Repeatability of Intra-ocular Pressure and Central Corneal Thickness Measurements Provided by a Non-contact Method of Tonometry and Pachymetry

Abstract

BACKGROUND:

To examine the repeatability of intra-ocular pressure (IOP) and central corneal thickness (CCT) measurements provided by the Tono-Pachymeter NT530P (Nidek, Japan), and to assess agreement of the device with Goldmann applanation tonometry (GAT) and ultrasound pachymetry (UP).

METHODS:

Sixty-two normal eyes of 62 subjects were included in the study. Three sessions of measurements, each consisting of three sets of measurements, were completed with each device. Repeatability was determined with the coefficient of variation (CoV) and the coefficient of repeatability (CoR) values. Agreement between devices was examined by Bland-Altman analysis and intraclass correlation coefficient (ICC) analyses.

RESULTS:

The CoV and CoR for IOP values were 18.4% and 5.5 mmHg with the NT530P and 16.6% and 4.3 mmHg with the GAT respectively. On average, NT530P overestimated the IOP compared with GAT by 1.3 mmHg. The 95% limits of agreement between the methods ranged from -5.9 to +3.3 mmHg, and the ICC for average IOP measures between devices was 0.64 (P < 0.001). The CoV and CoR for CCT measurements were 5.5% and 59.8 μm with the NT530P and 5.5% and 60.5 μm with UP. NT530P CCT readings were on average 13 μm thinner than those obtained with UP. The 95% limits of agreement (LoA) ranged from -7.4 to +33.1 μm, and the ICC for average CCT measures between devices was 0.93 (P < 0.001).

CONCLUSION:

The NT530P demonstrated high IOP and CCT measurement repeatability in the normal population studied. The device tended to slightly overestimate IOP compared to GAT. CCT values provided by NT530P were interchangeable with those of UP.

Optical Performance of the Cornea Six Years Following Photorefractive Keratectomy for Myopia

Abstract

PURPOSE:

To investigate the optical quality of the anterior cornea during a 6-year follow-up after photorefractive keratectomy (PRK) for myopia.

METHODS:

Forty-nine patients (98 eyes) underwent PRK using an excimer laser platform. Patients were subdivided into three groups according to their preoperative spherical equivalent refraction and amount of cylinder component: the low-myopia, the high-myopia, and the astigmatism group. Preoperative and 1-, 3-, and 6-year postoperative root-mean-square values of coma, spherical aberration (SA), and total high-order aberrations (HOA) were calculated over 3.50- and 6.00-mm pupil diameters. Modulation transfer function (MTF) values and point spread functions were calculated to describe the impact of myopic PRK on the optical performance of the cornea during follow-up.

RESULTS:

The amount of postoperative SA was higher (P < 0.05) than the preoperative state in both the low- and the high-myopia groups over 3.50- and 6.00-mm pupil sizes. The postoperative increase of coma was statistically significant (P < 0.05) only in the high-myopia group over both pupil sizes. Total-HOA increased (P < 0.05) after PRK in all the study groups over 6.00-mm pupil. A distinct increase in the ratios of MTF was calculated over 6.00-mm pupil, at low and middle spatial frequencies in the range between 5 and 15 cyc/deg, especially after the deepest myopic ablations.

CONCLUSIONS:

The high-order wavefront aberration of the anterior cornea stabilized 1-year after PRK for the treatment of myopia up to -9.00 D. The effect of induced HOA on the image optical quality of the cornea was increased mainly after the correction of high myopia over scotopic pupil.

Investigation of Corneal Topography After Deep Lamellar Endothelial Keratoplasty

Abstract

PURPOSE:

To analyze the 6-month anterior and posterior topographic changes of the cornea after deep lamellar endothelial keratoplasty.

METHODS:

Orbscan topographies of 22 eyes from 21 patients with corneal decompensation were retrospectively analyzed: 11 eyes received a 9-mm scleral access incision (large-incision group) and 11 eyes received a 5-mm scleral access incision (small-incision group). All the preoperative and postoperative corneal raw data were imported into custom software which computed the average composite corneal maps and difference maps for both study groups in order to evaluate the corneal response to the surgery. The software delineated 2 concentric zones of the cornea to characterize the regional response following the surgery: the central and peripheral regions.

RESULTS:

There were no significant differences (analysis of variance, <0.35 D, p>0.05) between 6-month postoperative and preoperative average anterior central corneal topographies in either group. At the end of follow-up, the average posterior curvature tangential map did not significantly differ from before surgery in either group (<0.35 D, p>0.05). However, a significant increase (>0.60 D, p<0.01) in the average posterior central astigmatic power of the cornea was found in both groups.

CONCLUSIONS:

Deep lamellar endothelial keratoplasty effectively preserves the preoperative keratometric corneal topography, minimizing changes in curvature and astigmatism of the cornea. The great predictability of corneal topography following deep lamellar endothelial keratoplasty is likely to be attributed to the minimal changes that occur in the anterior stroma, the portion of the cornea that appears to be mainly responsible for maintenance of corneal shape.

Surface Roughness of Intraocular Lenses With Different Dioptric Powers Assessed by Atomic Force Microscopy

Abstract

PURPOSE:

To analyze the optic surface roughness and morphology of 2 types of hydrophobic acrylic intraocular lenses (IOLs) with various dioptric powers using atomic force microscopy (AFM).

SETTING:

Technical University of Cluj-Napoca, Faculty of Mechanics, Cluj-Napoca, Romania.

METHODS:

Atomic force microscopy was used to characterize the topography of 2 types of hydrophobic acrylic IOLs from a single manufacturer (SN60AT and SA30AL) with dioptric powers ranging from 10.0 diopters (D) to 30.0 D. The AFM analysis was performed in contact mode using a V-shaped silicon nitride cantilever with a pyramidal tip curvature of 15 nm and a nominal spring constant of 0.2 N/m. Detailed surface characterization of the IOL optic was obtained using 6 quantitative parameters provided by the AFM software.

RESULTS:

Five of 6 roughness parameters indicated statistically significant differences (P<.05) between IOLs with different dioptric powers, with the 10.0 D IOL in both models providing the smoothest optic surface. Between models with the same dioptric power, the SN60AT model had lower values of each surface roughness parameter than the SA30AL model.

CONCLUSIONS:

Atomic force microscopy was an accurate tool for assessing the surface properties of IOL optics. Manufacturing processes were responsible for introducing detectable differences in the topography of IOL biomaterials with identical copolymer constituents but different dioptric powers. Nanometric analysis may assist IOL manufacturers in developing IOLs with optimal surface characteristics.

Analysis of Posterior Donor Corneal Parameters 1 Year After Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) Triple Procedure

Abstract

BACKGROUND:

Although Descemet stripping automated endothelial keratoplasty (DSAEK) was demonstrated to be effective for the treatment of endothelial corneal diseases, a variable hyperopic shift has been measured as a common occurrence postoperatively. The aim of this work was to investigate the variance in the corneal and refractive responses to DSAEK combined with phacoemulsification and implantation of intra-ocular lens (IOL), namely the DSAEK triple procedure.

METHODS:

The refractive, topographic, and anterior segment optical coherence tomography (AS-OCT) data of 23 eyes treated with DSAEK triple procedure were analyzed. A mean refractive IOL target of -1.04 +/- 0.09 D was calculated based on empirical data of our early experience to achieve emmetropia in all the eyes included in the study. Donor corneal parameters, i.e., graft diameter, thickness, and profile, were investigated in order to verify their possible role in the variable refractive shift after DSAEK.

RESULTS:

Although the 1-year mean refractive outcome was close to emmetropia (-0.01 +/- 0.89 D), the average difference between the targeted postoperative refraction and the 1-year postoperative spherical equivalent refraction was +0.98 +/- 0.87 D. Correlations of refractive change with central graft thickness (r = 0.36, p = 0.05) and graft diameter (r = 0.45; p = 0.03) were statistically significant. AS-OCT analysis revealed how the graft shape, with graft thicker in the periphery compared with the center, contributed to reduce the radius of curvature of the posterior cornea, thus favoring the hyperopic shift postoperatively.

CONCLUSIONS:

DSAEK triple procedure provides negligible changes in the surface topography, however with a variable amount of hyperopic shift postoperatively. Central graft thickness and graft profile together contributed to approximately two-thirds of the variance in refractive shift postoperatively. Lenticule diameter provided a minor influence on postoperative hyperopic shift than other graft parameters.

Long-term Anterior and Posterior Topographic Analysis of the Cornea After Deep Lamellar Endothelial Keratoplasty

Abstract

PURPOSE:

To analyze the 2-year topographic response of the cornea to deep lamellar endothelial keratoplasty (DLEK).

METHODS:

The Orbscan topographies of 24 eyes that underwent DLEK for corneal decompensation were retrospectively analyzed. Twelve eyes received a large-incision DLEK technique and 12 eyes received a small-incision DLEK. All the preoperative and postoperative corneal raw data were imported into a custom software program, which computed the average composite corneal maps and difference maps for both study groups to evaluate the corneal response to the surgery. The software delineated 2 concentric zones of the cornea to characterize the regional response after the surgery: the central and peripheral regions.

RESULTS:

At 2 years after surgery, no significant changes (<0.41 diopters; analysis of variance, P > 0.05) in the central topography configuration were measured in comparison with the preoperative state after DLEK procedures. On the other hand, a significant increase (P < 0.01) in the mean tangential curvature and astigmatic power of the anterior corneal periphery was measured after surgery, with higher changes after large-incision DLEK. No significant differences in the average curvature profile of the posterior corneal interface were measured after DLEK procedures (<0.40, P > 0.05) in comparison with the preoperative state.

CONCLUSIONS:

DLEK provides stable central corneal topography, with minimal changes in curvature and astigmatic power in the years after surgery. Moreover, the donor posterior cornea shows to maintain its vitality and integrity in the long-term postoperative period, with curvature values similar to the original posterior corneal interface.