How do you differentiate a sterile infiltrate from a microbial keratitis ulcer?

Sterile infiltrates are small (less than 1 mm), peripheral (near the limbus), multiple, and usually not accompanied by severe pain or an overlying epithelial defect staining with fluorescein. Microbial keratitis presents with a denser, usually larger, central or paracentral infiltrate with an overlying epithelial defect, significant pain, and purulent discharge. In practice, the distinction can be difficult, and any significant corneal infiltrate in a contact lens wearer should be treated as presumed microbial keratitis with topical antibiotics until cultures prove otherwise.

What is the most common organism causing contact lens-related microbial keratitis?

Pseudomonas aeruginosa is the most common causative organism in contact lens-associated bacterial keratitis and is particularly virulent. It produces proteolytic enzymes that rapidly liquefy corneal stroma and can progress to corneal perforation within 24 to 48 hours without treatment. Staphylococcus aureus (including MRSA) is the second most common. Treatment requires intensive topical fluoroquinolone antibiotics (ciprofloxacin or moxifloxacin) applied every 30 to 60 minutes initially, with gradual tapering as the infection responds.

What causes corneal neovascularization in contact lens wearers and how is it managed?

Corneal neovascularization occurs when chronic hypoxia stimulates VEGF and other angiogenic factors, causing limbal blood vessels to grow into the normally avascular cornea. Causes include low-Dk lens materials, extended wear, and tight-fitting lenses that reduce tear exchange. Any neovascularization extending more than 1 to 2 mm beyond the limbus requires refitting with higher-Dk silicone hydrogel lenses, reducing wearing time, or discontinuing contact lens wear. Ghost vessels (empty vascular channels that remain after hypoxia is corrected) may persist even after improving oxygen delivery.

What is giant papillary conjunctivitis and how is it recognized?

GPC (also called CLPC) is an immune-mediated inflammatory condition of the upper tarsal conjunctiva caused by chronic mechanical irritation from lens deposits, lens edge, or lens material. Examining the upper tarsal plate by everting the upper eyelid reveals large, cobblestone-like papillae (greater than 0.3 mm in diameter) that give the upper conjunctiva a velvety or cobblestone appearance. Symptoms include itching on lens insertion and removal, mucous discharge, and progressive lens intolerance. Switching to daily disposables minimizes deposit accumulation and is highly effective for many patients.

Why are daily disposable lenses often recommended for patients prone to complications?

Daily disposable lenses are replaced every day with a fresh pair, eliminating the deposit accumulation that causes GPC and increases infection risk, eliminating the need for lens care solutions (reducing MPS sensitivity), providing the freshest, most sterile lens at each wear, and removing the risk of case contamination. While they cost more per lens, the elimination of solution costs partially offsets this. They are particularly recommended for patients with a history of GPC, MPS sensitivity, frequent eye infections, or allergy-prone patients.

Contact Lens Complications for the CPO Exam

Contact lens complications range from minor discomfort to sight-threatening infections. Recognizing these complications early and knowing when to escalate to the physician is one of the most critical skills for a CPO working in a contact lens practice.

Microbial Keratitis

Microbial keratitis is a bacterial (or occasionally fungal or Acanthamoeba) infection of the corneal stroma. It is the most serious contact lens complication and can cause permanent corneal scarring and vision loss. Risk factors include:

Sleeping in lenses
Poor lens hygiene
Swimming in contact lenses
Extended wear modalities
Damaged or contaminated lens cases

Clinical features include severe pain, redness, photophobia, and a white or gray corneal infiltrate (opacification). The most common pathogens are Pseudomonas aeruginosa (particularly aggressive) and Staphylococcus aureus.

Any contact lens wearer with a painful red eye must be evaluated that day, not scheduled for a routine appointment. Microbial keratitis can progress from a small infiltrate to corneal perforation within days without treatment. Never advise a patient to continue wearing lenses through a red, painful eye.

Corneal Hypoxia and Neovascularization

The cornea depends on atmospheric oxygen for its metabolic needs. Contact lenses act as a partial barrier to this oxygen supply. Corneal hypoxia (oxygen deprivation) causes:

Corneal edema (microcysts, striae visible on slit lamp)
Increased susceptibility to infection
Limbal hyperemia (redness at the corneal periphery)
Corneal neovascularization: New blood vessels grow from the limbus into the normally avascular cornea to try to supply more oxygen. Any neovascularization extending more than 1 to 2 mm into the cornea requires lens discontinuation or refitting with higher-Dk lenses.

Switching patients to silicone hydrogel lenses with high Dk/t values significantly reduces hypoxia-related complications.

Giant Papillary Conjunctivitis (GPC)

Giant papillary conjunctivitis (GPC), now also called contact lens-associated papillary conjunctivitis (CLPC), is an immune-mediated reaction to lens deposits or the lens material itself. Large papillae (bumps) develop on the upper tarsal conjunctiva (under the upper lid), causing:

Itching, particularly when inserting or removing lenses
Mucous discharge
Lens awareness and reduced wearing time
Lens movement on the eye (papillae grip the lens and cause it to shift upward)

Treatment includes lens cleaning with enzymatic cleaners, switching to daily disposables (fewer deposits), using a different lens material, or temporarily discontinuing lens wear while using mast cell stabilizer drops.

Contact Lens-Associated Red Eye (CLARE)

CLARE is an acute inflammatory reaction occurring in patients sleeping in extended-wear lenses. It presents with sudden waking from sleep with a painful, red eye. Unlike microbial keratitis, CLARE is typically sterile (inflammatory, not infectious) and resolves within 24 hours after lens removal. The cause is bacterial endotoxins trapped under the lens during sleep. Despite the dramatic symptoms, vision is usually preserved and the cornea has no dense infiltrate. Management is lens discontinuation and lubricating drops; topical antibiotics are sometimes added empirically.

Superior Epithelial Arcuate Lesion (SEAL)

A SEAL is an arcuate (curved) epithelial split in the superior cornea, caused by mechanical interaction between a tight-fitting or thick-edged soft lens and the superior cornea under the upper lid. It appears as a curvilinear staining pattern with fluorescein at approximately the 10 to 2 o'clock positions. Management involves refitting with a flatter or thinner-edged lens.

3 and 9 O'Clock Staining in GP Wearers

GP lens wearers commonly develop desiccation staining at the 3 and 9 o'clock positions on the cornea (the horizontal meridian). This occurs because the rigid lens disrupts normal blink coverage and tear distribution across those areas, causing epithelial drying. Management includes proper lens edge design, lubricating drops, and ensuring blink completeness.

Key Takeaways

Microbial keratitis is the most serious complication; any painful red eye in a contact lens wearer is urgent and requires same-day evaluation.
Corneal hypoxia from low-Dk lenses causes edema, microcysts, and neovascularization; silicone hydrogel lenses reduce this risk.
GPC is an immune reaction causing papillae under the upper lid; daily disposables and enzymatic cleaning help.
CLARE is an acute sterile inflammatory response from sleeping in extended-wear lenses; resolves with lens removal.
Never advise a contact lens patient with pain, redness, and reduced vision to continue wearing their lenses.