May 2007

 

OPHTHALMOLOGY NEWS

 

Put a lid on it


by Matt Young EyeWorld Contributing Editor

   

A new study finds a connection between eyelids and corneal astigmatism

Despite the fact that the eyelid touches the cornea, it’s rare to come across an ophthalmologist talking about the eyelid’s impact on vision. Previous investigation has found that eyelid abnormality has an impact on vision. And certainly, pushing or pulling on one’s eyelid as a simple test can cause visual distortion. But a new study suggests that even in normal, young, and healthy subjects, there are correlations between eyelid morphology and corneal astigmatism. “Correlations found between corneal astigmatism and eyelid parameters indicated that in general, the angle of the eyelids was associated with the axis of corneal astigmatism,” according to lead study author Scott A. Read, Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Australia. The report appeared in the January 2007 issue of Investigative Ophthalmology & Visual Science. “Correlations between palpebral fissure angles and corneal J45 were significant for subjects with low and higher degrees of corneal astigmatism,” Dr. Read reported. “Most of the significant correlations between corneal astigmatism and the eyelid parameters in our population related to the axis of astigmatism rather than the magnitude.”

Dr. Read’s study may not change how refractive surgery patients are treated, but it sheds light on the concept that eyelids are doing more than just protecting eyes—they’re impacting vision as well.

Not just protectors

Researchers took corneal topography measurements as well as digital images of the anterior eye and adnexae for 100 young-adult participants. These subjects had a best-corrected visual acuity (BCVA) of 6/7.5 or better in the measured eyes. The corneal axial power best sphere showed a highly significant correlation with the horizontal palpebral fissure width (r = –0.428; P = 0.001), which meant the larger the horizontal eyelid dimensions were, the flatter the cornea was. Further, there were very significant links between eyelid angles and corneal astigmatism power vector J45. That indicated an important association between the axis of astigmatism and eyelid angle. Specifically, the palpebral fissure angle, the angle of the upper lid, and the angle of the lower lid were all significantly correlated with corneal J45. “Previous investigators have shown correlations between corneal astigmatism and eyelid parameters in subjects with eyelid abnormalities and with congenital malformation syndromes associated with abnormal palpebral fissure slanting and in children with high degrees of astigmatism,” Dr. Read said. “We have shown that associations between eyelid morphology and corneal astigmatism also occur in a population of healthy young-adult subjects.”

In general, the angle of the eyelid was associated with the axis of corneal astigmatism, he noted. The results also suggested that 10% to 25% of the variance seen in the angle of astigmatism could be accounted for by the angle of eyelids. However, other factors not studied such as eyelid tension, corneal rigidity, and even genetic factors associated with corneal shape could also influence the astigmatism angle.

Of note, the lower eyelid had stronger correlations in terms of eyelid morphology to corneal astigmatism than the upper eyelid.

“This is an interesting finding because pressure from the upper eyelid has been implicated in the cause of astigmatism,” Dr. Read wrote.

While Dr. Read did not find overwhelming correlations between the magnitude of astigmatism and eyelid morphology, a compelling hypothesis did emerge from the research that appears to be new in scientific literature.

“Our results suggest that the angle and curvature of the lower eyelid have an influence on the angle and magnitude of corneal astigmatism in some subjects,” Dr. Read reported. “A significant correlation was found between the magnitude of corneal J0 and the curvature of the lower eyelid for subjects exhibiting WTR [with-the-rule] corneal astigmatism. Flatter lower eyelid curvature was associated with greater degrees of WTR astigmatism. It is conceivable that the curve of the eyelid is related to eyelid tension. If it is, one would expect that a tighter lid would be associated with a flatter lower eyelid curve. Thus, the tension in the lower eyelid may be related to the magnitude of WTR astigmatism.”

The bottom line, however, is that multiple factors, including eyelid tension, eyelid position, and corneal physiological characteristics, all play a role in determining the magnitude of astigmatism, he noted. Is the lid a real problem? Meanwhile, Mark Packer, M.D., clinical associate professor, Casey Eye Institute, Oregon Health & Science University, Portland, Ore., said abnormal eyelids can induce astigmatism, but he’s more skeptical when it comes to associations between normal eyelid morphology and astigmatism. “It’s well known in pediatric ophthalmology that ptosis, for instance, can induce astigmatism,” Dr. Packer said. “Also, there are situations with adults [in which] something clearly abnormal like eyelid growth, tumor, or a blocked oil gland can push on the eye and induce astigmatism. You can mimick this yourself with your finger. Just push on your eyelid around the front of your eye, and you can see things go blurry because you’re inducing astigmatism.”

Curiously, Dr. Packer said, he has also had patients with residual astigmatism after cataract surgery say that if they push on their eye, they can see more clearly because the astigmatism goes away. But the way to recognize a visual problem caused by an eyelid is rather simple, he said, because something would be wrong with the eyelid itself—a bump, scar, tumor, or droopy lid, for example. “A normal-appearing eyelid isn’t going to induce astigmatism,” Dr. Packer said. “And by far, the vast majority of astigmatism is the corneal issue—it has to do with shape of the cornea.”

Editors’ note: Dr. Read has no financial interests related to his study. Dr. Packer has no financial interests related to his comments.

Contact Information

Packer: 541-687-2110, mpacker@finemd.com

Read: sa.read@qut.edu.au.

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