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0Phacoemulsification for Anisometropia Associated with Presenile Cataracts in Patients with High Myopia
Meng-Chi Wang, Li-Hsiang Chiou and Lin-Chung Woung1
Background: The conventional treatment for anisometropia brought on by asymmetric cataracts in presenile patients with high myopia is still controversial. In this report, we evaluate treatment results by chart review.
Materials and Methods: We reviewed the records of four patients under the age of 55 with high myopia and anisometropia associated with asymmetric lens opacity between fellow eyes. A four-step procedure was followed to confirm anisometropia induced by different degrees of lens opacity between the eyes. The eye with poorer best-corrected visual acuity (BCVA) in each patient underwent phacoemulsification with implantation of an intraocular lens. Different methods were used for vision correction in the fellow eyes, depending on the patient's lifestyle.
Results: All eyes that underwent cataract surgery achieved a BCVA of at least 6/6. Contact lenses were fitted in the fellow eyes of two patients and laser in situ keratomileusis (LASIK) was performed in the other two patients. Except for one of the eyes that underwent LASIK, each of the fellow eyes had satisfactory vision after correction.
Conclusion: Improved postoperative visual acuity was obtained in myopic eyes with presenile cataracts. LASIK may not be suitable for correcting refractive errors in fellow high myopic eyes in the early stages of cataracts.
(J Med Ultrasound 2004;12:38-42; KEY WORDS: • cataract • high myopia • anisometropia • phacoemulsification
Introduction
The prevalence of myopia is high in Taiwan: 12% among 6-year-old children and 84% among 16 to 18-year-old adolescents [1]. The incidence of high myopia (> 6.0 D) is also high in Taiwan, with 20% of female and 12% of male 18-year-olds affected.
Presenile cataract formation is a major complication of high myopia. In addition, the degree of lens opacity between fellow eyes may be asymmetric and result in significant anisometropia. Consequently, vision is compromised and hard to overcome with glasses. Considering the active lifestyle of these relatively young patients, prompt cataract extraction
Department of Ophthalmology, Taipei Municipal Yang-Ming Hospital, and 'Department of Ophthalmology, Taipei Municipal Zhong-Xing Hospital, Taipei, Taiwan.
Address correspondence and reprint requests to: Dr. Meng-Chi Wang, Department of Ophthalmology, Taipei Municipal Yang-Ming Hospital, 105 Yu-Sheng Street, Shih-Lin, Taipei, Taiwan. E-mail: mengl@ms8.hinet.net
©2004 Elsevier. All rights reserved.
may be warranted to restore binocular vision. However, cataract surgery is technically more difficult and the incidence of postoperative complications, such as retinal detachment, is higher in myopic eyes with long axial lengths. Other issues that should be taken into consideration with highly myopic anisometropic patients include the likelihood of a positive postoperative visual outcome and the determination of a postoperative target refractive status.
We reviewed several patients with high myopia who suffered from significant anisometropia resulting from the development of presenile cataracts. Phacoemulsification with implantation of a foldable intraocular lens (IOL) was performed for the eyes with denser lens opacity and greater myopic refraction. Through our analysis, we ascertained a way to predict the postoperative visual outcome and a postoperative method to correct refraction.
Materials and Methods
We reviewed the chart records of highly myopic patients under 55 years of age with anisometropia associated with asymmetric lens opacity who were seen by the same surgeon (MCW) between June 2000 and June 2001. Four patients were included in this study. The diagnosis of presenile cataract was based on slit-lamp findings of lens opacity, and the degree of lens opacity was graded according to the Lens Opacities Classification System (LOCS) II [2]. High myopia was defined as an eye with an axial length greater than 25.5 mm [3]. All patients reported a history free of ocular trauma, uveitis, diabetes mellitus, steroid use, or exposure to high-dosage ultraviolet light. Indirect ophthalmoscopy did not
reveal the presence of chorioretinal lesions.
To ensure these patients had not suffered from anisometropic amblyopia from early childhood and would benefit from cataract surgery, we used a four-step procedure with criteria for cataract-induced anisometropia (Table 1). If the two eyes differed in spherical equivalent (ATR) by more than 2 D and in presumed natural lens power (AP) by less than 2 D, cataract-induced anisometropia was confirmed. Phacoemulsification with implantation of a foldable IOL (Acrysof, MA60MA, Alcon Laboratories, Fort Worth, TX, USA) was performed in the eye with denser lens opacity and poorer vision.
Results
Four cases fulfilled the criteria for cataract-induced anisometropia, with ATRs considerably greater than APs. Patient information and preoperative clinical data are listed in Table 2. Phacoemulsification was uneventful in all eyes and all operated eyes achieved a postoperative best corrected visual acuity (BCVA) of at least 6/6. Postoperative clinical data are listed in Table 3. To attain binocular visual function, different methods were used to correct the refractive error in the unoperated eyes. Mild myopia to cope with frequent close-work was the target postoperative refraction of the operated eye in Patient 1. Since she had used rigid gas-permeable (RGP) contact lenses for many years, she continued to use them in both eyes for far vision and used the operated eye for close-work. Patient 2 was a housekeeper who seldom read, so emmetropia was set as the postoperative goal. Laser in situ keratomileusis (LASIK) was subsequently performed in the fellow eye because she did not want to wear a contact lens.
Table 1. Criteria for cataract-induced anisometropia
Step 1 The SRK-II formula is used to calculate the convergence power of the lens
P = A - 2.5 x AXL - 0.9K Step 2 The difference in presumed convergence power of the lens between fellow eyes is calculated using:
aP = Ipod - PosI = I2.5(AXLod - AXLos) + °.9(Kod - Kos)I Step 3 The difference in spherical equivalent between fellow eyes is calculated using:
aTR = ITRod - TRosI Step 4 The criteria for cataract-induced anisometropia are met when: ATR » AP and ATR > 2 D, AP < 2 D
P = presumed power of the natural, clear lens; A = constant; AXL = axial length; K = average keratometric reading of each eye; OD = right eye; OS = left eye; ATR = difference in spherical equivalent between fellow eyes; TROD = refractive error of the right eye; TROS = refractive error of the left eye; D = diopter.
Table 2. Preoperative data
Patient Age Sex LOCS II BCVA Refractive error K (D) AXL AP (D) ATR (D)
1 50 F OD N3 0.1 -13-0.5 x 8 46.5 26.01 1.502 3.75
OS N1 1.0 -9-1.0 x 170 46 25.73
2 38 F OD N2 0.2 -14.75-6.25 x 61 (2,000.9)
-6.25-2.5 x 151 (2,000.5) 42.8 27.60 1.582 11.5
OS N0 0.9 -5.75-1.25 x 15 42.43 26.93
3 45 M OD N1 0.6 -11.75-1.25 x 171 42.06 29.43 0.162 8.5
OS N3 0.02 -20.50-0.75 x 174 42.06 29.25
4 47 M OD N0 1.5 -6.5-0.75 x 67 39.25 29.67 0.778 7.625
OS N3 0.4 -14-1.0 x 110 (2,001.6)
-6.0-0.25 x 86 (2,000.1) 39.5 29.50
LOCS II = Lens Opacities Classification System II; BCVA = best corrected visual acuity; K = average keratometric reading; D = diopter; AXL = axial length of eyeball; AP = difference in presumed convergence power of the lens between fellow eyes; ATR = difference in spherical equivalent between fellow eyes; OD = right eye; OS = left eye.
Table 3. Postoperative data
Patient Operation Target refraction (D) Final refraction (D) BCVA CMFV
1 OD: PHCE -1.5 -1.75-1.5 x 174 (-2.5) 1.2 RGP
OS : None -9-1.0 x 170 1.5 RGP
2 OD: PHCE -0.5 +0.25-1.5 x 151 (-0.5) 1.0 None
OS : LASIK Emmetropia -0.5-0.5 x 21 1.0
3 OD: LASIK Emmetropia +0.25-2.0 x 96 0.6 PG
OS : PHCE -1.5 -1.25-1.5 x 7 (-2.0) 1.5 PG
4 OD: None -6.5-0.75 x 67 1.5 SCL
OS : PHCE -0.75 -0.25-1.0 x 58 (-0.75) 1.0 None
D = diopter; BCVA = best corrected visual acuity; CMFV = correction method for far vision; OD = right eye; OS = left eye; PHCE = phacoemulsification with intraocular lens insertion; RGP = rigid gas-permeable contact lens; LASIK = laser in situ keratomileusis; PG = spectacles; SCL = soft contact lens.
Patient 3 also underwent LASIK in the unoperated eye, but the BCVA was 6/10 due to LASIK-induced corneal astigmatism. Patient 4 spent a lot of time driving, so emmetropia was set as the goal following cataract surgery and a soft contact lens was fitted for the unoperated eye. The far vision correction method for each patient is summarized in Table 3.
Discussion
Patients with high myopia may experience the early development of lens opacity. The degree of lens opacity may differ significantly between fellow eyes and may not be associated with asymmetric axial lengths. Nuclear sclerosis seems to constitute the
Fig. Presenile cataract in a patient with high myopia showing dense sclerotic nucleus surrounded by epinucleus and a relatively clear cortex.
most common cause of presenile cataracts in high myopes and its effects on vision seem to differ from those of senile cataracts. With the same degree of nuclear sclerosis, patients with presenile cataracts usually suffer from a more rapid progression of myopic refractive error and worse BCVA than their senile counterparts. This variation may be explained, at least in part, by the heterogeneous nature of presenile cataracts, with dense nuclear opacity surrounded by an almost clear epinucleus and cortex (Fig.). In contrast, lens opacity tends to be more homogeneous in eyes with senile cataracts. Heterogeneous lens opacity may have a multifocal effect resulting in optical aberration and image distortion.
Before discussing the visual outcome of cataract surgery in highly myopic patients with significant anisometropia, the possibility of anisometropic amblyopia from early childhood should be ruled out. This is especially true when nuclear sclerosis is not severe. Although chart records or potential acuity testing with a potential acuity meter or laser interferometer may help clarify the issue, they may not be available. In this study, we found that, if we followed the four-step procedure using the selection criteria for cataract-induced anisometropia, we could be confident about the nature of the anisometropia.
In determining the postoperative target refraction, several factors need to be considered, including the refractive state of the fellow eye, the lifestyle and age of the patient (presbyopic status), and the manner
used to correct refractive error prior to surgery. If cataract surgery is not performed in the other eye, significant anisometropia will remain a problem. In patients who are used to wearing contact lenses, postoperative anisometropia can be overcome by using contact lenses. Although contact lens fitting is the safest method for correcting postoperative anisometropia if cataract surgery is performed in only one eye, options for patients intolerant of contact lenses do exist, each with their own disadvantages. LASIK surgery may cause unexpected astigmatism after the use of a deep broad beam excimer laser, making the calculation of IOL power difficult. Implantable contact lens insertion is associated with a high incidence of anterior lens subcapsular opacification [4]; and clear lens extraction carries the same risks as cataract surgery in eyes with a long axial length.
Sometimes, refractive surprise occurs after cataract surgery with IOL implantation in highly myopic eyes. The major reasons for the breakdown in the IOL power calculation are large variations in the measurements of axial length, unsuitable formulas for power calculation, and incorrect keratometric data caused by previous contact lens usage. The SRK/T or Holliday formulas are recommended for IOL power calculation in highly myopic eyes because a large hyperopic shift may occur with the SRK-II formula [5-7].
The incidence of postoperative retinal detachment is higher in relatively young patients with high myopia [8], especially in cases with intraoperative complications such as vitreous loss or disruption of the posterior capsule. Posterior capsule opacity is common following cataract surgery in cases with presenile cataracts, and may require Nd-YAG posterior capsulotomy. Since the incidence of retinal detachment increases after laser capsulotomy in eyes with a long axial length [8-10], steps should be taken to prevent this postoperative complication. The anterior capsule rhexis should be centered with a diameter of 5-5.5 mm so that the anterior capsule rim can cover the optic margin of the IOL. The capsular bag should be polished delicately after the cortex has been removed. In addition, acrylic IOLs with sharp edges have also been shown to reduce the risk of postoperative posterior capsular opacity [11,12]. Treatment of anisometropia associated with presenile cataract in high myopia is not as simple as treating senile cataracts. Care should be taken
in predicting the postoperative visual outcome, determining the postoperative refraction, choosing the suitable formula for IOL power calculation, and dealing with technical details intraoperatively.
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