Pseudomonas aeruginosa is one of the most common causes of bacterial keratitis and the number one infectious organism associated with contact lens wear. Because of this association, researchers investigated outcomes of Pseudomonas aeruginosa keratitis (PAK) in contact lens users and non-users, and found that those who don’t wear contacts had significantly worse visual outcomes and were more likely to require surgical intervention.

The retrospective cohort study included 214 PAK eyes of 207 patients—163 eyes (76%) of users and 51 eyes (24%) of non-users. The researchers compared clinical features, microbiologic results and treatment course between the groups. At baseline, average logMAR visual acuity was 1.39 among lens users and 2.17 among non-users. Final visual acuity was significantly better among users (0.76logMAR vs. 1.82logMAR).

“In our study, non-contact lens wearers with PAK had more severe features at presentation and more devastating outcomes, compared with contact lens wearers,” the researchers wrote in their paper. “Specifically, non-contact lens wearers exhibited inferior visual acuity outcomes and greater stromal necrosis, resulting in more frequent corneal procedures and a higher probability of losing the infected eye, compared with contact lens wearers.” Stroma necrosis increased the risk of procedural or surgical intervention in 13.5% of contact lens wearers and 49% of non-wearers.

Based on a machine learning algorithm, the following clinical features were strong predictors of a poor visual outcome, defined as worse than 20/40: worse initial visual acuity, older age, larger size of infiltrate or epithelial defect at presentation and greater maximal depth of stromal necrosis.

Importantly, however, the researchers pointed out, “The majority of non-contact lens wearers were older with pre-existing ophthalmic conditions, including corneal epithelial disease, glaucoma and/or prior corneal transplant.” Whereas, most contact lens wearers in the study had no pre-existing ophthalmic risk factors other than lens wear. Non-wearers were also more likely to be systemically immunosuppressed and institutionalized in subacute or long-term nursing facilities, places which have been associated with increased risk of communicable infection.

Ocular trauma was identified in approximately 14% of each group. The researchers noted, “Ocular surface disease, ocular trauma and history of corneal transplant or other ocular surgery have been cited previously as risk factors for keratitis. Patients developing keratitis can have more severe infectious courses and worse visual outcomes.”

Additionally, non-contact lens wearers tended to present for treatment later than wearers, seeking care an average of 4.9 days after symptom onset compared with 2.77 days. “This could be attributable to social factors such as older age and nursing home residence,” the researchers said.

Overall, initial visual acuity, older age, larger initial infiltrate, larger epithelial defect and presence of hypopyon correlated with poor final visual acuity in both groups. “Clinical features associated with worse visual outcomes in contact lens wearers were different from those in non-contact lens wearers,” the researchers wrote. “Interestingly, glaucoma was a feature in non-contact lens wearers. The chronic use of topical hypotensive medications by glaucoma patients could contribute to their infectious risk by compromising the ocular surface.”

They concluded that glaucoma, prior corneal transplant, topical steroid use at presentation, systemic immunosuppression and institutionalized medical are predictive of poorer visual outcome, as identified by the algorithm. “These ocular and medical comorbidities likely represent independent risk factors for PAK in non-contact lens wearers,” they wrote.