Changes in Corneal Astigmatism and High Order Aberrations After Clear Corneal Tunnel Phacoemulsiﬁ Cation Guided by Corneal Topography

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Changes in Corneal Astigmatism and High Order Aberrations After Clear Corneal Tunnel Phacoemulsiﬁ cation Guided by Corneal Topography

Yongxiang Jiang, PhD; Qihua Le, PhD; Jin Yang, MD; Yi Lu, MD

ataracts are the leading cause of visual impairment ABSTRACT and blindness in the world. Currently, phacoemul- PURPOSE: To study changes in corneal astigmatism C sifi cation with intraocular lens (IOL) implantation is and high order aberrations after clear corneal tunnel the most popular treatment for cataracts. With the improve- phacoemulsifi cation guided by corneal topography. ment in surgical techniques and the development of new technology, the recovery of visual function has improved.1-6 METHODS: All patients were randomly assigned to the In recent years, phacoemulsifi cation through a clear corneal test group or the control group. Corneal topography-guid- tunnel incision has become increasingly popular due to ease ed clear corneal tunnel phacoemulsifi cation followed by intraocular lens (IOL) implantation was performed on 22 of the technique, reduced length of surgery, little to no trau- eyes of 16 patients in the test group and conventional ma to the conjunctiva, less surgically induced astigmatism, temporal corneal tunnel phacoemulsifi cation and IOL im- and quick rehabilitation of vision.1,7 plantation were performed on 22 eyes of 21 patients in Corneal astigmatism plays an important role in the recov- the control group. The corneal astigmatism and high order ery of visual function after cataract surgery. The corneal re- aberrations were measured using the NIDEK OPD-Scan aberrometer and topographer preoperatively and up to 3 fractive changes are attributed to the location and size of the 1,8 months after surgery. The corneal astigmatism and sixth corneal incision. Conventional temporal corneal tunnel order root-mean-square (RMS) for corneal coma, trefoil, phacoemulsifi cation without sutures can produce with-the- spherical, secondary coma, and secondary spherical ab- rule astigmatism, because the corneal curvature at the me- errations at 4-mm pupil diameters were compared. ridian of the incision would be fl attened. Such changes are not optimal for all patients with cataracts. Long and Monica1 RESULTS: Fifteen (69%) eyes in the test group and 8 (36%) eyes in the control group achieved у20/25 uncor- reported that the placement of the incision on the steeper me- rected visual acuity 3 months after surgery, which was ridian of the cornea can be benefi cial if preoperative astig- statistically signifi cant (PϽ.05). The best spectacle-cor- matism was у0.75 diopters (D). The length of the incision rected visual acuity was у20/20 in 14 (63%) eyes in the is another important factor that may affect the postoperative test group and 10 (45%) eyes in the control group. The corneal astigmatism. The shorter the incision, the less the mean surgically induced astigmatism in the test group 8 was 0.58Ϯ0.39 diopters (D) compared with 0.73Ϯ0.41 corneal astigmatism. There are various types of IOLs avail- D in the control group. The change in corneal astigma- able for implantation in cataract surgery, and efforts are be- tism from preoperative to 3 months after surgery was ing made to reduce incision size.2,9 With the shortening of Ϫ0.17Ϯ0.32 D for the test group and 0.10Ϯ0.41 D corneal tunnel incisions from 5.5 mm to 4.1 mm, 3.5 mm, 3.2 for the control group, which was statistically signifi cant Ͻ mm, and 2.8 mm, visual function postoperatively has steadi- (P .05). The RMS value of trefoil aberrations increased, 1,8,10-12 and all other aberrations decreased at 3 months after ly increased. It is anticipated that the bimanual micro- surgery in the test group. The RMS values of all corneal incision technique will allow phacoemulsifi cation through a high order aberrations increased in the control group, 1.2- to 1.7-mm clear corneal tunnel incision.5,13-15 However, with the increase in trefoil being statistically signifi cant. The comparison of surgically induced high order aberrations between the two groups showed that corneal coma, From the Department of Ophthalmology, Eye and ENT Hospital of Fudan trefoil, and secondary coma were signifi cantly different. University, Shanghai, China. The authors have no financial or proprietary interest in the materials pre- CONCLUSIONS: Clear corneal tunnel phacoemulsifi ca- sented herein. tion and IOL implantation guided by corneal topography can yield better visual acuity by reducing the pre-existing Correspondence: Yi Lu, MD, Dept of Ophthalmology, Eye and ENT Hospital of Fudan University, Shanghai 200031, China. Tel: 86 021 64377134; astigmatism and inducing less corneal aberrations than Fax: 86 021 64377151; E-mail: [email protected] conventional temporal corneal tunnel phacoemulsifi cation. [J Refract Surg. 2006;22:S1083-S1088.]

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Olson and Crandall9 and Oshika and Tsuboi16 found disk corneal topography.7 The OPD-Station software that an incision Ͻ2.0 mm had no impact on corneal (NIDEK Co Ltd) was used to isolate corneal aberration curvature. The bimanual technique is not yet widely out to the sixth order. available, especially in developing countries. To correct pre-existing astigmatism and minimize SURGICAL TECHNIQUE surgically induced astigmatism, we adopted 2.6-mm All surgeries were performed under topical an- clear corneal tunnel phacoemulsifi cation and IOL esthesia by the same surgeon (L.Y.). Conventional implantation guided by corneal topography with the temporal corneal tunnel phacoemulsifi cation and incision placed at the steepest corneal meridian. The IOL implantation were performed on the patients goal was to evaluate the changes in corneal astigma- in the control group. A 2.6ϫ2.0- to 2.5-mm tempo- tism and high order aberrations after surgery compared ral clear corneal tunnel incision was used. A 0.6-mm with those achieved in traditional surgery with the in- wide paracentesis was carried out for the insertion cision placed temporally. The outcomes of the study of the chopper. Subsequently, Duovisc (Alcon Lab- may assist the surgeon in selecting the optimal surgical oratories, Ft Worth, Tex) was used to maintain the plan for individual cataract patients. anterior chamber, and a continuous curvilinear cap- sulorrhexis and hydrodissection were performed. PATIENTS AND METHODS Endocapsular phacoemulsifi cation of the nucleus with Phacochop or “stop-and-chop” techniques and PATIENT POPULATION cortical aspiration were performed using an Infi nite A total of 37 patients (44 eyes) between the ages of or Legacy phacoemulsifi er (Alcon Laboratories). The 54 and 82 years (mean age: 65.05Ϯ9.53 years) were anterior chamber and the capsular bag were refi lled randomly assigned to either the test group or the with Duovisc. A foldable IOL was inserted into the control group. Each case was numbered and those capsular bag using an injector cartridge system. The with odd numbers were assigned to the test group residual viscoelastic material was removed using an and those with even numbers to the control group. irrigation/aspiration handpiece. Balanced salt solu- A 2.6-mm clear corneal tunnel phacoemulsifi cation/ tion was injected through the paracentesis to main- IOL implantation guided by corneal topography was tain the anterior chamber. At the end of surgery, the performed on 22 eyes of 16 patients in the test group, wound was checked and found to be watertight. All and conventional temporal corneal tunnel phaco- surgeries were completed without sutures. Postop- emulsifi cation with IOL implantation was performed eratively, all patients were treated with topical 0.1% in 22 eyes of 21 patients in the control group. Selec- Tobradex (Alcon Laboratories) and 0.1% Pranoprofen tion criteria included good general health, absence (Sumika Finechem, Osaka, Japan) three times a day of corneal pathology during slit-lamp microscopy for 1 month. All patients in the test group underwent examination, no previous corneal or scleral surgery, the same surgical procedure as those in the control absence of severe retinal pathology that could affect group with the exception that incisions were placed the infrared ray refl ection from the macula during on the steepest corneal meridian, which were deter- ocular wavefront aberration measurement, and no mined using the OPD-Scan axial corneal topography. complications during or after surgery.2,7 An expla- nation of the study was given to all patients and in- STATISTICAL ANALYSIS formed consent obtained. The mean corneal astigmatism, the surgically induced astigmatism, and the root-mean-square (RMS) EXAMINATION of corneal coma, trefoil, spherical aberration, second- Clinical examinations were conducted preopera- ary coma, and secondary spherical aberration for a tively and at 1 week, 2 weeks, 1 month, and 3 months 4-mm pupil diameter before and after surgery were after surgery. Clinical examination included best spec- compared. The surgically induced astigmatism was tacle-corrected visual acuity (BSCVA) and uncorrected calculated and standardized using Jaffe’s vector analy- visual acuity (UCVA), manifest and cycloplegic refrac- sis. The statistics were performed using the STATA 8.0 tions, intraocular pressure, and anterior and posterior (Stata Corp, College Station, Tex) statistical software. segment evaluation. The corneal astigmatism and high The chi-square test, t test, Scheffe test, nonparametric order aberrations were measured using the NIDEK Wilcoxon signed-rank test, Mann-Whitney test, and OPD-Scan aberrometer/topographer (NIDEK Co Ltd, Kruskal-Wallis test were used to analyze the variables Gamagori, Japan), which uses skiascopy-based ocular studied. A P value Ͻ.05 was considered statistically aberrometry using 1440 infrared points and placido signifi cant.

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A B Figure 1. A) The mean values of corneal astigmatism in two groups preoperatively and 1 week, 2 weeks, 1 month, and 3 months after surgery. No statistically significant difference was noted between the mean value of corneal astigmatism at 1 week and 2 weeks, 1 month, and 3 months after surgery. *PϾ.05. B) The change in corneal astigmatism induced by cataract surgery 3 months postoperatively. The test group versus the control group, PϽ.05.

A B Figure 2. A) The amount of surgically induced corneal astigmatism at 1 week, 2 weeks, 1 month, and 3 months postoperatively in the test and control groups. No statistically significant difference was noted between the mean values of surgically induced corneal astigmatism at each time point. *PϾ.05. B) Surgically induced corneal astigmatism 3 months postoperatively in the test group versus control group (*PϾ.05). Surgically induced corneal astigmatism was analyzed using the vector method described by Jaffe.

RESULTS astigmatism at 1 week, 2 weeks, 1 month, and 3 months At 3 months after surgery, 15 (68%) eyes in the test after surgery in the test and control groups are shown group and 8 (36%) eyes in the control group achieved in Figure 2A. The mean surgically induced astigma- UCVA у20/25. This difference in postoperative UCVA tism at 3 months postoperatively was 0.58Ϯ0.39 D for was statistically signifi cant (PϽ.05). Fourteen (64%) the test group and 0.73Ϯ0.41 D for the control group. eyes achieved BSCVA у20/20 postoperatively in the This difference was not statistically signifi cant (PϾ.05) test group, and 10 (45%) eyes achieved BSCVA у20/20 (Fig 2B). postoperatively in the control group. This difference in The change of corneal high order aberrations for postoperative BSCVA was not statistically signifi cant 4-mm pupil diameters in the test and control groups (PϾ.05). are shown in Figures 3 and 4, respectively. Trefoil Figure 1A shows the mean values of corneal astig- increased at 3 months postoperatively in the test matism in both groups preoperatively and at 1 week, group. Coma, spherical, secondary coma, and sec- 2 weeks, 1 month, and 3 months after surgery. The ondary spherical aberrations decreased 3 months mean change in corneal astigmatism preoperatively to postoperatively in the test group (see Fig 3). None of 3 months in the test group was Ϫ0.17Ϯ0.32 D (preop- the changes in corneal higher order aberrations were eratively, 0.95Ϯ0.60 D and 3 months postoperatively, statistically signifi cant (see Fig 3). All of the corneal 0.78Ϯ0.56 D). The mean change in corneal astigma- high order aberrations in the control group increased tism preoperatively to 3 months in the control group 3 months postoperatively (see Fig 4). The only sta- was 0.10Ϯ0.41 D (preoperatively, 1.12Ϯ0.64 D and 3 tistically signifi cant change in individual aberrations months postoperatively, 1.22Ϯ0.55 D). The difference from pre- to postoperatively in the control group was in the mean change in corneal astigmatism between trefoil (PϽ.05) (see Fig 4). both groups was statistically signifi cant (PϽ.05) (Fig Figure 5 demonstrates a typical example of the in- 1B). The mean values of surgically induced corneal duced changes in corneal third order aberrations pre-

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Figure 3. Root-mean-square (RMS) value of corneal high order aberrations at 4-mm pupil diameters in the test group. Preoperative versus postoperative (*PϾ.05).

Figure 4. Root-mean-square (RMS) value of corneal high order aberrations at 4-mm pupil diameters in the control group. Preoperative versus postoperative (*PϾ.05; #PϽ.05).

Figure 5. A typical example of changes in third order corneal higher order aberrations for a 4-mm pupil diameter of an eye before and after surgery in the test group. A) Coma and trefoil aberrations before surgery. B) Aberrations at 3 months after surgery. C) Difference map of surgically induced third order aberrations before and after surgery.

and postoperatively in the test group. At 3 months after secondary coma were statistically signiﬁ cantly dif- surgery, a trefoil pattern dominates the third order ab- ferent (PϽ.05), whereas the spherical and secondary errations, and coma is diminished (see Fig 5). Figure 6 spherical aberrations were not signiﬁ cantly different demonstrates a typical example of the induced changes (PϾ.05) (Fig 7). in corneal third order aberrations pre- and postoperatively in the control group. At 3 months after surgery, DISCUSSION coma and trefoil dominate the third order aberrations The optical quality of the pseudophakic eye is de- and direction of the trefoil pattern has reversed (see termined by the combination of corneal and internal Fig 6). aberrations generated by the IOL2 and those induced The comparison of surgically induced corneal high- by surgery. Spherical aberration is determined by the er aberrations between the two groups at 3 months corneal asphericity.17 In this study, corneal astigma- after surgery show that corneal coma, trefoil, and tism and high order aberrations were evaluated as a

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Figure 6. A typical example of changes in third order corneal higher order aberrations for a 4-mm pupil diameter of an eye before and after surgery in the control group. A) Coma and trefoil aberrations before surgery. B) Aberrations 3 months after surgery. C) Difference map showing surgically induced third order aberrations.

Figure 7. Surgically induced high order aberrations at 3 months after surgery for the test group versus the control group (*PϾ.05; #PϽ.05).

measure of change in the cornea after cataract surgery. that in healthy younger subjects because of an increase A statistically signifi cantly greater number of pa- in aberrations postoperatively.19 The lower the aberra- tients in the test group read у20/25 with correction tions, the better the optical quality. Many studies show than in the control group (PϽ.05). Greater astigmatic cataract surgery with IOL implantation can increase correction occurred in the test group shown by the corneal aberrations2,17,20 and internal aberrations.21-25 statistically signifi cant change in corneal astigmatism However, Marcos et al2 found that corneal spherical from pre- to postoperatively (PϽ.05). Based on these aberration decreased after the surgery. This study re- data, we believe that a 2.6-mm clear corneal tunnel ports a similar result. phacoemulsifi cation and IOL implantation guided by The present investigators elected to study aberra- corneal topography can correct astigmatism as low as tions for a 4-mm pupil diameter, because pseudophakic 0.25 D, resulting in better postoperative visual acuity. eyes rarely dilate to 6 mm without dilating drops.7 This For higher preoperative astigmatism, a clear corneal investigation found no statistically signifi cant change incision placed at the steepest meridian may be ben- in any of the higher order aberrations postoperatively. efi cial.10 Although not statistically signifi cant, there This was likely due to the size and location of the in- were slight differences between groups with respect to cision. Another reason might be the small number of surgically induced astigmatism at 1 week, 2 weeks, 1 patients; thus sampling error cannot be fully excluded. month, and 3 months postoperatively. However, from In the control group, a statistically signifi cant increase 2 weeks to 3 months postoperatively, the corneal astig- was noted in trefoil postoperatively versus preopera- matism showed little change, indicating that the 2.6- tively (PϽ.05). The comparison of surgically induced mm clear corneal tunnel incision was fully stable by 2 higher order aberrations between the two groups weeks postoperatively. This fi nding is similar to that shows that corneal coma, trefoil, and secondary coma reported by Masket and Tennen.18 were signifi cantly different. These changes indicated The quality of the retinal image is primarily limited that 2.6-mm clear corneal tunnel phacoemulsifi cation by the aberrations of the eye.4 The total ocular aberra- and IOL implantation guided by topography produced tions include corneal aberrations and internal aberra- less corneal high order aberration and resulted in bet- tions. One study reported that the average retinal im- ter corneal optical quality. age quality of pseudophakic patients was worse than Clear corneal tunnel phacoemulsifi cation and IOL

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