Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Doctors focus on pupil size for safety of laser vision correction

07.05.2003


Exactly how a person’s eyes respond to low levels of light is even more crucial than doctors have thought in deciding who is and who isn’t a good candidate to have laser vision correction surgery, according to results announced today at the annual meeting of the Association for Research in Vision and Ophthalmology in Ft. Lauderdale. The findings should help doctors choose patients who are likely to fare well with the surgery, and to forego recommending treatment for others.


Dr. Scott MacRae taking light measurements along the roadways in Rochester.


Dr. Scott MacRae taking light measurements along the roadways in Rochester



In the earliest days of laser vision correction, some patients complained of worsened night vision after the surgery – some reported significant glare from light sources such as headlights at night, while others saw halos around bright lights. Occasionally, though much more rarely, patients undergoing the procedure still report such side effects.

Ophthalmologist Scott MacRae, M.D., professor of Ophthalmology and Visual Science at the University of Rochester Medical Center, recently studied the role of a patient’s pupil size in determining a patient’s outcome from the surgery. In a study of 340 patients, he found that generally the larger a patient’s pupils, the more likely that person is to have a problem with laser vision correction. MacRae also discussed the results at the recent annual meeting of the Association for Cataract and Refractive Surgery in San Francisco.


“This is not a problem for most people,” says MacRae, “but as the procedure becomes more common, we have to make sure that we remain vigilant to protect and enhance people’s eyesight.”

MacRae is part of a team that has used a technology known as adaptive optics to discover dozens of previously unknown subtle imperfections in the eye, and he has found that those imperfections loom more important as the pupil size gets larger. He reports that if a surgeon treats a large enough swath of the eye for such patients, those imperfections are minimized. His study shows that it’s essential that doctors treating patients with large pupils consider creating an especially large treatment zone.

He found that doctors must be especially careful when using a laser to correct vision on people whose pupils dilate to six millimeters or more, a group that comprises about 40 percent of the population. If physicians treat too small an area of the cornea, patients are likely to have a problem when their eyes are most dilated – at night.

To understand the problem, think of a window washer who should clean an entire window even when the inside blind is partway down. When the blind goes up, a person looking through the window wouldn’t get a clear view unless the previously covered section of the window was washed too. Likewise, MacRae says, surgeons must treat a large part of the cornea so that when the pupil widens, the entire pupil transmits light clearly.

Pupil size is especially critical if a person is extremely near-sighted. MacRae says that generally, people with pupils larger than seven millimeters should be checked very thoroughly before having the surgery done.

MacRae measures every patient’s pupils three different times using three separate instruments. He also makes three measurements of the thickness of the cornea, another crucial element in deciding who is a safe candidate. Overall he advises against surgery in more than 20 percent of patients who inquire about the surgery, especially patients who have large pupils and are extremely nearsighted.

“Oftentimes I’ll have a patient who is initially upset because I won’t treat them, but they become grateful as they realize that we’ve done what is best for them in the long run,” he says. “When the pupil dilates, aberrations can be troubling. You have to be really careful. Patients need to be wary of surgical centers that trivialize these issues.”

In recent months MacRae has taken to driving around Rochester-area roads at night to measure just how much light typically enters a person’s eye, to get a grasp on how wide their pupils are while they’re on the road. He has found that conditions change markedly from one street to the next – information that perhaps won’t surprise drivers but which hasn’t been tapped by ophthalmologists whose patients report night driving as one of their biggest concerns.

“There is tremendous variation, depending on where your eye is looking,” MacRae says. “Country roads can be nearly completely dark, while city streets are often brightly lit.” He found that the amount of light entering a driver’s eye on a country road during a rainy night might be 200 times less than what he or she encounters driving through a busy intersection seconds later. He also found that a typical night driver frequently confronts situations where he or she has less than one-tenth the amount of light that doctors, in their offices, assume their patients encounter at night.

Tom Rickey | EurekAlert!
Further information:
http://www.urmc.rochester.edu/

More articles from Health and Medicine:

nachricht Biofilm discovery suggests new way to prevent dangerous infections
23.05.2017 | University of Texas at Austin

nachricht Another reason to exercise: Burning bone fat -- a key to better bone health
19.05.2017 | University of North Carolina Health Care

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>