Epi-LASIK favored over tPRK for myopia treatment

Better predictability, less induced corneal spherical aberration occur in findings

By Cheryl Guttman Reviewed by Osamu Hieda, MD

San Francisco—Treatment of low-to-high myopia with transepithelial PRK (tPRK) has poorer predictability and results in greater induction of corneal spherical aberration compared with epi-LASIK, reported Osamu Hieda, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery. Dr. Hieda and his colleague Shigeru Kinoshita, MD, department of ophthalmology, Kyoto Prefectural University of Medicine, Kyoto, Japan, compared the two surface ablation procedures in two groups of 19 eyes each based on data collected at 6 months postoperatively and using multiple linear regression analysis.

The tPRK was performed using the EC-5000 Flexscan (Nidek) epithelial laser scraping technique and epi-LASIK was performed using the Epi-Lift (Gebauer) and EC-5000 laser. Predictor for outcome The results showed the type of surgery was a significant predictor for refractive outcome with overcorrection more likely in the tPRK eyes. With both techniques, there was a significant correlation between attempted spherical equivalent reduction and induced fourth-order corneal aberration, such that higher corrections were associated with greater increases in spherical aberration. However, the multiple regression analysis showed type of surgery was also a significant predictor of induced corneal spherical aberration with tPRK resulting in an approximate 0.2 im greater increase at all levels of correction compared with epi-LASIK.

"These findings were consistent with the hypotheses we established before undertaking this study," Dr. Hieda said. "In tPRK with the Flex-scan, the cornea is not ablated to an equal depth from the center to the periphery due to inconsistencies in epithelial thickness across the cornea. Flexscan also has the effect of myopic overcorrection. Eor these reasons, that technique leaves residual epithelial cells in the corneal periphery that lead to a decrease in optical zone diameter, overcorrection, and greater induction of corneal spherical aberration." The eyes in the two study groups were matched for attempted correction. Mean preoperative sphere and cylinder values in the epi-LASIK eyes were -5.78 and -0.67 D, respectively, and were -6.35 and -0.74 D in the tPRK eyes, respectively. There were also no significant differences between groups in gender distribution (about 60% female) or laterality.

However, the epi-LASIK group was significantly older than the patients in the tPRK group (mean 33 versus 26 years) and had a greater mean corneal thickness (548 versus 517 pm), A 9-mm epithelial flap was raised in the epi-LASIK procedures. The tPRK procedure used a 45-im deep, 8- to 8.5-mm epithelial laser scrape. All surgeries were performed using the same treatment nomogram (93% X sphere) and same ablation profile (OATZ Mo. 6; 4.5-mm optical zone, 8-mm transition zone), Corneal wavefront analysis was performed using the OPD-Scan (Nidek) at a 6-mm zone for up to sixthorder Zernike polynomials. To illustrate the differential effect of the two surgeries. Dr. Hieda presented wavefront maps from both eyes of a single patient who underwent tPRK in the left eye and epi-LASIK contralaterally for identical preoperative refractions. At 6 months after the surgery, ocular higher-order aberrations were 0.31 pm in the epi-LASIK eye and 1 im in the tPRK eye (Figure 1). "The difference could be explained in part by the fact that epi-LASIK induced less corneal spherical aberration," Dr. Hieda said

Ophthalmology Times, 9/15/2006

Of fetal testing and libido boosters

• Scientists at Xenomics have discovered a way to detect possible genetic diseases in a fetus by screening the mother's urine. In some chromosomal disorders, such as Gaucher's disease and Down syndrome, key pieces of fetal DNA pass through the mom's kidneys. The company is developing tests that can detect disease telltales at seven weeks, six sooner than today's more invasive procedures, and can also reveal the gender.


• In the British Journal of Ophthalmology, researchers at the University of Alabama at Birmingham reaffirmed the link between vision problems and erectile dysfunction drugs. They studied men who had histories of heart trouble, and found that those who had taken Viagra or Cialis were 10 times as likely to have optic nerve damage as those who had not.


• For women, meanwhile, caffeine may offer a natural boost to the libido. Scientists at Southwestern University in Georgetown, Tex., found that female rats were more interested in sex after a dose of caffeine, according to Pharmacology Biochemistry and Behavior. In the test, females returned for second encounters with males more quickly if they had received a moderate amount of the stimulant. The researchers are planning further studies to assess the effects of repeated exposure to caffeine.

The McGraw-Hill Companies, Copyright 2006

The world in focus

If you have faulty eyesight, getting it corrected is relatively straightforward — assuming you live in the developed world. But in poorer countries the network of optometrists, ophthalmologists and glasses makers is either inadequate or non-existent. In parts of sub-Saharan Africa, there is one optometrist to every million people, compared with one to every 4000 in the UK. People there have little choice but to make do with poor vision, and all the social and economic consequences that brings.

Hundreds of millions of people worldwide are visually impaired. Only a fraction of them receive vision correction, though, and most of those are in the developed world. Physicist Joshua Silver is trying to do something about it. While playing around with adjustable lenses one day, he discovered that he could correct his own slight near-sightedness, and that gave him an idea.

Silver set up a company to produce low-cost adjustable spectacles that can correct the vision of both far-sighted and near-sighted people. Now that the spectacles have been trialled in Africa and Asia, Silver tells Justin Mullins how they could help up to a billion people with vision problems in the developing world — and how atomic physics led him to the idea

How does an atomic physicist get involved in vision correction?
I have a habit of developing little bits of technology that interest me. I came to vision correction while playing around with certain types of lenses and mirrors that have the particular feature that you can change their power easily.

But what have lenses got to do with atomic physics?
Atomic physicists use light to study the properties of atoms, so we need optical elements such as mirrors and lenses. Optics is an integral part of experimental atomic physics.

How do these lenses work?
Each lens is a fluid-filled chamber bounded by a thin, clear plastic membrane. By changing the amount of fluid in the chamber, you change the curvature of the membrane. So what you have is a lens with variable power.

It's one thing playing around with variable-power lenses. It's quite another turning them into spectacles. How did that happen?
I'm slightly myopic. I need my vision corrected by about a dioptre and a half in each eye — a dioptre is a unit of measurement of the power of a lens. I found that if I looked through the lens I had made and changed the power, I could accurately correct my own vision. That made me think that this could be a way for other people to do the same.

It also made me wonder how many people there are in the world who need vision correction and don't have it.

How many are there?
In 1994 I met up with Björn Thylefors, an ophthalmologist who was, at that time, director of the World Health Organization's blindness prevention programme in Geneva. He said the number was about a billion. In our first conversation, I somewhat arrogantly told him that I thought I had a method which could deal with that problem. He said to me, "If you can do that, you should." And that set me off.

How do you correct the vision of so many people?
In the developed world, you go to an optometrist to get a prescription, the prescription is made up into a pair of glasses, and off you go. But that requires an infrastructure and a relatively large number of trained professionals. There is something like one optometrist for every 4000 people in the UK, for instance. In some countries in sub-Saharan Africa, the ratio is one optometrist to a million people. In Mali it's one to 8 million people. You could try to create more professionals, but it's very hard to do that. It would cost a fortune, and the infrastructure is not there for them to slot into. Another problem is that when you train professionals in developing countries, they often emigrate.

What's your plan?
My plan is very simple. If you can make a device that is relatively inexpensive to manufacture and can be self-administered, then you cut out the middleman and the bottleneck in treatment. That is what the adaptive spectacles are all about. My company, Adaptive Eyecare, now has a production line in China that makes these spectacles.

Who is using your glasses?
We've delivered 10,000 pairs to Ghana, which are being given out as part of an adult literacy programme. In Ghana, people were being taught to recognise words in large letters on a blackboard in the classroom, but weren't being given vision correction, and so couldn't read most types of print when they got home. Our spectacles solved that problem.

So if you are sitting in a classroom in Ghana and you are given a pair of adaptive spectacles, how do you correct your own vision?
The amount of fluid in the lens, and hence its curvature, is controlled by a removable syringe. Initially you set the spectacles so that they are at a high power compared to the power you actually need. You cover one eye and look, ideally, at an eye test chart, although other objects can work — such as the leaves on a nearby tree. Then you gradually change the power of that lens until your vision is at its sharpest, and repeat for the other eye. The whole process takes less than a minute. Then you set the lenses and discard the syringe. If you follow the protocol correctly, you should end up with accurately corrected vision.

How accurately can people correct their vision?
The evidence we have so far is that people can self-correct to about the same accuracy as if they were corrected by an optician. The glasses can't correct every type of vision error — they can't correct astigmatism, for instance — but they should work for more than 90 per cent of people requiring correction.

And the cost?
We think that a few days' income is an affordable target, and that varies from country to country. But it means that we need to be able to mass-manufacture the device at a cost in the region of one US dollar or so. Most modern ophthalmic lenses — even very high-quality ones — cost around a dollar, and we've got to be competitive with that. I'm sure we can be. But you've got to remember that there are other costs related to the manufacturing process that have to be taken into account, which makes it complex to calculate the price for the end-user.

How long before you achieve your goal of adaptive spectacles for all who need them?
The WHO has set a target of getting vision correction to most people who need it by 2020. If we've made a significant dent in that number by then, I think we will have achieved our goal.

"People can self-correct as well as if they were treated by an optician"

Profile
Joshua Silver is an atomic physicist at the University of Oxford who studies highly charged ions. He began his work on low-cost spectacles in the mid-1990s. His company, Adaptive Eyecare, is now supplying adaptive spectacles to the developing world (see www.adaptive-eyecare.com).

By: Mullins, Justin, New Scientist

Best Hospitals

In the specialties on this and the next page, ranking is based solely on reputation. Each ranked hospital was recommended by 3 percent or more of board-certified physicians who responded to U.S. News surveys in 2003, 2004, and 2005.

Chart Legend:
A - Rank
B - Hospital
C - Reputation (pct.)

A B
C

1 Bascom Palmer Eye Institute, Miami -
South 76.8

2 Wilmer Eye Institute, Johns Hopkins Hospital, Baltimore -
South 74.4

3 Wills Eye Hospital, Philadelphia -
Northeast 63.1

4 Massachusetts Eye and Ear Infirmary, Boston -
Northeast 41.3

5 Jules Stein Eye Institute, UCLA Medical Center, Los Angeles -
West 34.7

6 University of Iowa Hospitals and Clinics, Iowa City -
Midwest 21.9

7 Doheny Eye Institute, USC University Hospital, Los Angeles -
West 17.6

8 Duke University Medical Center, Durham, N.C. -
South 14.3

9 New York-Presbyterian Univ. Hosp. of Columbia and Cornell -
Northeast 7.7

10 University of California, San Francisco Medical Center -
West 7.6

11 Barnes-Jewish Hospital/Washington University, St. Louis -
Midwest 7.2

12 New York Eye and Ear Infirmary -
Northeast 7.1

13 Mayo Clinic, Rochester, Minn. -
Midwest 6.5

14 Cullen Eye Institute, Methodist Hospital, Houston -
South 6.0

15 Cleveland Clinic
Midwest 5.7

16 University of Michigan Medical Center, Ann Arbor -
Midwest 5.6

17 Emory University Hospital, Atlanta -
South 3.4

18 Manhattan Eye, Ear, and Throat Hospital, New York -
Northeast 3.3

Note: Rounding may produce apparent ties.

Glossary
Regions
Northeast: Conn., Maine, Mass., N.H., N.J., N.Y., Pa., R.I., Vt.

South: Ala., Ark., D.C., Del., Fla., Ga., Ky., La., Md., Miss., N.C., Okla., S.C., Tenn., Texas, Va., W.Va.

Midwest: Ill., Ind., Iowa, Kan., Mich., Minn., Mo., N.D., Neb., Ohio, S.D., Wis.

West: Alaska, Ariz., Calif., Colo., Hawaii, Idaho, Mont., Nev., N.M., Ore., Utah, Wash., Wyo.

U.S. News Score
Summarizes quality of inpatient care. Reputation and mortality each make up one third of the score. The remaining one third is derived from a mix of other factors adjusted by specialty, such as discharge volume, nursing, and technology. The top hospital in a specialty is scored at 100. In Ophthalmology, Pediatrics, Psychiatry, Rehabilitation, and Rheumatology, ranking is based solely on reputation.

Reputation (pct.)
Percentage of responding board-certified physicians surveyed by U.S. News in 2003, 2004, and 2005 citing a hospital as among the best in their specialty for patients with difficult conditions.

Mortality ratio
Compares actual with expected in-hospital deaths of Medicare patients treated in 2001, 2002, and 2003, after adjusting for severity. A ratio of 1.00 means the rates of actual and expected deaths are the same. Above 1.00 is worse than expected; below 1.00 is better. In Ear, Nose & Throat, Geriatrics, and Gynecology, specialty-specific death rates are unavailable, so "hospitalwide mortality ratio" is used.

Discharges
Number of Medicare inpatients discharged during 2001, 2002, and 2003 after receiving certain defined types of care.

Nurse/patient index

A ratio indicating the balance of nurses to patients. Higher is better. Nurses must be R.N.'s and on staff, not pro-vided by agencies or other outside sources. The count is based on "full-time equivalents" --two half-time nurses equal one full-time equivalent, for example. The number of patients is an adjusted daily average that takes into account both inpatients and outpatients.

Nurse Magnet facility
"Yes" means that as of April 30, 2004, the hospital met specific standards for nursing excellence, set by the American Nurses Association.

Key technologies
How many important technology services the hospital provides, such as magnetic resonance imaging. The maximum number varies by specialty from 3 to 9. Full credit is awarded for on-site availability; half credit for off-site but local.

Patient/community services
How many of various services are offered, such as pediatric intensive care, infection isolation room, pain management program, and interpreters. The maximum number varies by specialty.

Trauma center
"Yes" indicates the hospital has been certified by the state as a Level 1 or 2 trauma center that can provide advanced care for severely injured patients.

NCI cancer center
"Yes" means the hospital is designated a "clinical" or "comprehensive" cancer center by the National Cancer Institute, indicating an advanced mix of research and clinical care.

Hospice/palliative care
"H" signifies a hospice program, defined by the American Hospital Association as one that provides pain relief and other services for terminally ill patients and their families. "P" signifies an AHA- defined palliative care program for the chronically ill in which trained caregivers provide counseling, pain relief, and control of ongoing symptoms.

Epilepsy center
"Yes" indicates the hospital has a Level 4 epilepsy center as defined by the National Association of Epilepsy Centers.

Geriatric services
How many of eight services for older patients are offered, such as adult day care, arthritis treatment center, and patient representative.

Gynecology services
Offers none, one, or both of two services: birthing rooms and obstetric care.

Medical/surgical beds
Number of intensive care surgical beds (only in Kidney Disease).

U.S. News & World Report, L.P.