Stromal Abscesses and the Septic Eye

A stromal abscess occurs when an infectious agent(s) is inoculated into the corneal stroma (usually by trauma/ microtrauma) followed by epithelial healing, such that infection, cellular infiltration and inflammatory mediators are sequestered within the stroma. The epithelium provides a lipophilic barrier to drug entry to the hydrophilic stroma and hinders treatment.

The use of biphasic drugs (oil:water coefficient) helps to improve drug penetration. The preservative benzalkonium chloride present in many multidose topical eye medications damages epithelial cell junctions and can assist drug penetration, but often not sufficiently to combat the stromal abscess. Surgical debridement of the epithelium is sometimes used to help treat the stromal abscess (e.g. under standing sedation and topical anaesthesia with the handle end of a scalpel blade), but may need to be repeated during the healing period.

Stromal abscesses often involve fungal agents and the use of antifungal medications with good corneal penetration is recommended (e.g. voriconazole). If corneal vascularisation is present close to the abscess the use of oral fluconazole can be considered for some cases. Intrastromal corneal injections of antifungal agents can also be beneficial. Surgical excision of a stromal abscess with a grafting procedure to repair the defect is best achieved under general anaesthesia with the benefit of an operating microscope but standing surgical techniques have been published. We will briefly discuss some of the techniques described.

Rupture of a stromal abscess into the anterior chamber of the eye may lead to endophthalmitis (‘the septic eye’). This is particularly concerning when fungal agents are involved as they have a tropism for Descemet’s membrane and will therefore often migrate deeply within the stroma. Endophthalmitis can also occur secondary to haematogenous spread of an infectious agent (particularly in foals), secondary to intraocular surgery and contamination of ocular fluids with bacteria/fungi, and sterile endophthalmitis can occur secondary to severe trauma as well as secondary to a systemic septic focus (causing immune-mediated endophthalmitis).

Infectious endophthalmitis can be very challenging to treat, requires intracameral (+/- intravitreal) drug administration in addition to systemic, and is often unsuccessful. It is an excruciatingly painful condition, and in many cases enucleation may be the kindest option. Sterile (immune-mediated) endophthalmitis offers more hope, but rapid resolution of the inflammation is required if a visual and pain-free eye is to be achieved.

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