SAN FRANCISCO, CA--- Does cataract surgery increase the risk of vision loss in people with age-related macular degeneration (AMD)? How do people read faces to judge age or fatigue? Which has a larger impact on the "normal" decline of visual function as we age, genetic or environmental factors? These questions are explored in the February issue of Ophthalmology, the journal of the American Academy of Ophthalmology.
Age-Related Eye Disease Study (AREDS) Examines Macular Degeneration Risk Related to Cataract Surgery
Age-related macular degeneration (AMD) and cataract are leading causes of visual impairment in the United States. Both are related to aging, and they share other risk factors, but it has been unclear whether a direct causal link might be involved. Several large epidemiological studies had raised concern that cataract surgery might accelerate AMD progress and threaten vision. To address this concern, Emily Y. Chew, MD, of the National Eye Institute, and colleagues analyzed data for a cohort of participants in the Age-Related Eye Disease Study (AREDS). This cohort is the only large prospective study in which the severity of AMD was documented before and after cataract surgery and which included more than five years of in-depth participant follow-up.
AMD causes changes in the retina, the light-sensitive tissue that focuses images at the back of the eye, and severe AMD leads to loss of central vision. Cataract is cloudiness or opacity in the eye's lens that interferes with the clear focus of images on the retina.
AREDS researchers concluded there was little evidence that cataract surgery had a negative effect on progression to advanced AMD. "These data may provide some reassurance to patients with AMD who are considering cataract surgery," Dr. Chew said.
The primary purpose of the AREDS multicenter controlled randomized clinical trial was to assess whether antioxidant and mineral supplements affect progress to advanced AMD and development of cataracts. The cohort study included 4,577 participants (8,050 eyes) aged 55 through 81 at enrollment; it compared the risk of advanced AMD in patients who had cataracts removed versus the risk for those who did not have the surgery. All participants took either antioxidant/mineral supplements or placebos. Study eyes were examined every six months over five or more years. One analysis compared AMD progression in matched pairs of eyes, where one eye had cataract surgery after baseline but before developing advanced AMD, and the paired eye did not have cataract surgery. Matched pairs were determined based on similar risk factors for AMD, assigned antioxidant or placebo treatment, baseline AMD category, person's age, and other factors. Results of the matched pair analysis and of two other standard analytical models revealed no consistent pattern of accelerated AMD progression after cataract surgery.
Several factors may explain the divergent conclusions reached by AREDS and the earlier studies. The most likely cause would be that earlier studies had unintended biases or confounding variables. Also, techniques of cataract surgery and lens replacement have changed over time, and AREDS participant surgeries were performed more recently than those tracked in the combined-population studies. A significant number of subjects in earlier studies did not have lens replacement after cataract extraction, while AREDS participants were likely to have had ultraviolet-B light blocking lenses inserted, which may have protected their maculae and decreased AMD risk.
Old or Tired? How People Read and Rate Faces
A recent study led by Peter A. D. Rubin, MD, of the University of Tennessee Health Science Center, used eye-tracking methodology to determine how signs of age or fatigue are assessed. Based on their experiences with patients, the researchers hypothesized that the eye area would be especially important. Social psychology research confirms that an attractive appearance enhances everything from a person's self-esteem to job prospects, and Dr. Rubin's group wanted to learn which facial features are key to a youthful, lively appearance. They assumed this information would be useful to people considering plastic surgery.
Forty-seven young adults (15 males, 32 females) were recruited from student populations in the Boston area; all passed vision screening tests. In each of two sessions a participant viewed photo images of 48 older individuals on a computer monitor equipped with a camera that analyzed infrared reflection from the eye's pupil and cornea to determine duration and direction of the gaze. This device, located in the Brandeis University Emotion Laboratory of Derek Issacowitz, PhD, allowed Dr. Rubin's group to quantitatively measure gaze patterns related to subjective judgments about age and fatigue. The images showed individuals' faces in neutral expressions, photographed under standardized conditions; the faces were divided into "LookZones" for data analysis. After viewing the image for five seconds, the participant clicked a selection on a rating scale. Age was assessed in the first session and tiredness in the second.
In rating age, participants most often looked at the eye region (46%), the nose (19.2%), the forehead (13.3%), and the region between the eyebrows (10.6%). The eye region was also most frequently selected in rating fatigue (44.7%), followed by the nose (18%), forehead (13.7%) and area between the brows (12.3%). Participants also looked longest at the eye region in both assessment sessions, concentrating on the brow and lower lids. Since the eye region represents just 21% of the area of the face, clearly this area is disproportionately important to such judgments. Overall, results indicated a strong relationship between the way facial regions were used in assessments of age and of fatigue. Because static rather than video images were used, the study did not determine whether attention would be drawn toward the mouth during speech. The researchers note that people from age groups other than young adult might assess facial features differently than this study's participant group.
"Our results raise the possibility that aesthetic surgery to the eye region may be an efficient, effective intervention to enhance an individual's attractiveness by reducing how old or tired one appears," Dr. Rubin said. "Apparently, beauty is not only in the eye of the beholder, but also in the eye of the beholdee," he quipped. American Society of Plastic Surgery 2007 statistics list eyelid surgery as the fourth most common procedure performed in the United States. Dr. Rubin's next study will rate age and fatigue perceptions using images of patients before and after cosmetic surgery.
Visual Decline as We Age: Genetics or Environment?
Vision worsens for most of us as we age, even in the absence of eye diseases such as glaucoma or AMD. Elders who have good visual acuity (20/25 vision or better) may have trouble driving at night or adjusting when they move between indoor and outdoor light. Some declines are optic, such as presbyopia, reduced flexibility of the eye's lens, which causes poorer near vision for many people after age 40. Other declines are neuronal, related to the eye's ability to send images to the brain. Since crucial functions like reading and memory depend on vision, it is important to understand how "normal" aging occurs and discover what can be done to delay or prevent reduced function. In the first investigation of heredity's impact on neuronal visual decline, Ruth E. Hogg, PhD, of the University of Melbourne, Australia, and her colleagues used a classic twin study to explore genetic and environmental factors.
Study participants were a cohort of the AMD twin study by the University of Melbourne Centre for Eye Research, comprised of eighty-four twins (42 pairs, 21 identical and 21fraternal) between the ages of 57 and 75 who met study criteria for visual acuity and absence of eye disease. In each person the eye with the best visual acuity (or the right eye if acuity was equal in both eyes) was tested for adaptation to light level changes, for color detection, and for detection of gray tone gradations between image and background, termed contrast sensitivity. Taken together, these tests assess key visual functions needed in daily life. When test results showed that a visual ability declined at about the same age in identical twins, the trait was assumed to be under genetic control, and when the decline occurred at different ages, environmental factors were considered dominant. Results for identical twins and fraternal (non-identical) were compared, and when concordance between scores was higher for identical than for fraternal pairs, genetics was assumed to be the controlling factor.
Genetic factors appear to be strong determinants of sharp visual acuity and color discrimination, functions performed by cone cells pathways in the eye's retina, the tissue at the back of the eye that converts light into electronic images for relay to the brain. Genetic factors were not strongly correlated with night vision and the ability to adapt to light level changes, which are performed by retinal rod cells, implying that environmental influences are important to those functions. Autopsies and other studies have found that substantially more rod than cone cells are lost as eyes age. The flow of nutrients across the retinal membrane appears to be more important for rod cell than for cone cell function, and it is here that environmental factors—such as smoking, deficient nutrition, excessive sunlight exposure, and inflammation---may influence visual decline. Rod cell deterioration is accepted as a component of both general visual decline and age-related diseases like AMD, the most common cause of visual disability in elders.
"Our results support clinical and research efforts now underway to slow or stop age-related vision decline by modifying lifestyle factors and/or using specific medications," says Dr. Hogg.
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About the American Academy of Ophthalmology
AAO is the world's largest association of eye physicians and surgeons—Eye M.D.s—with more than 27,000 members worldwide. Eye health care is provided by the three "O's" – opticians, optometrists and ophthalmologists. It is the ophthalmologist, or Eye M.D., who can treat it all: eye diseases and injuries, and perform eye surgery. To find an Eye M.D. in your area, visit the Academy's Web site at www.aao.org
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