准分子激光角膜屈光术后人工晶状体度数计算的研究进展

曾行准分子激光角膜屈光手术的白内障患者,人工晶状体(IOL)度数的计算一直是个难题,如按常规方法计算,结果会产生较大误差,主要是术后出现不同程度的远视。本文就准分子激光角膜屈光术后角膜屈光力的测算、人工晶状体计算公式选择、前房深度测量、眼轴测量等影响人工晶状体度数计算的多种因素及其解决方法做一综述。     

Ray tracing software for intraocular lens power calculation after corneal excimer laser surgery

Purpose

To evaluate the accuracy of intraocular lens (IOL) power calculations using ray tracing software in eyes after myopic laser in situ keratomileusis (LASIK).

Methods

Twenty-four eyes of 17 cataract patients who underwent phacoemulsification and IOL implantation after myopic LASIK were analyzed retrospectively. The IOL power calculation was performed using OKULIX ray tracing software. The axial length was measured using the IOLMaster and keratometry data using TMS2N. The accuracy of the IOL power calculation using OKULIX was compared with those using the Camellin–Calossi, Shammas-PL, Haigis-L formulas and the double-K SRK/T formula using 43.5 diopters (D) for the Kpre.

Results

The mean values of the arithmetic and absolute prediction errors were 0.63 ± 0.85 and 0.80 ± 0.68 D, respectively. The arithmetic prediction error by OKULIX was a significant hyperopic shift of the distribution of the postoperative refractive errors compared to the Camellin–Calossi, Shammas-PL and Haigis-L formulas (P < 0.05), and the absolute prediction error showed no significant difference with other formulas. The prediction errors using OKULIX were within ±0.5 D in 10 eyes (41.7 %) and within ±1.0 D in 18 eyes (75.0 %). The percentages of eyes within ±1.0 D using OKULIX were comparable to those obtained using the Camellin–Calossi, the Shammas-PL formulas and the double-K SRK/T formula using 43.5 D for the Kpre, and significantly (P < 0.05) higher than that obtained using the Haigis-L formula.

Conclusions

IOL power calculations using OKULIX provided predictable outcomes in eyes that had undergone a previous myopic LASIK.     

Estimation of true corneal power after keratorefractive surgery in eyes requiring cataract surgery: BESSt formula

PURPOSE: To describe a new formula, BESSt, to estimate true corneal power after keratorefractive surgery in eyes requiring cataract surgery. SETTING: Moorfields Eye Hospital, London, United Kingdom. METHODS: The BESSt formula, based on the Gaussian optics formula, was developed using data from 143 eyes that had keratorefractive surgery. The formula takes into account anterior and posterior corneal radii and pachymetry (Pentacam, Oculus) and does not require pre-keratorefractive surgery information. A software program was developed (BESSt Corneal Power Calculator), and corneal power was calculated in 13 eyes that had keratorefractive surgery and required cataract surgery. RESULTS: In the eyes having phacoemulsification, target refractions calculated with the BESSt formula were statistically significantly closer to the postoperative manifest refraction (mean deviation 0.08 diopters [D] +/- 0.62 [SD]) than those calculated with other methods as follows: history technique (-0.07 +/- 1.92 D; P = .05); history technique with double-K adjustment (0.13 +/- 2.39 D; P = .05); Holladay 2 with K-values estimated with the contact lens method (-0.76 +/- 1.36 D; P = .03); Holladay 2 with K-values from Atlas topographer (Humphrey) (-0.55 +/- 0.61 D; P<.01). Using the BESSt formula, 46% of eyes were within +/-0.50 D of the intended refraction and 100% were within +/-1.00 D. CONCLUSIONS: The BESSt formula was statistically significantly more accurate than the other techniques tested. Thus, it could significantly improve intraocular lens power calculation accuracy after keratorefractive surgery, especially when pre-refractive surgery data are unavailable.     

A comparative analysis of intraocular lens power calculation methods after myopic excimer laser surgery

PURPOSE: To compare the accuracy and predictability of different intraocular lens (IOL) power calculation methods in eyes after myopic excimer laser surgery. METHODS: Phacoemulsification and IOL implantation outcomes in 37 eyes of 37 patients with prior LASIK or photorefractive keratectomy were documented (amount of correction=-6.92+/-3.12 diopters (D), range: -2.00 to -13.00 D). The theoretical IOL power that would have resulted in emmetropia was calculated (IOLemme). Using the clinical history keratometry and biometry, the IOL power was calculated using the following methods: Sanders, Retzlaff, Kraff (SRK)-T, SRK-T Double-K (DK), Holladay 1 DK, Hoffer Q DK, Holladay 2 DK, Feiz-Mannis, and Ladas-Stark corneal bypass. The calculated IOL power was compared to IOLemme and used to determine the mean error and mean absolute error of refractive outcome for each eye. RESULTS: The calculated IOL power using the SRK-T, Feiz-Mannis, and Holladay 1 DK methods were significantly different from IOLemme. The lowest mean absolute error was achieved using the Hoffer Q DK method (0.75+/-0.52 D), Holladay 2 DK (0.75+/-0.62 D), SRK-T DK (0.76+/-0.60 D), and Ladas-Stark (0.83+/-63 D). With the SRK-T DK method, 51.4% of eyes were within +/-0.50 D of emmetropia and 67.6% of eyes were within +/-1.00 D. The Holladay 2 DK method had the highest percentage (81.1%) of eyes within +/-1.00 D and 45.9% within +/-0.50 D. CONCLUSIONS: The refractive results of IOL implantation using the same biometry data in eyes after LASIK can vary markedly. The SRK-T DK, Hoffer Q DK, and Holladay 2 DK methods resulted in the highest accuracy.     

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.     

New formula for calculating intraocular lens power after laser in situ keratomileusis

PURPOSE: To assess the validity and accuracy of a proposed formula for keratometry (K) readings after laser in situ keratomileusis (LASIK). SETTING: The Eye Center and the Eye Foundation for Research, Riyadh, Saudi Arabia. METHOD: This studied comprised 34 eyes that had LASIK surgery. Refraction and an automated K-reading (auto-K) were performed preoperatively. Refraction, auto-K, and K-reading assessment by the clinical history method and the proposed formula were performed 4 to 12 weeks postoperatively. The proposed formula is K(postop) = K(preop) - [(N(c) - 1) x (R(a-postop) - R(a-preop))/(R(a-postop) x R(a-preop))], where K(postop) is the K-reading after LASIK, K(preop) is the K-reading before LASIK, N(c) is the index of refraction of the cornea (1.376), R(a-postop) is the radius of curvature of the anterior corneal surface after LASIK, and R(a-preop) is the radius of curvature of the anterior corneal surface before LASIK. RESULTS: Twenty patients (10 men, 10 women) were included in the study. The mean age of the patients was 30.58 years +/- 17.68 (SD) (range 18 to 44 years). Preoperatively, the mean spherical equivalent (SE) was -4.99 +/- 2.82 diopters (D) (range -1.12 to -15.00 D), the mean R(a) was 7.76 +/- 0.32 mm (range 7.33 to 8.50 mm), and the mean auto-K reading was 43.45 +/- 1.73 D (range 39.62 to 46.00 D). Postoperatively, the mean SE was +0.02 +/- 0.63 D (range -2.75 to +1.00 D), the mean R(a) was 8.63 +/- 0.53 mm (range 7.80 to 9.92 mm), and the mean K-reading assessed by auto-K, clinical history method, and the proposed formula was 39.17 +/- 2.35 D (range 34.00 to 43.25 D), 38.79 +/- 2.52 D (range 33.1 to 42.78 D), and 38.69 +/- 2.51 D (range 33.1 to 43.0 D), respectively. The results obtained by the proposed formula were similar to those obtained by the clinical history method (P =.098). Auto-K readings significantly overestimated the K-values (P<.0001) when compared to the proposed formula and clinical history method. CONCLUSION: The proposed formula was simple, objective, not dependent on refraction, and as accurate as the clinical history method in determining K-readings after LASIK.     

Determining corneal power using Orbscan II videokeratography for intraocular lens calculation after excimer laser surgery for myopia

PURPOSE: To assess the accuracy of Orbscan II slit-scanning videokeratography for intraocular lens (IOL) calculation in eyes with previous photorefractive surgery for myopia. SETTING: Private practice, St. Louis, Missouri, USA. METHODS: Corneal power (K) was measured by manual keratometry, Placido-based videokeratography (Atlas), slit-scanning videokeratography (Orbscan II), and contact lens overrefraction in 21 post-photoablation eyes having cataract surgery. Postoperative data collected after phacoemulsification were used to back-calculate corneal power (BCK). The BCK values were statistically compared at 3.0 to 6.0 mm central Orbscan II curvature and power measurements, including total axial power, total tangential power, total mean power, and total optical power. Similar comparisons were made to Atlas curvature at the 0.0 to 10.0 mm zones. RESULTS: The mean corneal power after refractive surgery based on BCK values using the Holladay 2 formula (BCK H2) was 39.35 diopters (D) +/- 2.58 (SD). The mean manual value (40.52 +/- 1.95 D) and Atlas-based values were statistically higher than BCK H2 values (P<.001). The mean corneal power calculated from historical data was 39.33 +/- 2.70 D (P = .83 to BCK H2; n = 19) and from contact lens overrefraction, 41.38 +/- 3.11 D (P = .19; n = 5). Orbscan II parameters (n = 21) of the total mean power (3.0 mm, 39.10 +/- 2.63 D), total tangential power (3.0 mm, 39.11 +/- 2.60), total axial power (5.0 mm, 39.19 +/- 2.55 D), and total optical power (3.0 mm, 39.08 +/- 2.78 D; 4.0 mm, 39.39 +/- 2.76 D) were statistically similar to both the historical and BCK H2 values (P>.11). If used prospectively, 80.9% of eyes would have been within +/-0.50 D of the targeted refraction using a 4.0 mm total optical power, 76.2% using a 5.0 mm total axial power, and 42.1% using the historical method. CONCLUSION: The Orbscan II 5.0 mm total axial power and 4.0 mm total optical power can be used to more accurately predict true corneal power than the history-based method and may be particularly useful when pre-LASIK data are unavailable.     

Severe fibrinous reaction after cataract and intraocular lens implantation surgery requiring neodymium:YAG laser therapy

Fibrous membrane formation on the anterior surface of an intraocular lens with occlusion of the pupil was noted in five patients having phacoemulsification and one patient having planned extracapsular cataract extraction. Initial onset of pain and decreased vision ranged from eight to 36 postoperative days. Since these patients did not respond fully to steroid therapy, the neodymium:YAG laser was used to disrupt the fibrinous membrane which occluded the pupil. In all but one case, the fibrinous reaction responded to laser therapy. Generally, less energy was required when laser therapy was initiated early in the treatment plan.     

No-history method of intraocular lens power calculation for cataract surgery after myopic laser in situ keratomileusis

PURPOSE: To prospectively evaluate the no-history method for intraocular lens (IOL) power calculation in 15 cataractous eyes that had previous myopic laser in situ keratomileusis (LASIK) and for which the pre-LASIK K-readings were not available. SETTING: Private practice, Lynwood, California, USA. METHODS: The predicted IOL power was calculated in each case. Also calculated were the mean arithmetic and absolute IOL predictor errors, range of the prediction errors, and number of eyes in which the error was within +/-1.00 diopter (D). RESULTS: The mean arithmetic IOL prediction error was -0.003 D +/- 0.63 (SD), and the mean absolute IOL prediction error was 0.55 +/- 0.31 D (range -0.89 to +1.05 D). Fourteen eyes (93.3%) were within +/-1.00 D. The results of the Shammas post-LASIK formula compared favorably to the results obtained with the optimized Holladay 1 (P = .42), Hoffer Q (P = .25), Haigis (P = .30), and Holladay 2 (P = .19) formulas and were better than the results obtained with the optimized SRK/T formula (P = .0005). CONCLUSION: The no-history method is a viable alternative for IOL power calculation after myopic LASIK when the refractive surgery data are not available.     

A new formula for intraocular lens power calculation after refractive corneal surgery

PURPOSE: When calculating the power of an intraocular lens (IOL) with conventional methods in eyes that have previously undergone refractive surgery, in most cases the power is inaccurate. To minimize these errors, a new IOL power calculation formula was developed. METHODS: A theoretical formula empirically adjusted two variables: 1) the corneal power and 2) the anterior chamber depth (ACD). From the average curvature of the entrance pupil area, weighted according to the Stiles-Crawford effect, the corneal power is calculated by using a relative keratometric index that is a function of the actual corneal curvature, type of keratorefractive surgery, and induced refractive change. Anterior chamber depth is a function of the preoperative ACD, lens thickness, axial length, and the ACD constant. We used our formula in 20 eyes that previously underwent refractive surgery (photorefractive keratectomy [n = 6], laser subepithelial keratomileusis [n = 3], laser in situ keratomileusis [n = 6], and radial keratotomy [n = 5]) and compared our results to other formulas. RESULTS: Mean postoperative spherical equivalent refraction was +0.26 diopters (D) (standard deviation [SD] 0.73, range: -1.25 to +/- 1.58 D) using our formula, +2.76 D (SD 1.03, range: +0.94 to +4.47 D) using the SRK II, +1.44 D (SD 0.97, range: +0.05 to +4.01 D) with Binkhorst, 1.83 D (SD 1.00, range: -0.26 to +4.21 D) with Holladay I, and -2.04 D (SD 2.19, range: -7.29 to +1.62 D) with Rosa's method. With our formula, 60% of absolute refractive prediction errors were within 0.50 D, 80% within 1.00 D, and 93% within 1.50 D. CONCLUSIONS: In this first series of patients, we obtained encouraging results. With a greater number of cases, all statistical adjustments related to the different types of surgery should be improved.     

Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy

OBJECTIVE: To assess the validity of corneal power measurement and standard intraocular lens power (IOLP) calculation after photorefractive keratectomy (PRK). DESIGN: Nonrandomized, prospective, cross-sectional, clinical study. PARTICIPANTS: A total of 31 eyes of 21 females and 10 males with a mean age at the time of surgery of 32.3 +/- 6.6 years (range, 24.4-49.5 years). INTERVENTION: Subjective refractometry, standard keratometry, TMS-1 corneal topography analysis, and pachymetry were performed before and 15.8 +/- 10.4 months after PRK for myopia (n = 24, -1 .5 to -8.0 diopters [D], mean -5.4 +/- 1.9 D) or myopic astigmatism (n = 7, sphere -2.0 to -7.5 D, mean -4.4 +/- 1.9 D; cylinder -1.0 to -3.0 D, mean -1.9 +/- 0.7 D). The IOLP calculations were done using two different formulas (SRK/T and HAIGIS). MAIN OUTCOME MEASURES: Keratometric power (K) and topographic simulated keratometric power (TOPO) as measured (Kmeas, TOPOmeas) and as calculated according to the change of power of the anterior corneal surface or according to the spherical equivalent change after PRK (Kcalc, TOPOcalc), IOLP for emmetropia, and postoperative ametropia for calculated corneal powers were assessed in a model. RESULTS: After PRK, mean Kmeas and TOPOmeas were significantly greater (0.4-1.4 D, maximum 3.3 D) than mean KRcalc and TOPOcalc (P < 0.0001). On average, the relative flattening of the cornea after PRK was underestimated by 14% to 30% (maximum, 83%) depending on the method of calculation. The mean theoretical IOLP after PRK ranged from + 17.4 D (SRK/T, TOPOmeas) to +20.9 D (HAIGIS, Kcalc) depending on the calculation method for corneal power and IOLP calculation formula used. For both formulas, IOLP values using keratometric readings were significantly higher (>1 D) than IOLP values using topographic readings (P < 0.0001). The theoretically induced mean refractive error after cataract surgery ranged from +0.4 to +1.4 (maximum, +3.1) D. Corneal power overestimation and IOLP underestimation correlated significantly with the spherical equivalent change after PRK (P = 0.001) and the intended ablation depth during PRK (P = 0.004). CONCLUSIONS: To avoid underestimation of IOLP and hyperopia after cataract surgery following PRK, measured corneal power values must be corrected. The calculation method using spherical equivalent change of refraction at the corneal plane seems to be the most appropriate method. In comparison with this method, direct power measurements underestimate corneal flattening after PRK by 24% on average. Use of conventional topography analysis seems to increase the risk of error. However, because this study is retrospective and theoretical, there is still a need for a large prospective investigation to validate the authors' findings.     

One-year results after combined cataract surgery and excimer laser trabeculotomy for elevated intraocular pressure

Background

Glaucoma is one of the most common reasons for blindness. Usually an elevated resistance to aqueous outflow is the reason, while aqueous humor production is still normal. Medical reduction of intraocular pressure (IOP) is the first-line therapy in most cases. The gold standard of surgical treatment is trabeculectomy (TE). But TE has a lot of postoperative complications. Therefore we prefer the combined procedure of cataract extraction plus excimer laser trabeculotomy (phaco-ELT) for a selected group of glaucoma patients. Indications are cataract together with moderately elevated IOP without medical therapy or a moderate cataract together with elevated IOP under medical therapy.

Patients and Methods

During ELT, 10 pores were created over 90° of the anterior chamber angle; 28 eyes of 28 patients (10 men and 18 women) were reexamined 12 months ± 2 weeks after combined phaco-ELT. Four patients were excluded because of IOP-lowering surgery during the follow-up. IOP, best corrected visual acuity, slit lamp biomicroscopy as well as glaucoma medication history (antiglaucoma drugs, AGD) were recorded.

Results

The mean age was 74.33±11.81 years. The diagnosis was primary open-angle glaucoma in 9 eyes, pseudoexfoliative glaucoma in 15 eyes, ocular hypertension in 3 eyes, and 1 post-traumatic secondary glaucoma. On average, phaco-ELT could reduce the IOP by 8.79±5.28 mmHg (?34.70%, p<0.001). AGD could be reduced by 0.79±1.50 (?62.70%, p=0.017) at the same time.

Conclusion

The ELT is easy to perform at the end of cataract surgery. Duration of surgery is only prolonged by 2 to 3 minutes. We found an average IOP reduction of 8.79 mmHg (?34.70%) and an average reduction of 0.79 AGD. It is known that the effect of IOP reduction is constant over time unlike argon or selective laser trabeculoplasty. If needed later on, filtering surgery is not compromised because there is no conjunctival touch during ELT and therefore no scarring of the conjunctiva. For a selected collective of glaucoma patients this procedure could be a good way to avoid trabeculectomy.     

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.     

准分子激光屈光性角膜手术后人工晶状体屈光度数的预测

目的　探讨准分子激光屈光性角膜手术后 ,不同公式预测人工晶状体屈光度数的准确性及其校正方法。方法　应用第二代经验公式、第三代理论公式和BinkhoistⅡ公式 ,分别于准分子激光原位角膜磨镶术 (laserinsitukeratomileusis,LASIK)前、后测算 6 0例 (12 0只眼 )近视患者矫正至正视眼所需的人工晶状体屈光度数 ,并应用F值计算与术眼原晶状体屈光力等值的人工晶状体屈光度数 ,即等值人工晶状体屈光度数。应用SPSS统计软件对数据进行统计学分析。结果　低度近视患者3个公式计算结果LASIK手术前、后比较 ,差异均无显著意义 (P >0 0 5 ) ;中、高度近视患者 3个公式计算结果LASIK术后均小于术前 ,差异有显著意义 (P <0 0 1)。 3个公式计算的LASIK手术前、后等值人工晶状体屈光度数差值 (differenceofequalintraocularlenspower,EILD)均与LASIK实际矫正屈光度数呈高度相关性 (P <0 0 1)。回归公式 :EILD =a +b×手术实际矫正屈光度数 ,其中第二代经验公式 :a =- 1 2 3,b =0 72 ;第三代理论公式 :a =- 1 0 3,b =0 5 2 ;BinkhoistⅡ公式 :a =- 1 4 4 ,b =0 5 0。结论　对于中、高度近视患者 ,准分子激光屈光性角膜手术后使用现有人工晶状体屈光度数测算公式 ,其结果均偏小 ,应用EILD校正可提高准确性。对     

青光眼患者白内障手术人工晶状体计算公式的选择

青光眼与白内障是导致失明的主要原因,手术是重要的治疗方式。青光眼患者具有高眼压、浅前房及短眼轴等临床特征,小梁切除术等抗青光眼术后眼部结构常发生改变。这些变化也导致了抗青光眼术后行白内障手术或青白联合手术与单纯白内障手术在人工晶状体(intraocular lens, IOL)屈光度计算准确性方面存在差异。同时青光眼患者自身的临床特征与抗青光眼手术造成的结构改变对于IOL屈光度预测准确性、屈光漂移的类型等方面的影响也表现出差异。本文就青光眼或抗青光眼术后患者行白内障手术或青白联合手术时屈光误差(refractive error, RE)产生的原因、屈光漂移特征及选择最合适IOL计算公式的最新研究进展进行综述。