Dhruv Srivastava

Differences in central and non-central keratoconus, and their effect on the objective screening thresholds for keratoconus.

To evaluate the differences in central and non‐central keratoconus (based on cone location), and their effect on the objective screening thresholds for keratoconus.

Femtosecond Laser-assisted Wavefront-guided LASIK Using a Newer Generation Aberrometer: 1-Year Results

PURPOSE To evaluate long-term outcomes of wavefront-guided LASIK with a new advanced aberrometer. METHODS Fifty eyes of 25 LASIK candidates with myopia and/or astigmatism underwent aberrometry (iDesign Advanced WaveScan; Abbott Medical Optics, Santa Ana, CA), femtosecond laser-assisted flap creation, and excimer ablation. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SEQ), and astigmatism outcomes were measured at 1, 3, 6, and 12 months postoperatively. RESULTS The sphere, cylinder, and SEQ were -4.29 ± 1.94, -0.75 ± 0.76, and -4.67 ± 2.01 diopters (D), respectively, preoperatively and 0.03 ± 0.13, -0.09 ± 0.13, and -0.02 ± 0.14 D, respectively, 12 months postoperatively (P < .001). The postoperative log-MAR CDVA (-0.07 ± 0.09) and UDVA (-0.04 ± 0.09) were better than the preoperative logMAR CDVA (0.07 ± 0.10) (P < .01). Ninety-four percent achieved a 12-month logMAR UDVA of 0.0 or less (20/20 or better Snellen) and 100% achieved 0.3 or less (20/40 or better Snellen), compared to a preoperative logMAR CDVA of 0.0 or worse in 54% and 0.3 or less in 100%. Postoperative SEQ was within ±0.50 D in 98%. The regression plot for achieved (y) vs intended (x) correction at 12 months was (y = 0.98 × - 0.09, R(2) = 0.99, P < .001). No cases lost CDVA. The target and 12-month surgically induced astigmatisms (TIA and SIA) were 0.91 ± 0.75 and 0.82 ± 0.70, respectively. The regression plot between them was SIA = 0.91 × TIA - 0.01 (R(2) = 0.95, P < .001). The angle of error was -0.29° ± 12.6° and index of success was 0.13 ± 0.25. There was only a mild, nonsignificant increase of higher-order aberrations after surgery, and the postoperative wavefront was stable on follow-up. CONCLUSIONS Wavefront-guided LASIK with iDesign aberrometry appears to be safe and effective in this long-term, consecutive case series.

Predictive Analysis Between Topographic, Pachymetric and Wavefront Parameters in Keratoconus, Suspects and Normal Eyes: Creating Unified Equations to Evaluate Keratoconus.

ABSTRACT Purpose: To perform prediction analysis between topographic, pachymetric and wavefront parameters in keratoconus, suspects, and normal cases and to look at the possibility of a unified equation to evaluate keratoconus. Methods: This cross-sectional, observational study was done in cornea services of a specialty hospital. Fifty eyes of 50 candidates with a diagnosis of normal, keratoconus suspect, and keratoconus were included in each group (total 150 eyes). All eyes underwent detailed analysis on Scheimplug + Placido device (Sirius, CSO, Italy). Main parameters evaluated were topographic [maximum keratometry (Max Km), average keratometry and astigmatism at 3, 5, and 7 mm], pachymetric [central and minimum corneal thickness (MCT) and their difference, corneal volume] and corneal aberrations [higher order aberrations root-mean-square (HOARMS), coma, spherical, residual].Central tendency, predictive fits and regression models, were computed. Results: The measured variables had a significant difference in mean between the three groups (Kruskal–Wallis, p < 0.001). Max Km, MCT, and HOARMS had significant fits with other topographic, pachymetric and wavefront parameters, respectively. Inter-relations between these three (Max Km, MCT, and HOARMS) were also stronger for keratoconus (R2 from 0.75 to 0.33) compared to suspect/normal eyes (R2 from 0.15 to 0.003). These three variables (Max Km, MCT and HOARMS) were used as representative variables to create the unified equations. The equation for the pooled data was (Kmax = 59.5 + 2.3 × HOARMS−0.03 × MCT; R2 = 0.7, p < 0.001). Conclusions: Major variables used for grading keratoconus (MaxKm, MCT, HOARMS) can be linked by linear regression equations to predict the pathology’s behavior.

Evaluation of the Robustness of Current Quantitative Criteria for Keratoconus Progression and Corneal Cross-linking.

PURPOSE To evaluate the robustness of numerical indications of corneal cross-linking by evaluating the inter-session reliability of recently used parameters of progression in keratoconus. METHODS In this observational study, 100 eyes of 100 patients with keratoconus underwent analysis with the Sirius Scheimpflug Topography System (CSO, Firenze, Italy) by a single user. Two sessions (three scans per session) were performed 2 to 4 weeks apart. Cases having poor quality scans, recent visual deterioration, and ocular surgery were excluded. The corneal variables measured were thinnest point and apex characteristics (pachymetry, polar coordinates), volume, central simulated keratometry (flat, steep, average, astigmatism), central corneal thickness, maximum elevation (anterior, posterior), symmetry indices (front, back), and Baiocchi-Calossi-Versaci index. Intra-session (first session, all three measurements) and inter-session (one measurement from each session, selected randomly) statistics were computed. RESULTS There were no significant differences in the six measurements for all variables (P > .05, analysis of variance). The intra-session and inter-session intraclass correlations were high (0.937 to 0.997) and within-subject standard deviations (Sw) were satisfactory (< 5 µm for thickness, < 0.50 diopters [D] for curvature, and < 0.11 mm, < 5° for polar coordinates). Inter-session repeatability (2.77 × Sw) was found to be satisfactory when compared to previously used central keratometric (> 1.00 D increase) or pachymetric (> 2%/> 5% decrease) guidelines to define progression. Apex power repeatability (1.24 D) was found to be poorer than previously used recommendations (1.00 D change). CONCLUSIONS The criteria used to define keratoconus progression were satisfactory when compared to inter-session reliability of corneal parameters. Because higher variability was noted at apex, its curvature repeatability cut-off may be raised to 1.25 D for identifying progressive keratoconus. [J Refract Surg. 2016;32(7):465-472.].

Single session, intrauser repeatability of anterior chamber biometric and corneal pachy-volumetric parameters using a new Scheimpflug+Placido device

Purpose To analyze single session, intrauser reliability of a Scheimpflug device for anterior chamber (AC) and corneal parameters. Methods In this observational study, 100 normal candidates underwent Scheimpflug analysis with Sirius 3D Rotating Scheimpflug Camera and Topography System (Costruzione Strumenti Oftalmici, Italy). Two scans in dark room conditions were performed by the same experienced user. The candidates were asked to keep both eyes closed for 5 min before the scans. Exclusion criteria were previous ocular surgery, corneal scarring and anterior segment/posterior segment anomalies. Only the right eyes were used for the analysis. Both corneal (central, minimum, and apical thickness, volume, horizontal visible iris diameter, and apical curvature) and anterior chamber (volume, depth, angle, horizontal diameter) measurements were evaluated. Results There was no difference in the means of repeated measurements (p > 0.05, ANOVA). Intraclass correlations between the measures were high and ranged from 0.995–0.997 for corneal to 0.964–0.997 for anterior chamber (AC) parameters. The precision of repeatability measures (1.96 × Sw) was approximately 5 μ for the central and minimum corneal thickness, 8 μ for the apical corneal thickness, 0.06 mm for AC (anterior chamber) depth and less than 2° for the AC angle. Conclusions Sirius Scheimpflug system has high repeatability for both corneal and AC parameters in normal eyes.

Implantable collamer lens in a case of corneal scar with anisometropic amblyopia in an adult: an expanded indication

A 35-year-old man, a unilateral high myope with corneal scarring, presented for evaluation. He had a stromal scar that started temporally, traversed along the pupillary zone partially and extended across the horizontal diameter of the cornea. The Descemets membrane appeared intact even though the scar was extending into deep stroma towards the nasal end, as seen in the optical coherence tomography image. The patient had an uncorrected distance visual acuity (UDVA) of 4/60 OD, which improved with a refraction of −9.0 DS/−1.50 DC at 15 to 6/18p and 6/6p OS. He underwent an uneventful toric implantable collamer lens (ICL) implantation of −15.0 D/−2.0 D at 102 after preoperative yttrium–aluminium–garnet (YAG) laser iridotomy in the right eye. The postoperative UDVA and corrected distance visual acuity for the right eye were 6/12 and 6/9p (with a refraction of +0.50 D/−0.50 D at 85), respectively. The corneal scar and topography were stable. This case reports an expanded indication for toric ICL in cases with corneal scar/opacity but good spectacle corrected visual acuity.

Single session, intra-observer repeatability of an advanced new generation Hartmann-Shack Aberrometer in refractive surgery candidates

© 2015 Journal of ophthalmic and Vision research | published by Wolters KluWer ‐ medKnoW Sir, Recently, a new aberrometer, the iDesign advanced Wavescan studio (Abbott Medical Optics, Santa Ana, CA, USA) has been launched for commercial use. This device is considered as a new, upgraded and more sensitive version of the Wavescan aberrometer (Abbott Medical Optics, Santa Ana, CA, USA). It has five times greater resolution, encompassing over 1,250 data points through a 7.0‐mm pupil as compared to 240 points for the Wavescan.[1] However, it remains to be seen if this increase in sensitivity would hamper instrument repeatability by picking up extra signal noise, especially during testing of wavefront aberrations, which are variable to some extent. In this consecutive case series, we measured the single user, single session repeatability of wavefront and other anterior segment measurements by iDesign in 100 refractive surgery candidates with no ocular morbidity except for refractive errors. The study had institutional review board approval and followed all tenets of the Declaration of Helsinki. Informed consent was obtained from all candidates. All candidates underwent a detailed evaluation and those with topographically evident keratoconus, dry eye, any previous surgical intervention in the eye or corneal scars/irregularity were excluded. All measurements were obtained by a single experienced user (DS) on the iDesign aberrometer. The candidates waited in the dedicated examination room for 30 minutes with eyes closed and the room lights shut off. Then the tests were carried out in dark room conditions. A five‐minute rest with the eyes closed was given between each measurement. The data is then analyzed by the instrument software, which looks for usable iris registration, wavefront data, and corneal topography data. The review screen shows a green icon for all these three data when measurements are practical for treatment or analysis. Three such consecutive ‘good’ measurements were taken. The right eyes were used for analysis. The data were noted and analyzed for a 6‐mm pupil diameter. Even though the machine provides output till 6th order aberrations for individual polynomials, the analysis was limited up to the 4th order to maintain clinical relevance and ease of interpretation as beyond 4th order, most values were exceedingly low. Polar Zernike coefficients were used for the study. All data was then transferred as jpeg images and manually entered into an MS Excel (Microsoft, Richmond, VA, USA) sheet. The data was then transferred to SPSS software version 16.0 (SPSS Inc., Chicago, IL, USA) for analysis. Mean and standard deviation of data for the three measurements (of 100 eyes) as well as the pooled data (n = 300) were derived. Analysis of variance was used to evaluate differences among the three measurements. The intra‐subject variation was assessed by the parameters described by Altman and Bland, including intra‐subject standard deviation (Sw) of the three consecutive measurements, intra‐subject precision (1.96 × Sw) and intra‐subject repeatability (2.77 × Sw).[2] The means, standard deviations, 95% confidence intervals of means and the range of data are detailed in Table 1. Mean values for measurement in the three groups were comparable (ANOVA P > 0.05 for all measurements, Table 1). Intra‐subject standard deviation (Sw), repeatability and precision values are presented in Table 2. The intraobserver Sw was 0.25 diopter (D) for sphere and 0.08 D Letter

Comparison of Ocular Monochromatic Higher-order Aberrations in Normal Refractive Surgery Candidates of Arab and South Asian Origin.

Purpose: To compare the ocular monochromatic higher.order aberration. (HOA) profile in normal refractive surgery candidates of Arab and South Asian origin. Methods: This cross.sectional, observational, comparative study was performed in the cornea department of a specialty hospital. Normal refractive surgery candidates with no ocular morbidity except refractive error were recruited. Refractive surgery candidates underwent a preoperative evaluation, including wavefront aberrometry with the iDesign aberrometer. (AMO, Inc., Santa Ana, California, United States). The HOA from right eyes were analyzed for HOA signed, absolute, and polar Zernike coefficients. Results: Two hundred Arab participants (group 1) and 200 participants of South-Asian origin (group 2) comprised the study sample. The age and refractive status were comparable between groups. The mean of the HOA root mean square (RMS) was 0.36 ± 17 μ and 0.38 ± 18 μ for Arab and South-Asian eyes, respectively (P < 0.05, rank sum test [RST]). Of the 22 higher order signed Zernike modes, only Z3−3, Z3−1, 31, Z4−4, Z4−2, Z40, Z44, and Z5−5 were significantly different from zero (one sample t-test, P < 0.002, with a Bonferroni correction of 0.05/22). All the signed and absolute Zernike terms were comparable between groups (RST, P > 0.002 [0.05/22]). The polar coefficients for coma, trefoil, spherical aberration, and tetrafoil were comparable between groups (P > 0.05, RST). Combined RMS values of third, fourth, fifth, and sixth order also were comparable between groups (P > 0.05, RST). Conclusions: Preoperative whole eye HOA were similar for refractive surgery candidates of Arab and South.Asian origin. The values were comparable to historical data for Caucasian eyes and were lower than Asian. (Chinese) eyes. These findings may aid in refining refractive nomograms for wavefront ablations.

Multivariate Analysis to Predict the Horizontal Anterior Chamber Diameter from Other Anterior Chamber Parameters Using Scheimpflug Imaging: Is There a Better Method Than Adding a Fixed Constant?

ABSTRACT Purpose: To evaluate the predictive association between the horizontal anterior chamber diameter (HACD) and other measurements using Scheimpflug imaging, and to assess whether a method superior to using fixed constants can be proposed. Methods: This hospital-based study was performed in the Cornea and Refractive Surgery Services, New Medical Center (NMC) specialty hospital, Abu Dhabi. Initially, 100 candidates were included serially in the model building group (group1). All candidates underwent detailed evaluation and Scheimpflug imaging (CSO, Sirus, Italy). Subsequently, another 100 candidates were included serially in the validation group (group 2). Candidates in both groups underwent the same tests. Results: In group 1, the mean HACD was 12.25 ± 0.48 mm. This measurement correlated significantly with the horizontal visible iris diameter (HVID), anterior chamber depth, angle (ACA), and volume (ACV) (r = 0.2–0.7). The overall regression equation was HACD = 5.62 + 0.01 × ACV + 0.45 × HVID − 0.013 × ACA (adjusted R2 = 0.66, p < 0.001). Situation-based equations derived from the outcomes of group 1 were tested in group 2. Equation A included all factors found significant during model-building, Equation B included only non-volumetric significant factors, and situation C only included the HVID. Equations D through F used direct substitution by HVID plus a constant to predict HACD (the constant was 0.0, 0.5, and 1.0 for Equations D, E, and F, respectively). The predicted HACD (pHACD) was within ±0.5 mm of the actual HACD (aHACD) in 93%, 88%, 87%, 83%, 69%, and 16% case for Equations A, B, C, D, E, and F, respectively. The mean prediction error was −0.14 ± 0.27 mm (p = 0.08), −0.15 ± 0.28 mm (p = 0.03), −0.18 ± 0.30 mm (p = 0.001), −0.18 ± 0.32 mm (p < 0.001), 0.33 ± 0.35 mm (p < 0.001), and 0.83 ± 0.35 mm (p < 0.001) for Equations A, B, C, D, E, and F, respectively. Conclusion: Regression equations using Scheimpflug-derived anterior chamber parameters may predict HACD to varying degrees, depending on the input parameters. Adding 0.5 or 1.0 mm to the corneal diameter (CD) to estimate the HACD is not recommended.

Assessment of bilateral pupillary centroid characteristics at varying illuminations and post‐photopic flash response using an automated pupillometer

The aim was to assess the symmetry and magnitude of illumination‐dependent centroid shift and of post‐photic flash re‐dilatation response for normal pupils.