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.

Analysis of Corneal Spherical Aberrations in Chinese Bilateral Ectopia Lentis Patients

Purpose: To analyze the anterior, posterior, and total corneal spherical aberrations (ASA, PSA, and TSA) in patients with Chinese bilateral ectopia lentis (EL).Methods: A cross-sectional study was conducted to evaluate corneal spherical aberration (CSA) using a Pentacam system at the 6-mm optical zone. Axial length, keratometry, astigmatism, and corneal asphericity were also determined.Results: This study included 247 patients (420 eyes) with a mean age of 18.1 years. The values of ASA, PSA, and TSA were 0.136 ± 0.100 μm, −0.118 ± 0.030 μm, and 0.095 ± 0.095 μm, respectively. In the EL patients with Marfan syndrome (MFS), ASA and TSA were significantly lower than in the non-MFS patients (0.126 ± 0.094 μm vs. 0.155 ± 0.107 μm, P = 0.004 for ASA; 0.085 ± 0.091 μm vs. 0.114 ± 0.099 μm, P = 0.003 for TSA), whereas PSA was not significantly different (P = 0.061). The values of ASA and TSA were significantly higher in the patients with EL aged ≥ 40 years old than in younger patients, whereas ASA and PSA were lower in patients aged &lt;10 years old than in older patients (all P &lt; 0.05). In the multiple linear regression analysis, age, keratometry, astigmatism, anterior asphericity, higher-order aberration (HOA), and lower-order aberration (LOA) were positively or negatively correlated with TSA in the patients with EL (r = 0.681, P &lt; 0.001).Conclusions: Corneal spherical aberration was low in the patients with EL especially for MFS and tended to increase with aging. Preoperatively, individual measurement of CSA was necessary for bilateral EL patients with MFS.

Functional optical zone after wavefront-optimized versus wavefront-guided laser in situ keratomileusis

Background: Many studies have used functional optical zone (FOZ) as a measure to compare different refractive laser treatment modalities. However, to our knowledge, no study has compared wavefrontoptimized (WFO) and wavefront-guided (WFG) laser in situ keratomileusis (LASIK) using FOZ. We compared the FOZ after WFO versus WFG LASIK in patients with myopia and myopic astigmatism.Methods: In this prospective comparative study, we included 100 myopic eyes of 50 patients with or without astigmatism. They were divided into two groups according to the platform used: WFO or WFG femtosecond LASIK. Using Holladay’s equivalent keratometry reading (EKR) report of Pentacam HR, FOZ was defined as a zone centered on the pupil center with a standard deviation (SD) of 0.5 D, around the mean EKR. The differences in FOZ between the two platforms were analyzed at 3 months postoperatively. Visual acuity, refractive error, corneal asphericity (Q-value), and root mean square of higher-order aberrations (RMS for HOAs) were evaluated and compared.Results: The mean ± SD of patient age was 26.64 ± 5.67 years. The preoperative characteristics of the two groups were comparable (all P > 0.05). The intended optical zone (IOZ) was 6 mm in both groups. The mean laser ablation depth was significantly greater in the WFG group (18 ?m per D) than in the WFO group (16 ?m per D) (P = 0.035). At 3 months postoperatively, the mean ± SD of FOZ diameter was 4.32 ± 0.94 mm (71.99 ± 15.68% of intended optical zone) in the WFO group and 4.16 ± 1.13 mm (69.33 ± 18.78% of intended optical zone) in the WFG group, with no significant difference between the two groups (P = 0.622). The change in corneal asphericity was greater in the WFG group than in the WFO group (P = 0.034). Postoperative mean corrected and uncorrected distance visual acuity, manifest refraction, and RMS for HOAs showed no significant difference between the two groups (all P > 0.05).Conclusions: We found that WFG LASIK resulted in greater ablation depth and change in corneal asphericity than WFO LASIK at 3 months postoperatively. However, there was no significant difference in FOZ diameter, refractive error, and RMS for HOAs between the two groups. Further research is needed to confirm these findings.

Effect of Corneal Tilt on the Determination of Asphericity

To quantify the effect of levelling the corneal surface around the optical axis on the calculated values of corneal asphericity when conic and biconic models are used to fit the anterior corneal surface. This cross-sectional study starts with a mathematical simulation proving the concept of the effect that the eye’s tilt has on the corneal asphericity calculation. Spherical, conic and biconic models are considered and compared. Further, corneal asphericity is analysed in the eyes of 177 healthy participants aged 35.4 ± 15.2. The optical axis was determined using an optimization procedure via the Levenberg–Marquardt nonlinear least-squares algorithm, before fitting the corneal surface to spherical, conic and biconic models. The influence of pupil size (aperture radii of 1.5, 3.0, 4.0 and 5.0 mm) on corneal radius and asphericity was also analysed. In computer simulations, eye tilt caused an increase in the apical radii of the surface with the increase of the tilt angle in both positive and negative directions and aperture radii in all models. Fitting the cornea to spherical models did not show a significant difference between the raw-measured corneal surfaces and the levelled surfaces for right and left eyes. When the conic models were fitted to the cornea, changes in the radii of the cornea among the raw-measured corneal surfaces’ data and levelled data were not significant; however, significant differences were recorded in the asphericity of the anterior surfaces at radii of aperture 1.5 mm (p < 0.01). With the biconic model, the posterior surfaces recorded significant asphericity differences at aperture radii of 1.5 mm, 3 mm, 4 mm and 5 mm (p = 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively) in the nasal temporal direction of right eyes and left eyes (p < 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively). In the superior–inferior direction, significant changes were only noticed at aperture radii of 1.5 mm for both right and left eyes (p = 0.05, p < 0.01). Estimation of human corneal asphericity from topography or tomography data using conic and biconic models of corneas are affected by eyes’ natural tilt. In contrast, the apical radii of the cornea are less affected. Using corneal asphericity in certain applications such as fitting contact lenses, corneal implant design, planning for refractive surgery and mathematical modelling when a geometrical centre of the eye is needed should be implemented with caution.

Posterior Corneal Asphericity Effect on Postoperative Astigmatism after EDOF Intraocular Lens Implantation in Cataract Patients

Aim. To assess the impact of posterior corneal asphericity on postoperative astigmatism. Methods. We included retrospectively 70 eyes of 70 patients that underwent cataract surgery. We included data of the Q value, Kmax, K1, K2, astigmatism AL, and ACD. We performed a vectorial analysis to calculate the astigmatic vectors. Results. Seventy eyes were evaluated. 40 eyes were of females (58%) and 30 of males (42%). The average cohort age was 73 ± 8.9 years. Axial length (AL) was 23.5 ± 0.9, anterior chamber depth (ACD) was 3.13 ± 0.3, and the average posterior Q value was −0.35 ± 0.2. The only significant predictive variable for the correction index (CI) was the posterior Q value (r = 0.24, p < 0.05) and for the surgically induced astigmatism (SIA) (β = 0.34, r = 0.58, p < 0.05). Conclusion. Posterior corneal surface asphericity significantly influences the surgically induced astigmatism and the overcorrection for cataract patients after Lucidis EDOF IOL implantation.

Evaluation of the Relationships between Corneal Parameters, Ocular Biometry, and Myopia Magnitude

Axial length of the eye correlates with the magnitude of myopia. However, there are conflicting reports on the relationship between certain corneal parameters with myopia magnitude. The objective of this study was to compare ocular biometry and corneal parameters between emmetropic and myopic groups. Participants (n=127) were categorized as emmetropia (spherical equivalent, SE, ±0.50D), low myopia (-0.75D≤SE<-6.00D) and high myopia (SE≥-6.00D). The difference in axial length, anterior chamber depth, and vitreous chamber depth between emmetrope, low myope, and high myope were highly significant (one-way ANOVA, all p<0.001) with significant correlations between SE and all these parameters (simple regressions, all p<0.001). However, central corneal thickness, corneal radius of curvature, and corneal asphericity between these groups, and the correlations between the ocular parameters with SE were not significantly different (all p>0.05). Corneal curvature correlated significantly with axial length (p=0.001) but not with myopia magnitude (p=0.91). Rather than myopia magnitude, axial length appears to be more sensitive to detect changes in corneal curvature in myopes. In conclusion, myopic patients’ axial length should be carefully considered for interventions that involve the cornea, such as orthokeratology and refractive surgery.

Quantification of Ocular Parameters To Create An Anatomical Eye Model for The Japanese Population

This prospective observational study aimed to evaluate the eye shape and visual function of Japanese people through a multicenter approach and to create a Japanese model eye. Uncorrected and corrected distance visual acuity (UDVA and CDVA, respectively) in the log minimum angle of resolution (logMAR), subjective and objective spherical equivalent values (SE) of ocular refraction, anterior and posterior corneal curvature (ACC and PCC, respectively), anterior and posterior corneal asphericity (ACA and PCA, respectively), central corneal thickness (CCT), anterior chamber depth (ACD), and ocular axial length (AL) were measured in the eyes of 250 participants (mean age = 46.5 ± 18.0 years, range: 20–90 years) across five institutions in Japan. The mean UDVA, CDVA, subjective SE, objective SE, ACC, PCC, ACA, PCA, CCT, ACD, and AL were 0.68, -0.08, -2.42 D, -2.66 D, 7.77 mm, 6.33 mm, -0.31, -0.39, 0.55 mm, 2.92 mm, and 24.78 mm, respectively. Age-related changes and sex-based differences were observed in the visual acuity, refraction, corneal shape, ACD, and AL. Although the sample size needs to be increased, the results of this study can be applied to the development of refractive correction methods and various vision-related fields.

Evaluation of a new nomogram for Ferrara ring segment implantation in keratoconus

AIM: To evaluate the short-term clinical outcomes of Ferrara rings in keratoconus using an optimized nomogram developed after several years of research and retrospective analysis of clinical data. METHODS: This prospective longitudinal non-comparative clinical trial evaluated 88 eyes of 88 patients (age 18-62y) with keratoconus diagnosis from two Spanish centers. Ferrara ring segment (AJL Ophthalmic) implantation was performed in all cases, using the mechanical procedure in 25 eyes (28.4%) and a femtosecond laser-assisted procedure in 63 eyes (71.6%). The ring segments implanted in each case were selected using a new optimized nomogram that considered variables such as anterior corneal asphericity and astigmatism or the discrepancy among astigmatism and coma orientations. Visual, refractive, corneal topographic, aberrometric, and pachymetric changes after surgery were evaluated during a 3-month follow-up. RESULTS: The implants induced a significant refractive change as well as an improvement in uncorrected (UDVA) and corrected distance visual acuity (CDVA; P<0.001). Postoperative CDVA of 0.10 logMAR or better was achieved in 28.4% and 46.5% of eyes, respectively. Two eyes (2.3%) lost two or more lines of CDVA whereas a total of 53.5% of eyes gained lines of CDVA. A significant central anterior and posterior corneal flattening was induced (P≤0.003), with a significant reduction of anterior (P<0.001) and posterior corneal astigmatisms (P=0.048), and a change in anterior asphericity (P<0.001). Total primary coma (6 mm pupil) change was also statistically significant (preoperative 3.66±3.04 µm vs postoperative 2.33±2.26 µm, P<0.001). No significant differences were found in the effect of ring segments between cases implanted using the mechanical and femtosecond techniques (P≥0.101). CONCLUSION: The implantation of Ferrara rings based on the nomogram evaluated is safe and effective for promoting a visual rehabilitation in keratoconus, with a relevant control of primary coma aberration.

Influence of Posterior Corneal Asphericity on Refractive Error of SRK-T and Barrett Formulas for Lucidis IOL

Purpose To evaluate the influence of posterior corneal asphericity on the refractive error using SRK-T and Barrett formulas for the intraocular lens (IOL) power calculation for Lucidis Extended Depth of Focus (EDOF) IOL. Setting This study was carried out at a tertiary ophthalmology center in Geneva, Switzerland. Design A retrospective study. Medical records from all enrolled patients were analyzed and the following information was extracted retrospectively, over 1 month following surgery. Methods We retrospectively reviewed 75 eyes that underwent cataract surgery and were implanted with a Lucidis EDOF IOL. We measured the posterior corneal asphericity (Q value), axial length (AL), and anterior chamber depth (ACD) and then calculated the IOL power using SRK-T and Barrett formulas. Results Seventy-five eyes were included, all of which had 1-month postoperative data. In the cohort, 32 eyes were from females (43%) and 43 from males (57%). The mean age of the study population was 73 ± 8.8 years. The mean AL was 23.5 ± 0.98 and the mean ACD was 3.13 ± 0.3. The mean posterior Q value was − 0.35 ± 0.2. In a regression analysis, we found a statistically significant relationship between the error in refraction prediction and the posterior Q value, irrespective of the formula used. The relationship between posterior corneal asphericity and the refraction prediction error was stronger for the Barrett II Universal formula than for the SRK-T formula. Conclusions Posterior corneal asphericity was correlated with the refractive error of calculation of both SRK-T and Barrett formulas, with a stronger correlation to the latter formula.

The Analysis of Corneal Asphericity and its Related Factors in Cataract Patients

Purpose: To determine the corneal asphericity and its related factors in cataract patients.Methods: This study enrolled 121 eligible eyes of 121 cataract patients. The corneal Q values of anterior and posterior surface were measured in the central 3.0, 4.0, 5.0, and 6.0 mm zone using the Sirius System. Age, gender, and corneal higher-order aberrations (HOAs) were recorded. Comparison of preoperative and postoperative Q value was conducted in 103 eyes of 103 patients three months after surgery.Results: The Q value of the anterior corneal surface at 6.0 mm zone and the posterior surface in 3.0, 4.0, 5.0, and 6.0 mm zone were statistically significant across the different age groups. The Q value of the posterior surfaces in 3.0, 4.0, 5.0, and 6.0 mm zone was statistically significant between the male and the female groups. The Q values of the anterior corneal surface in the 6.0 mm zone were positively correlated with Z40 cornea, Z40 CF, Z33,-3 CF, and total corneal HOAs; While the Q value of the posterior surface in the 6.0 mm zone were negatively correlated with Z31,-1 cornea, Z33,-3 cornea, Z33,-3 CF, Z31,-1CB, Z40 CB, and total corneal HOAs. Besides, no significant change was found in corneal Q value 3 months after surgery.Conclusion: There were great individual differences between the corneal asphericity of the cataract patients. Age, sex, and HOAs seemed to be correlated with the corneal asphericity. The preoperative Q value can be used as one of the parameters for personalized selection of intraocular lens.