Eyeworld

EW NEWS & OPINION September 2015 27 plano sphere the patient may accept the diopter of residual astigmatism in the non-dominant eye. An IOL exchange is probably a better option for the left eye if the patient and the doctor agree with the risks of a surgical complication being slightly higher. If an IOL exchange is opted for, Graham Barrett, MD, has an excellent formula for predicting the proper IOL (www.ascrs.org/ barrett-toric-calculator). "But there is a little more to this story than a simple refractive surprise. This patient was previously a successful gas permeable contact lens wearer. Prior to placing a toric IOL, I absolutely ensure that the patient rejects the very idea of ever wearing a gas permeable contact lens in the future. I prefer not to place a toric IOL in a current gas perme- able contact lens wearer. I want the patient to have failed gas perme- able contact lenses before cataract surgery. The reason here is that a gas permeable contact lens will yield the best vision possible for a patient with astigmatism or any type of corneal ectasia. A toric IOL will not be able to compete with the vision quality of a gas permeable contact lens. Patients will not be happy if their gas permeable contact lens bridge is unexpectedly burned by a toric IOL. Without a gas permeable contact lens, she will never see as good as she once saw. "My first order of business in this case would be careful counsel- ing and extended trial frame testing. If the patient expressed happiness with the vision in the trial frames and acknowledged the refractive limitations of surgery in someone with KCN then I could proceed. There is a very real possibility that she will only attain her best vision with spectacles. If this patient is unable or unwilling to accept the reality of her refractive situation, a truly informed consent regarding surgical risks and expectations is probably not possible, in which case I would be obligated to defer surgical correction." Dr. Beiko shared his thoughts on the case: "I would ask the OD what her refractive history was pre- viously. Since she has keratoconus, I suspect that she drifted toward in- creasing myopia with time. I would specifically ask if her recent history demonstrated this drift. If it did, I would encourage the patient to wait. "However, I suspect you opted for surgical intervention. If pushed to do something, I would place a piggyback in the right eye, targeting plano to –0.50 D. "In the left eye, rotation of the IOL using the Berdahl/Hardten calculator would leave some residual hyperopic cylinder of 1.00 D. Since rotation requires freeing up the lens, you might as well exchange it for the right power. I would opt for an IOL exchange for a higher power lens at the right axis." Dr. Hill commented: "For the right eye, the SN6AT7 appears to have corrected all of the refractive astigmatism, but there remains a +1.50 D spherical error. The same to- ric IOL model aligned with the same meridian but with +2.50 D more spherical power would change the refractive error from +1.50 D sphere to about –0.25 D sphere. This calcu- lation is done using Jack Holladay, MD's refractive vergence formula, which is an axial length indepen- dent exercise. The working plan would be a +9.50 SN6AT7 aligned with the 100 degree meridian. "For the left eye, there is a miss on both the sphere and the refrac- tive astigmatism. The wonderful tool by Drs. Berdahl and Hardten at www.astigmatismfix.com tells us that if the current refraction is –0.50 +2.00 x 25 (it's easiest to work in a plus cylinder format with toric IOLs), the toric IOL should be rotat- ed to an ideal meridian of alignment clockwise from 94 degrees to 74 de- grees. This would result in an antici- pated refractive error of plano +1.00 x 164. In addition, this tells us that the refractive axis has been flipped, the result of too much toric correc- tion. Going down two toric models to a SN6AT5 would be required to address this. Also, increasing the sphere power by +1.00 D would change the spherical equivalent from +0.50 D to something close to –0.25 D. The working plan would be a +12.50 D SN6AT5, aligned with the 74 degree meridian." What was done I decided that prior to moving for- ward with any surgical plan I had to be sure that the patient's refractive state was stable and that she would be happy with the quality of vision provided by this correction. I also wanted assurance that she under- stood her options in order to limit the potential for any future misun- derstanding. I brought her back on 3 separate occasions over a period of a few months for a repeat refraction and trial frame, which was consis- tent on each visit. She repeatedly told me that if she could have the vision she had with the trial frame but without having to wear glasses this would make her happy, and she Figures 5 and 6: Microscope view of patient's OS at the beginning and conclusion of IOL exchange procedure would prefer this option to return- ing to gas permeable contact lens wear. With this clearly established I decided to continue down the toric IOL path rather than removing them and replacing with monofocal implants to allow a return to gas permeable contact lens wear as an alternative option. I chose to operate on the right eye first. To manage the +1.5 D of hyperopia I placed a +2.0 STAAR AQ5010 piggyback lens, and the patient came back the next day extremely happy with 20/25 uncorrected vision. Her immediate enthusiasm for the outcome in this eye encouraged me to move forward with the left eye. First I looked at the Berdahl/ Hardten toric IOL calculator results and found that rotating this im- plant would leave the patient about +1.0-1.0 x 73 at best. I felt as others here did that if I was going to go through the trouble of freeing up this implant for rotation, I might want to consider the option of a lens exchange. I decided to use Dr. Barrett's for- mula for calculating IOL exchange in such situations to figure out what she needed in this eye. This formula predicted that based on her current situation, an exchange for a 12.5 Alcon T5 placed at 73 would make continued on page 28

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