Cornea Refractive Surgery Research Articles

个性化角膜屈光手术的建模及对散光修正的分析

个性化角膜屈光手术的建模及对散光修正的分析

Overview of Influence Factors on Corneal Thickness Measurement

Corneal thickness is an important parameter of the structure of an eyeball. Prior to cornea refractive surgery, the measurement of corneal thickness has been given general importance. With the development of measuring instruments, the measurement of corneal thickness is safer, more accurate and more comfortable. In this study, common clinical measuring methods and their influencing factors are discussed.

Objective evaluation of refractive data and astigmatism: quantification and analysis

The aim of this study was to present methods to improve the analysis of refractive data. A comparison of methods is used to analyse refractive powers using individual powers and aggregate data. Equations are also developed for the representation of the average power of a lens or refractive data as a univariate measure, which includes spherical, coma, and/or other aberrations. The equations provide a precise representation of refractive power, which is useful for comparing individual and aggregate data. Average lens power in the principal meridian can be adequately computed as can the average lens power through orthogonal and oblique meridians, providing a good univariate representation of astigmatism and refractive power. Although these formulae are perhaps not as easy to use as, for example, the spherical equivalent, they are more precise and superior in principle involving fewer approximations and are not subject to systematic bias. These effects are of significance when dealing with high-powered lenses such as intraocular lenses or the cornea. They need to be taken into account particularly for calculations of intraocular lens power, toric intraocular lenses, and cornea refractive surgery, especially if outcomes are to be improved. Such issues are of particular importance when dealing with aggregate data and determining statistical significance of treatment effects.

Positional and Rotational Stability of the Toric Phakic Intraocular Lens Under High +G<SUB>z</SUB> Environments

Phakic intraocular lens (PIOL) implantation is a surgical option for correction of refractive errors. PIOLs can be use to correct myopia, hyperopia, and astigmatism. It is a surgical option available to patients in addition to methods such as laser cornea refractive surgery, e.g., laser assisted in-situ keratomileusis (LASIK) and photo-refractive keratectomy (PRK). Visian implantable collamer lens (ICL) are posterior chamber lenses which are surgically positioned in a phakic eye in the sulcus between the iris diaphragm and the natural crystalline lens. This case report describes the stability of Visian toric ICL in a candidate with bilateral implants under high +Gz force exposure in a human centrifuge trainer. The subject was sequentially exposed to three incremental +Gz profiles of +5 Gz, +7 Gz, and +9 Gz. Pre- and post-+Gz exposure, ophthalmic examination revealed no ICL displacement, implant touch or induced cataract, or change in refractive error. The rotational stability of the toric implants was also demonstrated by identical subjective refractions in both eyes taken pre- and post-+Gz, exposure. A search of the literature did not reveal any published articles on intraocular stability of ICL in the +Gz environment. This case report suggests that ICL may be considered an alternative to laser refractive surgery for patients subjected to a high +G, environment such as military aviators.

Clinical study of intraocular lens power calculation methods after cornea refractive surgery

To evaluate the results of cataract surgery in myopia patients after laser in situ keratomileusis (LASIK) and to compare the predictability of various methods of intraocular lens (IOL) power calculation. Seventeen cases (24 eyes) who had LASIK for myopia were divided into two group by with or without history of corneal power data. Corneal power was obtained by autokeratometry, corneal topography, Pentacam and IOL Master. The IOL power was calculated with the clinical history method, Feiz-Mannis formula, Feiz-Mannis method and other methods. Postoperative final refraction and the deviation of the final spherical equivalent (SEQ) from the refractive target were measured 3 month after the surgery. Two sample t-test, linear correlation and regression analysis, paired t-test and Bland-Altman method of agreement were used to analyze these data. In the group with history data, the mean corneal power was (43.28 ± 1.21) D and the mean SEQ was (-15.33 ± 4.36) D before the LASIK surgery. In the group without history data, the mean SEQ was (-10.11 ± 3.12) D. Before cataract surgery, the mean corneal power was (36.96 ± 2.07) D and (36.85 ± 1.40) D in these two groups. The mean arithmetic refractive prediction error after cataract surgery was (-0.66 ± 1.27) D and (-0.47 ± 0.82) D in these two groups, respectively. Data calculated by using Hamed-Wang-Koch method, Masket Formula, Koch/Maloney method, Shammar method and Pentacam ERK method were lower than the emmetropic IOL power. Data calculated by using Feiz-Mannis Formula, Latkany Method, Savini method, Armberri Double K method were overestimated. The mean arithmetic errors of clinic history method, Corneal Passby Method and Haigis-L Formula were not significantly different from the predict refraction (P = 0.364, 0.318 and 0.069; t = 0.956, -1.057 and -1.911, respectively). There was strong correlation between the value calculated by using Feiz-Mannis Method or Haigis-L Formula and the true power (r = 0.921, 0.915; P = 0.000 and 0.000, respectively). But none of the values calculated by these method could fully agree with the true value. IOL power should be calculated accurately to avoid undercorrection. We recommend the combination of clinical history method, Feiz-Mannis Method, Corneal Passby Method and Haigis-L Formula for the calculation of IOL power.

Clinical analysis of measuring corneal thickness with non-contact method

To compare accuracy of the Pentacam with A-ultrasonoscope in the measurement of central corneal thickness. According to the degree of myopia, 107 myopic patients (211 eyes) were divided into four groups. The central corneal thickness was measured with the Pentacam system and A-ultrasonoscope. The results were compared statistically and the differences between these two methods were analyzed. Mean values of central corneal thickness measured by the Pentacam system and A-ultrasonoscope was (535.58 +/- 36.34) microm and (536.73 +/- 37.18) microm, respectively. There was no difference in the results obtained by these two methods in each myopia group (P > 0.05). The 95% limits of agreement were (-1.88, -0.42). The data shows that the results obtained by Pentacam system do not have significant difference as compared with that from the A-ultrasonoscope. The Pentacam system can provide precise results and has the advantage of simplicity and non-contact. Therefore, it would be a promising instrument for the evaluation of central corneal thickness before the cornea refractive surgery.