Corneal Topographic Indices Research Articles

Tear Film Function in Type 2 Diabetic Patients with Retinopathy

Purpose: To investigate whether diabetes mellitus is correlated with tear film dysfunction. Methods: Tear film function tests including tear film breakup time (BUT), fluorescein staining, Schirmer I test, rose Bengal staining, total tear protein detection, tear sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and TMS-4 corneal topography were performed. A dry-eye questionnaire was used. Results: Compared with the control group and nonproliferative diabetic retinopathy (NPDR) group, in the proliferative diabetic retinopathy (PDR) group, the BUT and the value of the Schirmer I test were reduced significantly (p < 0.01); corneal fluorescein staining scores, the positive rate of rose Bengal staining and the surface regularity index (SRI) and surface asymmetry index (SAI) were higher (p < 0.01); concentrations of lactoferrin and tear-specific prealbumin were lower (p < 0.01, p < 0.05, respectively). In diabetic patients, the SRI and SAI were positively correlated with fluorescein staining scores (r = 0.754, 0.480, p < 0.01, respectively), and the dry-eye symptoms were significantly related to an abnormal BUT and Schirmer I test (p < 0.01, respectively). Conclusion: The declined tear film function is severer in the patients with PDR than in those with NPDR. Besides the traditional methods, tear SDS-PAGE and TMS corneal topographic indices contribute to the discovery of tear film dysfunction in diabetic patients.

A New Method for Grading the Severity of Keratoconus

To define a new method for grading severity of keratoconus, the Keratoconus Severity Score (KSS). A rationale for grading keratoconus severity was developed using common clinical markers plus 2 corneal topographic indices, creating a 0 to 5 severity score. An initial test set of 1012 eyes, including normal eyes, eyes with abnormal corneal and topographic findings but not keratoconus, and eyes with keratoconus having a wide range of severity, was used to determine cutpoints for the KSS. Validation set 1, comprising data from 128 eyes, was assigned a KSS and compared with a clinician's ranking of severity termed the "gold standard" to determine if the scale fairly represented how a clinician would grade disease severity. kappa statistics, sensitivity, and specificity were calculated. A program was developed to automate the determination of the score. This was tested against a manual assignment of KSS in 2121 (validation set 2) eyes from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study, as well as normal eyes and abnormal eyes without keratoconus. Ten percent of eyes underwent repeat manual assignment of KSS to determine the variability of manual assignment of a score. From initial assessments, the KSS used 2 corneal topography indices: average corneal power and root mean square (RMS) error for higher-order Zernike terms derived from the first corneal surface wavefront. Clinical signs including Vogt striae, Fleischer rings, and corneal scarring were also included. Last, a manual interpretation of the map pattern was included. Validation set 1 yielded a kappa statistic of 0.904, with sensitivities ranging from 0.64 to 1.00 and specificities ranging from 0.93 to 0.98. The sensitivity and specificity for determining nonkeratoconus from keratoconus were both 1.00. Validation set 2 showed kappa statistics of 0.94 and 0.95 for right and left eyes, respectively. Test-retest analysis yielded kappa statistics of 0.84 and 0.83 for right and left eyes, respectively. A simple and reliable grading system for keratoconus was developed that can be largely automated. Such a grading scheme could be useful in genetic studies for a complex trait such as keratoconus requiring a quantitative measure of disease presence and severity.

Corneal Topographic Changes after Scleral Buckling

To evaluate corneal topographic changes and induced corneal astigmatism after scleral buckling (SB). This interventional case series includes all patients who had undergone scleral buckling for rhegmatogenous retinal detachment (RRD) during a 1-year period. Patients were divided into four groups according to type and extent of scleral buckling which depended on the discretion of a retina specialist. Videokeratography was performed for all patients preoperatively and repeated 1 and 3 months after SB. Thirty-nine eyes of 39 patients (29 male, 74.7%) with mean age of 50.35+/-20 years (range 13-80) were finally analyzed. There was no statistically significant difference among the groups in terms of preoperative corneal astigmatism, surface regularity index (SRI), surface asymmetry index (SAI), mean keratometry (mean K), and potential visual acuity (PVA ). Overall, preoperative mean K was 43.97+/-1.78 D, which reached 44.2+/-2.02 D and 43.92+/-2.16 D 1 and 3 months after the operation. Mean preoperative SRI was 0.58+/-0.4, which increased to 1.24+/-1.18 and 1.29+/-1.13 1 and 3 months after the operation respectively. Mean preoperative SAI was 0.39+/-0.21, which increased to 0.73+/-0.37 and 0.75+/-0.66 1 and 3 months after the procedure. Changes in SAI at 1 and 3 months following SB were significant (p values <0.001); however, these postoperative values were not significantly different. Mean preoperative PVA was 0.07+/-0.75 logMAR (equivalent to 20/20) but decreased to 0.24+/-0.25 (equivalent to 20/30) and 0.27+/-0.29 (equivalent to 20/40) 1 and 3 months after SB, respectively. Significant changes in corneal topographic indices including increases in SRI and SAI and a concomitant decrease in PVA may occur after SB procedures. These induced changes must be considered and appropriately addressed postoperatively to provide the best possible corrected vision.

Screening Patients With the Corneal Navigator

To present a corneal topography screening device for the detection of corneal ectasias and various refractive procedures based on corneal topography patterns. A database of corneal topography patterns were analyzed and used to "train" a neural network on nine different corneal topography patterns using nineteen corneal topography indices of corneal shape and power. Sample normal and corneal topographies were recognized correctly. The use of the corneal navigator to screen various corneal topographies aids clinical diagnosis.

Prediction of letter contrast sensitivity using videokeratographic indices

PURPOSE: To analyze the relationship between corneal topography and letter contrast sensitivity. METHOD: Experiments were conducted on 59 eyes of 51 patients who had best spectacle-corrected visual acuity of 20/20 or better and no ocular pathology except for the corneal shape. Thirty-nine eyes had an abnormal topographic pattern resulting from keratoconus, and the other 20 eyes showed a normal topographic pattern. Videokeratography was performed with the TMS-2 videokeratoscope, and the surface regularity index, surface asymmetry index, and coefficient of variation of power were obtained for each subject. Letter contrast sensitivity was measured with the CSV-1000LV with spectacle correction. The correlation between the number of correct letters and topographic indices was calculated. RESULTS: The abnormal topography group had a significantly greater loss of letter contrast sensitivity (median = 20 letters) than the normal control (median = 23 letters; P = .0001). There were statistically significant correlations between number of correct letters and the coefficient of variation of power ( r = −.77; P = .001), number of correct letters and surface regularity index (r = −.76, P = .001), and the number of correct letters and surface asymmetry index ( r = −.64; P = .001). The linear regression equation between number of correct letters and the coefficient of variation of power was the number of correct letters = −0.05 × the coefficient of variation of power + 23.2. CONCLUSIONS: Our results suggest that subtle visual deteriorations, which are barely detected by contrast sensitivity testing, can be predicted objectively by the corneal topographic indices.

Corneal changes after cataract surgery with 5.0 mm sutured and 3.5 mm sutureless clear corneal incisions

Purpose: To study corneal changes after endocapsular phacoemulsification cataract extraction and intraccular lens (IOL) implantation with a 3.5 mm clear corneal sutureless incision or a 5.0 mm clear corneal incision with an absorbable suture.Setting: Northwest Kansas Eye Clinic, Hays, Kansas, USA.Methods: In a prospective study, 200 eyes were randomly distributed into two groups. Group A comprised 100 eyes that had a silicone IOL inserted through a 3.5 mm sutureless clear corneal incision. Group B comprised 100 eyes that had a 5.0 mm poly(methyl methacrylate) (PMMA) IOL inserted through a 5.0 mm clear corneal incision; one half of the closures used a single radial suture (Group B,) and the other half, an X suture (Group B2). Preoperatively, corneal topography and corneal endothelial cell counts were performed. Six to 8 months postoperatively, they were repeated and evaluated. Differential topography was used to determine the difference between the preoperative and postoperative corneas. During the final postoperative visit, IOL centration was evaluated.Results: All closures produced only minimal changes in the corneal topographic indices. The postoperative corneas closely resembled the preoperative corneas. Polar K values showed a slight astigmatic shift in all groups. Group 132 was the only one to exhibit a with-the-rule shift. The change in endothelial cell counts was minimal and comparable in all three groups.Conclusion: The small amount of change in the corneal indices, especially in surface regularity, indicates that all corneas were relatively comparable and stable 6 to 9 months postoperatively regardless of the type of incision and closure method.