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Contact lenses can lead to disruption of the corneal and conjunctival epithelium. Fluorescein sodium (Fl) highlights compromised cells. Lissamine green (LG) mainly highlights areas of conjunctival compromise. Both are available as impregnated paper strips. Wet with a couple of drops of normal saline to produce a solution for use. Fl is available as a low molecular weight (LMW) version and a high molecular weight (HMW) version which does not penetrate hydrogel lenses. HMW Fl does not stain or fluoresce as well as LMW Fl so is less effective. Both LMW Fl and LG discolour soft contact lenses, so remove them prior to instilling the dye! Solution-induced staining will be dealt with separately.
How do I see it?
Wet the paper strip, wait for a few seconds allowing dye to dissolve. Shake excess LMW Fl off the strip, better results are obtained by using the full 'dose' of LG. Briefly and gently TOUCH the paper strip against the bulbar conjunctiva - DO NOT 'SMEAR' the strip across the conjunctival as this will damage the surface cells leading to staining. Ask the patient to blink gently a couple of times and take note of how readily the fluorescein spreads (in a tear-deficient eye Fl will mix more slowly).
To observe Fl, use the slit lamp with diffuse or broad beam with blue filter to excite fluorescence and low to medium (6-16X) magnification. A yellow barrier filter in the observation pathway cuts out blue light enhancing fluorescence of the damaged cells - particularly on conjunctiva. Adjust the illumination brightness. Identify any staining, narrow the beam to a parallelopiped and then optic section to examine depth of Fl uptake. Subtle staining is more obvious once the tear film has broken up.
LG takes a couple of minutes to penetrate damaged cells and will fade within five minutes. View with relatively low intensity diffuse white light, with low to medium magnification. A red filter in the observation system helps highlight stain. LG reveals areas of damage caused by mechanical trauma eg lid wiper epitheliopathy, lens edges and desiccation. LG corneal staining is unusual in contact lens wearers unless there is significant desiccation or chemical damage.
Examine the bulbar and palpebral conjunctiva and cornea.
Symptoms
? Often asymptomatic - use Fl and LG routinely
? Poor CL comfort, dryness, tired eyes, stinging on insertion (suggests solution sensitivity)
? May be associated with redness.
Signs
Pattern of uptake
? Punctate - small, individual dots
? Coalescing - larger, more irregular spots
? Confluent - patches of uptake
? Foreign body - lines of stain tracing path of FB as it washes across surface of cornea.
Depth of stain
? Damaged superficial layers take up Fl immediately on instillation
? If some tight junctions of epithelium are compromised, Fl will take more time to penetrate and dots of stain are less defined and may eventually allow Fl to reach the stroma
? If deeper tight junctions are compromised the Fl penetrates into the stroma very quickly - a parallelopiped shows Fl diffusing through stroma.
Extent and location of stain
? Divide the cornea into five zones: central (approx 6mm diameter), superior, nasal, inferior and temporal
? Conjunctival: superior, nasal, inferior, temporal, or palpebral
? Diffuse - over several zones
? Localised - limited to one zone.
Causes
Mechanical
? Tight or loose lens or a damaged lens. Stains cornea with Fl (punctate/coalescing) and conjunctiva (Fl and LG) limited to areas covered by lens either in primary position or on eye movements
? Superior epithelial arcuate lesion (SEAL) - line of stain between 10 and 2 o'clock position parallel to limbus typically 2mm onto cornea - cause - higher modulus material, back surface design not matching corneal topography
?e_STnSLid wiper epitheliopathy (LWE) - see two-minute guide to LWE.
Desiccation
? Worse as day progresses, drying environments, after driving or prolonged close work
? Soft lenses - inferior 'smile' of punctate/coalescing stain. Cause - poor quality tear film, poor blink pattern. Sleeping with eyes partly open (worse in the mornings)
? RGPs 3 and 9 stain, conjunctival and corneal. Cause - partial blink, poor lens wetting, poor edge finish, lens design (edge lift, overall size, thickness)
? Conjunctival LG stain on exposed conjunctiva.
Management
? Mechanical - reduce modulus, optimise lens movement, use design with well rounded edge
? Desiccation - improve tear quality, treat MGD, lubricating/rewetting drops, improve lens cleanliness, use moisture retaining material, blinking exercises.
Prognosis
? Staining resolves once cause identified and managed. If poor tear film or blink pattern desiccation staining may persist. If at low levels then CL wear can continue.
Differential diagnosis
Solution staining, keratitis, dry eye, epithelial basement membrane (map dot) dystrophy.
? Optometrist Andrew Elder Smith runs Contact Solutions Consultants which offers in-practice training to team members from optometrists to front of house. Training is tailored, and covers clinical and non-clinical aspects of patient and customer care