, depth, colour, margins, surface, staining, surrounding reaction and associated finding. In an examiner’s hands, “a corneal ulcer” becomes the question, “What did you see that lets you call it that?” A precise description earns marks even if your differential remains provisional.

The illumination techniques: technique, plane, sign

The most common failed viva answer is a technique named without an anatomical purpose. Learn each method as a relationship between the observation axis and the illumination axis.

These methods are not separate rituals. You may find a superficial opacity with diffuse illumination, use an optical section to judge depth, then use retroillumination to reveal its edges. State that progression. It sounds like an examination rather than a recital.

“Show me an optical section”

For an optical section, reduce the beam to a narrow slit and direct it obliquely through the cornea. Focus on the structure, not the patient’s eyelashes. Move illumination and microscope together as required to keep the slit in focus. You should be able to explain what the two bright corneal boundaries represent and where a lesion lies between them. Do not make up a numerical corneal depth in a practical station unless the station provides a measurement method.

The same narrow-beam principle helps you show relative peripheral anterior-chamber depth. The Van Herick method compares the apparent dark peripheral chamber gap with adjacent corneal optical-section thickness at the limbus. It is a screening estimate, not gonioscopy and not a final statement about angle anatomy.¹

The examiner may ask, “What will you do with a narrow peripheral estimate?” The defensible answer is: “I would document the finding and use gonioscopy when angle assessment is required, according to the clinical context and supervision available.” Do not convert a screening observation into a glaucoma diagnosis or a treatment instruction.

Cells and flare: describe what you see, then name the standard

Cells are discrete particles seen traversing a focused beam in the anterior chamber; flare is the beam’s visible scatter from protein in aqueous. In a viva, set the conditions first: a darkened room, a small intense beam, appropriate magnification and focus within the chamber. Then report whether you see cells, flare, fibrin, hypopyon or other supplied findings.

The Standardization of Uveitis Nomenclature (SUN) Working Group published terminology and grading conventions for anterior-chamber cells and flare.² That does not mean every case in an OSCE should receive a grade from memory. Say, “I would grade anterior-chamber cells and flare using SUN if the examiner requires a grade,” then describe the finding you can justify. A number without a method is weak; a careful observation plus the correct standard is stronger.

This is a viva, so be precise without over-diagnosing. Clinical management follows from the complete patient assessment, not from a rehearsed station phrase.

Filters, fluorescein and the question behind the question

Why cobalt blue? It excites fluorescein and makes fluorescein staining easier to see. A yellow barrier filter, when available, improves contrast. State what you observe: punctate staining, a linear defect, pooling, tear-film break-up pattern or no staining. Do not say fluorescein “diagnoses” an ulcer.

Why a red-free filter? It increases contrast for structures that absorb or transmit light differently from the surrounding red background. In a station, first identify the sign that becomes clearer; do not claim that the filter alone establishes a disease label.

Why use high magnification? Higher magnification characterises a local finding after you have located it. Low magnification is often better for orientation, extent and patient cooperation. “Maximum magnification for every step” is not a technique.

Why use retroillumination? To view a lesion against reflected light, commonly from the iris or fundus depending on the structure examined. It is particularly useful when contrast reveals a subtle opacity better than direct illumination.¹

The examiner follow-ups that separate method from memorisation

The last answer is worth practising. A station may show a corneal lesion, a shallow peripheral chamber, pigment, pseudoexfoliative material or an implanted lens. The examiner is not asking for a race to the diagnosis. They are testing whether you can make the finding visible, localise it, and state the limits of your inference.

A 90-second rehearsal script

Use this after looking at any slit-lamp photograph or patient under supervision:

1. “I have positioned the patient and adjusted the instrument. I will compare both eyes.”
2. “On diffuse illumination, the lids/conjunctiva/cornea show …”
3. “On direct focal illumination and optical section, the lesion is located at … and measures/extends …”
4. “The anterior chamber shows … under the stated examination conditions.”
5. “The iris, pupil and lens show …”
6. “I used [technique] because it demonstrates [interface/plane/sign].”
7. “My provisional interpretation is …; I would clarify it with … and document the finding before management discussion.”

If you cannot complete line 6, you have named a technique but not learned it. Repeat with a different beam setting, not by rereading the same paragraph.

For practical-viva structure, see the OSCE, Practical & Viva Voce Ready bundle. The Instruments in Ophthalmology notes are the matching on-site instrument-revision route, while the Ophthalmology Case Presentation Format is useful for turning observations into an orderly presentation. These are revision resources, not a substitute for supervised clinical examination. OphthaMCQ is independent and is not affiliated with examining colleges or societies.

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