Accuracy of Scheimpflug-derived corneal biomechanical and tomographic indices for detecting subclinical and mild keratectasia in a South Asian population.

PURPOSE: To test the predictive accuracy of the Belin-Ambrósio deviation index (BAD-D), the stiffness parameter A1 (SPA1), the Corvis biomechanical index (CBI), and the tomographic and biomechanical index (TBI) assessments for distinguishing subclinical and mild keratoconic eyes from normal eyes. SETTING: Medical Research Foundation, Sankara Nethralaya, Chennai, India. DESIGN: Retrospective case series. METHOD: In this cross-sectional clinical study, the following 3 groups of eyes were analyzed: very asymmetric ectasia with normal topography (very asymmetric-normal topography), mild keratoconus, and normal control. All eyes had comprehensive assessment with corneal topography (TMS-IV), Scheimpflug tomography (Pentacam HR), and dynamic Scheimpflug biomechanical analysis (Corvis ST). The outcome measures were the BAD-D, SPA1, CBI, and TBI. Receiver operating characteristic (ROC) curve analysis was performed to determine each parameter's predictive accuracy in distinguishing between eyes with subclinical or mild keratoconus and control eyes. RESULTS: The area under the curve (AUC) ROC values for the very asymmetric-normal topography and normal control comparison were 0.81 (BAD-D), 0.76 (SPA1), 0.78 (CBI), and 0.90 (TBI). The TBI (using cutoff value 0.16) showed the highest diagnostic accuracy (85%), with 84% sensitivity and 86% specificity. The AUC ROC values for the mild keratoconus and normal control comparison were 0.998 (BAD-D), 0.91 (SPA1), 0.97 (CBI), and 0.999 (TBI). The TBI (with a 0.63 cutoff) showed the highest accuracy (99.5%), with 99% sensitivity and 100% specificity. The TBI also showed the weakest correlation with mean keratometry, biomechanically corrected intraocular pressure, and central corneal thickness in normal eyes and keratoconic eyes. CONCLUSIONS: The TBI best distinguished eyes with mild ectasia from normal eyes and had the weakest correlation with biomechanical confounding factors, reinforcing the hypothesis that the TBI represents corneal biomechanical susceptibility.

Corneal epithelial permeability to fluorescein in humans by a multi-drop method.

PURPOSE: The permeability of the corneal epithelium to fluorescein Pdc is an indicator of the health of the ocular surface. It can be measured in a clinical setting by determining the accumulation of fluorescein in the stroma following administration of the dye on the ocular surface. Here we demonstrate a new multi-drop method for the measurement of Pdc by a spot fluorometer. METHODS: Twenty-nine healthy participants were recruited for this study. First, a probe-drop of fluorescein (0.35%, 2 µL) was instilled on the conjunctiva. The clearance of the dye from the tears was immediately measured using the fluorometer. Following this, two loading drops (2%; 6 µL each) were administered 10 min apart. Fifteen minutes later, the ocular surface was washed and fluorescence from the stroma Fs was measured. Permeability was calculated using Pdc = (Q x Fs)/ (2 x AUC), where Q is the stromal thickness and AUC is the area under the fluorescence vs. time curve for the loading drops. RESULTS: After the probe drop, the tear fluorescence followed an exponential decay (elimination rate constant; kd = 0.41 ± 0.28 per min; 49 eyes of 29 subjects), but the increase in Fs was negligible. However, after the loading drops, the measured Fs was ~ 20-fold higher than the autofluorescence and could be recorded at a high signal to noise ratio (SNR > 40). The intra-subject variability of kd was insignificant. Since fluorescein undergoes concentration quenching at > 0.5%, the value of AUC for the loading drops was estimated by scaling the AUC of the probe drop. The calculated Pdc was 0.54 ± 0.54 nm/sec (n = 49). A Monte Carlo simulation of the model for the multi-drop protocol confirmed the robustness of the estimated Pdc. CONCLUSIONS: The new multi-drop method can be used in place of the single-drop approach. It can overcome a lack of sensitivity in fluorometers of high axial resolution. The Pdc estimated by the multi-drop method is ~ 11-fold higher than previously reported but closer to the value reported for other drugs with equivalent octanol/water partition coefficient.

Corneal deposit after topical ciprofloxacin as postoperative medication after cataract surgery.

OBJECTIVE: To report 5 cases of corneal deposits after administration of topical ciprofloxacin as postoperative medication after uneventful cataract surgery. DESIGN: Observational Case Series. PARTICIPANTS: Five patients ranging from 60 to 72 years of age. METHODS: All cases were operated by small-incision cataract surgery technique and prescribed postoperatively ciprofloxacin and prednisolone acetate eye drops. All cases had corneal deposits on second follow-up visit (15 days after cataract surgery) with decreased visual acuity. Ciprofloxacin eye drops were immediately discontinued and replaced by topical artificial tear substitute and tobramycin eye drop along with prednisolone acetate. In 1 case, surgical debridement was done. RESULTS: Complete resolution of corneal deposit occurred in 2 months with good recovery of visual acuity in cases managed conservatively. The case with surgical debridement required more time for healing and visual recovery. CONCLUSIONS: More frequent and prolonged application of ciprofloxacin drops can lead to drug precipitation, which can interfere with surgical outcome.