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Rationale for choosing crossed monovision
LETTERS
Rationale for choosing crossed monovision 1
Zhang et al. present evidence that crossed monovision has higher satisfaction than conventional monovision. I have chosen to routinely offer mini-monovision for 20 years in thousands of patients using a choice of the dominant eye for near. Most cataract patients are older with small pupils and therefore enhanced depth of field. They also spend much more time with intermediate and near tasks rather than distance ones. In most cases, it is not possible to tell whether there had been a monofixation syndrome or even frank amblyopia earlier in life as a result of concurrent lens opacity. Therefore, as a primary option, I have recommended to my patients correcting the first eye for distance ( 0.25 diopter [D]). I select the eye with the more positive spherical error because it usually has the greater chance of poor reading speed, which is not as important for distance activities. Postoperatively, once it has been determined that the distance vision is adequate for ambulation and driving, the choice of midrange ( 1.25 to 1.75 D) in the second eye maintains moderate stereopsis while allowing reading of a typical magazine font. On the other hand, if the distance function is inadequate for driving after first-eye surgery, the patient is informed of the options of glasses for driving while targeting an intermediate focal point in the second eye versus targeting distance in the second eye with the patient using readers. If the distance function were inadequate even for ambulation, the second option is strongly recommended. If there is the potential for mild amblyopia or monofixation syndrome, why set the nondominant eye for near, as the patient could not read fluidly? I prefer to choose the ensured reading gain by setting the dominant eye for near, albeit with a slight risk for diplopia resulting from fixation switch diplopia.2 Key is a frank preoperative discussion of the possible outcomes. I would like to know whether Zhang et al. measured the binocular reading speed in the crossed and conventional monovision groups. I would predict the crossed group would have higher reading speeds, which could explain the higher satisfaction in the authors' crossed monovision group. William G. Myers, MD Chicago, Illinois, USA Financial Disclosure: Dr. Myers is a consultant to Leiter's Compounding.
346
Q 2016 ASCRS and ESCRS Published by Elsevier Inc.
REFERENCES 1. Zhang F, Sugar A, Arbisser L, Jacobsen G, Artico J. Crossed versus conventional pseudophakic monovision: patient satisfaction, visual function, and spectacle independence. J Cataract Refract Surg 2015; 41:1845–1854 2. Kushner BJ. Fixation switch diplopia. Arch Ophthalmol 1995; 113:896–899
Reply : We would like to thank Dr. Myers for his discussion. It is important to clarify that our crossed versus conventional intraocular lens (IOL) monovision study did show a slightly better result in the crossed group, for which we do not have a validated explanation. Possible explanations are as follows: (1) It was a small study, with only 30 pairs. (2) When deciding to elect crossed monovision, the surgeon was extra careful to make sure everything was lined up well to avoid any potential medical or legal issue because crossed monovision was out of “conventional” practice. (3) A few crossed monovision patients declined participation in the study for unknown reasons. Selection bias might have occurred if unhappy patients declined participation more frequently than happy ones. Further studies with a larger enrollment and prospective designs are warranted to draw a more definite conclusion. We still advocate conventional IOL monovision as the first choice based on several facts. First, various advantages have been suggested in correcting the dominant eye for distance vision.1 Second, at present, the authors are aware of only 2 studies2 (1 was our own) of crossed IOL monovision in the ophthalmology literature and more important, the conclusions from those 2 studies were only suggestive that crossed IOL monovision worked as well as conventional monovision as a group. Third, correcting the weaker eye to be the distant-fixating eye might have very unfavorable outcomes.3–5 Based on these studies, we actually do not routinely recommend performing surgery in the worse cataract eye first aiming for distance correction and the fellow eye aiming for near without regard to dominance. In cases of amblyopia and monofixation syndromes, we do not recommend monovision, especially not crossed monovision. We recommend correcting the healthier eye for better distance and making the limited eye slightly myopic, about 0.25 D myopic defocused, but not monovision. Our paper did not discuss this issue in detail because of limitations on the scope and length. A more detailed discussion might be available in the future.A
http://dx.doi.org/10.1016/j.jcrs.2016.02.006 0886-3350
Rationale for choosing crossed monovision 1
Zhang et al. present evidence that crossed monovision has higher satisfaction than conventional monovision. I have chosen to routinely offer mini-monovision for 20 years in thousands of patients using a choice of the dominant eye for near. Most cataract patients are older with small pupils and therefore enhanced depth of field. They also spend much more time with intermediate and near tasks rather than distance ones. In most cases, it is not possible to tell whether there had been a monofixation syndrome or even frank amblyopia earlier in life as a result of concurrent lens opacity. Therefore, as a primary option, I have recommended to my patients correcting the first eye for distance ( 0.25 diopter [D]). I select the eye with the more positive spherical error because it usually has the greater chance of poor reading speed, which is not as important for distance activities. Postoperatively, once it has been determined that the distance vision is adequate for ambulation and driving, the choice of midrange ( 1.25 to 1.75 D) in the second eye maintains moderate stereopsis while allowing reading of a typical magazine font. On the other hand, if the distance function is inadequate for driving after first-eye surgery, the patient is informed of the options of glasses for driving while targeting an intermediate focal point in the second eye versus targeting distance in the second eye with the patient using readers. If the distance function were inadequate even for ambulation, the second option is strongly recommended. If there is the potential for mild amblyopia or monofixation syndrome, why set the nondominant eye for near, as the patient could not read fluidly? I prefer to choose the ensured reading gain by setting the dominant eye for near, albeit with a slight risk for diplopia resulting from fixation switch diplopia.2 Key is a frank preoperative discussion of the possible outcomes. I would like to know whether Zhang et al. measured the binocular reading speed in the crossed and conventional monovision groups. I would predict the crossed group would have higher reading speeds, which could explain the higher satisfaction in the authors' crossed monovision group. William G. Myers, MD Chicago, Illinois, USA Financial Disclosure: Dr. Myers is a consultant to Leiter's Compounding.
346
Q 2016 ASCRS and ESCRS Published by Elsevier Inc.
REFERENCES 1. Zhang F, Sugar A, Arbisser L, Jacobsen G, Artico J. Crossed versus conventional pseudophakic monovision: patient satisfaction, visual function, and spectacle independence. J Cataract Refract Surg 2015; 41:1845–1854 2. Kushner BJ. Fixation switch diplopia. Arch Ophthalmol 1995; 113:896–899
Reply : We would like to thank Dr. Myers for his discussion. It is important to clarify that our crossed versus conventional intraocular lens (IOL) monovision study did show a slightly better result in the crossed group, for which we do not have a validated explanation. Possible explanations are as follows: (1) It was a small study, with only 30 pairs. (2) When deciding to elect crossed monovision, the surgeon was extra careful to make sure everything was lined up well to avoid any potential medical or legal issue because crossed monovision was out of “conventional” practice. (3) A few crossed monovision patients declined participation in the study for unknown reasons. Selection bias might have occurred if unhappy patients declined participation more frequently than happy ones. Further studies with a larger enrollment and prospective designs are warranted to draw a more definite conclusion. We still advocate conventional IOL monovision as the first choice based on several facts. First, various advantages have been suggested in correcting the dominant eye for distance vision.1 Second, at present, the authors are aware of only 2 studies2 (1 was our own) of crossed IOL monovision in the ophthalmology literature and more important, the conclusions from those 2 studies were only suggestive that crossed IOL monovision worked as well as conventional monovision as a group. Third, correcting the weaker eye to be the distant-fixating eye might have very unfavorable outcomes.3–5 Based on these studies, we actually do not routinely recommend performing surgery in the worse cataract eye first aiming for distance correction and the fellow eye aiming for near without regard to dominance. In cases of amblyopia and monofixation syndromes, we do not recommend monovision, especially not crossed monovision. We recommend correcting the healthier eye for better distance and making the limited eye slightly myopic, about 0.25 D myopic defocused, but not monovision. Our paper did not discuss this issue in detail because of limitations on the scope and length. A more detailed discussion might be available in the future.A
http://dx.doi.org/10.1016/j.jcrs.2016.02.006 0886-3350