Fluorescein staining and slit-lamp principles

The slit lamp combines a binocular microscope with an adjustable light source. A broad beam gives an overview, while a narrow beam aimed obliquely creates an optical section through transparent structures. Changing the width, angle and focus helps distinguish an epithelial defect from a stromal infiltrate, assess chamber depth and identify inflammatory material. These are practical skills requiring supervised experience. Magnification does not compensate for incomplete inspection, poor positioning or an examiner who cannot recognise the relevant abnormality.

Start by asking what happened and when. Record contact lens wear, overnight wear or water exposure, previous ocular surgery, recurrent symptoms and current drops, including steroids. Unless urgent irrigation takes precedence, assess each eye's vision before diagnostic drops blur the result. Inspect lids, conjunctiva, corneal clarity, pupil shape and gross chamber appearance using white light. Painful blepharospasm may make examination difficult; a supervised topical anaesthetic can help an appropriate surface examination, but relief of pain does not prove that the condition is harmless.

Adjust the chair, chin rest and forehead support so that the patient is comfortable and the lateral canthus aligns with the instrument marker. Explain that they should keep their forehead against the support and look where directed. Set the eyepieces for your vision and begin with modest magnification and broad illumination, increasing detail as required. Move the beam methodically across the cornea, then inspect relevant deeper structures with suitable illumination. Avoid prolonged bright exposure and stop if the patient becomes distressed or unstable. A handheld examination may be more practical in some patients, with its limitations stated.

Fluorescein is a diagnostic dye that highlights disruption of the corneal epithelial barrier under blue light. Use an uncontaminated single-use preparation, apply only enough to obtain useful staining and allow blinking to distribute it. Excess dye can obscure a small defect or mimic pooling, so remove excess with sterile saline where appropriate. Look across the whole cornea and describe whether staining is focal, linear, punctate or branching. Record its relationship to the visual axis and any underlying white opacity. A sketch with approximate dimensions is often more useful than simply recording that staining is positive.

The pattern guides further assessment rather than supplying a complete diagnosis. A traumatic abrasion can produce a local epithelial defect; repeated vertical marks may suggest material beneath the upper lid. Eversion can be useful when superficial foreign material is suspected, but must not be attempted when an open-globe injury is possible. A branching lesion raises concern for herpetic epithelial disease, while punctate staining has several causes, including tear-film disturbance, ultraviolet exposure and toxicity. Neither a small defect nor an improvement after anaesthetic excludes microbial keratitis. White stromal infiltration, contact lens use and disproportionate symptoms increase concern.

At the slit lamp, inspect for anterior chamber inflammatory cells, flare, layered white material or blood. A narrow beam and correct focus are needed to assess cells and flare; an inexperienced negative examination should not overrule a strongly suggestive history. A hypopyon may accompany severe corneal infection, intraocular infection or inflammation and needs urgent ophthalmic interpretation. After recent surgery or an intraocular injection, pain and worsening vision should trigger emergency contact even if the outside of the eye is not dramatically red.

A Seidel assessment looks for dilution of fluorescein by leaking aqueous fluid when a wound is subtle and assessment is appropriate. It does not involve pressing on the eye to provoke a leak. An obvious open globe needs protection and referral without further manipulation. A negative result can occur when a small wound has sealed or is plugged, so it cannot rule out penetration after a high-risk mechanism. Do not proceed to tonometry, forceful lid retraction or foreign-body removal simply because dye has not visibly streamed from the suspected wound.

Chemical exposure changes the order of care. Begin copious irrigation immediately with available clean water or suitable irrigation fluid and continue while obtaining urgent help. Remove a contact lens if readily possible without delaying irrigation. In a clinical setting, check ocular surface pH without interrupting initial treatment, assess again after irrigation and allow about five minutes before a repeat check to detect rebound from retained chemical. Irrigate further if pH is not near physiological and inspect the fornices for retained particulate material when safe and competent to do so. Severe pain is not required for a serious burn.

Conclude the examination with a decision about the cornea's safety and an explicit plan. Suspected microbial keratitis needs same-day specialist assessment, with contact lens wear stopped and the lens and case retained for the service if advised. Avoid starting an ocular steroid for an undiagnosed painful red eye. Topical anaesthetic used for examination should not become unsupervised ongoing symptom treatment. Explain how to seek urgent help for worsening pain, photophobia or reduced vision, and arrange reassessment when the diagnosis, healing or completeness of the examination remains uncertain.