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August consultation #4
CONSULTATION SECTION: CATARACT
- Laser in situ keratomileusis surgery to correct myopia alters the shape of the cornea, making it oblate and inducing greater positive spherical aberration that becomes more prominent under mesopic conditions because of pupil dilation. This and other HOAs cause nighttime myopia, glare, and halos. When cataract surgery is performed on a patient with a history of myopic LASIK, the induced positive spherical aberration can be offset with an IOL that has negative spherical aberration. Examples of IOLs to use in this situation include the Tecnis ZCB00 (Abbott Medical Optics, Inc.) with a spherical aberration of 0.27 mm or the Acrysof SN60WF (Alcon, Inc.) with a spherical aberration of 0.20 mm. The Crystalens IOL has zero spherical aberration. We recommend IOLs with zero spherical aberration for patients who have a history of hyperopic LASIK because the optical zone of the hyperopic LASIK ablation is smaller and might not be centered. The Crystalens optic is only 5.0 mm, whereas the patient’s mesopic pupil is 5.84 mm. This could be a factor in suboptimum night vision. The patient’s topography shows an oblate cornea with more flattening nasally. This topographic pattern could be secondary to a decentered ablation or from a smaller flap with a nasal hinge that entered the ablation zone. There is significant and asymmetric WTR corneal astigmatism and positive spherical aberration of 0.73 mm. The patient reported some symptomatic relief with the use of miotic drops; therefore, management should begin with a conservative approach using a topical a-agonist such as brimonidine drops. The good news is that the patient has improved vision with spectacles. The patient should be counseled to wear night-driving spectacles with antireflective coating to help her quality of vision. We are referred many patients who have side effects after laser vision correction (LVC) and/or cataract surgery. One philosophy is that “less is more.” We are typically not aggressive in recommending further surgery as long as the visual acuity and visual quality are acceptable with conservative therapy. We have found that taking time to explain the situation and stating that the cataract surgery was performed adequately can allay the patient’s anxiety. Knowledge is power. If the patient did not have reasonable spectaclecorrected visual acuity and the symptoms improved with a gas-permeable contact lens alone, the asymmetric corneal shape would be the culprit. If the patient refuses to wear a contact lens, the next step would be surgical correction. She would need topography-guided photorefractive keratectomy
1241
(PRK) or LASIK, depending on the residual stromal bed thickness (using anterior segment optical coherence tomography). A detailed discussion about complications, especially the risk for haze with PRK, cannot be overemphasized. When performing cataract surgery on any patient after LVC, we spend extra time counseling the patient regarding postoperative expectations. Unless the postoperative reality meets or exceeds the patient’s expectations, the patient will be disappointed. Therefore, it is critically important to manage expectations ahead of time. Deepinder Dhaliwal, MD Mona Sane, MD Pittsburgh, Pennsylvania, USA
- It is always difficult contemplating an IOL exchange after an otherwise successful cataract surgery, and that is what we are talking about hered to explant or not to explant. The patient in question has positive dysphotopsia after cataract surgery, 15 years after myopic LASIK, which did not produce significant glare and halos. The task at hand is to decipher the causes of positive dysphotopsia and to come up with a management option that can be reasonably expected to reduce these symptoms. The biggest cause is the residual refractive error, or for the purists in us, 2nd-order aberration. This has presumably been tried without eliminating the symptoms. I would imagine that spectacles would reduce the glare significantly, and I would try to convince the patient to have this minimally invasive option, for night driving only, especially considering that surgical options are not without risks and cannot guarantee success. If this fails, I would reluctantly choose to perform an IOL exchange. Of note is the patient's high corneal spherical aberration. If only wavefront-guided LASIK could actually reduce HOAs. I would relift the flap, apply custom excimer laser treatment, and treat the 2nd-order and 4th-order aberrations. Unfortunately, wavefront-guided LASIK actually increases HOAs, although less than conventional LASIK. Topography-guided LASIK might also be an option because there appears to be some irregular astigmatism on the cornea; however, it was there for 15 years without bothering the patient and it is probably unlikely to be the cause of the glare. Therefore, I would consider the different factors of a replacement IOL that would reduce the problem. The Crystalens IOL has a 5.0 mm optic, and from the slitlamp photograph, the capsulorhexis does not appear to overlap it as intended. Although not
J CATARACT REFRACT SURG - VOL 42, AUGUST 2016
- Laser in situ keratomileusis surgery to correct myopia alters the shape of the cornea, making it oblate and inducing greater positive spherical aberration that becomes more prominent under mesopic conditions because of pupil dilation. This and other HOAs cause nighttime myopia, glare, and halos. When cataract surgery is performed on a patient with a history of myopic LASIK, the induced positive spherical aberration can be offset with an IOL that has negative spherical aberration. Examples of IOLs to use in this situation include the Tecnis ZCB00 (Abbott Medical Optics, Inc.) with a spherical aberration of 0.27 mm or the Acrysof SN60WF (Alcon, Inc.) with a spherical aberration of 0.20 mm. The Crystalens IOL has zero spherical aberration. We recommend IOLs with zero spherical aberration for patients who have a history of hyperopic LASIK because the optical zone of the hyperopic LASIK ablation is smaller and might not be centered. The Crystalens optic is only 5.0 mm, whereas the patient’s mesopic pupil is 5.84 mm. This could be a factor in suboptimum night vision. The patient’s topography shows an oblate cornea with more flattening nasally. This topographic pattern could be secondary to a decentered ablation or from a smaller flap with a nasal hinge that entered the ablation zone. There is significant and asymmetric WTR corneal astigmatism and positive spherical aberration of 0.73 mm. The patient reported some symptomatic relief with the use of miotic drops; therefore, management should begin with a conservative approach using a topical a-agonist such as brimonidine drops. The good news is that the patient has improved vision with spectacles. The patient should be counseled to wear night-driving spectacles with antireflective coating to help her quality of vision. We are referred many patients who have side effects after laser vision correction (LVC) and/or cataract surgery. One philosophy is that “less is more.” We are typically not aggressive in recommending further surgery as long as the visual acuity and visual quality are acceptable with conservative therapy. We have found that taking time to explain the situation and stating that the cataract surgery was performed adequately can allay the patient’s anxiety. Knowledge is power. If the patient did not have reasonable spectaclecorrected visual acuity and the symptoms improved with a gas-permeable contact lens alone, the asymmetric corneal shape would be the culprit. If the patient refuses to wear a contact lens, the next step would be surgical correction. She would need topography-guided photorefractive keratectomy
1241
(PRK) or LASIK, depending on the residual stromal bed thickness (using anterior segment optical coherence tomography). A detailed discussion about complications, especially the risk for haze with PRK, cannot be overemphasized. When performing cataract surgery on any patient after LVC, we spend extra time counseling the patient regarding postoperative expectations. Unless the postoperative reality meets or exceeds the patient’s expectations, the patient will be disappointed. Therefore, it is critically important to manage expectations ahead of time. Deepinder Dhaliwal, MD Mona Sane, MD Pittsburgh, Pennsylvania, USA
- It is always difficult contemplating an IOL exchange after an otherwise successful cataract surgery, and that is what we are talking about hered to explant or not to explant. The patient in question has positive dysphotopsia after cataract surgery, 15 years after myopic LASIK, which did not produce significant glare and halos. The task at hand is to decipher the causes of positive dysphotopsia and to come up with a management option that can be reasonably expected to reduce these symptoms. The biggest cause is the residual refractive error, or for the purists in us, 2nd-order aberration. This has presumably been tried without eliminating the symptoms. I would imagine that spectacles would reduce the glare significantly, and I would try to convince the patient to have this minimally invasive option, for night driving only, especially considering that surgical options are not without risks and cannot guarantee success. If this fails, I would reluctantly choose to perform an IOL exchange. Of note is the patient's high corneal spherical aberration. If only wavefront-guided LASIK could actually reduce HOAs. I would relift the flap, apply custom excimer laser treatment, and treat the 2nd-order and 4th-order aberrations. Unfortunately, wavefront-guided LASIK actually increases HOAs, although less than conventional LASIK. Topography-guided LASIK might also be an option because there appears to be some irregular astigmatism on the cornea; however, it was there for 15 years without bothering the patient and it is probably unlikely to be the cause of the glare. Therefore, I would consider the different factors of a replacement IOL that would reduce the problem. The Crystalens IOL has a 5.0 mm optic, and from the slitlamp photograph, the capsulorhexis does not appear to overlap it as intended. Although not
J CATARACT REFRACT SURG - VOL 42, AUGUST 2016