New Eye Imaging Techniques Are On the Horizon

ScienceDaily (May 7, 2012) - The same technology used by astronomers to obtain clear views of distant stars is now being used by optometrists to perform incredibly detailed examinations of the living Eye.

An update on new developments in ocular imaging techniques -- and how they may affect clinical vision care in the not-too-distant future -- is presented in an article titled "Adaptive Optics Scanning Laser Ophthalmoscope-based Microperimetry" published in a special May issue of Optometry and Vision Science, official journal of the American Academy of Optometry.

Cutting-edge techniques now allow researchers to visualize the fine structure of the Eye in a way that was "not conceivable 20 years ago," according to a guest editorial by Scott Read OD PhD FAAO (Candidate) and colleagues. "As these advanced imaging methods continue to develop, the potential for imaging ocular structures down to the cellular level in everyday clinical practice has become a reality -- and the potential to improve patient care is truly stunning," Dr Read and coauthors add.

New Techniques Provide Cellular-Level Images of the Living Eye The special issue presents 30 reports on the latest, most advanced techniques for imaging and measurement of various Eye structures: the retina and optic nerve, lens and ciliary body, and the anterior Eye. Written by leading researchers and clinicians, the contributions provide a fascinating look at these remarkable new technologies, with a glimpse of their likely extensions into clinical practice.

As just one example, William S. Tuten, OD, MS, and colleagues of the University of California, Berkeley, report on the development and use of an "adaptive optics scanning laser ophthalmoscope." Adaptive optics refers to the use of advanced techniques to correct for optical aberrations through any transparent media. Originally developed for use in telescopes to correct for the distorting effects of the atmosphere, adaptive optics is now being applied to evaluating the structure and function of the human eye.

Dr. Tuten and colleagues have applied adaptive optics to perimetry -- also known as visual field testing -- on the microscopic scale. Perimetry is an important part of evaluation for patients with vision disorders including macular degeneration, retinitis pigmentosa, and diabetic retinopathy. Perimetry measures vision in all parts of the visual field, including the peripheral vision.

Promising Applications to Improve Clinical Vision Care The new paper describes (and illustrates) the use of adaptive optics-guided microperimtery to assess visual fields at an unprecedented level of detail. The technique can not only show limitations in visual fields, but can trace the defect to individual retinal photoreceptor cells. High-speed tracking is used to correct for normal eye movement, or "jitter," that is practically undetectable using conventional imaging techniques.

In addition, by using microscopic blood vessels as anatomical landmarks, the adaptive optics technique permits repeated studies to be repeated over time at a high level of precision. This offers unique opportunities for studying how treatments work on the cellular level, as well as following the effects of treatment over time in individual patients.

"This technique opens new horizons for clinician-scientists, and later clinicians, to better understand, and plot out, the relationships between vision and the retinal photoreceptors at a microscopic level," comments Anthony Adams, OD, PhD, Editor-in-Chief of Optometry and Vision Science. "It enables a new understanding of vision loss in patients with retinal disorders where there are discrete photoreceptor losses -- for example, macular degeneration."

Adaptive optics-guided microperimetery and other advanced imaging technologies described in the special issue have the potential to revolutionize the management of eye diseases, Dr. Read and colleagues believe. They conclude, "With ongoing improvements in imaging speed and resolution, and with the application of innovative methods to improve the clinical usefulness of ocular imaging techniques, the future of ocular imaging is bright!"

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Detecting Glaucoma Before It Blinds

Early detection and diagnosis of open angle Glaucoma important so that treatment can be used in the early stages of the disease developing to prevent or avoid further vision loss. Writing in a forthcoming issue of the International Journal of Medical Engineering and Informatics, researchers in the US have analyzed and ranked the various risk factors for open angle Glaucoma so that patients can be screened at an earlier stage if they are more likely to develop the condition.

Glaucoma is one of the main leading causes of blindness; it is a progressive and irreversible disease. Of the various forms of Glaucoma, open angle Glaucoma (OAG) is the most common and can cause the most damage. Unfortunately, unless a patient is undergoing regular screening from about the age of 40 years because of a family history, it is otherwise difficult to detect until substantial and irreversible vision loss has occurred. Glaucoma is the third leading cause of blindness worldwide and the second leading cause of blindness in the USA.

Now, Duo Zhou and colleagues at the University of Medicine and Dentistry of New Jersey, Newark, have used statistical collinearity analysis to evaluate risk factors for OAG, and logistic regression models to identify a minimum set of such risk factors for prognosis and diagnosis of the disease. Their study was based on more than 400 patients with subtle or severe vision problems who attended hospital. It reveals the relative risk of being a smoker, age, visual "field test" results, presence of a localized notch or thinning of the neuroretinal rim identified during standard eye examination, cup to disk ratio (a measure of restriction of the optic nerve at the back of the eye) and other factors.

The data are complex and separating out predictors from diagnostic factors was difficult, the team admits. However, they suggest that family history, medical history, current medications, geographic location, visual field test and ocular examination must all be considered in diagnosis and prognosis for OAG. They have excluded certain factors from the OAG prognosis: gender, race, family history of Glaucoma, diabetes mellitus, hypercholesterolemia, thyroid disease, migraine, Reynaud's disease and myopia as these have no direct effect on OAG development.

As revealed in the analyses, the odds of developing OAG will be increased by 91% with an increase in the Cup-to-Disc ratio of 0.1. Risk increases by 3% annually by age but decreases by 31% for every dB increase of mean deviation of Humphrey visual field. The odds of developing OAG will be 4.36 higher for patients with abnormal Humphrey visual filed overall test, 7.19 higher in patients with localized notch or thinning of the neuroretinal rim. Interestingly, patients with a smoking history seem to be less likely to develop OAG as compared to those with smoking history; although there are many smokers with OAG. Oddly, because of the location of the study, the team can also say that patients living in Atlantic/Quebec will be 73% less likely to develop OAG compared to their fellow Canadians in Ontario.

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Glaucoma, the silent thief...

When it comes to whether or not you will develop exfoliation syndrome (ES) -- an eye condition that is a leading cause of secondary open-angle glaucoma and increased risk of cataract as well as cataract surgery complications -- age, gender and where you live does matter.

"Although many studies from around the world have reported on the burden of the disease, some aspects of the basic descriptive epidemiologic features, which may help shed light on the cause, are inconsistent," said Louis Pasquale, M.D., study co-author and director of Massachusetts eye and Ear's glaucoma Center of Excellence. "In this study we found that women are more vulnerable to this disease then men, that ES is not a disease of Norwegian descent, and that where you live does matter when it comes to developing the disease."

Researchers from the Mass. eye and Ear, Harvard Medical School, Boston, Mass., Department of Medicine, Channing Laboratory, Brigham and Women's Hospital, Boston, Mass., Department of Ophthalmology and Visual Sciences, and University of Michigan, Ann Arbor, Mich., set out to find out how demographic and geographic risk factors are associated with ES. Their study, the "Demographic and Geographic Features of Exfoliation glaucoma in two United States-Based Prospective Cohorts" is published in the January 2012 issue of Ophthalmology.

Researchers used data from 78,955 women in the Nurses' Health Study (NHS) and 41,191 men in the Health Professionals Follow-up Study (HPFS) residing throughout the continental United States who were prospectively followed for 20 years or more and who provided lifetime residence information to examine the descriptive epidemiologic features of ES or exfoliation glaucoma suspect (EGS).

This study confirmed established associations with age and family history and exfoliation glaucoma or exfoliation glaucoma suspect (EG/EGS), as well as provided new data on associations with gender, eye color and ancestry. "Importantly, those with a lifetime residential history of living in the middle tier and south tier of the United States was associated with 47% and 75% reduced risks, respectively, compared with living in the northern tier, and across the life span, residence at age 15 was the most strongly associated with risk, followed by current residence," the authors wrote.

The study showed an increased risk in females, but it was unclear as if gender-specific differences in the eye, such as axial length differences or environmental factors related to lifestyle, account for why women are more at risk for this disease.

Other findings include:

• A positive family history of glaucoma was associated with a more than doubling of risk.


• Neither Scandinavian decent nor Southern European ancestry was associated with risk when compared with the larger reference group of mainly other white persons in the study, which indicates that there may be strong environmental factors that may increase risk among populations in Scandinavian countries. Overall the study lacked adequate power to determine whether incidence rates differed by minority groups.


• Iris ( eye) color did not seem to be a risk factor.

"This large prospective cohort study demonstrates that there is a positive association between latitude and ES risk that is robust and not related to demographic features or other systemic covariates," Dr. Pasquale explained. "Another manuscript we published recently suggests that lower ambient temperature interacts with increased solar exposure to increase the risk of ES. This new work demonstrates a relation between increasing latitude and a condition with a strong predisposition to glaucoma. More work is needed to determine how environmental factors conspire to contribute to ES."

According to the National eye Institute, ES is the major known cause of open-angle glaucoma, and is one of the leading causes of blindness. With the rapid aging of the U.S. population, the number of individuals affected by the disease will increase to more than three million by 2020.

ScienceDaily (Jan. 1, 2012) —

http://www.sciencedaily.com/releases/2012/01/120101143342.htm

The above story is reprinted from materials provided byMassachusetts Eye and Ear Infirmary.

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