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What delays corneal healing: eye drops and toxic agents
This is the most useful family in this review, and the least consulted. Faced with an ulcer that will not close, the first question is not “what can I add?” but “what can I remove?”. In a substantial share of delayed healing, the answer lies in the current prescription.
The mechanisms are documented and convergent. Benzalkonium chloride, the preservative in most multidose drops, is a cationic detergent that disrupts tight junctions and kills epithelial cells, with a cumulative effect proportional to the number of daily instillations. Topical NSAIDs suppress prostaglandins required for epithelial migration. Corticosteroids have a dual role: indispensable against the inflammation that destroys, harmful to the epithelium that repairs.
Two situations deserve to be known in their own right: topical anaesthetic abuse, which produces a characteristic and often missed ring keratopathy, and the epithelial toxicity of aminoglycosides and fluoroquinolones given for long periods.
Overview
| Agent | Mechanism | Level of evidence |
|---|---|---|
| Benzalkonium chloride (BAK) | Surfactant that solubilizes membranes and disrupts tight junctions → loss of epithelial barrier function, ↓goblet cell d… | Oxford I–III Negative · Strong Present · to be eliminated |
| Topical corticosteroids | Benefit: ↓phospholipase A2 → ↓prostaglandins/leukotrienes; ↓inflammatory infiltrate, cytokines, neovascularization and k… | Oxford I–II Negative (epithelium/melting) Strong (both effects) |
| Topical NSAIDs | COX inhibition → ↓prostaglandins (analgesia, ↓macular edema). However, COX products (e.g., 12-HHT via the BLT2 receptor)… | Oxford I–III Negative · Strong Present · FDA warning |
| Topical anesthetic abuse | Sodium channel blockade plus direct epithelial cytotoxicity: inhibition of migration, mitosis, and adhesion, damage to m… | Oxford IV Negative · Strong (consensus) Present · avoidable |
| Epithelial toxicity of aminoglycosides / fluoroquinolones | Aminoglycosides: direct epithelial cytotoxicity, inhibition of proliferation/migration, delayed closure (worst with fort… | Oxford II (exp.) · IV (clin.) Negative · Moderate–Strong Present · established |
Benzalkonium chloride (BAK) — toxic preservative
Quaternary ammonium detergent, 0,004–0,02 % in numerous multidose eye drops
Surfactant that solubilizes membranes and disrupts tight junctions → loss of epithelial barrier function, ↓goblet cell density, tear film instability, oxidative stress, pro-inflammatory cytokines and apoptosis (epithelium, limbal stem cells, nerves, keratocytes). Dose- and duration-dependent effect: delays/inhibits epithelial closure and worsens persistent epithelial defects (PEDs).
Level of evidenceOxford I–II (mechanistic + clinical comparative studies; II–III for delayed healing as an endpoint) · Scale: Strong (epithelial toxicity).
Detailed sheet →Topical corticosteroids — dual role
Prednisolone acetate 1 %, dexamethasone 0,1 %, loteprednol 0,5 %, fluorometholone, difluprednate
Benefit: ↓phospholipase A2 → ↓prostaglandins/leukotrienes; ↓inflammatory infiltrate, cytokines, neovascularization and keratocyte fibrosis (↓haze). Downside: inhibit keratocyte proliferation and collagen synthesis → ↓wound tensile strength; delay epithelial migration; potentiate collagenolytic melting (keratolysis) and perforation, especially over a defect or a "dry"/inflamed cornea; mask/worsen infection (bacterial, HSV, fungal, Acanthamoeba); ↑IOP, cataract.
Route & dosingTopical; prednisolone acetate 1 % every 1–6 hours in a tapering schedule; loteprednol/FML (lower IOP risk) for maintenance. Taper cautiously.
Level of evidenceOxford I–II (anti-inflammatory efficacy — SCUT; delayed healing/↓wound strength — experimental studies + melting case series) · Scale: Strong for both aspects.
Detailed sheet →Topical NSAIDs — epithelial delay & melting risk
Ketorolac 0,4/0,5 %, diclofenac 0,1 %, bromfenac, nepafenac, flurbiprofen
COX inhibition → ↓prostaglandins (analgesia, ↓macular edema). However, COX products (e.g., 12-HHT via the BLT2 receptor) are required for epithelial migration → NSAIDs delay re-epithelialization; loss of prostaglandin-mediated cytoprotection combined with unchecked MMP/collagenase activity can precipitate sterile stromal melting, ulceration, and perforation (classically generic diclofenac; dry/rheumatoid/diabetic/postoperative corneas, combination with corticosteroids).
Route & dosingTopical 2–4×/day; limited duration (typically ≤3–4 days after PRK) to reduce melting risk.
Level of evidenceOxford II–III (melting: large series/pharmacovigilance data, FDA warnings); I–II experimental (delay) · Scale: Strong.
Detailed sheet →Topical anesthetic abuse — toxic keratopathy
Proparacaine 0,5 %, tetracaine, oxybuprocaine, lidocaine — chronic self-administration
Sodium channel blockade plus direct epithelial cytotoxicity: inhibition of migration, mitosis, and adhesion, damage to microvilli/junctions, corneal neurotoxicity. Result: non-healing persistent epithelial defect, immune ring infiltrate, melting/perforation, endophthalmitis/evisceration in severe forms. Loss of sensation worsens the injury.
Route & dosingThe problem is repeated self-dosing. Never prescribe for home analgesia.
Level of evidenceOxford IV (case series; no RCTs for ethical reasons) but mechanistically robust and consistent · Scale: strong consensus of harm.
Detailed sheet →Epithelial toxicity of aminoglycosides / fluoroquinolones
Gentamicin, tobramycin, neomycin; ciprofloxacin, ofloxacin, moxifloxacin — dose-dependent
Aminoglycosides: direct epithelial cytotoxicity, inhibition of proliferation/migration, delayed closure (worst with fortified formulations and neomycin: punctate keratopathy, PED, pseudomembranes). Fluoroquinolones: better tolerated but inhibit keratocytes/epithelium in vitro; ciprofloxacin precipitates as white crystalline deposits in ulcers (mechanical hindrance to epithelialization). Keratocyte toxicity at high concentration for both classes.
Route & dosingTopical; commercial concentrations generally well tolerated; fortified formulations (tobramycin/gentamicin ~14 mg/mL) reserved for severe keratitis, then tapered.
Level of evidenceOxford II (consistent experimental data) · IV clinical · Scale: Moderate–Strong.
Detailed sheet →Key points
The approach comes down to three moves. Simplify: withdraw every non-essential drop, and switch the essential ones to preservative-free unit doses. Suspend topical NSAIDs whenever an epithelial defect is present. Reassess corticosteroids: neither stop them on principle nor continue them out of habit, but match potency and frequency to the state of the epithelium.
And think of anaesthetic abuse in a keratopathy that resists everything, particularly in a patient whose pain settles abnormally well in the consulting room: the diagnosis is made by history, not at the slit lamp, and it has to be considered to be made.
The other families in this review
Updated 26 August 2026