Corticosteroids & NSAIDs

Topical Corticosteroid Mechanism

Corticosteroids are the most potent anti-inflammatory agents in ophthalmology because they act upstream of any single inflammatory mediator. Rather than blocking one enzyme in one pathway, they diffuse into cells and bind intracellular glucocorticoid receptors, which suppress the transcription factors NF-κB and AP-1. Those factors drive expression of a wide range of inflammatory genes, so this single genomic action broadly reduces production of prostaglandins, leukotrienes, cytokines, and phospholipase A2 (partly through induction of annexin-1/lipocortin, which itself inhibits phospholipase A2 upstream in the arachidonic acid cascade). That breadth explains both why steroids outperform NSAIDs against significant inflammation and why their side-effect profile runs wider.

Potency and Corneal Penetration

Not all topical steroids are interchangeable, and the differences are deliberate pharmaceutical design choices, not just concentration differences.

Prednisolone acetate 1% is one of the most potent topical ocular steroids available; its acetate formulation gives it excellent corneal penetration. That combination makes it the standard choice for moderate-to-severe anterior uveitis and significant post-surgical inflammation, where maximal anti-inflammatory effect is the priority.

Fluorometholone (FML) sits at the opposite end of the spectrum. The absence of the C-21 hydroxyl group lowers its glucocorticoid receptor affinity and potency, weakening how strongly it activates glucocorticoid receptors in the trabecular meshwork. It also penetrates the cornea poorly. Both properties lower its systemic and intraocular bioavailability, which is why it's preferred over a potent agent like prednisolone for milder indications such as allergic conjunctivitis, where limiting IOP-raising risk matters more than maximal potency.

Difluprednate 0.05% takes the opposite design strategy: dual fluorine substitution at C-6 and a butyrate ester at C-17 substantially increase its glucocorticoid receptor binding affinity and corneal penetration relative to prednisolone. Corneal esterases hydrolyze the butyrate ester to release the active difluoroprednisolone, giving it a potent intraocular anti-inflammatory effect at only twice-daily dosing rather than the four-times-daily schedule prednisolone acetate typically requires.

Steroid-Induced Glaucoma and Cataract

The two most serious ocular side effects of chronic topical corticosteroid use are posterior subcapsular cataract (PSC) and steroid-induced ocular hypertension/glaucoma. Both risks scale with the potency, frequency, and duration of steroid exposure. Steroid-response IOP elevation occurs in a genetically influenced subset of the population, classically cited at up to roughly a third of people, and a FKBP51 gene variant is among the factors modulating individual glucocorticoid receptor sensitivity.

The molecular mechanism of steroid-response glaucoma extends the same genomic glucocorticoid receptor signaling described above to trabecular meshwork (TM) cells specifically. Glucocorticoid receptor activation in the TM upregulates myocilin (MYOC) and drives deposition of extracellular matrix proteins (fibronectin, laminin, and others) in the juxtacanalicular region of the trabecular meshwork. The resulting increase in ECM stiffens this tissue and raises resistance to aqueous outflow, the primary mechanism behind the IOP rise. Steroid-responders can show pressure increases of 10 mmHg or more, with the highest risk from the most potent topical agents.

Loteprednol etabonate was engineered specifically to reduce this risk. It uses a "retrometabolic" or soft-drug design: the molecule is built to be rapidly metabolized to inactive carboxylic acid metabolites after it exerts its anti-inflammatory effect, rather than persisting active in the tissue. This limits how much active drug lingers to occupy glucocorticoid receptors in the trabecular meshwork, meaningfully reducing steroid-response IOP elevation while still providing useful anterior segment anti-inflammatory activity. It is the defining trade-off of the whole drug class, deliberately engineered into a single molecule.

Central serous chorioretinopathy is a less common corticosteroid complication that is easy to miss because it isn't limited to the topical ocular route. Case-control data put the odds ratio for steroid exposure near 7, and the effect holds for oral, inhaled, intranasal, epidural, and intravitreal steroid use, not just eye drops. Steroids raise choroidal capillary permeability and disrupt retinal pigment epithelium ion pump function, letting fluid collect under the neurosensory retina at the macula. A patient who develops sudden central metamorphopsia or a paracentral scotoma while on any form of corticosteroid, even one prescribed for an unrelated condition, should raise this diagnosis before assuming a primary retinal problem.

Intravitreal and Suprachoroidal Steroid Delivery

For posterior segment disease, steroid can be delivered by routes other than eye drops entirely.

The dexamethasone intravitreal implant (Ozurdex) is biodegradable. It is built on a PLGA (poly lactic-co-glycolic acid) polymer matrix that erodes over time, releasing dexamethasone over approximately 4-6 months before dissolving completely, with no surgical removal required.

The fluocinolone acetonide implant (Iluvien) takes the opposite design: it is non-biodegradable, releasing fluocinolone acetonide continuously at a very low dose (roughly 0.2 micrograms/day) for up to 36 months. It's approved for chronic diabetic macular edema in pseudophakic patients and for non-infectious posterior uveitis, and for some patients this provides disease control for two to three years between treatments, the longest duration of any available intravitreal steroid option, at the cost of leaving a permanent implant in the eye.

Suprachoroidal triamcinolone acetonide (Xipere) is a genuinely different delivery route rather than a different formulation: a hollow microneedle injects triamcinolone directly into the suprachoroidal space, achieving high choroidal and retinal drug concentrations while limiting anterior segment exposure. That limits the lens and IOP risks associated with a standard intravitreal injection. It's approved for uveitic macular edema.

Sub-Tenon triamcinolone acetonide injection (40 mg/mL Kenalog) is an older, simpler technique: the depot diffuses trans-sclerally after injection into the sub-Tenon space, providing a sustained posterior segment anti-inflammatory effect for roughly 1-3 months. It remains useful for unilateral posterior uveitis, cystoid macular edema, and as a surgical adjunct during vitreoretinal procedures.

Corticosteroids and HSV Keratitis

Topical NSAIDs

Topical ophthalmic NSAIDs (ketorolac, diclofenac, nepafenac, bromfenac) act through a single, narrower mechanism than steroids: inhibition of cyclo-oxygenase (COX) enzymes, which reduces prostaglandin synthesis in the arachidonic acid cascade. That narrower mechanism is why they lack the IOP-raising and cataractogenic risks of steroids, but it also makes them less potent against significant inflammation.

Key clinical uses include inhibiting intraoperative miosis (prostaglandins cause pupillary constriction during surgery), controlling post-cataract-surgery pain and inflammation, treating chronic cystoid macular edema (Irvine-Gass syndrome), and providing a surface analgesia adjunct for corneal pain.

Bromfenac achieves a longer dosing interval (once or twice daily) than ketorolac's four-times-daily regimen because its brominated aromatic ring confers greater lipophilicity, improving corneal penetration, tissue binding, and intraocular half-life. Nepafenac, by contrast, is a prodrug: it penetrates the cornea inactive and is hydrolyzed by intraocular tissue amidases into its active metabolite, amfenac, which then inhibits COX-1 and COX-2. That targeted intraocular activation improves bioavailability where it's needed while limiting systemic and ocular-surface NSAID exposure.

In the post-cataract-surgery setting specifically, NSAIDs reduce prostaglandin-mediated capillary leakage and cystoid macular edema risk. They complement rather than replace topical steroid anti-inflammatory effects, and combining the two classes is standard protocol in many centers.

High-Yield Pearls

• Steroid mechanism: glucocorticoid receptor → suppresses NF-κB/AP-1 → broadly reduces prostaglandins, leukotrienes, cytokines, phospholipase A2.
• Steroid-response glaucoma mechanism: MYOC upregulation + ECM deposition in the juxtacanalicular trabecular meshwork → increased outflow resistance.
• Loteprednol = retrometabolic soft-drug design, metabolized to inactive metabolites after effect, lower IOP risk.
• Ozurdex is biodegradable (~4-6 months); Iluvien is non-biodegradable (~36 months).
• NSAIDs act by COX inhibition only; nepafenac is a prodrug activated by ocular amidases to amfenac.
• Never use topical steroid monotherapy in active HSV epithelial keratitis.

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