This ten-year retrospective study offers a comprehensive evaluation of 172 patients of culture-proven Pseudomonas aeruginosa keratitis managed at a tertiary referral center. The majority of patients required hospitalization and intensive treatment, with surgical intervention necessary in over two-thirds of patients. Notably, corneal perforation occurred in nearly one-quarter of patients, and endophthalmitis developed in 13.9%, underscoring the potentially sight-threatening nature of this infection. Final visual outcomes remained poor in most cases, with a mean BCVA of 1.92 LogMAR at six months. Age, male gender, and comorbid conditions such as HTN and CAD were significantly associated with a higher likelihood of requiring surgery. While disease severity and outcomes varied, antimicrobial susceptibility testing revealed preserved sensitivity to key antibiotics—especially Amikacin, Ciprofloxacin, Ceftazidime, and Levofloxacin—supporting their continued use in empiric therapy.

One of the major strengths of this study is its relatively large sample size compared to similar reports from various countries. Our study represents one of the most extensive single-center investigations of Pseudomonas aeruginosa keratitis to date, surpassing the sample sizes reported in many prior studies across diverse regions including Iran [12], the United States [21], Europe [22], South America [23], India [24], and East Asia [25]. This robust sample size strengthens the reliability of our findings and supports broader generalizability of clinical patterns, risk factors, and treatment outcomes in Pseudomonas aeruginosa keratitis.

Age and gender distribution in our cohort appear to reflect the dominant predisposing factors for Pseudomonas aeruginosa keratitis in our region. In our study, trauma was the most common identified risk factor (30.2%), while contact lens use accounted for only 13.4% of cases. This contrasts with patterns in high-income countries, where contact lens wear is often the primary risk factor, frequently associated with younger, predominantly female patients [26, 27]. For example, Enzor et al. reported that patients with Pseudomonas aeruginosa keratitis who wore contact lenses had a mean age of 39.2 years, compared to 71.9 years among non–contact lens wearers [26]. In the same study, females predominated among contact lens users (61.3%), whereas the gender distribution was more balanced among non–lens users (52.9% female vs. 47.1% male); in our study, the near-equal gender distribution likely reflects the lower prevalence of contact lens use and the predominance of trauma as the main risk factor [26]. A similar pattern of male predominance and trauma as the leading risk factor was observed in the study from Romania [22]. These findings suggest that regional differences in socioeconomic status, lifestyle, and occupational exposure not only influence risk factors but also shape the demographic profile of Pseudomonas aeruginosa keratitis.

The incidence of corneal perforation in our cohort was notably high, occurring in 23.84% of cases. This figure is considerably elevated compared to similar studies. For instance, Enzor et al. reported a perforation rate of 9.8% in a cohort exclusively composed of patients with Pseudomonas aeruginosa keratitis, making their population directly comparable to ours [26]. In broader studies that analyzed bacterial keratitis regardless of the causative organism, the reported rates of perforation were generally lower: 19% in the study by Kusumesh et al. [28], 11.5% in the report by Jin et al. [29], and 10.8% in the series by Almulhim et al. [30]. These comparisons underscore the particularly severe disease burden observed in our population and may reflect later presentation or limited access to early ophthalmic care.

This severity is further highlighted by the exceptionally high rate of therapeutic PKP in our study. A total of 61 patients (35.5%) required one or more graft procedures, with 30.8% undergoing at least one keratoplasty and several needing repeated surgeries. This is substantially higher than the 6.5% rate of tectonic grafting reported by Enzor et al. in a similarly defined population of Pseudomonas aeruginosa keratitis [26]. Even in broader studies that included various bacterial pathogens, the proportion of patients requiring keratoplasty was typically lower—for instance, Das et al. reported a rate of 23.1% among 13,625 cases of non-viral microbial keratitis [31]. Taken together, these findings reinforce the aggressive clinical course and high surgical burden observed in our cohort.

In our cohort, the incidence of endophthalmitis was markedly high at 13.95%, which stands in stark contrast to previous reports. The reported incidence of endophthalmitis following microbial keratitis in the literature ranges from 0.29% to 6.1% [32,33,34]. Notably, these studies examined bacterial keratitis in general and did not distinguish by causative organism [32,33,34]. The significantly higher rate observed in our study may reflect the inherently aggressive nature of Pseudomonas aeruginosa infections [25], and the overall poorer outcomes in our patient population. On univariate analysis, age ≥ 50 years was associated with significantly higher odds of endophthalmitis; however, after multivariate adjustment for age, gender, systemic comorbidities, and baseline vision, no independent predictors remained significant. Compared with the series by Christopher et al. [35], which identified presenting vision of LP/NLP, history of cataract surgery, and full-thickness ulcer/perforation as important risk factors, our cohort did not show similar associations. These differences may be explained by pathogen-specific effects, since our study exclusively evaluated Pseudomonas aeruginosa keratitis, as well as referral bias in a tertiary care setting. Future research should specifically investigate endophthalmitis as a distinct outcome in Pseudomonas aeruginosa keratitis, given its alarming frequency and potential for severe visual morbidity.

Antibiotic susceptibility patterns of Pseudomonas aeruginosa vary significantly across regions, influenced by local prescribing practices, antibiotic availability, and infection control measures [25, 36, 37]. In our study, resistance to commonly used antibiotics remained relatively low: ciprofloxacin and gentamicin each showed resistance rates below 3%, and ceftazidime and amikacin resistance were similarly low at 1.74%. These findings are consistent with global reports from earlier decades, where ciprofloxacin and gentamicin resistance remained under 10% in most countries during the 1990–2003 period [25]. However, significant geographic variability has been documented. For instance, in a study from India covering the 1992–2003 period, resistance to ciprofloxacin reached 30%, and gentamicin resistance climbed to 46%, underscoring the importance of continuous regional surveillance [25, 36].

Our findings highlight a discrepancy between empiric treatment regimens and actual in vitro susceptibility patterns, particularly regarding cefazolin. While empiric use of cefazolin remains common in our setting, culture data indicate limited efficacy, underscoring the need to refine empiric protocols. Although secondary treatment data suggest that clinicians frequently adjusted therapy once susceptibility results became available, we were unable to quantify the exact timeliness of these adjustments due to the retrospective nature of our study. This represents an important limitation and reinforces the need for future prospective studies that track real-time decision-making in relation to culture results.

In contrast, beta-lactam antibiotics—particularly older-generation cephalosporins—demonstrated markedly reduced efficacy in our cohort. Cefazolin, for example, showed only 1.16% sensitivity, with over 59% of isolates being resistant. This finding aligns with literature describing beta-lactam resistance in nosocomial Pseudomonas infections, often mediated by mechanisms such as metallo-beta-lactamase production [38, 39]. Similar to our findings, the study by Nagaraju Konda et al. also reported high resistance rates to chloramphenicol among Pseudomonas aeruginosa isolates, underscoring its limited utility in the treatment of bacterial keratitis caused by this pathogen [24]. These results support the continued use of ciprofloxacin, ceftazidime, and amikacin as empiric therapy for Pseudomonas aeruginosa keratitis in our setting, while also highlighting the limited utility of first-generation cephalosporins and the need for stewardship policies tailored to local resistance profiles.

Compared with the long-term trend data reported in the study by Joseph et al., which documented a steady rise in antimicrobial resistance over three decades, our results indicate relatively preserved susceptibility [40]. In particular, ciprofloxacin resistance in our cohort remained below 3%, contrasting with the rising resistance rates reported in India, where ciprofloxacin resistance in gram-negative isolates increased from 11.5% to 18.7%. Similarly, while Joseph et al. reported a significant decline in susceptibility of gram-positive isolates to cefazolin (95.5% to 66%) and amikacin (88% to 55%), our Pseudomonas isolates retained high susceptibility to amikacin, with resistance rates below 2%. However, our study also demonstrated markedly reduced efficacy of older-generation beta-lactams such as cefazolin, underscoring the need for continued surveillance to monitor emerging resistance trends in ocular pathogens [40].

In our study, diabetes mellitus was significantly associated with a higher incidence of corneal perforation, suggesting that systemic metabolic status may influence keratitis severity. This observation is supported by findings from Almulhim et al., who similarly reported poorer clinical outcomes in diabetic patients with infectious keratitis [30]. Several studies have proposed that diabetes mellitus contributes to both structural and functional abnormalities of the cornea, impairing epithelial integrity and delaying wound healing [41, 42]. These changes increase the risk of secondary infection, prolong disease duration, and often reduce responsiveness to medical therapy. As a result, diabetic patients are more likely to require surgical intervention to control disease progression and preserve ocular integrity [42].

In our study, older age was significantly associated with worse visual outcomes at the 6-month follow-up, a higher likelihood of surgical intervention, and an increased incidence of endophthalmitis. These findings are consistent with previous research, including the study by Thamizhselvi et al., which reported poorer clinical outcomes in older patients with Pseudomonas keratitis [43]. Age-related physiological changes in the ocular surface—such as reduced corneal sensation and decreased subepithelial nerve density—may contribute to this vulnerability [44]. For example, Niederer et al. demonstrated a linear decrease in corneal nerve density of approximately 0.9% per year in healthy individuals [45]. This gradual decline in corneal innervation impairs epithelial maintenance, delays wound healing, and reduces the eye’s defense against microbial invasion [45].

Beyond host factors such as age, pathogen-related characteristics may also influence clinical outcomes. A study by Choy et al. highlighted the role of the type III secretion system (T3SS) genotype in determining prognosis [46]. In their cohort, invasive strains were more common in older males and patients with a history of ocular surgery or trauma, and were significantly associated with worse presenting and final visual acuity, larger and deeper infiltrates, and delayed epithelial healing. In contrast, cytotoxic strains were strongly linked to contact lens wear. Importantly, invasive strains were identified as independent poor prognostic factors for final vision and time to re-epithelialization, with a trend toward higher fluoroquinolone resistance. Taken together, these findings suggest that both host-related vulnerabilities (such as advanced age) and pathogen-specific virulence mechanisms (such as T3SS genotype) contribute to the unfavorable outcomes frequently observed in Pseudomonas aeruginosa keratitis [46].

This study has several limitations that should be acknowledged. First, its single-center design may limit the generalizability of the findings to broader populations with varying healthcare access and regional pathogen profiles. Second, the retrospective nature of data collection inherently introduces potential biases, including variability in documentation and loss of certain clinical details. Additionally, our center—being a national tertiary referral hospital located in the capital—serves patients from distant provinces. As a result, many patients returned to their hometowns for postoperative care, and consistent long-term follow-up beyond six months was not feasible for the majority of cases. Consequently, we were unable to evaluate late visual outcomes or long-term graft survival. These limitations highlight the need for future multicenter, prospective studies with standardized long-term follow-up protocols to better characterize the extended clinical course and therapeutic response of Pseudomonas aeruginosa keratitis across diverse populations.