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.

Overview of Objective Methods for Assessing Dynamic Changes in Optical Quality.

Quality of vision has been emphasized in ophthalmologic clinical practice in recent years. The optical or visual performance of the human eye is not static and fluctuates over time. Considering the major origins of temporal fluctuations in optical or visual performance, quantitative assessment of the dynamic changes in the optical quality of the entire eye is important. This review provides an overview of the clinical application of the objective methods for assessing dynamic changes in optical quality, particularly those associated with accommodation, the precorneal tear film, the prelens tear film, and contact lens movement and fitting.

Evaluation of corneal epithelial and stromal thickness in keratoconus using spectral-domain optical coherence tomography.

PURPOSE: We sought to assess the corneal thickness of the epithelium and stroma in keratoconic and normal eyes by spectral-domain optical coherence tomography (SD-OCT). METHODS: Fifty-seven keratoconic and 20 normal eyes were studied. The eyes were examined by SD-OCT, and the keratoconic eyes were subdivided into 2 groups: those showing only smooth corneal thinning and corneal protrusion on the image (KC1 group) and those showing abnormalities in the Bowman layer or in the stroma, or in both (KC2 group). The thicknesses at the corneal vertex and at the superior, inferior, nasal, and temporal cornea 1.5 mm from the corneal vertex in the KC1 group were compared with those in the normal group. The OCT findings in the KC2 group were described. RESULTS: The epithelial thickness at the corneal vertex and at the inferior and temporal cornea, and the stromal thickness at all points were significantly thinner in the KC1 group than in the normal group (p < 0.05). The epithelial and stromal thicknesses at the corneal vertex were significantly correlated in the KC1 group and the normal group (r (2)  = 0.427, p < 0.0001).The epithelial thickness in the KC2 group was not uniform owing to Bowman layer scarring, stromal scars, and secondary corneal amyloidosis. CONCLUSIONS: Although epithelial thinning is associated with stromal thinning, when the cornea remains clear, the epithelial thickness may vary because of the irregularity of the stroma beneath the epithelium in patients with keratoconus.

Spontaneous bleb formation in a presumed pellucid marginal corneal degeneration with acute hydrops.

PURPOSE: To report a case of spontaneous bleb formation in a presumed pellucid marginal corneal degeneration with acute hydrops. METHODS: A 51-year-old man reported sudden ocular pain with a lower conjunctival mass in his left eye. A clinical examination was performed to investigate this lesion. RESULTS: The intraocular pressure in the left eye was markedly lower compared with that in the opposite eye. Slit-lamp examination of the left eye showed a conjunctival mass inferior to the corneoscleral limbus adjacent to corneal epithelial and stromal edema without perforation. Corneal topography showed the typical bow tie appearance of corneal steepening rotated 120 degrees clockwise. The right eye was totally normal. Fourier-domain optical coherence tomography with a corneal anterior module adaptor clearly showed a break in Descemet membrane and a ruptured corneal stromal cleft under the conjunctiva near the corneal limbus that resulted in spontaneous bleb formation. The cornea gradually healed after bandage treatment; the spontaneous bleb became smaller and the corneal stromal cleft and edema regressed at 3 months with corneal scarring. The intraocular pressure in the left eye recovered to the same level as that in the opposite eye in association with the decreased bleb size. CONCLUSIONS: This case indicated that spontaneous bleb formation in a pellucid marginal corneal degeneration should be included in the differential diagnosis of a conjunctival mass of unknown origin.

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 Descemet's 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.

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.

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.