Reasons of postoperative astigmatism

At present, cataract extraction offers great improvement for uncorrected and best corrected visual acuity and rapid postoperative rehabilitation. Cataract surgery is now treated as refractive surgery. Postoperative astigmatism has remained the only obstacle to the achievement of good, uncorrected visual acuity after cataract surgery. Postoperative astigmatism is a very complex clinical problem. The main influence on its appearance has preoperative astigmatism as well as shape and length of anterior chamber opening, suturing technique and wound healing.     

Surgical correction of postoperative astigmatism

The photokeratoscope has increased the understanding of the aspheric nature of the cornea as well as a better understanding of normal corneal topography. This has significantly affected the development of newer and more predictable models of surgical astigmatic correction. Relaxing incisions effectively flatten the steeper meridian an equivalent amount as they steepen the flatter meridian. The net change in spherical equivalent is therefore negligible. Poor predictability is the major limitation of relaxing incisions. Wedge resection can correct large degrees of postkeratoplasty astigmatism. Resection of 0.10 mm of tissue results in approximately 2 diopters of astigmatic correction. Prolonged postoperative rehabilitation and induced irregular astigmatism are limitations of the procedure. Transverse incisions flatten the steeper meridian an equivalent amount as they steepen the flatter meridian. Semiradial incisions result in two times the amount of flattening in the meridian of the incision compared to the meridian 90 degrees away. Combination of transverse incisions with semiradial incisions describes the trapezoidal astigmatic keratotomy. This procedure may correct from 5.5 to 11.0 diopters depending upon the age of the patient. The use of the surgical keratometer is helpful in assessing a proper endpoint during surgical correction of astigmatism.     

Control of postoperative astigmatism.

Thirty-six eyes with excessive astigmatism following cataract extraction via a corneal section were subjected to suture adjustment. This was performed six to eight weeks postoperatively under topical anaesthesia. The cases were selected from a large volume of corneal section cases because they had over 3.0 dioptres astigmatism. We reduced astigmatism significantly in the majority. There were no serious complications.     

Surgical correction of postoperative astigmatism

The photokeratoscope has increased the understanding of the aspheric nature of the cornea as well as a better understanding of normal corneal topography. This has significantly affected the development of newer and more predictable models of surgical astigmatic correction. Relaxing incisions effectively flatten the steeper meridian an equivalent amount as they steepen the flatter meridian. The net change in spherical equivalent is, therefore, negligible. Poor predictability is the major limitation of relaxing incisions. Wedge resection can correct large degrees of postkeratoplasty astigmatism, Resection of 0.10 mm of tissue results in approximately 2 diopters of astigmatic correction. Prolonged postoperative rehabilitation and induced irregular astigmatism are limitations of the procedure. Transverse incisions flatten the steeper meridian an equivalent amount as they steepen the flatter meridian. Semiradial incisions result in two times the amount of flattening in the meridian of the incision compared to the meridian 90 degrees away. Combination of transverse incisions with semiradial incisions describes the trapezoidal astigmatic keratotomy. This procedure may correct from 5.5 to 11.0 diopters dependent upon the age of the patient. The use of the surgical keratometer is helpful in assessing a proper endpoint during surgical correction of astigmatism.     

白内障术后角膜散光的临床观察

通过对472例（556眼）白内障患者随机分组：施行不同切口，术前与术后随访观察角膜屈折力的变化。发现角膜缘切口组术后早期平均散光度较高，顺规性散光发生率高，且向逆规性散光转化。而巩膜隧道式切口组与术前对照无明显差异。并讨论引起散光的原因。     

Prediction of postoperative astigmatism in cataract surgery

Background: The purpose of this study was to predict postoperative astigmatism using refraction, keratometry, and other preoperative information after phacoemulsification with posterior chamber intraocular lens (IOL) implantation.Methods: A retrospective study was conducted of 176 eyes of 161 patients undergoing phacoemulsification for visually significant cataract with capsular bag or sulcus IOL fixation at the Hunter Holmes McGuire Veterans Administration Medical Center, Richmond, Va. Eyes with complications and final-corrected visual acuity of less than 20/60 were excluded. Keratometric and refractive astigmatism were described by Jackson cross-cylinder with-the-rule (J₀) and oblique (J₄₅) components. Preoperative predictors of postoperative refractive J₀ and J₄₅ were determined by univariate and multivariate regression analysis.Results: The final multivariate model to predict postoperative with-the-rule astigmatism was J_{0Postoperative} = 0.24 × J_{0Preoperative} 0.46 × J_0Keratometic − 0.08 (coefficient of determination [r²] = 0.51, all p < 0.001). The multivariate model based on expected predictors of oblique astigmatism was J_{45Postoperative} = 0.10 × J_{45Preoperative} + 0.23 × J_{45Keratometric} + 0.01, (r² = 0.05, p = 0.09 for J_{45Preoperative} and 0.03 for J_{45Keratometric}). Temporal clear cornea (as opposed to superior scleral tunnel) incisions, and use of sutures in scleral tunnel incisions, were not predictive of postoperative astigmatism.Interpretation: Postoperative astigmatism can be estimated from preoperative astigmatism using the following weighted average: two-thirds keratometric and one-third refractive astigmatism. Preoperative refraction may predict postoperative astigmatism independent of keratometry because keratometry reflects only the paracentral anterior (not posterior) corneal curvature.     

Intraocular implants: the postoperative astigmatism.

A series of 100 cases of intraocular implants has been considered, especially with regard to the postoperative astigmatism. This was found to be far higher than in a similar series of cases subjected to the same techniques without an implant. The operative results appear to be as good as in any conventional series, except for 2 cases. The reason for the excessive astigmatism (average 2.84 D) is not clear but the following factors have been suggested: (1) faulty surgical technique, that is, irregular corneal healing; (2) astigmatic errors in the actual intraocular lens itself; (3) tilting of the intraocular lens; (4) the intraocular lens, owing to its own inherent weight, may pull on the iris and ciliary body and even distort the cornea on healing. A summation of all these factors could produce an undesirably high degree of astigmatism.     

Effect of suture material on postoperative astigmatism.

Two hundred patients were enrolled in a randomized, prospective clinical trial comparing the use of 10-0 nylon, 10-0 polypropylene (Prolene), 11-0 polyester (Mersilene), and 10-0 polyethylene (Novafil) suture materials on the amount and decay curves of surgically induced astigmatism following intraocular lens (IOL) surgery. Patients with Mersilene and nylon sutures had the highest amounts of induced with-the-rule (WTR) cylinder (significantly more than Prolene) at one day after surgery. However, the WTR cylinder decayed rapidly for nylon during the first three months but more slowly for Mersilene because of its lack of stretchability. The Prolene group had the lowest level of induced WTR cylinder at one day, but against-the-rule (ATR) drift occurred, leaving cases with ATR astigmatism by a year. The nylon group had the second highest amount of induced WTR cylinder at one day, which had decayed to ATR cylinder by five months. Between one and two years postoperatively, the nylon group experienced a significant ATR shift. The amount of early induced WTR cylinder seemed to be related to the knot-tying technique and tissue gripping characteristics, whereas the shape of the decay curve was related to the material characteristics of the suture.     

松解性角膜切开术治疗术后中高度散光的临床观察

目的对人工晶体植入术和穿透性角膜移植术后一年以上,存在中高度散光的患者行松解性弧形角膜切开术,观察其临床疗效.方法10例(10眼),其中人工晶体植入术4例,穿透性角膜移植术5例,人工晶体、穿透性角膜移植联合术1例,均术后一年以上,3mm视区内的角膜散光≥2.00D,近视≤2.00D,患者的裸眼视力均可矫正.根据角膜地形图确定角膜最高屈折力的径线位置.用6.5mm环钻在角膜中央刻痕,在显微镜下用德国Martin Instrument单刃红宝石刀在屈折力最大的径线上,沿环钻的刻痕作一对弧形切口,深度为角膜厚度的1/2～2/3,切口长度为2～3个钟点.结果通过角膜地形图和检影验光发现术前3mm视区的平均角膜散光为3.46±0.99D,术后6个月为2.05±0.75D,统计学检验有显著性差异P＜0.01;术前10例患者的裸眼视力为4.05±0.12,术后6个月的视力明显提高为4.45±0.11.结论本文对手术适应证、技术、角膜散光变化和并发症进行讨论,从而证实弧形角膜切开术是一项简单安全、能快速提高视力的方法.     

白内障超声乳化摘除联合小梁切除术后的散光变化

目的　研究两种不同切口白内障超声乳化摘除联合小梁切除术后的散光变化。方法　两组患者分别接受双路切口和单路切口白内障超声乳化摘除联合小梁切除术,其中双路切口手术组2 0只眼,单路切口手术组18只眼。术后1周、1、3个月分别测量散光。结果　两联合手术组术后1周时与术前比较散光度差异显著(P <0 .0 5 ) ,而1个月以后各组与术前差异均不显著(P >0 .0 5 )。结论　联合手术可能增加术后散光,但1个月内可以趋于稳定,有利于视力恢复。     

Small incision cataract surgery: changes in postoperative astigmatism

The course of postoperative astigmatism was studied in 2 groups of patients following phacoemulsification and IOL implantation. In the first group a soft posterior chamber lens (IOGEL, Alcon) was introduced through a 6.5 mm scleral pocket incision. In group 2 the IOGEL lens was implanted through a 3.5 mm incision using a new instrument. The patients in group 2 had lower postoperative astigmatism and achieved stable refraction significantly earlier than group 1 patients. Three weeks postoperatively changes in refraction were seen in only a few cases. The small-incision technique significantly accelerates the visual rehabilitation of cataract patients.     

Value of qualitative keratometry for the correction of postoperative astigmatism

The use of a per operative qualitative Keratometer is of interest in prevention of astigmatism in cataract extraction. Our study, which included two groups of forty patients each, demonstrated that the Karickhoff Keratometer can markedly decrease the degree of immediate post-operative astigmatism = gain of 2.38 delta in comparison with the control group and astigmatism less than or equal to 2 in 35% of the cases.     

准分子激光原位角膜磨镶术中不同的微型角膜刀对术后散光的影响

目的 研究准分子激光原位角膜磨镶术（LASIK）中不同的微型角膜刀对术后散光的影响。方法158人（24眼）随机分为H230型微型角膜刀组80人（124眼）和HT230型微型角膜刀组78人（124眼）。所有患者均随访6个月,并对其术前、术后1,3,6个月的散光及其轴的绝对改变和矢量改变进行分析。结果LASIK术后1,3,6个月,散光的绝对值,H230型组分别为0.23D±0.38 D,0.15±0.37D和0.13 D±0.38 D,而 HT230型组分别为0.18D±0.41,0.14 D±0.43D和0.12D±0.42D;散光的矢量值,H230型组分别为0.53D±0.28 D,0.46 D±0.30 D和0.46 D±0.30D,而HT230型组分别为0.46 D±0.33 D,0.50 D ±0.37 D和0.41±0.35D。手术所致散光矢量的改变（包括轴的改变）,除术后3个月时两组间无显著性差异,余均具有显著性差异（术后1个月时,P=0.04;3个月时,P=0.06;6个月时,P=0.02）。结论H230型比HT230型微型角膜刀更易引起较大的散光轴改变,而HT230型比H230型微型角膜刀所致的术后散光改变更趋向于逆规性散光。     

The value of the Terry keratometer in predicting postoperative astigmatism

The Terry keratometer was used immediately before and immediately after cataract surgery. The results were compared with keratometry readings taken before surgery and readings taken on the morning of the first postoperative day. The mean preoperative cylinder in 27 eyes was 1/2 diopter less than that measured prior to the start of surgery. Preoperative readings and readings obtained prior to the start of surgery differed by more than 1 diopter in 37% of eyes. The keratometer readings obtained at the end of the surgery in 63 eyes were flatter than those obtained on the first postoperative day. Forty-four percent of the intraoperative cylinder readings differed from postoperative readings by more than 2 diopters. The factors which can produce errors with the use of this instrument include changes in intraocular pressure, the effect of the lid speculum, rectus suture tension, the alignment of the eye with respect to the keratometer , and user experience.     

切口位置对晶状体超声乳化术后散光的影响

目的探讨晶状体超声乳化吸出手术中切口位置对术后散光的影响。方法白内障80例(98眼)分为两大组,其中第一大组,又根据术前角膜地形图再分为AB两组:A组为顺规性散光组,作上方巩膜隧道切口;B组为逆规性散光组,作颞侧透明角膜切口,分别行超声乳化术加折叠式人工晶状体植入术;第二大组均作上方切口。术后观察3天,1月、3月和6月的角膜平均散光和裸眼视力情况。结果两大组在术后不同时间内角膜散光度之间有显著性差异。术后1月分别为(0.57±0.30)D和(1.20±0.59)D。结论根据患者术前角膜地形图,顺规性散光患者采用上方巩膜隧道切口,逆规性散光采用颞侧透明角膜切口。早期视力以颞侧透明角膜切口者恢复佳。     

小切口超声乳化白内障吸除术后角膜散光的变化

目的　探讨小切口超声乳化白内障吸除联合后房型人工晶状体植入手术后角膜散光情况及手术性散光度的变化。方法　对 38例 (38只眼 )白内障患者行上方巩膜倒眉状小切口超声乳化白内障吸除联合人工晶状体植入手术。分别于术前 ,术后 1d、1个月及 3个月使用角膜地形图仪及自动屈光仪进行角膜散光情况检测。结果　平均角膜散光度术后 1d、1个月及 3个月分别为 (1 10± 0 71)、(1 0 8± 0 6 6 )及 (0 87± 0 5 5 )D ;术后 3个月与术前比较差异无显著性 (P >0 0 5 )。平均手术性散光度术后 1d、1个月及 3个月分别为 (1 37± 1 0 3)、(1 2 4± 0 93)及 (1 0 4± 0 75 )D ;术后 3个月与术后 1d比较差异有显著性 (P <0 0 5 )。结论　上方巩膜倒眉状无缝线小切口对术后角膜散光影响小 ;将手术性散光的度数及轴位变化进行矢量分析 ,可综合评价手术致角膜屈光状态的改变 ;角膜地形图可准确反映角膜曲率变化 ,对评价白内障手术后角膜散光变化具有重要的临床意义。