Comparison of corneal measurements in keratoconic eyes using rotating Scheimpflug camera and scanning-slit topography

AIM: To compare the anterior segment measurements obtained by rotating Scheimpflug camera(Pentacam) and Scanning-slit topography(Orbscan IIz) in keratoconic eyes.METHODS: A total of 121 patients, 71 males(58.7%)and 50 females(41.3%)(214 eyes) with the diagnosis of keratoconus(KC) were enrolled in this study. Following diagnosis of KC by slit-lamp biomicroscopic examination, central corneal thickness(CCT), thinnest corneal thickness(TCT), anterior chamber depth(ACD),and pupil diameter(PD) were measured by a single examiner using successive instrumentation by Pentacam and Orbscan.RESULTS: There was no significant difference between the two instruments for the measurement of CCT and TCT. In contrast, scanning-slit topography measured ACD(3.46±0.40 mm vs 3.38±0.33 mm, P =0.019) and PD(4.97 ±1.26 mm vs 4.08 ±1.19 mm, P 【0.001) significantly larger than rotating Scheimpflug camera.The two devices made similar measurements for CCT(95% CI:-2.94 to5.06, P =0.602). However, the mean difference for TCT was-6.28(95% CI:-10.51 to-2.06, P =0.004) showing a thinner measurement by Orbscan than by Pentacam. In terms of the ACD, the mean difference was 0.08 mm(95%CI: 0.04 to 0.12, P 【0.001) with Orbscan giving a slightly larger value than Pentacam. Similarly, Orbscan measurement for PD was longer than Pentacam(95% CI:0.68 to 1.08, P 【0.001).CONCLUSION: A good agreement was found between Pentacam and Orbscan concerning CCT measurement while comparing scanning-slit topography and rotatingScheimpflug camera there was an underestimation for TCT and overestimation for ACD and PD.

Three-year follow-up in advanced pediatric keratoconus:thin corneas may not have pachymetry properly assessed after crosslinking

AIM:To analyze the crosslinking(CXL)effects in pediatric keratoconus,and to identify the patients’corneal characteristics whose pachymetry could not be adequately evaluated by Scheimpflug method after procedure.METHODS:Consecutive pediatric patients with progressive keratoconus underwent CXL were included.Best-corrected visual acuity(BCVA)and spheric equivalent(SE)were measured before and after CXL.After CXL,groups 1 and 2 were divided based on the posterior surface Pentacam quality specifications(QS):"OK"(Group 1)and"not OK"(Group 2).The mean(RmF and RmB)and minimum(RminF and RminB)radius of curvatures of the anterior and posterior corneal surfaces,and the thinnest pachymetry(Pmin)were measured preoperatively at 3,6,12,24,and 36 mo.Haze was annotated.RESULTS:Twenty-six patients(14 men,mean age 14±1.8 y)and median Kmax of 59.9 D initially and 61.4 D preoperatively were treated.BCVA was not different before and 24 mo after CXL.Group 2 statistically differed to group 1 in that SE was more myopic before and with no difference 24 mo after CXL;RmF and RmB were steeper and Pmin was thinner pre-surgically.Group 2,in which pachymetric changes could not be adequately evaluated after surgery,presented with significant RmF flattening,a shift to hyperopia,and more haze after CXL.CONCLUSION:Patients whose pachymetry could not be adequately evaluated after CXL had steeper and thinner corneas before surgery.The predictive factors for impaired QS after CXL are RmF,RmB,and Pmin.In advanced keratoconus,alternative methods to analyze pachymetry and the posterior surface should be considered.

Measurements of anterior segment parameters using three different non-contact optical devices in keratoconus patients

AIM:To evaluate the measurements of anterior segment parameters using three different non-contact optical devices in keratoconus patients.·METHODS:A hundred and one eyes of 55 keratoconus patients were enrolled in this study.The mean age was26.2 ±8.9 years.The inclusion criteria were keratoconus stage I to III according to the Amsler-Krumeich keratoconus classification.All the measurements were done by the same operator,under the mesopic light condition and repeated with three different optical methods;Visante,Orbscan and Pentacam.The evaluated anterior segment parameters were anterior chamber depth(ACD),central and thinnest corneal thickness(CCT and TCT) and pupil diameter(PD).·RESULTS:The mean CCT measured by Visante,Orbscan and Pentacam were as follows:462.0 ±48.1μm,463.9±60.9μm,476.5±45.3μm,respectively(P =0.873).The mean ACD values were 3.34±0.33mm,3.26±0.33mm,3.49±0.40mm,respectively(P=0.118).The mean PD measurements were 5.11 ±1.14mm,4.80 ±0.85mm,3.80 ±1.38mm,respectively(P 【0.001).The mean TCT measurements of Visante,Orbscan and Pentacam were 437.9 ±48.2μm,447.6±60.6μm and 459.9±44.0μm,respectively(P =0.214).The Visante and Orbscan measured CCT similarly,while Pentacam measured CCT thicker than the other two.The Visante measured TCT thinner than the other two devices.In ACD measurements,Orbscan was the one giving the lowest values.PD was measured differently by the devices.·CONCLUSION:Although TCT,CCT and ACD measurements acquired by Visante,Orbscan and Pentacam in keratoconus patients are similar,PDmeasurements show large differences among the devices.