Do Large Pupils Cause Problems After LASIK?

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Posted on 8th January 2014 by Pacific ClearVision Institute in General |LASIK

It’s been suggested that people with large pupils have a greater risk of glare and halos around lights at night after LASIK surgery than people with normal-sized pupils. But is that really true?

In a study published this month in Journal of Refractive Surgery, researchers analyzed 19 studies published in peer-reviewed journals since 2002 that investigated the effect of pupil size on LASIK outcomes.

None of the reviewed studies showed a correlation between pre-operative pupil size and persistent night vision complaints after LASIK surgery when the surgical ablation zone (the area of the cornea that’s reshaped by the laser) was 6.0 mm in diameter or larger and the follow-up period was at least three months.

Studies that did find a correlation between pupil size and night vision complaints after LASIK included patients with ablations smaller than 6.0 mm or did not specify ablation size. Studies with mixed conclusions either followed patients for fewer than three months or found that patients showed an improvement in night vision over time.

The researchers concluded that in these studies, patients with large pupils did not appear to have an increased risk of night vision problems after modern LASIK surgery (which typically involves a laser ablation zone of 6.0 mm or larger), when compared with patients with smaller pupils and when patients were examined after a follow-up period of three months or longer.

New Gene Test Could Help LASIK Candidates Avoid Certain Complications

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Posted on 2nd July 2013 by Pacific ClearVision Institute in General |LASIK

Why are some people bad candidates for LASIK? Because they have a genetic condition called Avellino corneal dystrophy (ACD), which causes the development of white or grayish granular deposits in the cornea.

Normally these spots develop slowly, over many years, causing a gradual clouding of vision. But LASIK surgery can worsen the density of the cloudiness to the point of severely diminished vision.

A new gene test offered by Avellino Laboratory USA may be crucial in identifying people who carry the ACD gene and therefore should not receive LASIK. According to a study that was published in Ophthalmic Epidemiology, one out of every 870 people is at risk of carrying the gene.

Often people with ACD do develop the small white spots in time to be disqualified by their LASIK surgeon. But for those who don’t yet have any spots in their cornea, the Avellino-GENE Detection System (AGDS) Test offers a safe way to discover if they carry the gene.

The AGDS Test involves a cheek swab that is sent to Avellino Lab USA for testing. Results are available in a couple of days. Typically the test costs around $100, though some clinics include it in the overall cost for LASIK surgery. It is not covered by insurance, but people can use their Flex Spending Accounts to pay for it.

‘OK’ Contact Lenses Work by Flattening Front of Cornea, Not the Entire Cornea

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Posted on 18th March 2013 by Pacific ClearVision Institute in General |LASIK

A contact lens technique called overnight orthokeratology (OK) brings rapid improvement in vision for nearsighted patients. Now a new study shows that OK treatment works mainly by flattening the front of the cornea, reports a recent study, “Posterior Corneal Shape Changes in Myopic Overnight Orthokeratology,” appearing in the March issue of Optometry and Vision Science.

“This study appears to show that it is only, or primarily, the very front surface layers of the cornea that are altered by OK contact lens treatment,” comments Anthony Adams, OD, PhD, Editor-in-Chief of Optometry and Vision Science. The study was performed by Jeong Ho Yoon, PhD, of University of Choonhae Health Science, Ulsan, Republic of Korea, and Helen A. Swarbick, PhD, FAAO, of University of New South Wales, Sydney, Australia.

Overnight Orthokeratology Works — But How?

Orthokeratology is a clinical technique to reduce nearsightedness (myopia) using specially designed rigid contact lenses to manipulate the shape of the cornea — the transparent front part that lets light into the eye. Dr Adams likens OK therapy to orthodontic treatment using braces to change the alignment of the teeth.

He explains “Wearing these lenses overnight for about six hours is currently the treatment approach for most clinicians who use OK for the temporary correction of low to moderate myopia.” But it has been unclear exactly how OK works to reduce myopia: Do the contact lenses reshape just the front surface of the cornea, or do they bend and flatten the entire cornea?

To find out, Drs Yoon and Swarbick had 18 young adults with “low” (relatively mild) myopia wear OK lenses overnight for 14 days. Using sophisticated techniques, the researchers made detailed measurements of corneal shape and thickness before, during, and after treatment.

As in previous studies, wearing OK contact lenses led to reduced myopia, thus improving vision. The changes were significant after the first night wearing OK lenses, By 14 days, myopia was almost completely eliminated and the participants had near-normal uncorrected (without glasses) visual acuity.

Results ‘Achieved Primarily through Remodeling of Anterior Cornea’

These changes were linked to significant flattening of the anterior (front) portion of the cornea. Like the vision changes, the change in corneal shape was significant after the first night wearing OK lenses. Although corneal flattening continued throughout the 14-day treatment period, about 80 percent of the change occurred in the first four days.

In contrast, OK lenses caused only a small and temporary change in the shape of the posterior (rear) cornea, and only slight thinning of the central cornea. “Overall, our results support the current hypothesis that the OK refractive effect is achieved primarily through remodeling of the anterior corneal layers, without overall corneal bending,” according to Drs Yoon and Swarbick.

Overnight OK contact lenses provide an effective treatment for relatively mild myopia. It requires custom-made rigid contact lenses designed to accommodate the shape and desired change of the patient’s eye. While OK lenses provide an alternative to LASIK surgery for correction of myopia, the patient must continue nightly contact lens wear to maintain the improvement.

The authors hope their results “will provide a more complete picture of overall corneal changes during myopic OK.” In particular, the study demonstrates that overnight OK lenses don’t change the curvature of the posterior cornea — “at least in the first two weeks of lens wear.”

Accelerated Corneal Crosslinking Procedure Receives CE Approval; Designed to Strengthen Eye Surface After LASIK

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Posted on 28th January 2013 by Pacific ClearVision Institute in General |LASIK

A procedure called Lasik Xtra, which is designed to strengthen the cornea after LASIK, has received CE approval for marketing in the European Union. It was just approved in Canada as well.

Marketed by Avedro, Inc., Lasik Xtra is a corneal crosslinking procedure that applies the company’s VibeX riboflavin ophthalmic solution to the eye’s surface (cornea), and then uses Avedro’s KXL System to irradiate the cornea with UV-A rays. Lasik Xtra is an accelerated form of crosslinking — Avedro says it takes two minutes — which makes it more convenient to combine with LASIK.

Avedro said that in April it will report on studies that show the procedure has helped people who received hyperopic LASIK, which tends to regress more than myopic LASIK, to maintain the vision correction they had received from LASIK.

Although corneal crosslinking has not received FDA approval yet, Avedro’s VibeX solution has received orphan drug approvals from the agency. Orphan drug status is usually conferred on treatments for rare medical conditions (in this case, keratoconus, which is a gradual thinning of the cornea).

Super Glue: Tests Show That Adhesive Could Improve Safety of LASIK Eye Surgery

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Posted on 2nd October 2012 by Pacific ClearVision Institute in LASIK

Kansas State University researchers have developed a glue mixture that may reduce risks after laser vision correction surgery.

Stacy Littlechild, a recent bachelor’s degree graduate in biology originally from Wakeeney, is the lead author of two studies that describe a new protocol involving fibrinogen, riboflavin and ultraviolet light that could improve the safety of the corrective surgery.

One study that demonstrates the ability of a glue to bind corneal surfaces has been published in the June edition of the journal Investigative Ophthalmology & Visual Science, or IOVS. Another study details the molecular mechanisms of how the glue creates adhesion and also will be published in IOVS.

LASIK, or laser-assisted in-situ keratomileusis, surgery uses a laser to reshape the cornea, the eye’s outer layer that helps the eye focus. Many patients have the surgery so they do not have to depend on glasses or contact lenses.

During the procedure, a flap is cut in the cornea so that a laser can remove corneal tissue. The hinged flap is returned to its original position and is held on to the laser-modified cornea with nothing but surface tension.

The cornea has a limited ability to firmly re-adhere the LASIK flap and does not fully heal after the procedure, said Gary Conrad, university distinguished professor in the Division of Biology. Conrad, the principal investigator of the research, studies eye development and was Littlechild’s adviser.

“Although LASIK produces a flap that remains clear and normally lays smoothly on the modified corneal surface, if the eye is hit with blunt force trauma — from an auto airbag or a tennis ball, for example — the flap simply peels open again, resulting in contamination inside the cornea and requiring immediate medical attention, which can include corneal transplantation,” he said.

Cornea transplantation replaces part of the cornea with cornea tissue from a donor and is the most common type of organ transplantation in the U.S. Rejection occurs in about 20 percent of cornea transplants, according to the Mayo Clinic.

“Although a cornea transplant is a routine outpatient procedure, we need to do everything we can to avoid such a transplant,” Littlechild said. “These patients are in pain, out of work and can’t see for a few days afterward. If we can decrease the need for transplants by using a glue, then we won’t impede lives as much and protect patients from having future surgeries.”

In the first study, Littlechild tested the glue using corneas removed from dogfish sharks and rabbits to measure adhesive strength.

She discovered that using glue made from fibrinogen and riboflavin and then binding proteins and glue together using ultraviolet light — the type used in tanning salons — provided the best adhesion to keep the cornea’s flap in place. The substance is a nontoxic biodegradable glue that is used in cataract surgery and does not leave a cloudy scar.

“The idea is that if you use the glue, you’ll either reduce or alleviate the risk associated with LASIK surgery,” Littlechild said. “The hope is that you would never have to worry about needing a transplant later.”

In a second study, Littlechild analyzed specific molecular interactions that are responsible for the adhesion. She found that both covalent and zinc-mediated non-covalent mechanisms contributed to the adhesion.

The finding could prompt further development of the glue and could reveal alternative uses throughout the body, Littlechild said. The glue has the potential to bond other body tissues that are similar in chemical and molecular composition to the cornea.

For instance, tendon tissue that connects muscle to bone is similar to the cornea. Tendon tissue often heals slowly because it does not have many blood vessels; likewise, the cornea does not have any blood vessels.

Other collaborators in the research include Gage Brummer, a senior in biochemistry and premedicine, Prairie Village; John Tomich, professor of biochemistry; and Yuntao Zhang, research assistant professor of biology. Scott McCall, a May 2010 bachelor’s graduate in biochemistry, was the lead author on a related study detailing the effects of riboflavin and ultraviolet light used for strengthening the cornea connective tissue to treat keratoconus, the second-most frequent symptom requiring corneal transplantation.

Research funding came from the Maine IDeA Network for Biomedical Research Excellence in support of work at the Mount Desert Island Biological Laboratory in Salisbury Cove, Maine; the Kansas State University Johnson Cancer Research Center; Kansas IDeA Network for Biomedical Research Excellence; National Center for Research Resources; and the National Eye Institute of the National Institutes of Health.

Littlechild plans to attend Cardiff University in Wales, Great Britain, to earn a doctorate in biophysics. Littlechild presented posters at two annual ophthalmology meetings that led to the invitation to continue her research at Cardiff.

“I would not be where I am today without Kansas State University and Dr. Conrad’s continued support and patience,” said Littlechild, who originally applied for a student office job in the Division of Biology until she received a phone call from Conrad. “I owe my undergraduate success and everything that develops from it to Dr. Conrad’s unfailing efforts.”

Super Glue: Tests Show That Adhesive Could Improve Safety of LASIK Eye Surgery

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Posted on 28th August 2012 by Pacific ClearVision Institute in LASIK

Kansas State University researchers have developed a glue mixture that may reduce risks after laser vision correction surgery.

Stacy Littlechild, a recent bachelor’s degree graduate in biology originally from Wakeeney, is the lead author of two studies that describe a new protocol involving fibrinogen, riboflavin and ultraviolet light that could improve the safety of the corrective surgery.

One study that demonstrates the ability of a glue to bind corneal surfaces has been published in the June edition of the journal Investigative Ophthalmology & Visual Science, or IOVS. Another study details the molecular mechanisms of how the glue creates adhesion and also will be published in IOVS.

LASIK, or laser-assisted in-situ keratomileusis, surgery uses a laser to reshape the cornea, the eye’s outer layer that helps the eye focus. Many patients have the surgery so they do not have to depend on glasses or contact lenses.

During the procedure, a flap is cut in the cornea so that a laser can remove corneal tissue. The hinged flap is returned to its original position and is held on to the laser-modified cornea with nothing but surface tension.

The cornea has a limited ability to firmly re-adhere the LASIK flap and does not fully heal after the procedure, said Gary Conrad, university distinguished professor in the Division of Biology. Conrad, the principal investigator of the research, studies eye development and was Littlechild’s adviser.

“Although LASIK produces a flap that remains clear and normally lays smoothly on the modified corneal surface, if the eye is hit with blunt force trauma — from an auto airbag or a tennis ball, for example — the flap simply peels open again, resulting in contamination inside the cornea and requiring immediate medical attention, which can include corneal transplantation,” he said.

Cornea transplantation replaces part of the cornea with cornea tissue from a donor and is the most common type of organ transplantation in the U.S. Rejection occurs in about 20 percent of cornea transplants, according to the Mayo Clinic.

“Although a cornea transplant is a routine outpatient procedure, we need to do everything we can to avoid such a transplant,” Littlechild said. “These patients are in pain, out of work and can’t see for a few days afterward. If we can decrease the need for transplants by using a glue, then we won’t impede lives as much and protect patients from having future surgeries.”

In the first study, Littlechild tested the glue using corneas removed from dogfish sharks and rabbits to measure adhesive strength.

She discovered that using glue made from fibrinogen and riboflavin and then binding proteins and glue together using ultraviolet light — the type used in tanning salons — provided the best adhesion to keep the cornea’s flap in place. The substance is a nontoxic biodegradable glue that is used in cataract surgery and does not leave a cloudy scar.

“The idea is that if you use the glue, you’ll either reduce or alleviate the risk associated with LASIK surgery,” Littlechild said. “The hope is that you would never have to worry about needing a transplant later.”

In a second study, Littlechild analyzed specific molecular interactions that are responsible for the adhesion. She found that both covalent and zinc-mediated non-covalent mechanisms contributed to the adhesion.

The finding could prompt further development of the glue and could reveal alternative uses throughout the body, Littlechild said. The glue has the potential to bond other body tissues that are similar in chemical and molecular composition to the cornea.

For instance, tendon tissue that connects muscle to bone is similar to the cornea. Tendon tissue often heals slowly because it does not have many blood vessels; likewise, the cornea does not have any blood vessels.

Other collaborators in the research include Gage Brummer, a senior in biochemistry and premedicine, Prairie Village; John Tomich, professor of biochemistry; and Yuntao Zhang, research assistant professor of biology. Scott McCall, a May 2010 bachelor’s graduate in biochemistry, was the lead author on a related study detailing the effects of riboflavin and ultraviolet light used for strengthening the cornea connective tissue to treat keratoconus, the second-most frequent symptom requiring corneal transplantation.

Research funding came from the Maine IDeA Network for Biomedical Research Excellence in support of work at the Mount Desert Island Biological Laboratory in Salisbury Cove, Maine; the Kansas State University Johnson Cancer Research Center; Kansas IDeA Network for Biomedical Research Excellence; National Center for Research Resources; and the National Eye Institute of the National Institutes of Health.

Littlechild plans to attend Cardiff University in Wales, Great Britain, to earn a doctorate in biophysics. Littlechild presented posters at two annual ophthalmology meetings that led to the invitation to continue her research at Cardiff.

“I would not be where I am today without Kansas State University and Dr. Conrad’s continued support and patience,” said Littlechild, who originally applied for a student office job in the Division of Biology until she received a phone call from Conrad. “I owe my undergraduate success and everything that develops from it to Dr. Conrad’s unfailing efforts.”

Accelerated Corneal Crosslinking Procedure Receives CE Approval; Designed to Strengthen Eye Surface After LASIK

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Posted on 4th April 2012 by Pacific ClearVision Institute in General |LASIK

A procedure called Lasik Xtra, which is designed to strengthen the cornea after LASIK, has received CE approval for marketing in the European Union. It was just approved in Canada as well.

Marketed by Avedro, Inc., Lasik Xtra is a corneal crosslinking procedure that applies the company’s VibeX riboflavin ophthalmic solution to the eye’s surface (cornea), and then uses Avedro’s KXL System to irradiate the cornea with UV-A rays. Lasik Xtra is an accelerated form of crosslinking — Avedro says it takes two minutes — which makes it more convenient to combine with LASIK.

Avedro said that in April it will report on studies that show the procedure has helped people who received hyperopic LASIK, which tends to regress more than myopic LASIK, to maintain the vision correction they had received from LASIK.

Although corneal crosslinking has not received FDA approval yet, Avedro’s VibeX solution has received orphan drug approvals from the agency. Orphan drug status is usually conferred on treatments for rare medical conditions (in this case, keratoconus, which is a gradual thinning of the cornea).

Smoking may increase risk of haze after PRK, study says

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Posted on 30th March 2011 by Pacific ClearVision Institute in General |LASIK

Smoking appears to be a risk factor for corneal haze in patients undergoing laser vision correction surgery to treat -5.0 diopters (D) or more of myopia, according to a recent study.

The research was headed by J. Richard Townley, MD, who was clinical director of ophthalmology services at Lackland Air Force Base (San Antonio, Texas) at the time of the study and is now affiliated with Massachusetts Eye & Ear Infirmary in Boston.

Dr. Townley and colleagues conducted a retrospective review of medical charts of more than 25,000 patients who underwent laser vision correction, with the objective of determining the percentage of these patients who developed corneal haze in association with smoking.

A total of 157 patients developed post-operative haze that was graded more than “mild.” Among them, 127 had been treated with PRK, 32 had undergone LASEK, and one patient had undergone LASIK.

The amount of treatment ranged from 3.9 D of farsightedness to -8.0 D of nearsightedness.

The researchers found that smokers undergoing laser vision surgery for the correction of -5.0 D of myopia or more were significantly more likely to develop corneal haze than non-smokers or smokers undergoing laser surgery to correct lesser amounts of refractive error.

Based on the results of the study, Dr. Townley recommended that refractive surgery candidates should be encouraged to stop smoking. Longer use of topical steroid medications after laser eye surgery also might lower the risk of corneal haze among smokers, he said.

Dr. Townley cautioned that because the rate of corneal haze in this study population was so low, a large multi-center prospective study would be helpful to reach definitive conclusions about the risk of corneal haze after refractive surgery associated with smoking.

LASIK safe, effective for adults with amblyopia

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Posted on 3rd March 2011 by Pacific ClearVision Institute in General |LASIK

LASIK is safe and effective for the correction of myopia in adults with amblyopia in one eye, according to a new study.

Researchers in Israel evaluated the effects of LASIK in adult patients with mild to moderate refractive amblyopia caused by significant inequality in the degree of myopia in their two eyes.

The retrospective study evaluated 30 nearsighted patients with unilateral amblyopia who underwent same-day bilateral LASIK. Prior to surgery, the corrected distance visual acuity (CDVA) in amblyopic eyes was approximately 20/35 or worse.

All LASIK procedures were performed using a Technolas 217z excimer laser (Bausch + Lomb), and patients ranged in age from 18 to 53 years (mean: 31 years).

Results of the study included:

  • Myopia was significantly reduced in all treated eyes.
  • Mean CDVA was slightly improved in both amblyopic and non-amblyopic eyes.
  • Five of 30 eyes with mild to moderate amblyopia gained two to four lines of corrected distance visual acuity.

The study authors concluded laser eye surgery for the correction of nearsightedness was safe and effective in eyes with mild to moderate unilateral amblyopia.

SOURCE: LASIK correction of vision in adults with unilateral amblyopia. Journal of Refractive Surgery. January 2011.

Minimum age of some people seeking LASIK can be lowered, researchers say

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Posted on 2nd March 2011 by Pacific ClearVision Institute in General |LASIK

It may be safe for some young people under the age of 21 to undergo LASIK surgery without significant risk of a recurrence of nearsightedness, according to a new study.

Researchers in Jordan recently conducted a large-scale study of the stability of refractive errors to determine which types of patients are most likely to have stable vision correction after refractive surgery and which are at greatest risk for refractive change.

The retrospective study evaluated the refractive errors of 46,384 consecutive patients seen at a single outpatient clinic in Amman, Jordan. Patients were distributed into four groups, based on refractive error:

  • Emmetropia — Those with no nearsightedness, farsightedness or astigmatism.
  • Low to moderate myopia — Those with up to -6.00 diopters (D) of nearsightedness.
  • High myopia — Those with greater than -6.00 D of nearsightedness.
  • Hyperopia — Those with any degree of farsightedness.

The age of the patients in the study ranged from 3 to 82 years.

Analysis of the study data revealed:

  • Patients with less than -1.00 D of myopia at age 10 and less than -3.00 D of myopia at the time of LASIK surgery (after age 21) had no change in their nearsightedness after age 18.
  • Among patients with high myopia, 7.4 percent demonstrated corneal changes that did not stabilize until age 30.
  • Patients with hyperopia tended to experience a progression of their refractive error from age 30 to age 50.
  • Based on the results of the study, the researchers concluded that the minimum age of patients undergoing LASIK for the correction of less than -3.00 D of myopia can be safely lowered from 20 years to 18 years with little risk of progression of myopia after surgery.

    The researchers also said that all patients seeking laser vision correction should be educated prior to surgery regarding the risk of progression of refractive error and other possible risks and LASIK complications, based on their required correction.

    SOURCE: Age and refraction in 46,000 patients as a potential predictor of refractive stability after refractive surgery. Journal of Refractive Surgery. August 2009.