PAUL HUGHES, MD
Bilateral LASIK for myopic astigmatism overcorrected both of the patient's eyes but her left to a greater degree. I find her manifest refraction hard to believe and think her undilated wavefront refraction more credible. I think this patient's problem relates to three areas: (1) accommodation; (2) residual refractive error; and (3) a decreased quality of vision due to higher-order aberrations.
I believe that she is using accommodation to correct the hypermetropic astigmatism in her left eye and is thus inducing myopia in her right eye. As a result, her right eye is more symptomatic. If one treats her right eye and corrects the cycloplegic hypermetropic astigmatism, she will be worse off when she accommodates to correct her left eye.
I would recommend a contact lens trial to demonstrate to the patient that her main problem is an overcorrected left eye (ie, a +1.00D soft contact lens on her left eye will improve the poor vision in her right eye). Hard contact lenses would be a better option than soft, spherical lenses, because the former would also correct her astigmatism.
The patient should be informed that she requires a correction of both eyes. If she agreed to bilateral enhancements, I would treat her left eye first with slightly less than her dilated wavefront refraction (ie, +0.75 +0.81 X 164). I would then treat her right eye, again with slightly less than her dilated wavefront refraction (ie, plano +0.66 X 104).
The trap in this case is not recognizing the role of accommodation and allowing for it when performing the enhancement. I would complete a wavefront-optimized treatment using the Allegretto excimer laser (Wavelight Laser Technologie AG, Erlangen, Germany).
GUY M. KEZIRIAN, MD, FACS
In Figure 1, pachymetry with the Orbscan topographer (Bausch & Lomb, Rochester, NY) shows a central ablation of approximately 130µm, corresponding to about 10.00D of myopic correction at 6.5mm. It also shows a zone where the steepness rapidly increases, a finding detected as a large amount of spherical aberration and coma on aberrometry. There is a small amount of residual refractive error in the form of with-the-rule astigmatism and some hyperopia. The cycloplegic refraction (Figure 2) suggests that she is attempting to compensate for the refractive error with accommodation.
The differences in the manifest and cycloplegic aberrometry measurements (Figures 2 and 3) are interesting and show the benefit of the patient's accommodation. Cycloplegia shifts the aberrations superiorly, causing them to take on the appearance of coma, with the resultant increase in visual disturbance shown in the point-spread function.
This patient would benefit from a remodeling procedure to enlarge the optical zone, with concurrent treatment of her residual refractive error. The best results for optical zone remodeling today are obtained using topographically guided treatments. Topography allows direct imaging of the corneal contour and prevents the treatment of lens-based aberrations on the cornea. Provided there is adequate tissue to proceed, topography-guided LASIK would be my preference for this patient.
MIRKO JANKOV, MD
First, I would perform a second evaluation with a topographer I have found to be reliable, such as the Allegro Topolyzer (Wavelight Laser Technologie AG) or the Oculus Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany). I doubt that the optical zone is indeed sufficiently large, considering the amount of myopia (-6.00D) that was originally treated. The Orbscan's elevation map with floating best-fit sphere (Figure 1) shows a typical pattern of a small optical zone: a doughnut-shaped elevation around a small, more depressed, central area. A change in the power of wavefront sphere from 4 to 6mm by more than 2.00D (Figure 2 and 3), while the difference between manifest and cycloplegic sphere is only 0.50D as expected, clearly demonstrates that a large amount of spherical aberration is present in this eye—a hallmark of a small optical zone.
If the spherical aberration were the only aberration (in significant amounts) in this eye, I would simply perform a topography-guided treatment in order to enlarge the optical zone. Two important details, however, draw my attention: (1) the eye's astigmatism changes its power and axis when the pupil is dilated, and (2) significant coma is present even with a small pupil. I would therefore verify that the crystalline lens is not causing this patient's astigmatism. How much cylinder is induced because the shape of the crystalline lens changes as the pupil dilates? How much of her poor visual quality is due to a combination of other higher-order aberrations that have been misinterpreted as astigmatism?
I would also repeat the wavefront measurements with a large pupil but perform dilation with a weak mydriatic agent (eg, phenylephrine 5% or even 10%, two drops every 5 minutes, measurement taken 30 minutes after instillation). This analysis would be the “manifest” wavefront refraction; it would be free of an astigmatic shift due to a change in lenticular shape. In the spherical part of the planned correction, I could easily take into account the expected amount of accommodation.
The presence of significant coma (both third and fifth order, although the former to a greater degree), higher-order astigmatism, and spherical aberration leads me to believe that a wavefront-guided treatment would be the best option.
MATTHIAS J. MAUS, MD
The patient complains about a diminished quality of vision without specifying the circumstances (ie, driving at night or light sensitivity). The fact that the patient does not wear glasses, despite her residual refractive error, may be the first reason for her poor perceived quality of vision. Residual astigmatism is well known to enable patients to see without glasses, while reducing the overall quality of the retinal image, especially at night.
A LASIK enhancement targeting physiological asphericity is an option, but which refraction is the right one? The difference in sphere, cylinder, and axis between the manifest and cycloplegic refractions necessitates further evaluation. The topography appears normal for a post-LASIK eye, but it shows different axes compared with the two refractions. There is no evidence that her poor quality of vision is due to a specific disorder in the shape of her cornea. I would therefore recommend against a topography-guided retreatment.
The wavefront-based refraction in the dilated and undilated eye shows greater variance (up to 2.25D) than the phoropter-based measurements. The reason must relate to higher-order aberrations. Coma and trefoil remain about the same regardless of dilation, and most other higher-order aberrations are of minor importance. Spherical aberration (C12), however, is three times greater in this eye with a dilated versus an undilated pupil. This difference definitely accounts for the change in the eye's refraction. The overall higher-order RMS of approximately 0.80 is known to cause poor visual quality, especially in low-lighting conditions when the pupil enlarges.
I recommend a wavefront-guided retreatment using the wavefront measurement that was acquired with dilated pupils. This refraction accords with the cycloplegic refraction.
Section editor Karl G. Stonecipher, MD, is Director of Refractive Surgery at TLC in Greensboro, North Carolina. Dr. Stonecipher may be reached at (336) 288-8523; email@example.com.
Paul Hughes, MD, is Senior Medical Consultant at Southline Eye Centre in Hurtsville, New South Wales, Australia. He states that he holds no financial interest in the products or companies mentioned herein. Dr. Hughes may be reached at +61 2 9585 2585;
Mirko Jankov, MD, is a senior clinical and research fellow at the University of Crete in Greece. He is a clinical consultant for Wavelight Laser Technologie AG. Dr. Jankov may be reached at +30 2810 39 4807; firstname.lastname@example.org.
Guy M. Kezirian, MD, FACS, is President of Surgivision Consultants, Inc., in Scottsdale, Arizona. He is a consultant to Wavelight Laser Technologie AG. Dr. Kezirian may be reached at (480) 664-1800; email@example.com.
Matthias J. Maus, MD, is Medical Director of Refractive Surgery at Augenzentrum Maus+Heiser in Cologne, Germany. He is a clinical consultant to Wavelight Laser Technologie AG. Dr. Maus may be reached at +49 221 8601613; firstname.lastname@example.org.