Refractive Surgical Problem

CONSULTATION SECTION

ized wavefront LASIK should offer an excellent surgical option for this problem in the future; however, my 6-month experience with the Bausch & Lomb Zyoptix system suggests we have a long way to go before we are ready for this type of complex corrective ablation. At present, I would recommend a trial of RGP contact lenses to improve the visual quality. If these are not tolerated, soft contact lenses would at least improve the UCVA in both eyes. The distortion and glare could be further minimized with the use of a miotic drop such as low-dose pilocarpine 1/8%. A trial of brimonidine tartrate (Alphagan威) may also be of benefit as it is better tolerated than pilocarpine drops by patients and reduces that scotopic pupil size by an average of 2.0 mm. The use of contact lenses and drops could be enough to significantly improve the visual quality, UCVA, and BCVA so the patient can manage until custom wavefront LASIK ablations become more refined. LOUIS E. PROBST, MD Chicago, Illinois, USA

f The history and clinical findings suggest that this is a case of decentered ablation. The most important complaint of the patient—glare—can be attributed to (1) the decentered ablation, (2) an optical zone smaller than the scotopic pupil, or (3) the refractive error. I would like to ascertain the manifest refraction, after which I would put the patient on a trial of spectacles or contact lenses (hard or toric for the astigmatism) to correct the residual power. If this does not help reduce the glare, I would give the patient pilocarpine 0.5% drops to reduce the pupil size when he is doing work in dim illumination (eg, driving). This will make the pupil smaller than the optical zone operated on and thus help reduce the glare. If the patient does not improve with this conservative treatment, surgical treatment can be done. With a pachymetry of approximately 490 ␮m in both eyes, repeat LASIK can be performed to center the ablation and keep the optical zone larger than the scotopic pupil. In this case, Topolink LASIK is a viable option. The Topolink software basically compares the shapes of the target asphere with the corneal shape actually measured. The target shape is fitted from beneath to the actual cornea for a given planned optical zone size. The differ-

ence between the target and actual shapes is then ablated. As tissue cannot be added but only ablated, any overlap between the target and actual shape must be outside the planned optical zone. The Topolink software represents a new approach to customized ablation. It calculates a certain lenticule of corneal tissue to be removed. The scanning laser removes this tissue even if its shape is asymmetrical or irregular. AMAR AGARWAL, MS, FRCS, FRCOPHTH(LON) Chennai, India

f This patient’s undercorrection is likely to have been primary and caused by a combination of 2 principal factors: corneas that were too flat to achieve or maintain such a large attempted correction and loss of effect of the treatment by its decentration from the visual axis. Further tests (eg, repeat pachymetry), if showing above-anticipated thickness, would indicate a primary undercorrection (or epithelial regression) from an ectasia. An ectasia would show less-than-expected thickness, calculated from the remaining (255 ␮m) corneal bed tissue (plus flap). Serial refraction, topography, and pachymetry readings identify developing ectasia. The treatment decentration was temporal on the right cornea and nasal on the left cornea. This suggests that the nystagmus was direction sensitive and at the time of ablation, the patient damped the gaze at levoversion to achieve stability during fixation. This resulted in decentration, beam obliquity, and induced corneal astigmatism as the tracker followed the left gaze. Manually held fixation concentric upon the pupil might have been more effective. At this stage, it is important not to intervene surgically in any way but rather wait for stability of refraction and corneal readings. Further corneal tissue removal would be unwise as the calculated remaining thickness from the first treatment might be inadequate for corneal structural integrity. Contact lens wear could be offered to the patient during this time. Lenticular surgery can be done later. This could be in the form of implantable contact lenses if the crystalline lenses are clear and the surgeon has sufficient experience and confidence with this procedure. Most likely, lens extraction and implantation is the favored option if this is acceptable to the patient where loss of accommodative power is understood. A large-diameter optic

J CATARACT REFRACT SURG—VOL 28, MARCH 2002

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(6.5 mm) and elimination of the remaining refractive error are likely to reduce troublesome symptoms. NOEL ALPINS, MD, FACS Cheltenham, Australia

ment is the same as that of arcuate cuts. Thus, in this patient I would suggest inserting an Intacs segment (0.45 mm thick) in the same place as the arcuate cuts at a depth of 70% of corneal thickness and on the inner portion of the LASIK flap edge. IOANNIS G. PALLIKARIS, MD Heraklion, Crete, Greece

f Eccentric ablations are a problem for both patient and surgeon. Even though the development of tracking systems in excimer laser units has reduced the incidence of eccentric ablations, patients treated with first- and second-generation laser systems or patients with special problems such as nystagmus represent a scientific problem and challenge. An ablation is considered eccentric when its center does not correspond to the center of the optical axis while the corneal meridians modify their shape from sphere to parabolic. The problem in these patients is that the decentration of the ablation zone produces glare as a result of the prismatic effect. The aim of management of eccentric ablations is to restore a normal topographic map. There are several options and alternatives for these patients. Diagonal ablations and custom topography-controlled excimer laser ablations have been tried in eccentric PRK procedures but not in post-LASIK eccentric ablations because the disturbed healing of the flap after LASIK may be an additional source of error in the assessment of these procedures. I think that the proper way to treat this patient is to proceed immediately with arcuate keratotomy. I recommend using retrobulbar anesthesia as difficulties could arise during the procedure because of the patient’s nystagmus. As the decentration is toward 200 degrees in the right eye and toward 180 degrees in the left eye, I would suggest an arcuate cut of 90 degrees, at a depth of 90% to 95% of the cornea and at a 7.0 mm zone. The cut would be placed along the same axis but 180 degrees opposite the direction of decentration (between 65 degrees and 335 degrees in the right eye and 45 degrees and 315 degrees in the left eye). If the results are not as expected, a second arcuate cut in a smaller zone could be performed after 1 month. The problem with arcuate cuts is that the effect in patients younger than 45 years is not the expected. Therefore, other options are to try to recenter the ablation zone using an Intacs segment or photoablatable lenticular modulator. The effect of using an Intacs seg396

f This case is a refractive surgeon’s nightmare because of the extreme decentration of the ablation zone. Fortunately, the patient did not have a decrease in BCVA. However, the glare seems to bother him. I would guess that the preoperative subjective manifest refraction was difficult to determine accurately. Possibly, the preoperative manifest refraction was more myopic. In addition, some degree of regression of the refractive result is possible 15 months postoperatively. First, I would make sure that the refraction is stable and correct later if necessary. What are the pachymetry readings at 15 months? If there is enough tissue left to correct the decentered ablation, I would relift the flap and perform an aberration-corrected ablation. Peribulbar anesthesia could be used. Furthermore, squint surgery could be performed to lessen the horizontal nystagmus. If there is not enough stromal tissue left, I would consider implanting a toric phakic or pseudophakic IOL. GERNOT I.W. DUNCKER, MD Halle/Saale, Germany

f I believe that ablational surgery was not indicated in this case because of the low K-readings preoperatively and because of the poor BCVA. The “left” decentered ablation in both eyes was probably induced by the surgical technique; that is, poor fixation (possibly the slow horizontal movement of the nystagmus was to the right side) or poor tracking. In any case, decentered ablations are more common in flat corneas with low vision. A positive finding is that the postoperative BCVA is unchanged and it seems the patient is complaining because of the undercorrection, not so much because of the decentered treatment. An Orbscan is needed to evaluate the anterior elevation and corneal pachymetry map and to provide subjective and objective evaluation of the quality of vision especially under dim illumination.

J CATARACT REFRACT SURG—VOL 28, MARCH 2002