Tomoya Nakagawa

Higher-Order Aberrations Due to the Posterior Corneal Surface in Patients with Keratoconus

PURPOSE This study was designed to investigate higher-order aberrations (HOAs) due to the posterior corneal surface in keratoconic eyes compared with normal eyes. METHODS We studied 24 normal and 28 keratoconic eyes. The anterior/posterior corneal heights and pachymetric data were obtained with a rotating Scheimpflug camera. HOAs for 6 mm pupils were calculated from the differences between the height data and the best-fit sphere, using an original program for each corneal surface. The reference axes of the measurements were aligned with the primary line of sight. The HOAs were expanded with normalized Zernike polynomials. For each pair of standard Zernike terms for trefoil, coma, tetrafoil, and secondary astigmatism, one value for the magnitude and axis was calculated by Zernike vector analysis. RESULTS The mean total corneal HOAs (root mean square [microm]) from the anterior/posterior surfaces were significantly (P < 0.001) higher in keratoconic (4.34/1.09, respectively) than in control eyes (0.46/0.15). The mean magnitude of each Zernike vector terms for trefoil, coma, and spherical aberration from the anterior/posterior surfaces was significantly (P < 0.001) higher in keratoconic (0.77/0.19, 3.57/0.87, -0.44/0.17) than control eyes (0.09/0.04, 0.33/0.07, 0.25/-0.07), respectively. The mean axes by vector calculation for coma due to the anterior (63.6 degrees ) and posterior surfaces (241.9 degrees ) were in opposite directions. CONCLUSIONS Corneal HOAs on both corneal surfaces in keratoconic eyes were higher than in control eyes. Coma from the posterior surface compensated partly for that from the anterior surface. Residual irregular astigmatism in patients with keratoconus wearing rigid gas permeable contact lenses can be estimated by measuring the HOA from the posterior corneal surface.

Corneal topographic analysis in patients with keratoconus using 3-dimensional anterior segment optical coherence tomography

PURPOSE: To assess a new corneal topographer based on 3‐dimensional anterior segment optical coherence tomography (OCT‐based corneal topographer) for analyzing corneal topography in patients with keratoconus. SETTING: Osaka University Graduate School of Medicine, Osaka, Japan. DESIGN: Evaluation of diagnostic test or technology. METHODS: Keratoconic eyes and normal control eyes were assessed using a rotating Scheimpflug–based corneal topographer and an AS OCT‐based corneal topographer. The OCT‐based corneal topographer, a 1310 nm swept‐source device, captures 8192 points during 0.34 second for 16 radial scans of the corneal topography. The success rate of precisely digitizing the corneal surfaces, patterns of the color‐coded maps, central corneal thickness (CCT), and central axial power were compared between the 2 devices. RESULTS: Forty keratoconic eyes and 30 control eyes were assessed. The OCT‐based corneal topographer measured corneal configurations despite corneal opacities. The success rate of precisely digitizing the corneal surfaces in keratoconic eyes was 95% using OCT and 80% using the Scheimpflug‐based corneal topographer. The color‐coded maps of the anterior and posterior corneal elevations, CCT, and corneal axial power maps generated by the 2 devices agreed well. The correlations between the CCT values and between the central corneal axial power values measured by the 2 devices were well correlated in both groups. CONCLUSIONS: The OCT‐based corneal topographer, with its faster acquisition time, provided more consistent measurements than the Scheimpflug‐based corneal topographer. The OCT‐based corneal topographer seems promising for evaluating highly irregular corneas, as in cases of advanced keratoconus. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Characteristic higher-order aberrations of the anterior and posterior corneal surfaces in 3 corneal transplantation techniques.

PURPOSE To investigate the corneal higher-order aberrations (HOAs) of the anterior and posterior corneal surfaces in eyes that underwent penetrating keratoplasty (PK), deep anterior lamellar keratoplasty (DALK), and Descemet stripping automated endothelial keratoplasty (DSAEK). DESIGN Retrospective, case-control study. METHODS study population: Twenty-four eyes underwent PK, 28 eyes underwent DALK, and 19 eyes underwent DSAEK; 29 normal eyes served as controls. observation procedures: The anterior and posterior corneal heights and pachymetric data were obtained with a Scheimpflug-based corneal topographer. Corneal HOAs for 4-mm pupils were calculated from the height data and were expanded with normalized Zernike polynomials. The HOAs resulting from the anterior and posterior corneal surfaces were compared among the procedures. main outcome measures: Anterior and posterior corneal HOAs (root mean square). RESULTS Control eyes had significantly lower total HOAs and Zernike vector terms of the anterior and posterior surfaces than the other groups, except for spherical aberration. The mean anterior corneal surface total HOAs in the PK, DALK, DSAEK, and control groups were 1.38 ± 0.67 μm, 1.19 ± 0.57 μm, 0.61 ± 0.33 μm, and 0.21 ± 0.07 μm, respectively. The anterior corneal HOAs in the DSAEK group were significantly less than those in the PK group (P < .001) and DALK group (P < .001). The mean posterior corneal surface total HOAs were, respectively, 0.20 ± 0.09 μm, 0.24 ± 0.11 μm, 0.27 ± 0.15 μm, and 0.07 ± 0.02 μm. There were no significant differences in the posterior corneal HOAs among the treatment groups. CONCLUSIONS Because the refractive indices between the anterior and the posterior surfaces differed greatly, eyes that undergo DSAEK have lower anterior corneal HOAs compared with PK or DALK eyes. However, the anterior and posterior corneal HOAs in DSAEK eyes still were greater than those in control eyes.

Quality of vision in eyes after selective lamellar keratoplasty.

Abstract: With the increasing popularity of selective lamellar keratoplasty procedures, it is important to characterize the optical differences among penetrating keratoplasty (PK), deep anterior lamellar keratoplasty (DALK), and Descemet stripping automated endothelial keratoplasty (DSAEK). The impact of optical differences on the visual acuity (VA) in eyes after keratoplasty is significant. Quantitative evaluation of corneal higher-order aberrations (HOAs) of anterior and posterior surfaces using a rotating Scheimpflug-based corneal topographer, showed that eyes that undergo DSAEK have lower anterior corneal HOAs compared with eyes subjected to PK or DALK. In DSAEK, the anterior corneal surfaces are not replaced, which is in contrast to PK or DALK, where they are replaced. Through evaluation of corneal scatter with a densitometry program associated with the rotating Scheimpflug-based corneal topographer, 3 characteristic patterns of corneal scatter were found in eyes that had undergone keratoplasty. Investigation of the impact of corneal HOAs and corneal scatter on VA after keratoplasty showed that the VA was correlated significantly with corneal scatter.

Corneal topographic analysis by 3-dimensional anterior segment optical coherence tomography after endothelial keratoplasty.

PURPOSE To investigate the characteristics of the corneal topography with three-dimensional (3-D) anterior segment optical coherence tomography (AS-OCT) following Descemets stripping automated endothelial keratoplasty (DSAEK). METHODS Thirty-four eyes of 33 patients following DSAEK were studied. In addition to conventional topographic maps, the elevation map of the intrastromal interface and pachymetric maps of the host and graft were obtained by corneal topographic analysis using 3-D AS-OCT. The coefficient of variation of the corneal power (CV-Pa, CV-Pp) and root mean squares of the corneal elevation (RMS-Ea, RMS-Ep) of the anterior and posterior corneal surfaces were determined. Based on the combination of the regularity and irregularity of the anterior and posterior surfaces, subjects were classified into four types: type 1, regular/regular; type 2, irregular/regular; type 3, regular/irregular; and type 4, irregular/irregular. RESULTS The average graft decentration was 0.59 ± 0.23 mm. The proportion of types 1, 2, 3, and 4 were 59%, 9%, 24%, and 9 %, respectively. The CV-Pa (25.8 ± 8.9) and CV-Pp (-73.9 ± 18.0) of the type 1 corneas were significantly better than that of type 2 and type 3 corneas, respectively. The RMS-Ea (5.1 ± 1.3) and RMS-Ep (26.0 ± 7.3) of the type 1 corneas were significantly better than that of type 2 and type 3 corneas. CONCLUSIONS An OCT-based corneal topographer might be useful in determining the factors associated with optical quality of the cornea following DSAEK by analyzing the topographic characteristics of host and donor separately.

Higher-Order Aberrations of Anterior and Posterior Corneal Surfaces in Patients With Keratectasia After LASIK

PURPOSE We investigated higher-order aberrations (HOAs) of the anterior and posterior corneal surfaces in patients with keratectasia after LASIK. METHODS The subjects comprised four groups: 12 eyes with keratectasia after LASIK, 30 eyes following LASIK without keratectasia, 30 keratoconic eyes, and 30 normal eyes. Corneal HOAs due to the anterior and posterior corneal surfaces for 6-mm pupils (root mean square [μm]) were obtained using a Scheimpflug-based corneal tomographer and compared among the four groups. RESULTS There were significant differences in total HOAs of the anterior and posterior corneal surfaces (mean ± SD) in the keratectasia (2.49 ± 1.37 and 0.83 ± 0.57), keratoconus (4.50 ± 2.57 and 1.18 ± 0.65), LASIK (0.84 ± 0.25 and 0.14 ± 0.04), and normal (0.52 ± 0.15 and 0.17 ± 0.06) groups except for between keratoconus and keratectasia at the posterior surface. Keratectasia and keratoconus showed similar coma-dominant patterns at both surfaces, and there were no significant differences in the Zernike terms between both groups except for the total HOAs and coma aberration at the anterior surface. CONCLUSIONS Although flap creation and laser ablation were supposed to center on the primary line of sight in LASIK, keratectasia after LASIK showed coma-dominant HOAs at both corneal surfaces. This suggests that the cornea in keratectasia has optical properties similar to those in keratoconus.

Quantitative Evaluation of the Natural Progression of Keratoconus Using Three-Dimensional Optical Coherence Tomography.

PURPOSE We quantified the chronologic progression of keratoconus using anterior segment optical coherence tomography (AS-OCT). METHODS A total of 217 eyes from 113 patients with keratoconus, keratoconus suspect, or forme fruste keratoconus were evaluated by corneal tomography using swept-source OCT. Age-dependent changes in the radius of the posterior best-fit sphere (Rpost), minimum corneal thickness (Tmin), and distance from the thinnest point to the corneal vertex (Dmin) were examined over follow-up periods of up to 5.79 years and were analyzed using generalized estimating equation (GEE) nonlinear regression model. RESULTS Annual changes in Rpost (mean, -0.017 mm) and Tmin (-2.69 μm) were significantly higher in younger patients (P < 0.01, GEE nonlinear regression) and in patients with higher maximal K value (Kmax; P < 0.01, GEE nonlinear regression), whereas no changes were observed in Dmin. Even in patients 30 years or older, 14% of eyes revealed remarkable progression in Rpost. In eyes with acute hydrops, annual changes in Rpost (-0.22 mm) and Tmin (-33.8 μm) before acute corneal hydrops were more than 10 times faster than those in other eyes (P < 0.001, GEE nonlinear regression). CONCLUSIONS Chronologic measurements of corneal tomography in keratoconus demonstrated that the progression of steepening at posterior corneal surface was found not only in patients under 30 years but also in older patients, particularly in advanced keratoconus. The rate of progression can be measured by mapping of corneal curvature and thickness using OCT, and the risk of progression was greater in younger patients with steeper Kmax.

Corneal ablation with new 193 nm solid-state laser: preliminary experiments.

PURPOSE: To assess the ability of a newly developed 193 nm solid‐state laser to ablate the cornea. SETTING: Osaka University, Osaka, Japan. METHODS: A prototype laser engine was developed by combining a 1547 nm laser diode, fiber amplifiers, and 5 stages of a frequency‐conversion system using CsLiB6O10 crystals as the last stage. Poly(methyl methacrylate) (PMMA) plates were exposed to the prototype laser beam to determine the relationship between the fluence and ablation rate. Laser irradiation of porcine corneas was performed to induce morphological changes, and the quality of the lesions was determined by light and scanning electron microscopy. RESULTS: The relationship between the fluence and ablation rate of the 193 nm solid‐state laser was comparable to that of the argon–fluoride excimer laser. Light and scanning electron microscopy of the porcine corneas showed that the linear and square lesions had sharp, clean edges. CONCLUSIONS: Smooth ablations of PMMA plates and porcine corneas were obtained by the laser. Further investigations must be conducted to determine whether this laser can be an alternative laser source for keratorefractive surgery.