Twenty-four hours intraocular pressure in keratoconic eyes assessed by applanation tonometry and Tono-Pen AVIA

AIM: To assess intraocular pressure (IOP) during the daily curve of intraocular pressure (DCPo) in keratoconic eyes and compare Goldmann applanation tonometer (GAT), without and with astigmatism correction (nGAT and cGAT) and Tono-Pen AVIA (TPA) assessment methods. METHODS: Thirty-nine keratoconic eyes of 24 patients were assessed. DCPo was evaluated with five IOP measurements; four were performed with a GAT (nGAT and cGAT), and a Tono-Pen AVIA (TPA) at various times throughout the day. RESULTS: Mean IOP DCPo values (mm Hg) were: nGAT, 9.9±2.6; cGAT, 11.3±2.6; TPA 12.3±3.1. Mean IOP DCPo differences (mm Hg) and Spearman's correlation coefficients were as follows: cGATc-nGAT, 1.32±1.31, rs=0.879 (P<0.01); cGAT-TPA, -1.02±2.08, rs=0.723 (P<0.01); and nGAT-TPA, -2.35±2.23, rs=0.730 (P<0.01). Bland-Altman analysis for agreement between cGAT-TPA and nGAT-TPA mean IOP DCPo measurements revealed a mean difference of 1.02 (95%CI, 0.35-1.70) and 2.35 (95%CI, 1.62-3.07) mm Hg, respectively. Regression analysis yielded the following equation: TPA IOP=5.49+0.775×cGAT-0.015×ACD-0.299×corneal astig matism, which allowed us to infer TPA IOP values from other parameters. CONCLUSION: In keratoconic eyes, IOP peaks of DCPo measurements are identified at 6 a.m., independent of the tonometer. The mean DCPo values are: TPA>cGAT>nGAT. IOP TPA measures are predictive of cGAT values, adjusted according to anterior chamber depth and corneal astigmatism.

Astigmatism correction of convex aspheres using the subaperture stitching Hindle test

We propose an astigmatism correction method for the subaperture stitching Hindle test to measure hyperbolic convex aspheres. Astigmatic wavefront errors arise from misaligned Hindle setups, mechanical runout errors of the rotational motion for stitching, and the surface error of the target itself. Because these errors are combined, they cannot be separated in the conventional subaperture stitching Hindle tests. We exploited the rotational periodicity of each error to distinguish the surface figure error from other astigmatic error sources and rectified the Hindle test results with a third-order astigmatism. Using the subaperture stitching Hindle test, we averaged two sets of measurement data with a 180° rotational phase difference between them to calculate the astigmatic surface error. The proposed method was verified experimentally by comparing it with the results from a commercial stitching interferometer from QED Technologies; only subnanometer differences in the root-mean-square values were obtained. Therefore, the proposed method calibrated the system errors from the test surface wedge and the rotational decenter easily, thereby reducing the mechanical costs and alignment efforts and making it more accessible than a sophisticated mechanism.

Correction of postkeratoplastic astigmatism by intrastromal corneal segments implantation using a femtosecond laser

Background. After penetrating keratoplasty, mild to high induced corneal astigmatism was observed in each case. The existing choice of correction of postkeratoplastic astigmatism is aimed at fi nding an individual approach in order to compensate for it and not weaken the biomechanical properties of the corneal graft.The aim: to analyze the clinical, functional, and morphological results of postkeratoplastic astigmatism correction by implantation of intrastromal corneal segments using a femtosecond laser.Methods. 22 patients were examined before and 1 year after surgery. The operation was performed under local anesthesia: stage I – an intrastromal tunnel was formed using a femtosecond laser “Femto Visum” 1 MHz (Optosystems, Russia); stage II – the intrastromal corneal segments were implanted. The results were assessed using standard and special research methods using optical coherence tomography Visante OCT (Zeiss, Germany), keratotopography (Tomey-5, Japan), optical corneal analyzer ORA (Reichert, USA), laser tindalemetry FC-2000 (Kowa, Japan) and confocal microscope Confoscan-4 (Nidek, Japan).Results. Before the operation, uncorrected visual acuity averaged 0.09 ± 0.05, after a year – 0.50 ± 0.16; best corrected visual acuity – 0.30 ± 0.12 and 0.60 ± 0.05 respectively; cylindrical component of refraction – –10.29 ± 3.12 and –2.20 ± 0.64 D respectively; mean keratometry value – 43.59 ± 2.14 and 38.56 ± 1.75 D respectively; corneal hysteresis – 7.92 ± 1.22 and 8.95 ± 1.05 mm Hg respectively; corneal resistance factor – 7.01 ± 1.81 and 8.44 ± 1.44 mm Hg respectively; protein fl ux in the moisture of the anterior chamber – 2.97 ± 0.28 and 3.04 ± 0.24 f/ms respectively; endothelial cell density – 1521 ± 327 and 1475 ± 419 cells/mm2 respectively.Conclusion. Intrastromal corneal segments implantation into a corneal graft using a femtosecond laser has efficiency and safety method in correcting postkeratoplastic astigmatism.

Astigmatism Correction during Femtosecond Laser-assisted Transepithelial Arcuate Keratotomy Using the Wound Open Method

Purpose: The purpose of this study was to compare corneal astigmatism correction between “wound open” and “wound intact” methods during femtosecond laser-assisted transepithelial arcuate keratotomy.Methods: From April 2016 to December 2018, a retrospective survey was conducted on patients undergoing femtosecond laser cataract surgery at the Ophthalmology Department of Samsung Medical Center. Size comparison and vector analysis of corneal astigmatism before and after surgery were performed in the wound open and wound intact groups.Results: In the wound open and wound intact groups, the target-induced astigmatism (TIA) was 1.28 ± 0.55; and 1.26 ± 0.29 diopters, the surgically induced astigmatism (SIA) was 0.80 ± 0.52; and 0.53 ± 0.32 diopters, and the correction index (CI) was 0.63 ± 0.28; and 0.43 ± 0.26, respectively. The astigmatism correction was superior in the wound open group (p = 0.048, p = 0.025). In a subgroup with TIA < 1.2 diopters, there were no significant differences in SIA or CI between the two groups; however, in the subgroup with a TIA > 1.2 diopters, the SIA was 1.09 ± 0.59; and 0.54 ± 0.37 diopters and the CI was 0.60 ± 0.28; and 0.36 ± 0.23 in the wound open and wound intact groups, respectively (p = 0.022, p = 0.047). Thus, astigmatism correction was superior in the wound open group.Conclusions: The wound open method during femtosecond laser-assisted transepithelial arcuate keratotomy was superior for astigmatism correction compared to the wound intact method.

Correction of Pre-Existing Astigmatism with Phacoemulsification Using Spherical Intraocular Lens and Wave front Guided Surface Ablation: A Retrospective Case Series

Objective: To evaluate safety and efficacy of using spherical intraocular lens followed by wavefront guided surface ablation in correction of preexisting regular corneal astigmatism. Methods: This retrospective case series study included 20 eyes of 16 patients having visually significant cataracts and co-existing regular corneal astigmatism. The patients underwent phacoemulsification with spherical intraocular lens and wavefront guided PRK three months later. Results: There was a statistically significant difference for Uncorrected Visual Acuity UCVA, Best Corrected Visual Acuity BCVA, Manifest Refraction Spherical Equivalent MRSE, and refractive astigmatism postoperatively regarding all these parameters (P˂0.05). Conclusion: Astigmatism correction during or even after cataract surgery is a safe and effective method to improve visual outcomes. Longer period of follow up are required to evaluate stability of this technique and possibility of regression.

Corneal Asphericity and Higher-Order Aberrations after FS-LASIK and Trans-PRK for Myopia

Objective. To compare the corneal asphericity and higher-order aberrations (HOAs) of femtosecond laser-assisted in situ keratomileusis (FS-LASIK) with Smart Pulse Technology (SPT) assisted transepithelial photorefractive keratectomy (Trans-PRK) for myopia and myopic astigmatism correction. Methods. This prospective study analyzed 88 eyes of 44 patients treated with FS-LASIK and 64 eyes of 32 patients treated with Trans-PRK. All eyes had low to moderate myopia with or without astigmatism (spherical equivalent (SE) <−6.00 diopters). The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), SE, asphericity (Q value) of the anterior corneal surface, index of surface variance (ISV), corneal higher-order aberrations (HOAs), vertical coma (Z3−1), horizontal coma (Z31), and spherical aberration (Z40) over a 6 mm diameter central corneal zone diameter were evaluated preoperatively and 1, 3, and 6 months postoperatively. Results. At 6 months, the UDVA and SE were −0.14 ± 0.06 and 0.33 ± 0.33D in FS-LASIK and −0.15 ± 0.06 and 0.35 ± 0.37D in Trans-PRK. There was no difference between the two groups in the postoperative UDVA and SE ( P > 0.05 ). After FS-LASIK and Trans-PRK, the Q values in the 6, 7, 8, and 9 mm zones and ISV of the anterior corneal surface significantly increased ( P < 0.001 ). At 1, 3, and 6 months after surgery, corneal HOA, Z3-1, Z31, and Z40 in both groups were significantly increased compared with those before surgery, with statistically significant differences ( P < 0.001 ). At 1, 3, and 6 months after surgery, the Z3−1 of the Trans-PRK group was significantly lower than that of the FS-LASIK group ( P < 0.001 ). ΔHOA and ΔZ40 were dramatically correlated with the ΔQ value for both FS-LASIK and Trans-PRK procedures. The ΔQ was significantly correlated with the preoperative SE, AD, and AD/CCT after both two procedures (all P < 0.001 ). Conclusions. Both FS-LASIK and Trans-PRK caused the anterior corneal surface to become flatter, and the morphology of the corneal surface was irregular. Corneal HOAs were significantly increased after the two procedures. Trans-PRK using SPT introduced less corneal vertical coma than FS-LASIK. Corneal asphericity changes contributed to the corneal aberrations changes following FS-LASIK and Trans-PRK.

Mathematical solutions to the problem of creating basic decenter optical mirror models from the coma and astigmatism correction conditions

A serious drawback of reflective optics is a center without central screening that degrades the image quality. To eliminate it, rotations or displacements of mirrors are introduced, but there appear even-order non-elementary aberrations that must be corrected. The creation of compositions with decentered catoptric elements requires further development of the calculation and methodological base. The exact formulas are obtained for calculation of real rays from the astigmatism and coma correction conditions for the given angles of incidence of the main ray on the mirror surfaces and the “oblique” thickness d, that determines their mutual position. Based on the proposed formulas, a new method for parametric calculation of decentered mirror systems has been created, which allows one to compose algorithms and to design both basic models and complex mirror systems from off-axis mirrors. The development of new algorithms for two- and three-mirror off-center lenses will increase the accumulated potential of computational optics. The scope of the proposed technique can be expanded in terms of the number of components.

Long-term changes in the refractive effect of a toric intraocular lens on astigmatism correction

Purpose To examine the long-term changes in the astigmatism-correcting effect of a toric intraocular lens (IOL) after stabilization of surgically induced astigmatic changes due to cataract surgery. Methods Unilateral eyes of 120 patients that received a toric IOL for against-the-rule (ATR) or with-the-rule (WTR) astigmatism were enrolled. Manifest refractive and anterior corneal astigmatism, and ocular residual astigmatism which is mainly derived from internal optics were examined preoperatively, at approximately 2 months postoperatively (baseline) and at 5 ~ 10 years postbaseline. The astigmatism was decomposed to vertical/horizontal (Rx) and oblique components (Ry), which was compared between baseline and 5 ~ 10 years postbaseline. Results In the eyes having ATR astigmatism, the mean Rx and Ry of the manifest refractive and corneal astigmatism significantly changed toward ATR astigmatism between the baseline and 5 ~ 10 years postbaseline (p ≤ 0.0304), but those of ocular residual astigmatism did not change significantly between the 2 time points. In the eyes having WTR astigmatism, the Rx and Ry of refractive, corneal, and ocular residual astigmatism did not change significantly between the 2 time points. Double-angle plots revealed an ATR shift in refractive and corneal astigmatism and no marked change in the ocular residual astigmatism in the eyes with ATR astigmatism, and there is no change in this astigmatism in the eyes with WTR astigmatism. Conclusion The long-term changes with age in the effect of a toric IOL significantly deteriorated due to an ATR shift of corneal astigmatism in the eyes having ATR astigmatism, while it was maintained in eyes having WTR astigmatism, suggesting that ATR astigmatism should be overcorrected.