角膜屈光手术后的人工晶状体度数计算

角膜屈光手术后用现行的角膜曲率检测方法测量角膜屈光力不精确,导致该类患者白内障手术时人工晶状体度数计算偏低,术后呈较严重的远视状态。随着接受准分子激光角膜屈光手术人数的增加,此问题在未来将日益突出。围绕这一问题,不少学者提出多种修正方案,以期提高角膜屈光手术后人工晶状体度数计算的准确性,本文就此进行综述。     

准分子激光屈光性角膜手术后人工晶状体度数的计算

准分子激光屈光性角膜手术后,患者发生白内障需行白内障摘除及人工晶状体植入术时,按常规方法计算人工晶状体屈光度往往会在术后产生远视,而这样的误差主要来源于角膜屈光力的测算误差和计算公式的误差,另外还有眼轴长度测量和有效人工晶状体位置计算的准确性降低这两个方面的原因.因此,对于曾行角膜屈光手术的白内障患者,术前运用适当的方法准确估算角膜屈光力,并选择合适的人工晶状体计算公式,可以减少屈光误差.     

重视眼内屈光手术视觉质量的研究

有效提高眼内屈光手术视觉质量是该类手术临床应用的前提。视觉质量是一个综合因素,与手术安全性、人工晶状体材料与度数计算、眼球相关参数测量和心理物理感知等有关。本文就此类手术的视觉质量及其相关因素分析进行述评。     

Impact of ultrasound and optical biometry on refractive outcomes of cataract surgery after penetrating keratoplasty in keratoconus

AIM: To analyse the impact of ultrasound and optical intraocular lens (IOL) calculation methods on refractive outcomes of cataract phacoemulsification performed after penetrating keratoplasty (PK) in keratoconus. METHODS: Phacoemulsification cataract surgery was performed on 42 eyes of 34 patients with keratoconus who had previously undergone PK. The IOL power was determined by using both standard and corneal topography-derived keratometry using the SRK/T formula. We used two independent methods-ultrasound biometry (UB) and interferometry [optical biometry (OB)] for IOL calculation. The analysed data from medical records included demographics, medical history, best corrected visual acuity (BCVA) on Snellen charts, technique of IOL calculation and calculation formula and its impact on final refractive result. RESULTS: BCVA ranged from 0.01 to 0.4 (mean 0.09±0.19) before surgery and ranged from 0.2 to 0.7 (mean 0.38±0.14) at 1mo and from 0.2 to 1.0 (mean 0.56±0.16) (P<0.05) at 3mo, postoperatively. The refractive aim differed significantly from the refractive outcome in both the UB and OB groups (P<0.05). There was no statistically significant difference in the accuracy of the two biometry methods. CONCLUSION: The refractive aim in keratoconus eyes post-PK is not achieved with either ultrasound or OB.     

白内障合并高度近视患者术后屈光力预测的研究进展

白内障合并高度近视患者术后实际屈光力与术前目标屈光力存在差异,常见远视漂移。针对这类患者术后的屈光误差,除了传统的预留近视度数的方法外,国际上出现了更精准、有效的解决方法,如优化眼轴长度、采用新一代公式(Barrett Universal Ⅱ、Olsen、Hill-RBF、Ladas Super公式以及FullMonte方法)、术中屈光生物测量。本文将以高度近视患者的术后屈光误差为核心,阐述现有方法的研究进展。     

Intraocular lens power calculation after keratorefractive surgery

The number of keratorefractive procedures designed to correct refractive errors has dramatically increased over the last few years. The techniques for cataract extraction and intraocular lens implantation have evolved into a refractive surgical procedure as well as an operation to improve best corrected visual acuity and/or spectacle independence. The calculation of intraocular lens power for a desired refractive target can be challenging in post-refractive surgically treated eyes, given the frequent case reports of "refractive surprises" after cataract surgery. After corneal refractive surgery, the direct use of the measured topographic or keratometric values, with no correction, results in less accurate calculation of intraocular lens (IOL) power required for cataract surgery than calculation in virgin eyes. After laser refractive surgery for myopia, this could result in an overestimation of the corneal power and subsequent underestimation of the IOL power, therefore leading to a hyperopic outcome after phacoemulsification. Conversely, after laser refractive surgery for hyperopia, inaccuracy in the keratometric power estimation could result in a myopic outcome after phacoemulsification. Despite current progress in this subject, awareness of the shortcomings of classical methods and suggested strategies to improve accuracy can be valuable to clinicians. This article provides an overview of the possible sources of error in intraocular lens power calculation in post-keratorefractive patients, and reviews the methods to minimize intraocular lens power errors.     

Optic biometry in intraocular lense calculation for cataract surgery. Comparison with usual methods

PURPOSE: To compare axial length and intraocular lens power calculated from three biometry methods, then to study refractive postoperative results to assess the predictive value of each method. MATERIAL AND METHODS: This prospective study included 40 eyes planned for cataract surgery. Two skilled operators participated in this study: One for the surgery and the other for the biometry and measurement of intraocular lens power. For intraocular lens power, we used the optic biometer from Zeiss and the echograph B Ultrascan from Alcon. IOL power calculation was performed using the usual mathematical formulas based on 3 biometry methods. 1--keratometry measurement, anterior chamber depth (ACD), and axial length using optical biometry; 2--keratometry measurement using the Javal keratometer and biometry using the B mode ultrasonography; 3--keratometry measurement using the Javal keratometer and biometry using A mode ultrasonography. RESULTS: The average age of our patients was 69.5 years old, ranging from 52 to 81 years old. The average axial length was 23.46 mm with, ranging from 20 to 32.73 mm. The average keratometry with optic biometry was 43.97 diopters +/- 1.44 versus 43.84 diopters +/- 1.45 with the Javal keratometer. 40 eyes were examined and there were 4 failures (10%) for axial length measurement by optic biometry because the cataract was very dense. Biometric preoperative results with the 3 methods show that there was a statistically significant difference between the A mode and the B mode optic biometry (P < 0.006). On the other and, there was no statistical difference between optic biometry and the B mode. CONCLUSION: Optic biometry has a number of advantages. This is new method, is non invasive, easy to use, with no contact, and it is reliable. Results with this method are more precise than with ultrasonic biometry. For high myopia, optic biometry is a very valuable method. Its limits are total cataract and intraocular opacities; in these cases ultrasonic biometry is the best method.     

Difficult cases in biometry measurement

A few problems have not yet been resolved concerning intraocular lens (IOL) power calculation in difficult cases. Patients can be divided into three groups: Group 1, patients with no previous ocular surgery but with unusual anatomy (staphyloma, high hyperopic eyes, etc.); Group 2, patients with previous surgery except refractive surgery; Group 3, patients with previous refractive surgery. Various techniques must be used to increase the accuracy of IOL calculation. B-mode biometry and optical coherence tomography are suitable tools to increase the accuracy of axial length measurement. Computerized videokeratography can be helpful. However, the most difficult cases seem to be those in Group 3.     

Challenges and approaches in modern biometry and IOL calculation

The introduction of new intraocular lenses (IOLs), industry marketing to the public and patient expectations has warranted increased accuracy of IOL power calculations. Toric IOLs, multifocal IOLs, aspheric IOLs, phakic lenses, accommodative lenses, cases of refractive lens exchange and eyes that have undergone previous refractive surgery all require improved clinical measurements and IOL prediction formulas. Hence, measurement techniques and IOL calculation formulas are essential factors that affect the refractive outcome.Measurement with ultrasound has been the historic standard for measurement of ocular parameters for IOL calculation. However the introduction of optical biometry using partial coherence interferometry (PCI) has steadily established itself as the new standard. Additionally, modern optical instruments such as Scheimpflug cameras and optical coherence tomographers are being used to determine corneal power that was normally the purview of manual keratometry and topography.A number of methods are available to determine the IOL power including the empirical, analytical, numerical or combined methods. Ray tracing techniques or paraxial approximation by matrix methods or classical analytical ‘IOL formulas’ are actively used in for the prediction of IOL power. There is no universal formula for all cases – phakic and pseudophakic cases require different approaches, as do short eyes, long eyes, astigmatic eyes or post-refractive surgery eyes. Invariably, IOLs are characterized by different methods and lens constants, which require individual optimization. This review describes the current methods for biometry and IOL calculation.     

Advances in cataract surgery

Cataract surgery is a technique described since recorded history, yet it has greatly evolved only in the latter half of the past century. The development of the intraocular lens and phacoemulsification as a technique for cataract removal could be considered as the two most significant strides that have been made in this surgical field. This review takes a comprehensive look at all aspects of cataract surgery, starting from patient selection through the process of consent, anaesthesia, biometry, lens power calculation, refractive targeting, phacoemulsification, choice of intraocular lens and management of complications, such as posterior capsular opacification, as well as future developments. As the most common ophthalmic surgery and with the expanding range of intraocular lens options, optometrists have an important and growing role in managing patients with cataract.     

Intraocular lens power calculation after corneal refractive surgery

PURPOSE OF REVIEW: Keratorefractive procedures designed to decrease refractive errors have gained enormous popularity among ophthalmologists and patients. As the post-refractive surgery patient population ages, visually significant cataracts will develop. With advances in techniques for cataract extraction and intraocular lens implantation, cataract surgery has evolved into a refractive surgical procedure as well as an operation to improve best corrected visual acuity. This raises expectations in terms of desired postoperative refractive status and uncorrected visual acuity. Although performing modern cataract surgery in post-refractive surgery eyes is technically no more complicated than operating on virgin eyes, the calculation of intraocular lens power for a desired refractive target can be challenging and complicated. This has become increasingly apparent as case reports of "refractive surprises" after cataract surgery appear in the literature more frequently. RECENT FINDINGS: This paper reviews the current clinical experience with intraocular lens power determination after cataract surgery in post-keratorefractive patients, provides an overview of possible sources of error in intraocular lens power calculation in these patients, and analyzes methods to minimize intraocular lens power errors. SUMMARY: The clinical and routine methods of intraocular lens power determination after keratorefractive surgery need to be modified to improve accuracy. Our knowledge of this subject is still evolving. Given the enormous impact of this problem on clinical practice, awareness of the shortcomings and suggested methods to improve accuracy can be valuable to clinicians.     

Comparison of the Zeiss IOLMaster and applanation A-scan ultrasound: biometry for intraocular lens calculation

Purpose: A comparison of axial length estimates using applanation A‐scan ultrasound and the Zeiss IOLMaster was conducted. The accuracy in predicting postoperative refraction determined by each method was also compared. Methods: A cross‐sectional study was performed on 51 eyes in 46 patients presenting to clinical practice for cataract surgery assessment. Preoperative measurement of axial length was performed with applanation ultrasound and the IOLMaster. The IOLMaster measurements were used to determine the intraocular lens power based on the SRK/T formula. Postoperative refractive outcomes were obtained and spherical equivalent calculated and compared to the predicted refractive error with each biometric method. Results: On average the axial lengths measured by the IOLMaster were longer by 0.15 mm compared to ultrasound biometry (P < 0.01). Using the IOLMaster over applanation ultrasound biometry significantly improved the postoperative refractive outcome from 0.65 D to 0.42 D (P = 0.011). Conclusions: The IOLMaster provides an accurate axial length measurement and results in accurate intraocular lens power calculation based on the SRK/T formula. It is quick and easy to use and provides a non‐contact technique with no risk of infection or corneal abrasion.     

Surgery for 4 refractive errors in 1 patient

We report a case of cataract extraction with implantation of a multifocal intraocular lens (IOL) after photorefractive keratectomy for myopia and astigmatism and subsequent laser thermal keratoplasty for surgically induced hyperopia. Good refractive results were obtained using standard biometry techniques for calculation of the IOL power.     

眼球生物测量在白内障手术中的应用进展

眼球生物测量是指应用各种检查手段对眼球结构的各种参数进行测量,为眼部疾病的诊断和治疗提供参考依据。在白内障手术中,眼轴测量误差引起的人工晶状体度数计算偏差是导致术后屈光误差的主要原因,因此精确的生物测量具有重要的临床意义。本文对当前临床常见眼球生物测量仪器的进展作一综述。     

Intraoperative optical refractive biometry for intraocular lens power estimation without axial length and keratometry measurements

PURPOSE: To correlate intraoperative aphakic autorefraction to conventional emmetropic intraocular lens (IOL) calculations and derive an empiric predictive model for IOL estimation based on optical refractive biometry without axial length and keratometry measurements. SETTING: Institutional Review Board of the University of Southern California, Los Angeles County General Hospital, Los Angeles, California, USA. METHODS: A pilot group of 22 eyes of 22 patients scheduled for cataract surgery were enrolled in a prospective trial. All patients had a standard preoperative workup with subsequent cataract extraction and IOL implantation according to conventional biometric measurements and IOL calculations. Intraoperative autorefractive retinoscopy was used to obtain aphakic autorefraction and to measure the aphakic spherical equivalent before lens implantation. A linear regression analysis was used to correlate the aphakic spherical equivalent to the final adjusted emmetropic IOL power to empirically derive a refractive formula for IOL calculation (optical refractive biometry method). A second validation series of 16 eyes was used in a head-to-head comparison between the optical refractive biometry and the conventional IOL formulas. A subset of 6 eyes from the validation series were post-refractive cases having subsequent cataract surgery. RESULTS: Intraoperative retinoscopic autorefraction was successfully obtained in all 22 patients in the pilot group and all 16 patients in the validation group. The spherical equivalent of the aphakic autorefraction correlated linearly with the final adjusted emmetropic IOL power (P<.0001, with adjusted r(2)=.9985). The relationship was sustained over an axial length range of 21.43 to 25.25 mm and an IOL power range of 12.0 to 25.5 diopters (D). In a subsequent validation series of 10 standard and 6 post-laser in situ keratomileusis (LASIK) cataract cases, the optical refractive biometry method proved to be a better predictive model for IOL estimation than conventional formulas; 83% of the LASIK eyes and 100% of the normal eyes were within +/-1.0 D of the final IOL power when aphakic autorefraction was used, compared with 67% of LASIK eyes and 100% of the normal eyes, using the conventional methodology. CONCLUSIONS: A new model for IOL power calculation was derived based on an optical refractive methodology that breaks away from the conventional art introduced by Fyodorov in the 1960s. A purely refractive algorithm is used to predict the power of the IOL at the time of surgery without the need for axial length and keratometry measurements. This method bypasses some limitations of conventional biometry and shows promise in the post-refractive cataract cases.     

角膜屈光手术后人工晶状体度数计算公式的选择

角膜屈光手术后的患者发生白内障并行人工晶状体置换手术时,如果按常规计算公式选择人工晶状体的度数,往往会在术后产生不同程度的屈光不正,主要来源于角膜屈光力的测算误差和计算公式的误差,以及眼轴长度测量和有效人工晶状体位置计算的准确性降低等方面的原因.因此,对于曾行角膜屈光手术的白内障患者, 术前应运用适当的方法估算角膜屈光力,并正确地选择合适的人工晶状体度数计算公式,从而减少晶状体置换术后引起的屈光误差.     

角膜屈光手术患者的白内障摘除联合人工晶体植入手术

目的 研究有角膜屈光手术史患者行白内障摘除植入工晶体度数的确定和术中术后并发症.方法 选取有角膜屈光手术史患者4例4只眼,测量患者的眼轴、角膜曲率和前房深度,分别带入Holladay、Binkhorst及其回归公式计算人工晶体度数,对患者行超声乳化白内障吸除联合人工晶体植入术,术后随访3个月,记录裸眼视力、矫止视力和屈光状态.结果 4例均以选择计算结果中最大的人工晶体度数,结合各自不同的情况有所增减,植入了人工晶体,术后屈光状态与预测值的偏差＜1D;1例在手术中出现了透明角膜隧道切口附近的放射状角膜瘢痕裂开,1例在手术后出现了局限在LASIK角膜瓣区域的角膜水肿.结论 采用多个计算公式同时计算,有可能减小误差,其中,Binkhorst二次回归公式的计算结果预测性比较好.     

非正常眼轴眼前节参数测量和IOL度数计算公式研究进展

屈光性白内障手术的良好效果取决于多种因素,主要包括术前精确的生物测量和人工晶状体(IOL)度数的准确计算。非正常眼轴术前眼部生物测量精确性较低,且术后屈光状态预测与正常眼轴眼相比误差较大,这为获得术后最佳视觉质量带来了很大挑战。近期,新型光学生物测量仪的临床应用,个体化的IOL度数计算公式的研发和应用,使IOL度数选择更加精确。本文针对非正常眼轴白内障患者术前眼部参数测量及IOL度数计算公式的选择近3a最新相关研究进展进行综述,以期为临床应用提供参考。     

Difficult lens power calculations

PURPOSE OF REVIEW: Although cataract extraction seems to be feasible without major technical obstacles, the surgical technique has changed completely, and patients are no longer satisfied with good spectacle-corrected vision but anticipate complete visual rehabilitation after cataract surgery, without correction. To fulfill this desire, toric or accommodative intraocular lenses are of increasing popularity, and the intraocular lens power calculation after keratorefractive surgery has been improved. RECENT FINDINGS: In this review article, we provide an overview of different mathematical strategies of calculating the intraocular lens power with standard formulas and with new algorithms, such as paraxial or numeric ray-tracing. These enhanced techniques may improve the validity of lens power calculation due to reduction of the prediction error, especially in cases with high or excessive corneal astigmatism and after refractive laser surgery. Furthermore, a new calculation scheme for the determination of bitoric eikonic intraocular lenses allows a distortion-free imaging in astigmatic eyes. The biometric determinants for the different formulas and calculation schemes are discussed in detail. SUMMARY: In difficult cases, standard calculation schemes are overemployed and new mathematical algorithms are necessary to adequately address these problems. Ray-tracing algorithms and other complex mathematical computation schemes are of increasing interest and will more and more replace conventional calculation formulas for determination of intraocular lens power.