Khashia Farooq
Fluorescein for Non-Ophthalmologists: A Practical Guide
Introduction
Fluorescein staining is a simple bedside technique that can reveal corneal epithelial defects that may otherwise be difficult to see. It can help identify conditions such as corneal abrasions, microbial keratitis and herpetic corneal disease, as well as detect aqueous leakage following penetrating injury.
The important skill is not simply recognising that the cornea stains, but interpreting the pattern of staining in the clinical context and identifying findings that require urgent ophthalmological assessment.
When is fluorescein useful?
Fluorescein should be considered when assessing patients with (1):
- ocular trauma or suspected corneal abrasion
- foreign body sensation
- a painful or photophobic red eye
- contact lens-associated eye pain or redness
- suspected corneal infection
- possible penetrating corneal injury
Visual acuity should be measured before the examination wherever possible. The cornea should first be inspected with white light for a foreign body, corneal opacity or infiltrate before fluorescein is applied.
How to perform fluorescein staining
Fluorescein is commonly available either as drops or impregnated paper strips (1).
If using a strip:
- Moisten the fluorescein strip with a small amount of sterile normal saline.
- Gently pull down the lower eyelid.
- Touch the strip to the lower conjunctival fornix rather than directly onto the cornea.
- Ask the patient to blink several times to distribute the dye across the ocular surface.
- Examine the cornea using a cobalt-blue light, ideally with a slit lamp where available.
Areas of epithelial loss take up fluorescein and appear bright green under blue illumination (1). A topical anaesthetic such as proxymetacaine may facilitate examination of a very painful eye. However, topical anaesthetic drops should not routinely be supplied for ongoing analgesia outside an appropriate clinical protocol as it can slow corneal healing (2).
What does fluorescein show?
Corneal abrasion
A corneal abrasion appears as a well-demarcated area of bright fluorescein staining representing loss of corneal epithelium (3). The pattern may provide a clue to the cause. Multiple vertical linear abrasions should raise suspicion of a foreign body beneath the upper eyelid (4). The upper lid should therefore be everted and the subtarsal surface examined where appropriate.
Most uncomplicated abrasions occur following minor trauma and present with acute pain, watering, photophobia and foreign body sensation. However, not every staining epithelial defect should automatically be labelled an abrasion. The surrounding cornea must also be examined.
Corneal ulcer and microbial keratitis
A corneal ulcer typically consists of an epithelial defect that stains with fluorescein overlying or adjacent to a white or grey corneal stromal infiltrate (5). This distinction is clinically important because microbial keratitis is potentially sight-threatening and may progress rapidly.
Patients commonly present with:
- pain
- redness
- photophobia
- reduced vision
- watering or discharge
- a visible corneal opacity or infiltrate.
Contact lens wear is an important risk factor. A painful red eye in a contact-lens wearer should not be assumed to represent a simple abrasion or conjunctivitis. UK guidance recommends same-day ophthalmological assessment where contact lens-associated keratitis is suspected (6).
Dendritic staining
Herpes simplex epithelial keratitis classically produces a branching dendritic epithelial ulcer with terminal bulbs (7). The base of the dendrite stains with fluorescein. Patients may present with unilateral redness, discomfort, photophobia and blurred vision (7). A suspected dendritic ulcer warrants ophthalmological assessment because antiviral treatment may be required (7). It is important to note that inappropriate topical corticosteroid treatment can worsen active epithelial infection.
The Seidel test
Fluorescein can also identify aqueous leakage from a full-thickness corneal injury (8). Apply concentrated fluorescein around the area of suspected injury and observe under cobalt-blue illumination. In a positive Seidel test, clear aqueous humour leaking through the wound dilutes the fluorescein, producing a stream or ‘waterfall’ through the surrounding fluorescent dye (4).
A positive Seidel test indicates a full-thickness corneal or scleral defect and therefore an open globe injury until proven otherwise (4). This is an ophthalmological emergency. A negative Seidel test also does not completely exclude an open globe, as small wounds may spontaneously seal or become plugged.
Table 1. Common fluorescein staining patterns and their associated diagnoses
| Fluorescein finding | Diagnosis |
| Localised bright-green epithelial defect after trauma | Corneal abrasion |
| Vertical linear staining | Subtarsal foreign body |
| Staining epithelial defect + white/grey infiltrate | Microbial keratitis/corneal ulcer |
| Branching lesion with terminal bulbs | HSV epithelial keratitis |
| Clear stream through fluorescein | Positive Seidel test/open globe |
Conclusion
Fluorescein staining is one of the most useful examination techniques available to the non-ophthalmologist assessing an acute eye problem.
A simple abrasion produces an epithelial defect. An epithelial defect with a corneal infiltrate should raise concern for microbial keratitis. A branching dendrite suggests herpetic keratitis, while aqueous streaming through fluorescein indicates a positive Seidel test and possible open globe injury. Recognising these patterns allows clinicians not only to identify common corneal abnormalities, but more importantly to recognise the patients in whom delay in ophthalmological assessment may threaten vision.
References
1. Srinivas SP, Rao SK. Ocular surface staining: current concepts and techniques. Indian J Ophthalmol. 2023;71(4):1080-9. doi:10.4103/ijo.IJO_2137_22
2. Lawrenson AL, Lawrenson JG. Cochrane corner: topical anaesthetics for pain control following corneal abrasions. Eye (Lond). 2024;38(4):646-7. doi:10.1038/s41433-023-02762-y
3. Domingo E, Moshirfar M, Zeppieri M, Zabbo CP. Corneal abrasion. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated 2024 Jan 8 [cited 2026 Oct 28]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532960/
4. National Institute for Health and Care Excellence. Corneal superficial injury: how should I assess a person with suspected superficial corneal injury? Clinical Knowledge Summaries [Internet]. London: NICE; 2024 [cited 2026 Oct 28]. Available from: https://cks.nice.org.uk/topics/corneal-superficial-injury/diagnosis/assessment/
5. Arbabi EM, Kelly RJ, Carrim ZI. Corneal ulcers in general practice. British Journal of General Practice. 2018;68(666):49-50. doi:10.3399/bjgp17x694385
6. Shahid SM, Ahmed SN, Khan Y. Eye problems in contact lens wearers. BMJ. 2019:l6337. doi:10.1136/bmj.l6337
7. Bagga B, Kate A, Joseph J, Dave VP. Herpes simplex infection of the eye: an introduction. Community Eye Health. 2020;33(108):68-70.
8. Zhou Y, DiSclafani M, Jeang L, Shah AA. Open Globe Injuries: review of evaluation, management, and surgical Pearls. Clin Ophthalmol. 2022;16:2545-59. doi:10.2147/opth.s372011