March 2019

CORNEA

Research highlight
A “battle” between the sexes over astigmatism change with age


by Vanessa Caceres EyeWorld Contributing Writer

“While we know that patients tend to progress to ATR astigmatism over time, the sex differences in terms of time of progression [in the study] ... have implications for our practice and refractive targets.”
—Danielle Trief, MD

Study finds more ATR astigmatism at a younger age in male patients

Physicians may need to adjust their astigmatism corrections not only for a patient’s age but also depending on whether the patient is male or female, according to a recently published study.1 Led by Ken Hayashi, MD, Hayashi Eye Hospital, Fukuoka, Japan, researchers found in their prospective case series that against-the-rule (ATR) corneal astigmatism was larger in males and ATR astigmatic change with age began earlier in males.

Study details

The observational cohort study included 1,000 eyes of patients at Hayashi Eye Hospital seen between December 2016 and March 2017. Patients did not have any corneal pathology, did not wear contacts, and did not have a history of ocular surgery or inflammation. Researchers continued patient screenings until they enrolled 100 eyes of male patients and 100 eyes of female patients each in five age groups: 40 to 49 years, 50 to 59 years, 60 to 69 years, 70 to 79 years, and 80 years or older.
Videokeratographic evaluations were performed with the Topographic Modeling System version 5 (TMS-5, Tomey, Nagoya, Japan). The system includes a Scheimpflug camera and a Placido ring topographer.
Researchers obtained various astigmatism measurements, including simulated keratometry, simulated K vales of the posterior, anterior, and total cornea, and the determination of with-the-rule (WTR) versus ATR astigmatism. They also determined the corneal astigmatism vector (magnitude and meridian) using a power vector analysis. Changes in astigmatism of the total cornea between decades were calculated using the power vector analysis.

Corneal astigmatism findings

Researchers made several findings about corneal astigmatism difference between sexes and with age. Highlights include the following.
Mean magnitude. The mean magnitude of the total and anterior cornea astigmatism was significantly smaller in male versus female eyes in the 40 to 49 and 50 to 59 age groups. However, it did not differ significantly between males and females after age 60. There were no significant differences in posterior corneal astigmatism in any age group.
For total cornea, in male eyes, the mean magnitude lowered significantly from the baseline age of 40 to age 50, then increased up until age 80. In female eyes, it lowered significantly from ages 40 to 60 then increased again up until age 80.
Vertical-horizontal and oblique corneal astigmatism. Using paired t test, the mean J0 of the total and anterior cornea was significantly smaller in male eyes as compared to female eyes. Using the multivariate analysis of variance, the mean J0 and J45 values of the total and anterior cornea were significantly smaller in male eyes. For the posterior cornea, the mean J0 of the posterior cornea was significantly greater in male eyes at age 50, but it did not differ significantly between the sexes at other ages.
In the posterior cornea, the mean J0 and J45 values were significantly smaller in male versus female eyes only at age 50.
Patient age was negatively correlated with the J0 of the total and anterior cornea but positively correlated with the J0 of the posterior cornea. The corneal astigmatism changed toward ATR astigmatism with age.
Difference in corneal shape. There was a gradual progression of a horizontal bowtie pattern, indicating an ATR shape change with age. “This horizontal bowtie pattern became prominent in male eyes at 60 years of age and in female eyes at 70 years of age, and the change was more prominent in male eyes than in female eyes,” according to the researchers.
Corneal astigmatism distribution. More eyes had ATR versus WTR astigmatism. The number of eyes with WTR astigmatism was significantly lower in male eyes compared with females at 40, 50, and 60 years in the total cornea and at 40 and 60 years in the anterior cornea. The type of astigmatism did not differ significantly in the posterior cornea.
Patient age. Patient age correlated significantly with an ATR change of the total and anterior cornea. It weakly correlated with a WTR change of the posterior cornea.

Analyzing the results

The study findings could make a difference in the target correction that cataract surgeons aim for to correct preexisting astigmatism.
“We consider that with-the-rule astigmatism should be maintained more in females and against-the-rule astigmatism may be corrected more in males when performing astigmatism correction in cataract or refractive surgery,” Dr. Hayashi said.
“While we know that patients tend to progress to against-the-rule astigmatism over time, the sex differences in terms of time of progression [in the study] were very interesting and have implications for our practice and refractive targets,” said Danielle Trief, MD, assistant professor of ophthalmology, Edward S. Harkness Eye Institute, Columbia University Medical Center, New York.
Based on the results, patients may need to be counseled that their astigmatism may change over time, even after placement of an astigmatism-correcting lens, Dr. Trief said.
“It would be great to one day have a formula that predicts that amount of astigmatic change over time, taking into account sex and age, now that we know that these variables are important considerations,” she said.
Researchers were not sure why the ATR change with age appeared to happen earlier in male versus female eyes. However, they did note that some previous research shows corneal astigmatism changes depend on external influences such as upper eyelid tension and the actions of the medial rectus muscle as well as corneal structure changes with age, including a progressive thickening of the stromal collagen bundle and a decrease in interfibrillar spacing. “These internal structural changes might lead to corneal shape and astigmatic changes with age. It could be that these external and internal influences occur earlier in male eyes than in female eyes,” the researchers wrote.
One possible limitation with the study, according to Dr. Trief, is that it was done in a Japanese hospital with highly myopic patients. The results could be different for patients of other ethnicities and with lower myopia, she said. “It would be interesting to see if the authors’ findings are reproducible across other demographics,” she said.
Dr. Hayashi and fellow researchers think their study is the first published one to compare sex-related differences in corneal astigmatism and shape dependent upon patient age.
The researchers would like to further determine the optimal target astigmatism according to patient age of males versus females, Dr. Hayashi said.

Reference

1. Hayashi K, et al. Sex-related differences in corneal astigmatism and shape with age. J Cataract Refract Surg. 2018;44:1130–1139.

Editors’ note: The physicians have no financial interests related to their comments.

Contact information

Hayashi
: hayashi-ken@hayashi.or.jp
Trief: dft2102@cumc.columbia.edu

A “battle” between the sexes over astigmatism change with age A “battle” between the sexes over astigmatism change with age
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