Table 5

Significant predictors for requiring surgery following failure of primary treatment of suspected microbial keratitis

Characteristics		Primary treatment failure requiring surgery		Risk ratio		95% CI	p Value
Characteristics		No	%	Risk ratio		95% CI	p Value
“Crude” estimates of risk ratio with no adjustment for confounding factors
Age 60+ years	10/42	40.0	—	—	<0.001
Age < 60 years	0/76	0.0
Culture positive ulcer >5 mm²	7/26	26.9	8.3	2.3–29.7	<0.001
Other ulcers	3/92	3.3
Hypopyon present	5/15	33.3	6.9	2.3–20.9	0.003
Hypopyon absent	5/103	4.9
Previous corneal disease	8/38	21.1	8.4	1.9–37.8	0.002
No previous corneal disease	2/80	2.5
Topical steroids before diagnosis	5/19	26.3	5.2	1.7–16.3	0.01
No prior steroid	5/99	5.1

In the age group 60+ years old
Culture positive ulcers	9/24	37.5	6.7	0.94–48.6	0.026
Other ulcers	1/17	5.6
Previous corneal disease	8/21	38.1	4.0	0.96–16.7	0.032
No previous corneal disease	2/19	9.5

In the 60+ year old group, presence of hypopyon was a borderline risk factor (RR 2.5 (0.9–7.1), exact p=0.117), as was the presence of large culture positive ulcers (RR 2.8 (0.8 9.5), exact p=0.143). There were only 10 cases requiring surgery, all in the older age group. The small sample had little power in detecting significant predictors in regression analysis with adjustment for confounding factors, none was detected.