In addition to glaucoma, XFS has been linked to cataract formation and to an increased incidence of complications, such as zonular dialysis or capsular rupture, during cataract surgeries. It has also been linked to lens dislocation and central retinal vein occlusion.
A new study in the medical journal Archives of Ophthalmology, which is published monthly by the American Medical Association, indicates that the risk for XFS is higher in certain latitudes. Researchers at the University of Michigan analysed data from 600,000 patients over the age of 60 who received eye care of any type. XFS was found in 3,300 of the patients.
The research cross-referenced patient diagnoses with geographic residence according to billing ZIP codes and placed them into one of three large regions across the US. The results indicate that patients residing in the northern tier, above latitude 42 degrees north, were 110% more likely to have XFS than patients who resided in the middle tier. Patients who resided in the southern tier were found to be 17% less likely to suffer XLS than middle tier residents.
Researchers believe that the ambient temperatures and level of sun exposure as they pertain to geographic latitude may have some beneficial effect as they increase. The exact risk factors and thresholds for XLS development remain undetermined.
The axial tilt of the Earth means that non-equatorial regions of the planet undergo a change of seasons each year. The axis is tilted by a little over 23 degrees, which does not sound like much, but that tilt is responsible for the differences between a frigid winter day and a hot summer afternoon.
Moving south through the northern hemisphere toward the equator, which is at latitude zero, the effect of the tilt decreases, seasonal variations diminish, and the mean temperature increases. Researchers are not sure how these environmental changes could repress XLS.
Most studies of XLS target specific patient populations, and comparison of results from one study to another can be misleading. For example, studies have been conducted within tightly controlled age groups, populations with specific clinical diagnoses, and populations who take certain classes of medications. This study focused on patients over the age of 60 who were receiving medical treatment for some type of visual impairment, and study results may not necessarily correlate with statistics for the general population.
Les writes about laser vision correction for Personal Eyes where you can find out more about eye procedures to suit your lifestyle.