Corneal Q-value Research Articles

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

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. 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. 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. 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.].

Effect of Limbal Incision Positions on Corneal Q-Value in Cataract Surgery: A Retrospective Study of Monofocal IOL and Trifocal IOL

Effect of Limbal Incision Positions on Corneal Q-Value in Cataract Surgery: A Retrospective Study of Monofocal IOL and Trifocal IOL

Analysis of Corneal Asphericity according to Age and Gender

Purpose : The purpose of this study was to investigate the distribution of corneal asphericity of all ages in Koreans and changes in corneal asphericity according to age and gender. Methods : A total of 317 people(317 eyes) were analyzed retrospectively. The refractive error was analyzed by the autorefractometer. The corneal asphericity and curvature were measured in the central 6 mm zone of the cornea and analyzed by a rotating scheimplug camera. Results : The anterior and posterior corneal Q-values were -0.17±0.18(ranged -0.84 to 0.72) and -0.11±0.29(ranged -0.89 to 1.27), respectively. As the age group increased, the anterior corneal Q-value did not show a significant difference(p=0.359), while the posterior corneal Q-value showed statistically significant differences of 0.01±0.18, 0.10±0.29, -0.12±0.22, -0.20± 0.25, -0.27± 0.20 and –0.33±0.31 in the 30s, 40s, 50s, 60s, 70s and over 80’s, respectively(p＜0.001). The posterior corneal Q-value was negatively correlated with the age(r=-0.480, p＜0.001). Conclusion : The anterior corneal Q-value did not show a significant difference in gender and age while the posterior corneal Q-value changed from oblate to prolate shape as the age increased.

Corneal asphericity and the effects of the corneal refractive surgery on it

The corneal asphericity refers to most normal corneal surface is an aspherical flat oval, which is helpful to improve the visual quality.In most cases, corneal aspherical coefficient Q-value is negative, and different normal Q-value is reported in literatures, corneal Q-value is influenced by many factors, quadrants have great effects on it, the influence of age is weak, there are correlation between myopic degree, ocular axial length, radius of curvature, intraocular pressure and Q-value.The corneal refractive surgery is one of the most important methods to correct refractive errors, but it has negative effects on the corneal asphericity, and then results in glare, visual quality degradation and other issues.Different corneal refractive surgeries would have different effects on the corneal asphericity.Wavefront aberration-guided femtosecond laser in situ keratomileusis（LASIK) surgery and Q-value guide LASIK are superior to standardized LASIK, the change of Q-value after femtosecond lenticule extraction（FLEx) surgery is less than that after wavefront aberration guided LASIK.The influence of femtosecond laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) on Q-value are rarely reported.In addition, the Q-value changes from negative to positive after corneal refractive surgery of myopia, the variation tendency is opposite after hyperopia surgery.Q-value variation is highly correlated to spherical equivalent, the impact of laser and healing still needs further exploration.In order to further exploring of the corneal asphericity and getting a better effect of surgery, here is a review about normal corneal asphericity and the effects of the corneal refractive surgery on it. Key words: Cornea; Asphericity; Q-value; Refractive surgery

Simulated Effect of Corneal Asphericity Increase (Q-factor) as a Refractive Therapy for Presbyopia

To determine the theoretical effect of an increase in the negative Q-factor (hyperprolateness) on the refractive state and its effect on presbyopia treatment. Ray tracing software was used to simulate the Navarro eye model. To simulate refractive therapy, corneal Q-factor ranged from 0 to -1.50. Refractive state of the model eye was defined as the target vergence required to maximize retinal image quality according to several image quality metrics. The change of refractive state produced by pupil constriction from 6 to 2 mm was estimated. For 0 ≥ Q ≥ -0.6, spherical aberration of the model eye is positive, therefore, pupil miosis causes a hypermetropic shift in refractive state. Over the range -0.6 ≥ Q ≥ -1.5, spherical aberration becomes negative and pupil constriction causes the eye's far point to approach the eye, inducing a myopic shift. A maximum 0.60-diopter myopic shift in refractive state due to pupil constriction occurred for Q=-1.25. Optical modeling predicts that surgically induced negative corneal Q-value will produce a change in the refractive state of the eye after pupillary miosis.

Analysis of corneal asphericity in patients after phacoemulsification

To investigate the distribution of corneal Q-value in the age-related cataract patients and aspherical features of cornea before and after the phacoemulsification (PHACO). Thirty-nine eyes of 30 age-related cataract patients in our department were included. Transparent cornea incision at the temporal cornea was applied for patients with cornea astigmatism < 1.00 D and transparent cornea incision at the maximum curvature meridian for patients with cornea astigmatism > or = 1.00 D in PHACO. All patients were followed up to 3 months, corneal Q-value, corneal curvature, astigmatism were examined before and after PHACO, distribution of corneal Q-value and their correlation factors were analyzed. The mean corneal Q-value before and after the PHACO was -0.07 +/- 0.22 and -0.11 +/- 0.16, respectively. There was no statistical difference between the corneal Q-values before and after surgery (t = 1.14, P = 0.26). The mean of corneal curvature before and after the PHACO was (44.6 +/- 1.92) D and (44.70 +/- 1.47) D, respectively. There was no statistical difference between corneal curvature before and after the operation (t = -0.69, P = 0.50). The corneal Q-value was negatively co-related with corneal curvature before the surgery (r = -0.46, P = 0.003). The mean astigmatism power before and after the HACO was (0.67 +/- 0.43) D and (0.66 +/- 0.42) D, respectively. There was no statistical difference between astigmatism power before and after the surgery (t = -0.24, P = 0.82). There was no relationship between the corneal Q-value and astigmatism power before surgery (r = -0.24, P = 0.14). The corneal Q-value of aged patients is in normal distribution, is negative in the majority, and showed a negative relationship with corneal curvature. There is no statistical difference between the corneal Q-value, corneal curvature, and astigmatism power before and after PHACO surgery.

Corneal Asphericity and Retinal Image Quality: A Case Study and Simulations

The optical quality of retinal images is dependent on the refracting elements of the eye including the nominally aspheric cornea and crystalline lens. This paper presents a retrospective theoretical analysis of the impact of corneal asphericity on the quality of retinal images. Clinical data are from the VISX Incorporated CustomVue IDE. Topography, contrast sensitivity, and visual acuity data were collected from 278 myopic eyes before and after wavefront-guided laser surgery. The measured corneal surface of each eye was fitted to a conic, and a Q-value was computed for a 5.5-mm pupil. A model eye was used to simulate various amounts of optical asphericity. Preoperatively, most corneas exhibited negative conic shape constants. Postoperatively, corneas were about equally divided between positive and negative conics. There was no statistically significant correlation between the shape of the cornea and the subjects' perceptions of image quality including contrast sensitivity and visual acuity. Simulations showed that the corneal Q-value can vary from more to less prolate depending upon the shape of the internal surface. Following wavefront-guided laser in situ keratomileusis (LASIK), contrast sensitivity is usually good and is not dependent upon the corneal conic shape. Better visual outcomes are more likely with a customized shape than a standard best conic shape.