18.3 Slit Lamp & Anterior Segment Photography
Key Takeaways
- Anterior segment photography uses the slit lamp's own illumination techniques, so the imaging decisions are the same as the examination decisions.
- A diffuse wide beam documents overall appearance; a narrow optical section documents lesion depth.
- Retroillumination against the red reflex is the technique for photographing transparent findings.
- A scale reference or a measured slit beam width allows lesion size to be documented objectively.
- Cobalt blue illumination with fluorescein documents epithelial defects, and a yellow barrier filter markedly improves contrast.
Photography follows examination technique
Anterior segment photography is simply slit lamp examination with the image recorded. The illumination technique that best shows a finding to the eye is the technique that best photographs it.
| Finding | Illumination | Typical magnification |
|---|---|---|
| Overall lid, conjunctiva, red eye | Diffuse, wide beam, diffuser in | Low (6–10×) |
| Corneal lesion depth | Optical section, 0.5–1 mm beam at 45–60° | Medium to high (16–25×) |
| Corneal lesion in three dimensions | Parallelepiped, 2–3 mm beam | Medium |
| Iris transillumination, lens vacuoles, posterior capsule opacity, keratic precipitates | Retroillumination off the iris or the red reflex | Medium |
| Endothelial guttata | Specular reflection | High |
| Faint corneal haze or oedema | Sclerotic scatter | Low to medium |
| Epithelial defect, dendrite, Seidel test | Cobalt blue with fluorescein, plus a yellow barrier filter | Medium |
| Conjunctival staining | White or red-free with lissamine green | Low to medium |
| Angle structures | Gonioscopy lens with a narrow beam | Medium |
The single most valuable technical addition to fluorescein photography is a yellow (Wratten #12 or similar) barrier filter over the observation path. It blocks the reflected blue excitation light and passes only the emitted green fluorescence, transforming a washed-out blue image into a high-contrast one.
Exposure and settings
Flash and illumination. Anterior segment structures are far more reflective than the retina, so flash levels are much lower than for fundus photography. Start low and increase. A dark iris needs more light than a blue iris; a white sclera or a bright corneal reflex can blow out the highlights.
Depth of field is shallow at high magnification, so focus precisely on the plane of interest rather than on the general eye. When the lesion spans depth — an infiltrate extending into stroma — capture several images focused at different planes.
The corneal light reflex is a persistent nuisance: a specular highlight sits wherever the illumination reflects straight back. Move the illumination arm off-axis so the reflex falls outside the area of interest, or accept it at the edge of the frame rather than over the lesion.
Beam angle. A larger angle between illumination and observation arms gives more modelling and depth information; a smaller angle gives flatter, more evenly lit images. For documentation of a surface lesion, 30 to 45 degrees is usually a good compromise.
Documenting size and depth
A photograph without scale cannot support a judgement about progression.
Methods to record size:
- Measure the slit beam height using the slit lamp's calibrated control, then photograph with the beam adjacent to the lesion. The beam becomes the ruler.
- Record the magnification setting and the working distance so the image can be calibrated.
- Photograph a reticule or measuring graticule in the same session.
- Include a recognisable anatomical reference — the limbus, the pupil margin — in the frame.
Documenting depth requires an optical section: the narrow beam cuts a visible cross-section of the cornea, and the lesion's position within that section places it in the epithelium, anterior stroma, deep stroma or endothelium. This is the single most useful image in the assessment of an infiltrate or a scar.
Protocols for common findings
Corneal ulcer or infiltrate. Capture (1) a diffuse low-magnification overview with the lids showing, (2) a parallelepiped of the lesion at medium magnification, (3) an optical section through the lesion to document depth, (4) a cobalt blue with fluorescein image to show the epithelial defect, and (5) an image showing any hypopyon with the beam across the anterior chamber. Record the measured lesion dimensions alongside.
Pterygium. Diffuse illumination with the eye in primary gaze and again in the gaze that best exposes the lesion; document the extent of corneal encroachment in millimetres from the limbus, which is the number that drives the surgical decision.
Cataract. Retroillumination against the red reflex documents cortical spokes and posterior subcapsular plaques; an optical section documents nuclear colour and density. Dilate first.
Posterior capsule opacification. Retroillumination through a dilated pupil, before and after YAG capsulotomy.
Lid lesions. External photography with a scale, in primary gaze, plus a close view. Document dimensions and the relationship to the lid margin and puncta.
Anterior chamber angle. Through a gonioscopy lens, with a narrow beam, documenting the visible structures and the degree of pigmentation.
Iris lesions. Diffuse for colour and surface, retroillumination to show transillumination, and an optical section or oblique beam to show elevation.
Pre- and post-operative documentation. Match the field, magnification, illumination technique and gaze position to the pre-operative image, or the comparison is worthless.
Infection control at the photographic slit lamp
The photographic slit lamp is a shared, high-touch device.
- Disinfect the chin rest and forehead bar between patients.
- Use fresh chin rest tissue for each patient.
- Clean the joystick and controls at the intervals your protocol specifies.
- Never touch the objective or the eyepiece optics with anything but approved lens tissue and solution; fingerprints there appear on every subsequent image.
- For a patient with suspected adenoviral conjunctivitis, use disposable coverings where available, clean thoroughly afterwards, and consider deferring non-urgent photography.
Recording and labelling
Every image needs: patient identifiers, date and time, laterality, the illumination technique used, the magnification, and any filter or dye applied. A fluorescein image without a note that fluorescein was instilled can be misread as spontaneous staining; a retroillumination image without a technique note can be misread as an opacity rather than a transillumination defect.
Consent. External and anterior segment images frequently include recognisable facial features. Confirm the patient understands what will be captured, and obtain explicit additional consent for any use beyond the clinical record — teaching, publication or marketing. Record that consent in the chart.
Which illumination technique best documents the depth of a corneal infiltrate?
Adding a yellow barrier filter to cobalt blue fluorescein photography achieves what?
How can lesion size be objectively documented at the slit lamp?
Which technique is used to photograph posterior capsule opacification?
Why must the illumination technique and magnification be recorded with each anterior segment image?