Women Have Bigger Pupils Than Men

ScienceDaily (Apr. 26, 2012) - From an anatomical point of view, a normal, non-pathological eye is known as an emmetropic eye, and has been studied very little until now in comparison with myopic and hypermetropic eyes. The results show that healthy emmetropic women have a wider Pupil diameter than men.

Normal, non-pathological emmetropic eyes are the most common type amongst the population (43.2%), with a percentage that swings between 60.6% in children from three to eight years and 29% in those older than 66.

Therefore, a study determines their anatomical pattern so that they serve as a model for comparison with eyes that have refractive defects (myopia, hypermetropia and stigmatism) pathological eyes (such as those that have cataracts).

"We know very little about emmetropic eyes even though they should be used for comparisons with myopic and hypermetropic eyes" Juan Alberto Sanchis-Gimeno, researcher at the University of Valencia and lead author of the study explained.

The project, published in the journal 'Surgical and Radiologic Anatomy' shows the values by gender for the central corneal thickness, minimum total corneal thickness, white to white distance and Pupil diameter in a sample of 379 emmetropic subjects.

"It is the first study that analyses these anatomical indexes in a large sample of healthy emmetropic subjects" Sanchis-Gimeno states. In recent years new technologies have been developed, such as corneal elevation topography, which allows us to increase our understanding of in vivo ocular anatomy.

Although the research states that there are no big differences between most of the parameters analysed, healthy emmetropic women have a wider Pupil diameter than men.

"It will be necessary to investigate as to whether there are differences in the anatomical indexes studied between emmetropic, myopic and hypermetropic eyes, and between populations of different ethnic origin" the researcher concludes.

How the human eye works

Light penetrates through the Pupil, crosses the crystalline lens and is projected onto the retina, where the photoreceptor cells turn it into nerve impulses, and it is transferred through the optic nerve to the brain. Rays of light should refract so that they can penetrate the eye and can be focused on the retina. Most of the refraction occurs in the cornea, which has a fixed curvature.

The Pupil is a dilatable and contractile opening that regulates the amount of light that reaches the retina. The size of the Pupil is controlled by two muscles: the Pupillary sphincter, which closes it, and the Pupillary dilator, which opens it. Its diameter is between 3 and 4.5 millimetres in the human eye, although in the dark it could reach up to between 5 and 9 millimetres.

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Laser's Precision and Simplicity Could Revolutionize Cataract Surgery

 

Two new studies add to the growing body of evidence that a new approach to Cataract surgery may be safer and more efficient than today's standard procedure. The new approach, using a special femtosecond laser, is FDA-approved, but not yet widely available in the United States. It's one of the hottest topics this week at the 115th Annual Meeting of the American Academy of Ophthalmology.

Research reported Oct. 23 by William W. Culbertson, MD, of the Bascom Palmer Eye Institute at the University of Miami School of Medicine, and by Mark Packer, MD, of Oregon Health and Sciences University, confirms several advantages of laser Cataract surgery.

Laser Lens Fragmentation Boost Safety by Reducing Need for Ultrasound

Dr. Culbertson's team studied how pre-treating Cataracts with the femtosecond laser affected the level of ultrasound energy needed to soften the Cataracts. This emulsification is performed so that the Cataracts can be easily suctioned out. Surgeons want to use the lowest possible level of ultrasound energy, since in a small percentage of patients it is associated with slower recovery of good vision after surgery and/or problems with the cornea, which is the clear outer layer of the eye. Ideally, in appropriate cases, ultrasound use would be eliminated altogether.

In Dr. Culbertson's prospective, randomized study, 29 patients had laser Cataract surgery with a femtosecond laser in one eye and the standard Cataract procedure, called phacoemulsification, in the other. Laser surgery included: a laser capsulotomy, which is a circular incision in the lens capsule, followed by laser lens fragmentation, then ultrasound emulsification and aspiration. Lens fragmentation involved using the laser to split the lens into sections and then soften it by etching cross-hatch patterns on its surface. Standard surgery included a manual incision, followed by ultrasound emulsification and aspiration. After Cataract removal by either method, intraocular lenses were inserted into eyes to replace the natural lens and provide appropriate vision correction for each patient.

The use of ultrasound energy use was reduced by 45 percent in the laser pre-treated eyes compared with the eyes that received the standard Cataract surgery procedure. Also, surgical manipulation of the eye was reduced by 45 percent in eyes that received laser pre-treatment as compared to manual standard surgery. This study involved the most common types of Cataracts, those graded 1- 4. Dr. Culbertson notes that these findings may not apply to higher grade cataracts.

"In clinical practice, surgeons would expect safer, faster cataract surgery when laser pre-treatment is performed before cataract removal," said Dr. Culbertson. "The combination of precision and simplification that is possible with the femtosecond laser represents a major advance for this surgery."

Laser Lens Fragmentation Protects Corneal Endothelial Cells

Dr. Packer's team at the Oregon Health and Sciences University in Portland, Oregon, assessed the safety of laser cataract surgery in terms of loss of corneal endothelial cells, as measured after cataract surgery. Measuring endothelial cell loss is one of the most important ways to assess the safety of new cataract surgery techniques and technology. These cells preserve the cornea's clarity, and since they don't regenerate, they must last a lifetime. Dr. Packer's study found that when laser lens fragmentation was used in 225 eyes, there was no loss of endothelial cells, while the 63 eyes that received standard treatment had cell loss of one to seven percent.

"Our finding, that laser lens fragmentation appears to protect corneal endothelial cells, represents a significant benefit of this new surgery," said Dr. Packer. "This procedure is safer than standard cataract treatment and is likely to mean better vision and fewer eye health concerns for cataract patients, over the long term."

Earlier studies of femtosecond laser cataract surgery found other benefits. The laser allows the surgeon to make smaller, more precise incisions and to perform improved capsulotomies, which is the removal of part of the lens capsule that make intraocular lens (IOL) placement more secure. This reduces the chance that an IOL will later become displaced. Also, laser cataract surgery appears to improve results in patients who opt for advanced technology IOLs, plus corrective corneal incisions, to achieve good all-distance vision.

Femtosecond lasers have been used by ophthalmologists for years in refractive surgery such as LASIK, in-corneal transplants, and in other procedures. In 2009, a new type of femtosecond laser that could reach deep enough into the eye to be used in cataract removal was approved by the FDA. In addition to Dr. Culbertson's and Dr. Packer's presentations, key sessions on the topic at the Academy's 2011 Annual Meeting include a special session in the Sunday afternoon program, Spotlight on Femtosecond-Assisted Cataract Surgery: The Tough Questions, Femtosecond Laser Cataract Surgery: the Future,a video presentation,and two new instruction courses.

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The Pupils Are the Windows to the Mind

The eyes are the window into the soul -- or at least the mind, according to a new paper published in Perspectives on Psychological Science, a journal of the Association for Psychological Science. Measuring the diameter of the Pupil, the part of the eye that changes size to let in more light, can show what a person is paying attention to. Pupillometry, as it's called, has been used in social psychology, clinical psychology, humans, animals, children, infants -- and it should be used even more, the authors say.

The Pupil is best known for changing size in reaction to light. In a dark room, your Pupils open wide to let in more light; as soon as you step outside into the sunlight, the Pupils shrink to pinpricks. This keeps the retina at the back of the eye from being overwhelmed by bright light. Something similar happens in response to psychological stimuli, says Bruno Laeng of the University of Oslo, who cowrote the paper with Sylvain Sirois of Université du Québec à Trois-Rivières and Gustaf Gredebäck of Uppsala University in Sweden. When someone sees something they want to pay closer attention to, the Pupil enlarges. It's not clear why this happens, Laeng says. "One idea is that, by essentially enlarging the field of the visual input, it's beneficial to visual exploration," he says.

However it works, psychological scientists can use the fact that people's Pupils widen when they see something they're interested in.

Laeng has used Pupil size to study people who had damage to the hippocampus, which usually causes very severe amnesia. Normally, if you show one of these patients a series of pictures, then take a short break, then show them another series of pictures, they don't know which ones they've seen before and which ones are new. But Laeng measured patients' pupils while they did this test and found that the patients did actually respond differently to the pictures they had seen before. "In a way, this is good news, because it shows that some of the brains of these patients, unknown to themselves, is actually capable of making the distinction," he says.

Pupil measurement might also be useful for studying babies. Tiny infants can't tell you what they're paying attention to. "Developmental psychologists have used all kinds of methods to get this information without using language," Laeng says. Seeing what babies are interested in can give clues to what they're able to recognize -- different shapes or sounds, for example. A researcher might show a child two images side by side and see which one they look at for longer. Measuring the size of a baby's pupils could do the same without needing a comparison.

The technology already exists for measuring pupils -- many modern psychology studies use eye-tracking technology, for example, to see what a subject is looking at, and Laeng and his coauthors hope to convince other psychological scientists to use this method.

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Contact Lenses Provide Extended Pain Relief to Laser Eye Surgery Patients

Scientists are reporting development of Contact lenses that could provide a continuous supply of anesthetic medication to the eyes of patients who undergo laser eye surgery -- an advance that could relieve patients of the burden of repeatedly placing drops of medicine into their eyes every few hours for several days.Their report appears in ACS' journal Langmuir

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Anuj Chauhan and colleagues explain that more than 1 million laser eye correction procedures are performed each year in the U.S. The surgery enables most patients to see clearly without eye glasses or Contact lenses. The procedure known as LASIK is the most common type of laser eye surgery, but complications can develop if the patient undergoes trauma or is hit very hard at any time after the procedure. Photorefractive keratectomy (PRK) doesn't have this complication, and that's why it is preferred for athletes and those in the military. A downside to PRK, however, is a longer period of pain after surgery. To ease their pain, PRK patients place drops of several medications, including anesthetics, into their eyes every few hours, which can interfere with daily life and increase the risk of drug overdose. PRK patients receive a special "bandage Contact lens" after surgery to help the outer layer of the eye heal.

The researchers tested whether anesthetics loaded onto this type of lens could release the drugs over time automatically. They found that adding vitamin E to the lenses extended the time of release of three commonly used anesthetics from just under two hours to up to an entire day -- or a few days in some instances. The vitamin E acts as a barrier, keeping the anesthetics on the eye, right where they are needed. The researchers say that, in the future, these lenses could serve as bandage Contact lenses after PRK surgery while also delivering necessary pain medications.

The authors acknowledge funding from the University of Florida.

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New Light Shed On How Retina's Hardware Is Used in Color Vision

Biologists at New York University and the University of Würzburg have identified, in greater detail, how the Retina's cellular hardware is used in color preference. The findings, published in the latest issue of the Proceedings of the National Academy of Sciences (PNAS), enhance our understanding of how eyes and the brain process color.

Light can serve as an attractive or repulsive landmark for orientation -- we identify an object or a light source at a certain location in visual space, then approach it or retreat from it. This process, called phototaxis, was the focus of the PNAS study.

Conducted by biologists at New York University's Center for Developmental Genetics and the Department of Genetics and Neurobiology at the University of Würzburg in Germany, the research specifically examined the photoreceptor cells in the Retinas of the fruit fly Drosophila. Drosophila is a powerful model for studying the color vision process as it is amenable to very specific genetic manipulations, allowing researchers to analyze how its visual system functions when different elements of its Retina are affected.

The visual systems of most species contain photoreceptors with distinct spectral sensitivities that allow animals to distinguish lights by their spectral composition (i.e., color). In Drosophila, six of these (R1-R6) are responsible for motion detection and are sensitive to the brightness or dimness of a broad spectrum of light. Two others (R7 and R8) are used for color vision by comparing ultraviolet light (UV), detected by R7, with green or blue light detected by two types of R8. The NYU and University of Würzburg biologists investigated how photoreceptor types contribute to phototaxis by blocking the function of either R7 or R8, or a combination of a range of photoreceptors (R1-R6, R7 and/or R8).

In the study, they constructed two sets of "Y-shaped mazes" with two different types of light at the ends of each: UV and blue in one and blue and green in the other. Under this arrangement, the fly would show a preference for certain type of light (UV vs. blue in one maze; blue vs. green in the other) by moving toward it. The researchers could then link specific preferences to the make-up of each fly's visual system.

In a "UV vs. blue" choice, flies with only R1-R6 and flies with only R7/R8 photoreceptors preferred the blue to the UV light. This finding suggested that these two sets of photoreceptors (R1-R6 and R7/R8) function separately in phototaxis as flies with only one of these sets showed similar preferences. In addition, flies without a functioning R7 photoreceptor preferred the blue to the UV light, whereas flies without R8 preferred UV. In the "blue vs. green" maze, flies without a functioning blue R8 photoreceptor preferred green, whereas those with a defective for green R8 photoreceptor preferred blue. This shows that each subclass of photoreceptors [R1-R6, R7, R8 (blue), R8 (green)] is used by the fly to distinguish colors and setup its innate color preference. In a previous work, the same authors had shown that motion detection only involves R1-R6 and not R7 and R8, suggesting that there are two independent channels in the fly visual system -- one for motion and one for color.

"This simple insect can achieve sophisticated color discrimination and detect a broader spectrum of colors than we can, especially in the UV," said NYU biologist Claude Desplan, one of the study's authors. "It is a great model system to understand how the Retina and the brain process visual information.

The research was supported by a grant from the National Institutes of Health.

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