Eye Color and Ocular Health: Keeping An “Eye” On Pain Tolerance

Aside from the blessing of vision, our eyes hold a wealth of information, from athletic abilities to pain tolerance and a predilection towards certain diseases. Understanding the role of exercise and even eye color in protecting our personal training clients’ ocular health may help stave off some highly detrimental conditions. Acknowledging the attributes of our given eye color might also help us learn more about how we “see” the world.

Eye Color and Pain Perception

Science has proven that human pain correlates with a variety of unlikely factors, such as gender, age, and hair color. Eye color, too, may soon join this list. Researchers found that individuals with darker eyes tended to experience a heightened sensation of pain as compared to those with lighter eye color, whether during exercise or in the ensuing post-workout recovery period.

Dr. Inna Belfer, Associate Professor of Anesthesiology at the University of Pittsburgh, presented some interesting results at the 2014 meeting of the American Pain Society. She recruited 58 healthy pregnant women, 24 of whom had dark eyes, with the remaining 34 constituting the light-eyed group. The women’s responses to pain, measured both before and after giving birth using a variety of questionnaires, revealed perplexing outcomes.

“There have been previous studies about the relationship of gender, age, and hair color to pain, but this is the first research on eye color.  This work may improve our knowledge of genetic contributions to pain and analgesia,” she said.

Her research showed that healthy women with light-colored eyes exhibited a higher pain tolerance than those with brown or hazel eyes. In addition to pain tolerance, the results indicated that women with brown eyes also experienced increases in anxiety, depression, and sleep disturbances in comparison to those with blue, green, or hazel eyes.

Always with an eye on the future, Dr. Belfer shares, “If we can prove that eye color is another genetic biomarker, it would be great because that’s exactly what we are looking for. Biomarkers can be instantly recognized, aren’t invasive, and can save time and money. We are constructing a pain genome and are figuring out how it can be used in the future, so basically the more we know the better it will make the treatment process.”

Eye Color and Visual Acuity of Sports Performance

Recent studies have indicated that eye color also plays a role in athletic performance. Dark-eyed individuals versus athletes with blue, green, or hazel eyes, seem to excel at reactive sports such as tennis, ping-pong, and the increasingly popular sport of pickleball.

The body’s ability to utilize properly trained muscles for different sports certainly remains important to athletic success. However, the demands on the visual system during athletic performance rank among the most rigorous of any activity. Given that vision so strongly influences the capacity of an athlete to execute the multitasking required in a majority of sports, scientists have gravitated toward investigating the link between skill and vision. Most of the research efforts have focused on identifying the visual skills necessary for particular sports and striving to determine if the skills of athletes differ from those of their less sports-minded cohorts.

Although more studies are needed to draw more conclusive results, data so far have suggested that certain visual skills do in fact play a vital role in the performance of selected sports. Currently, it certainly appears that the visual skills of athletes and nonathletes do differ. The next logical step will involve research to support whether enhancing the visual skills of athletes might result in improved athletic performance.

Can Extreme Exercise Change Color Perception and Vision Changes?

While we know inherently that arduous exercise causes intense fatigue, the scientific world recently discovered a potential link to changes in vision. Scientists at the University of Ljubljana in Slovenia recently studied whether changes in color vision that occasionally follow exertion to an anaerobic level resulted purely from extreme fatigue.

Many factors influence the onset of physical fatigue, such as intensity and duration of physical effort, individual fitness levels, and sleep deprivation. Perhaps less commonly known or understood, physical fatigue also compromises aspects of visual performance and visuomotor skills, contrast sensitivity, and color vision.

Changes in the ocular pathway responsible for processing colored visual information often occur during mountaineering, or any training at high altitude. However, such transient changes return to normal upon cessation of the high-altitude exertion and the subsequent return to the initial altitude. Researchers presume this comes about due to induced acidosis; more studies may reveal additional substantiating data.

Exercise and Intraocular Pressure

You know when the optometrist blows a puff of air at your eye during an eye exam? This is called tonometry, and is measuring how much your cornea will  flatten under that pressure, i.e., intraocular pressure. Cardiovascular/aerobic exercise tends to lower intraocular pressure (IOP) in the eyes and confer some protection to the retinal ganglion cells. Over one million of these tiny cells lie in the human retina and are responsible for transmitting all visual information to the brain. Keeping them healthy and safe helps promote and protect good eyesight.

Eye Health and Disease Risk

A healthy diet and regular exercise play important roles in reducing both high blood pressure and elevated cholesterol levels, two of the main culprits of vision problems and eye disease. Regular exercise also helps increase blood flow to the optic nerve and retina, ensuring those cells receive the necessary nutrients and oxygen for optimal performance.

As most health and fitness professionals know, cardiovascular exercise may also help minimize the risk of developing diabetes. Left unchecked, diabetes can lead to damage in the blood vessels of the retina and frequently ends up causing blindness.

According to the American Association of Ophthalmology, a study undertaken by Dr. Paul Foster demonstrated that individuals who engaged in moderate physical exercise were about 25% less likely to develop glaucoma than their sedentary counterparts.

Experts offer the following suggestions ~

• Running/brisk walking for 30 minutes each day can reduce one’s risk of age-related cataracts.

• Moderate-intensity, low-impact exercises can help significantly reduce pressure inside the eyes, particularly in young adults already living with, or at a higher risk of, glaucoma.

Macular Degeneration and the Exercise Link

Several studies have recently delved into the link between regular exercise and the development of both glaucoma and macular degeneration. Macular degeneration, the primary cause of severe vision loss after the age of 60, consists of a deterioration/breakdown of the eye’s macula, a small area in the retina responsible for central vision.

A study examining the medical history of more than 3,800 subjects found that those who exercised 3x/week were less likely to develop macular degeneration than those who lived inactive lifestyles. A pair of studies conducted in 2009 focused solely on distance athletes. Researchers found that running reduced the risk of cataracts and age-related macular degeneration. A 2014 study, the results of which appeared in the Journal of Neuroscience, explored a similar question using mice. Although still lacking sufficient data to prove that exercise can prevent macular degeneration in humans, the existing research seems to point in that direction.

The Weightlifting Paradox

While we have learned about the benefits of exercise to overall health, and eye health in particular, engaging in strenuous weightlifting can cause temporary but significant increases in intraocular pressure. Some ophthalmologists who care for patients already at a high risk of developing glaucoma may suggest they avoid arduous weightlifting and engage in other aspects of daily exercise. Utilizing the Valsalva maneuver during a weightlifting session poses the greatest risk.

The Valsalva maneuver refers to any forced expiration/exhalation against a closed glottis. While this sensation might occur upon straining during a bowel movement, or even while playing the trumpet/trombone/saxophone, typically this sort of exertion occurs without incident. One can think of a Valsalva maneuver as the moment when, upon exerting maximal effort, one holds one’s breath while tightening the muscles of the trunk. This straining induces blood pressure changes, paving the way for the potential of increased intraocular pressure.

Typically, energy in the bloodstream exists in three interchangeable forms: pressure from cardiac output/vascular resistance, hydrostatic pressure from gravitational forces, and the pure kinetic energy of blood flow.

Based on the characteristic hemodynamic changes, or how blood flows through the blood vessels, experts have divided the Valsalva maneuver into four distinct phases:

• Phase I – the onset of strain, associated with a transient rise in blood pressure.
• Phase II – positive intrathoracic pressure leads to a reduced venous return to the heart. Stroke volume then falls, causing a subsequent dip in blood pressure, thereby activating the baroreceptors in the carotid sinus and aortic arch. Ultimately the individual experiences significant episodes of tachycardia, increased cardiac output, and vasoconstriction, resulting in the recovery of blood pressure to normal values.
• Phase III – also known as the transient phase, whereby the release of strain induces a sudden dip in blood pressure.
• Phase IV – blood pressure rises above the baseline, due to the resumption of normal venous return to the heart stimulated by the sympathetic nervous system experienced in Phase II. This forces stimulation of the baroreflex, leading to bradycardia and the return of blood pressure to the baseline.

One recent study out of New Zealand focused solely on weightlifting and its effect on eye pressure. Twenty-four volunteers participated by engaging in a series of leg presses. This particular study relied on the 45-degree leg press apparatus; the seat of this machine reclines at an angle while the subject pushes his legs upward in a diagonal direction. While the participants were reclined, scientists took readings of intraocular pressure before, during, and immediately after execution of the leg press.

The data revealed a considerable increase in IOP during the exercise itself. While normal pressure readings range anywhere from 9-21 mm Hg, the leg press induced readings exceeding 26 mm Hg. Fortunately, levels stabilized within 60 seconds after concluding the move.

Isometric Exercises

It appears that an isometric squat held for one minute might also induce a rise in IOP. Interestingly, increasing repetitions brought about an incremental increase in intraocular pressure, depending upon the mode of exercise. Therefore, the type of exercise performed and the number of repetitions executed can affect how high eye pressure rises.

Eye Color and Disease Risk

While eye color cannot definitively predict health outcomes nor visual acuity, some research data suggest that certain health risks may relate to eye color.

One study, the results of which appeared in the journal Cancer Causes and Control, found that individuals with light-colored eyes — blue, green, or hazel — align with a higher risk of basal cell and squamous cell carcinomas.

Another study done in 2000 revealed that having brown eyes posed a greater risk of developing cataracts. However, the lack of more recent studies to corroborate this evidence indicates the need for considerably more research into this area.

Blue-eyed individuals comprise 8% of the general population. While beautiful to look at, such eye color often indicates a higher risk for Type 1 diabetes and hearing loss, as well as a predilection for alcohol addiction. Interestingly, such individuals tend to experience a lower risk of depression.

People with hazel eyes, about 5-8% of the population, generally have a lower pain tolerance, but show a preponderance toward anxiety and digestive issues. Green eyes, the rarest color, account for a mere 2% of the world’s population. Green-eyed individuals demonstrate a higher tolerance to pain, but also a higher risk of cancer.

Eye color, vision, and exercise together open up a whole new perspective on our overall health. When training clients, take the time to mention ocular health, including ways in which their workouts may be helping them to better “see” the future!

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