June 2007

 

CATARACT/ IOL

 

Cataracts more likely develop in dominant eye?


by Matt Young EyeWorld Contributing Editor

 

 

A stained capsule during cataract surgery. A new study suggests the dominant eye will have a cataract first.

Source: Mark Packer, M.D.

Research focuses on laterality and the eye

In this world—to modify an old adage—nothing is certain but death, taxes and cataracts. Now researchers suggest they even know which eye will likely get cataract first: the dominant one. According to Senol Dane, Department of Physiology, Medical School, Ataturk University, Turkey, in a study of right- and left-eye dominant patients, cataracts formed earlier in the dominant eye. “In the sighting-dominant eye, the lens becomes a more spherical shape during sighting to near points in comparison to the other eye,” Dr. Dane reported in the March 2007 issue of Laterality. “Therefore, it may be expected that a cataract in the dominant eye would form earlier than in the non-dominant eye.”

Further, in right-handed patients, cataracts also usually formed earlier in the right eyes. In left-handed patients, cataracts tended to form earlier in left eyes. But some ophthalmologists briefed on the results of this study were quite surprised, and one had serious doubts.

Startling results

The formation of the cataract was earlier in the right eye in 29 of 44 right-handed patients, and only 13 in the left eye. It occurred at the same time in two eyes in two patients. Of 12 left-handed patients, the formation of the cataract was earlier in the left eye in nine cases and in the right eye in only three cases. These findings indicated “a significant correlation between handedness and the eye of the earlier cataract,” Dr. Dane wrote. Furthermore, the formation of the cataract was also earlier in the right eye of 27 of 33 right-eyed patients, but earlier only in six patients in the left eyes of right-eyed patients. In left-eyed patients, the formation was earlier in the left eye of 16 of 21 left-eyed patients, while only earlier in the right eye in 4 left-eyed patients. Again the difference was statistically significant. “There are two possible explanations for the cataract-proneness of the dominant eye,” Dr. Dane reported. “First, it may result from the more spherical shape of the lens in the dominant eye during the sighting to near points. Second, it may be a result of more light entering the dominant than the non-dominant eye.”

Dr. Dane’s conclusions follow others he has reported with regards to laterality and the eye. Earlier, Dr. Dane had reported that IOP was higher in right eyes than in left eyes of men, right-handers, and right-eyed subjects. Dr. Dane concluded that “the dominant eye has higher intraocular pressure compared to the nondominant one, and there is a relationship between hand preference and the intraocular pressure.”

Defending the conclusion

If you still find this logic hard to swallow, Dr. Dane has a deeper explanation. “The sighting-dominant eye, as in the present study, is active but the other eye is passive in the focusing of the eyes on a point,” Dr. Dane noted. “The number of parasympathetic impulses is greater in the dominant eye compared to the passive one.”

Dr. Dane continued: “In contrast, the motoric-dominant eye is the better eye at motoric movements … and motoric dominance of the eye is not related to the focusing of the lens. In the sighting-dominant eye, the lens becomes a more spherical shape during sighting to near points in comparison to the other eye. Therefore, it may be expected that a cataract in the dominant eye would form earlier than in the non-dominant eye.”

Nonetheless, some ophthalmologists find the results hard to believe. Louis D. “Skip” Nichamin, M.D., Brookville, Pa., called the results “surprising.” He was not previously aware of such an association nor did he have a ready explanation for it. If the results did prove true, however, they wouldn’t have significant impact upon the detection of a cataract because the cataract itself is straightforward to diagnose.

The results could yield better insight into the formation of the cataract, Dr. Nichamin said. It could have implications for the pathogenesis of the cataract—how it is formed for instance, he said. Bjorn Johansson, M.D., Ph.D., Linkoping University Hospital, Sweden, said he himself is one such individual that is a right-handed person with a dominant left eye, and thus has a particular interest in laterality. “Conclusions should be drawn with caution from this study because of the limited size (56 patients) and because dominant hand and dominant eye need not be on the same side in one individual. On the other hand, should these results hold water this is good news,” Dr. Johansson said, referring to the study results. That’s because cataract surgeons typically treat the worse eye first (in terms of cataract formation), he said. “If the dominant eye is the one with the most cataract, we will have more satisfied patients with one-eye surgery,” he said. In other words, considering cataracts are frequently operated upon on different surgical days, patients more often will get vision in their dominant eye back first (because those are likely the ones with more cataract formation), and they will tend to be happier as a result, he said. “Nevertheless in clinical reality most patients suffering from bilateral cataract who have been operated in only one eye will return with a request to have also the other eye operated”, Dr. Johansson concluded.

Editors’ note: Dr. Dane has no financial interests related to this study. Drs. Nichamin and Johansson have no financial interests related to their comments.

Contact Information

Dane: sdane@atauni.edu.tr

Johansson: bjorn.johansson@lio.se

Nichamin: 814-849-8344, nichamin@laureleye.com

Cataracts more likely develop in dominant eye? Cataracts more likely develop in dominant eye?
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