How Abnormal Is the Noncorneal Biometry of Keratoconic Eyes?

Accuracy of intraocular lens power formulas in eyes with keratoconus: Multi-center study in Japan

PURPOSE

To assess the accuracy of intraocular lens (IOL) power formulas, namely, SRK/T, Haigis, Barrett Universal II, Barrett True-K for keratoconus, Kane formula, and Kane formula for keratoconus, for cataract with keratoconus in Japanese eyes.

SETTING

Five surgical sites in Japan.

DESIGN

A retrospective case series.

METHODS

Eyes with keratoconus undergoing cataract surgery were included. Postoperative refraction was compared with the prediction by the formulas. Visual acuity, manifest spherical equivalent, prediction error (PE), and mean absolute errors (MAEs) were determined 1 month postoperatively. The PE within 0.50 diopter (D), 1.00 D, and 2.00 D were compared between IOL formulas. Subgroup analysis based on the steepest keratometry (stage 1, ≤ 48 D; stage 2, > 48 D and ≤ 53 D; and stage 3, > 53 D) was performed. The relationship between PE and preoperative biometric data were assessed.

RESULTS

Fifty eyes were included. The MAE of the Barrett True-K for keratoconus, Kane keratoconus, and Kane formulas were significantly lower than that of Haigis. A statistically significant difference in the prediction accuracy within ± 0.50 D was found between Kane keratoconus and Haigis. The prediction accuracy of the Barrett True-K for keratoconus, SRK/T, and Kane within ± 1.00 D was statistically significant compared with that of Haigis. In stage 3, the Barrett True-K for keratoconus had a significantly lower MAE than SRK/T and Haigis.

CONCLUSION

Keratoconus-specific formulas were more accurate than existing formulas in Japanese eyes. The Barrett True-K formula for keratoconus had higher prediction accuracy in severe keratoconus.

Evaluation of ocular biometric parameters in keratoconic eyes relative to healthy myopic eyes

OBJECTIVE

To assess the biometric features of keratoconic eyes using the Lenstar LS900 and Pentacam systems relative to healthy myopic eyes.

MATERIALS AND METHODS

Seventy-three eyes of keratoconic subjects and 83 eyes of control subjects were enrolled. To evaluate the reproducibility of the Lenstar and Pentacam devices' measurements, keratometric readings [in flattest meridian (Kf), in steepest meridian (Ks), and mean (Km)], central corneal thickness (CCT), and anterior chamber depth (ACD) were obtained using both systems. Axial length and lens thickness (LT) were measured by the Lenstar. The compatibility between the two devices was investigated using the Bland-Altman statistical method.

RESULTS

Axial length was longer in the myopic group than in eyes with keratoconus (24.94  ±  0.7 and 23.88  ±  0.96 mm, respectively, p < 0.001). LT and vitreous depth were also higher in the myopic group, although ACD values were similar. Compared to the Lenstar, the Pentacam measured the ACD and CCT values higher in the myopia group [with a difference of 0.07  ±  0.12 mm (p <0.001) and 4.47  ±  11.33 µm (p  =  0.001), respectively] and measured the CCT values higher in the keratoconus group. Pentacam found all keratometry values significantly lower than Lenstar in the keratoconus group.

CONCLUSIONS

Axial length was longer in the myopic eyes due to the differences starting from the lens and extending to the posterior segment. Lenstar and Pentacam can be used interchangeably for Km, Kf, and ACD in the myopic group and only for ACD in the keratoconus group.

Toric intraocular lens power calculation in cataract patients with keratoconus

Purpose

Intra-ocular lens (IOL) power calculation in eyes with keratoconus typically results in hyperopic postoperative refractive error. We investigated the visual and refractive outcomes in keratoconus patients having cataract surgery with a toric IOL and compared IOL power calculation accuracy of conventional formulae and keratoconus specific formulae.

Setting

Ein-Tal Eye Center, Tel-Aviv, Israel.

Design

Retrospective case-series study.

Methods

Post-operative visual acuity and manifest refraction were examined. The error in predicted refraction and IOL power calculation accuracy within a range of 0.5 to 2.0 diopters were compared between different IOL calculating formulae.

Results

Thirty-two eyes with keratoconus were included. Visual acuity improved in all cases and subjective astigmatism decreased from -2.95+/-2.10 D to -0.95+/-0.80 D (p<0.001). Mean absolute errors were: Barrett True-K for keratoconus with measured or predicted posterior corneal power, 0.34 D; Barrett Universal II, 0.64 D; Kane Formula, 0.69 D; Kane Formula for keratoconus, 0.49 D; SRK/T, 0.56 D; Haigis, 0.72 D; Holladay 1, 0.71 D and Hoffer Q, 0.87 D. Barrett True-K formula with measured posterior corneal power, SRK/T and Kane Formula for keratoconus resulted in a prediction error within 0.5 D of 87.5%, 59.4% and 53.1%, respectively.

Conclusions

Cataract removal with a toric IOL significantly improves visual acuity and decreases astigmatism in keratoconic eyes with a topographic central relatively regular astigmatic component. Keratoconus specific formulae resulted in lower mean error in predicted refraction compared with conventional calculating formulae. Utilizing the posterior corneal power within the Barrett True K formula for keratoconus improved IOL power prediction accuracy.

Baseline Findings in the Retrospective Digital Computer Analysis of Keratoconus Evolution (REDCAKE) Project

PURPOSE

To present the baseline data for a large cohort of patients with keratoconus enrolled in the Retrospective Digital Computer Analysis of Keratoconus Evolution (REDCAKE) study.

METHODS

Eight centers contributed the Scheimpflug tomographical data for 906 patients with keratoconus, 743 measured with a Pentacam and 163 with a Galilei. The stage of keratoconus at baseline, the location of the reference points, minimum pachymetry (Pmin), and maximum keratometry (Kmax) were analyzed. The intereye asymmetry was evaluated for Kmax (anterior and posterior), Pmin, and keratoconus stage. Average maps and elevation profiles were calculated for each degree of keratoconus.

RESULTS

Keratoconus was more frequently diagnosed in men (73%) than in women (27%). At baseline, 500/1155 eyes (43%) presented with moderate to severe changes in the posterior surface, whereas moderate/severe changes were only found in 252 and 63 eyes when evaluating anterior surface and pachymetry, respectively. The location of Pmin was usually inferotemporal (94% OD and 94% OS), while the location of Kmax showed more variability and significantly higher distance from apex (P < 0.05). The keratoconus presentation was chiefly asymmetric for all the parameters studied. Clear differences between stages could be identified in the maps and elevation profiles.

CONCLUSIONS

The staging map set presented can be used as a graphical guidance to classify keratoconus stage. Keratoconus presented asymmetrically, and generally the posterior surface was more affected than the anterior surface or the thickness. Asymmetry is playing a role in KC detection. Although Pmin was almost invariably located inferotemporally, Kmax location showed higher variability and distance from the apex.

Ocular dimensions of the Chinese adolescents with keratoconus

Background

Adolescent KC is a special segment of the general KC population because an adolescents’s eyes are still susceptible to blurred vision and optical defocus during the sensitive period of ocular and visual development. In the present study, we evaluated the ocular dimensions of 53 KC adolescents.

Methods

One hundred and six KC eyes of 53 (42 boys and 11 girls) KC adolescents (age 15.5 ± 1.7 years, range 11 to 18) were involved in this retrospective study. The eye with more severe KC (Severe Group) of each patient was compared with their less affected eye (Mild Group). Optical axial length (OAL) was measured by optical coherence biometry (IOL-master). Central corneal thickness, anterior chamber depth (ACD), flat keratometry value, steep keratometry value, and maximum keratometry value were assessed with an anterior segment analyzer (Pentacam HR). Anterior segment length (ASL) was manually measured from the 25 scheimpflug images captured by the Pentacam HR with the mean value recorded. The posterior segment length (PSL) was calculated with the formula “PSL = OAL-ASL”.

Results

The mean ACD, OAL, ASL, and PSL values of the Severe Group were 3.51 ± 0.32 mm, 24.76 ± 1.24 mm, 4.01 ± 0.30 mm and 20.76 ± 1.15 mm.While those of the Mild Group were 3.36 ± 0.29 mm, 24.97 ± 1.40 mm, 3.94 ± 0.35 mm and 21.03 ± 1.31 mm. The Severe Group has significantly higher ACD (t = 4.539, P < 0.001) value but lower OAL (t = − 3.120, P = 0.003) and PSL (t = − 4.537, P < 0.001) values when compared with those of the Mild Group. For the Severe Group, the Kmax values were significantly correlated with the SE values (R = − 0.385, P = 0.004), the ACD values (R = 0.375, P = 0.006), the ASL values (R = 0.308, P = 0.025) and the PSL values (R = − 0.317, P = 0.021), but not with the OAL values (R = − 0.220, P = 0.114). In the Mild Group, the Kmax values were negatively correlated with the SE (R = − 0.577, P < 0.001), OAL(R = − 0.533, P < 0.001), and PSL (R = − 0.523, P < 0.001) values, but not with ACD (R = − 0.110, P = 0.434) or ASL (R = − 0.182, P = 0.192) values.

Conclusions

For adolescent KC, the more keratoconic eyes may be characterized by deeper ACD but shorter OAL and PSL, when compared with the less affected ones.

SyntEyes KTC: higher order statistical eye model for developing keratoconus

PURPOSE

To present and validate a stochastic eye model for developing keratoconus to e.g. improve optical corrective strategies. This could be particularly useful for researchers that do not have access to original keratoconic data.

METHODS

The Scheimpflug tomography, ocular biometry and wavefront of 145 keratoconic right eyes were collected. These data were processed using principal component analysis for parameter reduction, followed by a multivariate Gaussian fit that produces a stochastic model for keratoconus (SyntEyes KTC). The output of this model is filtered to remove the occasional incorrect topography patterns by either an automatic or manual procedure. Finally, the output of this keratoconus model is matched to that of the original model for normal eyes using the non-corneal biometry to obtain a description of keratoconus development.

RESULTS

The synthetic data generated by the model were found to be significantly equal to the original data (non-parametric Mann-Whitney equivalence test; 145/154 passed). The variability of the synthetic data, however, was often significantly less than that of the original data, especially for the higher order Zernike terms of corneal elevation (non-parametric Levene test; p < 0.05/154). These results remained generally the same after applying either filter procedure to remove the synthetic eyes with incorrect topographies. Interpolation between matched pairs of normal and keratoconic SyntEyes appears to provide an adequate model for keratoconus progression.

CONCLUSION

The synthetic data provided by the proposed keratoconus model closely resembles actual clinical data and may be used for a range of research applications when (sufficient) real data is not available.