Comprehensive Assessment of Posterior Corneal Asphericity Change Calculated by Tangential Radius of Curvature After FS-LASIK and SMILE.

PURPOSE: To evaluate changes in posterior corneal asphericity (ΔQ) using the tangential radius of curvature after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures. METHODS: One hundred twenty right eyes of myopic patients who underwent either FS-LASIK or SMILE procedures were analyzed using Sirius 3D corneal topography for assessment. The tangential radius was employed to calculate both preoperative and postoperative posterior corneal Q-values across each semimeridian. After both surgical interventions, the ΔQ value variations across the 360° semimeridional regions of the posterior corneal surface were compared. RESULTS: A marked postoperative increase in the posterior corneal Q-value was documented. No significant differences were noted between the postoperative Q-values or ΔQ-values of the two surgical approaches. Among patients with moderate myopia, postoperative Q-value exhibited considerably lower increases and ΔQ-value significantly smaller than their counterparts with high myopia. Moreover, the fluctuation in ΔQ across semimeridional regions was less evident in patients with moderate myopia than in those with high myopia. Notably, the degree of ΔQ fluctuation across semimeridional regions was similar between both surgical categories. These data offer insights into variations in the posterior corneal surface after refractive surgeries depending on the degree of myopia, illuminating their clinical relevance. CONCLUSIONS: Both FS-LASIK and SMILE introduce notable changes to posterior corneal asphericity among patients with different myopia intensities. Furthermore, the influence on the asphericity across the entire posterior surface is similarly distributed between FS-LASIK and SMILE techniques. [J Refract Surg. 2024;40(3):e133-e141.].

Comparative Change in Anterior Corneal Asphericity After FS-LASIK and SMILE.

PURPOSE: To evaluate changes in anterior corneal asphericity (ΔQ) by calculating tangential radius (rt) after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE). METHODS: Sirius corneal topography (Costruzione Strumenti Oftalmici) was used to evaluate 120 right eyes from patients with moderate and high myopia who had previously undergone FS-LASIK and SMILE. The preoperative and postoperative tangential radii obtained in reference to various semi-meridional regions and radii zones were compared. Variation in ΔQ values in semi-meridional regions across 360 degrees of the anterior surface after FS-LASIK and SMILE were compared. RESULTS: The tangential radii in the 1.2- and 1.8-mm radii zones were lower in patients who underwent SMILE compared to those who underwent FS-LASIK. The tangential radii in the 2.4- and 3-mm zones were higher in patients who underwent SMILE compared to those who underwent FS-LASIK. In both the moderate and high myopia groups, postoperative Q-values and ΔQ-values were lower in patients who had undergone SMILE than in patients who had undergone FS-LASIK. Postoperative Q-values and ΔQ-values were lower in the moderate myopia group than in the high myopia group for FS-LASIK and SMILE. The magnitude of variation in ΔQ as a function of semi-meridional region was lower in patients who had undergone SMILE than in patients who had undergone FS-LASIK. CONCLUSIONS: FS-LASIK and SMILE alter anterior corneal tangential radius and anterior corneal asphericity in patients with moderate or high myopia. SMILE is more effective than FS-LASIK in preserving normal anterior corneal asphericity. [J Refract Surg. 2021;37(3):158-165.].

Group Analysis of Q Values Calculated with Tangential Radius of Curvature from Human Anterior Corneal Surface.

OBJECTIVE: To calculate the Q values from the human anterior corneal surface with the tangential radius of curvature and analyze its distribution characteristics in different age and refractive status groups. METHODS: Tangential power maps of the anterior cornea from Orbscan II were acquired for 201 subjects' right eyes. They were divided into groups of adults and children and then divided further into subgroups according to the refraction status. The Q values of each semimeridian were calculated by the tangential radius with a linear regression equation. The Q value distribution in both the nasal cornea and temporal cornea were analyzed. RESULTS: The mean temporal Q values of the emmetropia group of adults and all children's groups were significantly different from the mean nasal Q value. The mean nasal corneal Q values were more negative in children. The adult group showed differences only in the low myopia group. The mean Q value of the nasal cornea among different refractive groups of children was significantly different, and so was the temporal cornea between the adult myopia and emmetropia group. CONCLUSION: The method using the tangential radius of curvature combined with linear regression to obtain anterior surface Q values for both adults and children was stable and reliable. When we analyzed the anterior corneal Q value, area division was necessary.

Comprehensive Evaluation of Anterior Corneal Change in Asphericity Calculated by the Tangential Radius of Curvature after LASIK.

To evaluate the change in the anterior corneal asphericity (ΔQ) comprehensively calculated using the tangential radius (rt ) after LASIK. Forty-two right eyes were evaluated using the Orbscan II corneal topographer. The pre- and postoperative Q-values of the flat principal semimeridians calculated by the sagittal radius were compared to those by the tangential radius. The Q-value of each semimeridian in the horizontal region was calculated by rt . Fourier fitting was used to model the 360-semimeridional variation of Q-values and to fit the Q-values in the vertical region before and after surgery. There were significant differences in Q-values between the two methods before (P < 0.001) and after surgery (P = 0.003). A significant increase in postoperative Q-value was detected compared to preoperative Q-value (P < 0.001) calculated by rt . The 360-semimeridional variation of the Q-values was well fitted with a third- and fourth-degree Fourier function before and after surgery. The ΔQ-value distribution presented double valley variation, with the amount of ΔQ being lowest in the near-vertical regions and highest in the near-horizontal regions. Calculating the Q-value with rt combined with Fourier fitting, we evaluated 360 ΔQ-values' variation of semimeridians of the entire anterior corneal surface and then displayed true and complete anterior corneal shape after LASIK.

[Evaluation of tear film and meibomian gland function in dry eye patients using Keratograph 5M].

Objective: To assess the application of Keratograph 5M in evaluating tear film and meibomian gland function in patients with dry eye. Methods: A total of 144 eyes were recruited in the study, in which 72 eyes were from patients diagnosed with dry eye and 72 eyes were from healthy subjects. All subjects finished following tests or examinations:ocular surface disease index (OSDI) to evaluate eye symptoms; Keratograph 5M examination to obtain tear meniscus height (TMH), noninvasive tear break-up time (NIBUT) including first NIBUT (NIBUT-Fir) and average NIBUT (NIBUT-Ave), and infrared meibography; and fluorescein sodium staining to obtain fluorescein tearbreak-up time (FBUT). Results: Dry eye group had higher OSDI score than healthy control group, but its TMH, NIBUT-Fir and NIBUT-Ave were lower than those in healthy control group (all P<0.01). Total meiboscore in dry eye group was higher than that in healthy control group (P<0.01), and it showed a significant correlation with NIBUT-Fir and NIBUT-Ave (r=-0.449 and -0.398, P<0.01), but no correlation with ages was observed (r=0.031, P>0.05). The NIBUT-Fir and NIBUT-Ave showed a significant correlation with FBUT (r=0.833 and 0.727, P<0.01). Conclusion: Keratograph 5M is a convenient, accurate and non-invasive method to assess the function of tear film and meibomian gland, and the new meibography scoring system can evaluate the function of meibomian gland objectively and succinctly.

Corneal elevation in a large number of myopic Chinese patients.

PURPOSE: To establish a normative database for corneal elevation in Chinese myopic patients who underwent refractive surgery, and analyze the association of corneal elevation with sex, age, and ocular parameters. METHODS: A total of 3000 eyes in 1500 patients were evaluated with the Pentacam. Anterior and posterior elevations were measured at the apex and thinnest point. Normative thresholds were defined according to the Tukey method. Univariate and multivariate analyses were performed to assess the association of corneal elevation with sex, age, and ocular parameters. RESULTS: Normal upper limits for corneal elevation in adult Chinese were 4.95µm, 5.25µm, 6.2µm, and 11.0µm at the anterior apex, anterior thinnest point, posterior apex, and posterior thinnest point, respectively. Thinner corneal pachymetry at the apex and greater anterior corneal astigmatism tended to show greater anterior corneal elevation values. Younger age, greater anterior corneal astigmatism, lower anterior and posterior keratometry, and shallower anterior chamber depth resulted in greater posterior corneal elevation values. CONCLUSIONS: Locally derived thresholds may offer higher sensitivity and specificity when screening eyes for myopic refractive surgery, and keratoconic and post-orthokeratology eyes. Anterior and posterior corneal elevation at the apex and thinnest point were associated significantly with anterior corneal astigmatism, showing a positive correlation.

[Analyses of TGFBI gene mutation spectrum in four Chinese families with corneal dystrophy].

OBJECTIVE: To identify the genetic mutation of TGFBI gene in four Chinese families with corneal dystrophy. The pedigrees were Reis-Bücklers corneal dystrophy (RBCD), Avellino corneal dystrophy (ACD), lattice corneal dystrophy type I(LCDI) and lattice corneal dystrophy type I/IIIA (LCDI/IIIA) (n = 1 each). METHODS: Genomic DNA was extracted from leukocytes from 22 patients, 22 phenotypic normal family members and 100 normal controls from February 2010 to October 2012. And 17 exons of TGFBI gene were amplified by polymerase chain reaction and sequenced directly. The corneas were examined with slit-lamp biomicroscope and photographed. RESULTS: Mutations of TGFBI gene occurred in all 22 patients, including R124L (c.371G > T) in 14 patients with RBCD, R124H (c.371G > A) mutation in 1 patient with ACD, R124C (c.370C > T) mutation in 3 patients with LCDIand H626R (c.1877A > G) mutation in 4 patients with LCD I/IIIA. The mutations were absent in all participating unaffected family members and normal controls. CONCLUSIONS: TGFBI gene-linked corneal dystrophy has close genotype-phenotype relationship. And R124 is a mutant hotspot of TGFBI gene of corneal dystrophy.

Three-dimensional model for human anterior corneal surface.

The anterior corneal asphericity (Q) with the tangential radius is calculated, and a three-dimensional (3-D) anterior corneal model is constructed. Tangential power maps from Orbscan II are acquired for 66 young adult subjects. The Q-value of each semimeridian in the near-horizontal region is calculated with the tangential radius. Polynomial fitting is used to model the 360-semimeridional variation of Q-values, and to fit the Q-values in the near-vertical region. Furthermore, a customized 3-D anterior corneal model is constructed. The 360-semimeridional variation of Q-values is well fitted with a seventh-degree polynomial function for all subjects. The goodness of fit of the polynomial function was >0.9, and the median value was 0.94. The Q-value distribution of the anterior corneal surface showed bimodal variation. Additionally, the Q-values gradually become less negative from the horizontal to the vertical semimeridians in the four quadrants. The 3-D surface plot of the anterior corneal surface approximated a prolate ellipsoid. Using a method to calculate the Q-value with the tangential radius combined with polynomial fitting, we are able to obtain the Q-value of any semimeridian. Compared with general models, this method generates a complete shape of the anterior corneal surface using asphericity.

[Macular and retinal nerve fiber layer thickness in myopic children by three-dimensional OCT].

OBJECTIVE: To investigate the variations of macular thickness and peripapillary retinal nerve fiber layer (RNFL) thickness in myopic children. METHODS: A total of 96 eyes from 48 myopic children at department of Ophthalmology, Second Affiliated Hospital of Wenzhou Medical College from September 2010 to March 2012 were enrolled in this study and divided into three groups (low, moderate and high myopia group) according to the severity of myopia. Another 33 eyes from 19 emmetropic children were recruited as control group. The macular thickness and peripapillary RNFL thickness of the myopic children measured by optical coherence tomography were compared with that of the control group. RESULTS: The mean thickness of nasal, superior and inferior regions of outer-ring macular in the high myopia group were 276 µm, 294 µm, 285 µm respectively, which were significantly lower than that in the control group (P < 0.05). The mean thickness of superior of outer-ring macular in the low and moderate groups were 302 µm, 301 µm respectively, and the inferior of outer-ring ones were 288 µm, 283 µm respectively, which were significantly lower than that in the control group (P < 0.05). The temporal region of peripapillary RNFL thickness was significantly greater, and the other six regions of RNFL thicknesses were significantly lower in the high group than in the control group (P < 0.05). The central-1 mm, superior region of inner-ring, temporal and superior region of outer-ring macular thickness had positive correlations with spherical equivalent (SE) (P < 0.05). There was a negative correlation between the temporal peripapillary RNFL thickness and SE, while positive correlations were found between other regions of peripapillary RNFL thickness and SE (P < 0.05). CONCLUSIONS: The thicknesses of macular and peripapillary RNFL of myopic children have already redistributed before apparent changes of funds.

Anterior corneal asphericity calculated by the tangential radius of curvature.

We propose a method of calculating the corneal asphericity (Q) and analyze the characteristics of the anterior corneal shape using the tangential radius. Fifty-eight right eyes of 58 subjects were evaluated using the Orbscan II corneal topographer. The Q-values of the flat principal semi-meridians calculated by the sagittal radius were compared to those by the tangential radius. Variation in the Q-value with semi-meridian in the nasal and temporal cornea calculated by the tangential radius was analyzed. There were significant differences in Q-values (P<0.001) between the two methods. The mean Q-values of the flat principal semi-meridians calculated by tangential radius with -0.33 ± 0.10 in the nasal and -0.22 ± 0.12 in the temporal showed more negative than the corresponding Q-values calculated by the sagittal radius. The Q-values calculated by tangential radius became less negative gradually from horizontal semi-meridians to oblique semi-meridians in both nasal and temporal cornea. Variation in Q-value with semi-meridian was more obvious in the nasal cornea. The method of calculating corneal Q using the tangential radius could provide more reasonable and complete Q-value than that by the sagittal radius. The model of a whole anterior corneal surface could be reconstructed on the basis of the above method.