Case Control study for Ocular surface risk factors in Microbial Keratitis

INTRODUCTION: The cornea is constantly exposed to minor trauma from dust and other objects in the environment. However, the vast majority of these insults go un-noticed because of the excellent protective and restorative properties of the ocular surface. A healthy ocular surface is one with a normal tear film, absence of adnexal disease e.g. meibomitis / blepharitis, and normal corneal sensation. However, in some individuals, a seemingly minor insult to the cornea (which in most people would heal spontaneously) does not heal, but results in a corneal ulcer, which is one of the leading causes of corneal blindness. Most of these patients appear to have a normal ocular surface on clinical evaluation. It is assumed that the bacterial load present on the object causing the trauma (mud / plant branch, etc.) is so high as to be the cause of the corneal ulcer in these patients. However, it is possible that there may be additional risk factors in these individuals that are sub-clinical, which diminished the natural immunity of the cornea against corneal infections. Additionally, duration of treatment and the time taken for the ulcer to heal may be prolonged in the presence of an abnormal ocular surface. OBJECTIVES: 1. To determine decreased corneal sensation, adnexal inflammatory conditions, tear film abnormalities are risk factor for developing corneal ulcers. 2. To find threshold value of corneal sensation for development of corneal ulcer. METHODS: A case control study was done in 55 cases and 55 controls who are age, sex and diabetes matched. Descriptive statistics were reported using Mean ± SD and statistical significance was obtained with two independent sample t test. Categorical variables were reported using Frequency and Percentage and their statistical significance obtained using Pearson Chi Square test/ Fishers exact test as appropriate. Binary Logistics was done for to assess risk factors. Receiver operating characteristic curve was obtained to attempt to arrive at an ideal cutpoint of corneal sensation in controls. RESULTS: Corneal sensitivities in cases were lower as compared to controls (p – value = 0.003). Meibomitis was present in 40% of cases and 27.3% of controls (p –value = 0.158). Blepharitis was higher in cases (43.6%) as compared to controls (18.2%) was statistically significant (p = 0.004). Presence of dry eye was higher in controls (p value < 0.001) which was significant. A cut-off value of corneal sensation as measured could not be determined. CONCLUSION: Identifying and treating ocular surface risk factors prevent development of corneal ulcer and thereby the corneal blindness