WFO LASIK: What does it stand for?

by admin on February 8, 2012

WAVEFRONT-Optimized LASIK (WFO): Allegretto Standard Treatment

Introduction: A Perfect Sphere

The aspheric Q-value for a sphere is 0 with 50 µm of positive spherical aberration

A perfect sphere already possesses some spherical aberration because the peripheral corneal rays are being refracted more than the more central corneal rays.

The Normal Cornea

Nature has designed the human eye (cornea) not to be a perfect sphere, but rather aspheric: in fact a three-dimensional prolate ellipsoid, like a bullet or a tulip. It’s steeper in the centre and flatter in the periphery, in order to reduce or eliminate the spherical aberration of the entire eye.” If the `eye was designed to be more spherical or even oblate, a lot more spherical aberration would have been present.

The aspheric Q-value of the normal adult prolate cornea is -0.26 with 25 µm of positive spherical aberration. (Youth: 0 amount of spherical aberration because 25 µm of positive corneal spherical aberration is negated by 25 µm of negative lenticular spherical aberration. ; Age 40: -0.26 (25 µm); Age 60: 50 µm)

The normal pre-operative prolate cornea is halfway (Q = -0.26) between a sphere (Q = 0) and a perfect ellipsoid (no spherical aberration), at Q = –0.52. So, while the cornea still has positive spherical aberration, it is only about half as much as a sphere (Q-value = 0)

Asphericity quotient

The key to (1) not inducing or (2) reducing spherical aberration in the eye during refractive surgery, is to (1) preserve or (2) increase the natural prolate shape of the cornea during refractive surgery.

The Q-value for a sphere is 0, while the Q-value for a prolate ellipsoid is negative and for an oblate ellipsoid positive.

The average Q-value for a normal human cornea is about –0.26. If the cornea were a perfect ellipsoid, with no spherical aberration, the Q-value would be approximately –0.52, So, while the cornea still has positive spherical aberration, it is only about half as much as a sphere (Q-value = 0), because it is halfway between a sphere and a perfect ellipsoid, at Q = –0.52.

Presbyopic shift

In wavefront-guided refractive surgery, a cornea with a Q-value of –0.26 translates to 25 µm of positive spherical aberration over a 6-mm optical zone. In a young person (20 years old or younger) the 25 µm of spherical aberration in the cornea is “cancelled out” by 25 µm of negative spherical aberration in the crystalline lens, he said.

The crystalline lens increases in positive spherical aberration over time, but the cornea remains constant (when corneal disease is not present).

By age 40, the crystalline lens changes from a negative spherical aberration to a spherical aberration of about 0, resulting in about +25 µm of spherical aberration. By age 60 years, the total eye has about 50 µm of spherical aberration: 25 µm from the cornea and 25 µm from the lens.

The WaveLight Allegretto Wave excimer laser system is the only laser system approved in the United States that has implemented the peripheral energy compensation into its standard platform. WaveLight refers to this as a wavefront-optimized profile, distinguishing it from wavefront-guided treatment.

“The Allegretto system achieved the same results as wavefront-guided treatments (FDA) because it had the same radial compensation modification incorporated into its system that the wavefront-guided treatments have,” according to Dr. Holladay.

Laser ablation overview

Applying aspheric treatments to refractive surgery procedures can significantly reduce spherical aberration and the consequent effects of glare and haloes, improving postoperative visual results.

Laser ablations that are calibrated on flat surfaces (and consequently under-correct the corneal periphery) and changes in the crystalline lens over time all contribute to spherical aberration in the human eye and diminish visual performance. A surface that is prolate – steeper in the center and flatter in the periphery – can reduce spherical aberration and “bring rays into a perfect point of focus.

For the middle-aged eye

Surgeons can reduce spherical aberration by using an excimer laser that maintains or increases the prolate shape of the natural cornea. Correcting these higher-order aberrations returns the eye closer to the physiologic optics of the young human eye.

Standard corneal refractive surgical laser treatments transform the patient’s prolate cornea into an oblate cornea, inducing spherical aberration. Standard laser treatments, for both surface and stromal bed ablation, have been calibrated on flat surfaces, and they do not take into account that the cornea is a dome, where the effect of the energy is reduced proportional to the oblique incidence of the energy. As a result, such treatments put an inadequate amount of energy into the corneal periphery. In fact, standard laser treatments can induce spherical aberration to a Q-value of up to 100 µm to 150 µm.

Traditional LASIK

Most patients undergoing traditional LASIK surgery in the past were very happy with their daytime vision but were aware of lesser quality vision at night or at dawn or dusk. The reason is that LASIK lasers had less effect in the peripheral parts of the cornea and an oblate (more cornea removed on top than sides thus flattening the front of the eye) shape was created that increased glare at night because of an increase of ‘spherical aberration’ caused by the eye’s shape.

In Traditional LASIK, much less lasering occurs on the sides of the eye. Laser has reduced the prolate shape to a more oblate shape now. No radial compensation prolate function is present in the algorithm.

This treatment is expected to induce some spherical aberration (and thus increase the existing spherical aberration) with the peripheral rays now being refracted even more than before.

The Q-value for an oblate ellipsoid is positive (Q-value of up to 100 µm to 150 µm).

Modified laser treatments: Wavefront-Optimized vs. Wavefront-Guided

With the development of wavefront-guided laser surgery, some laser manufacturers have incorporated a “radial compensation function” into their ablation profiles to compensate for under-treatment in the periphery by standard laser algorithms, Dr. Holladay said.

Companies have implemented the new prolate function into their wavefront-guided systems to alter the laser energy power in the corneal periphery and reduce induced spherical aberration. However, they did not incorporate this modification into their standard laser treatments.

A: WAVEFRONT-Optimized LASIK: WFO (Allegretto Standard Treatment)

WFO LASIK is the standard treatment on the Wavelight Allegretto laser, a laser that is designed to compensate for the expected inducement in spherical aberration by increasing the number of laser shots in the periphery of the cornea in order to create a prolate corneal shape. It however does not attempt to address the issue of existing spherical aberration or any of the other higher-order aberrations that may be present like coma, trefoil etc.

This compensation however, alone, should theoretically prevent the induction of additional spherical aberration and thus worsening of the quality of night vision, by maintaining the existing corneal relationship that exists: central steepness and peripheral flatness.

After wavefront-optimised laser surgery (Allegretto Standard treatment)

Prolate Cornea Shape

No new induced spherical aberration to be expected because the peripheral rays are being refracted less than before and all the rays are intersecting at the same point. A radial compensation prolate function is present in the algorithm.

B: Custom LASIK: WAVEFRONT-Guided LASIK: WFG

Custom LASIK is the ability to treat prescriptions on an individual basis. Each patient has a unique corneal curvature, a unique corneal asphericity as well as a unique wavefront pattern that is as unique as a fingerprint. Wavefront-Guided (Customized) treatments are designed to correct EXISTING higher order aberrations of the eye.

This treatment theoretically reduces existing spherical aberration because. After WFG surgery, the peripheral rays on the cornea are refracted less than before and all the rays intersecting at the same point as in a prolate cornea. It also incorporates a radial compensation prolate function to minimize induction of more spherical aberration.

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The dawn of an ophthalmic wonder drug!

by admin on January 30, 2012

Treating neovascular AMD remains a challenge to most retina specialists.

Patients are referred to us by a variety of physicians and optometrists, all in an attempt of preventing the central visual blindness that so often accompanies this disease.

Recalling my earliest days after my fellowship in 1985, I had nothing to offer patients presenting with typical manifestations of a CNV (choroidal neovascular membrane). We documented them wonderfully, photographed the lesions and studied and classified them ad nauseum. Alas, all to no avail. Lesions outside the central macula could be lasered directly and they did well in most cases. They were however rare.

Then came along PDT (photodynamic therapy with Visudyne), which we used for a number of years with variable success. It was not until Avastin came along a few years ago that changed the world. It rejuvenated medical and surgical retina practices the world over. Here we had a new drug that actually worked, and in virtually every case. It did not matter whether the lesion was small, medium or large. Neither did it matter what the fluorescein picture looked like. If you could identify the lesion to be due to a neovascular entity, it would likely stop the disease dead in its tracks!

I embraced the use of intra-vitreal Avastin therapy soon after its discovery. I have used it in hundreds of patients safely and effectively. It remains the most used anti-wet AMD drug in the USA and Canada and likely the world. It is cheap, safe, easy to administer and works in almost every case of nAMD with CNV. It works even better in other cases of CNV not due to nAMD, such as myopia with a Fuch’s spot, toxoplasmosis, RPA with CNV and the list goes on and on!

Now I’m using it in virtually every vascular disease of the retina with incredible success. Diseases like diabetic macular edema, macular edema due to BRVO, CRVO, post-CE/IOL, and so forth. It works in chronic macular edema due to a variety of other diseases including cases of CSR to name but a few. Most of my traditional recipes taught me in retina school have long since been abandoned in favour of these new paradigms of therapy. A new dawn is upon us!

Not only retina diseases are cured with Avastin. I wouldn’t dream of treating a NVG patient now without rushing to Avastin therapy first. Laser therapy has become an adjunct therapy in virtually every disease where Avastin helps.

The sad part of this story is that some physicians are still so hung up by the fact that Avastin is ‘off-label’ in these diseases that they have denied their patients this treatment for years to the detriment of those very patients. That however is another story for another day. Much of what we use in ophthalmology today is off-label, like intraocular antibiotics and steroids, the use of MMC and at least 2 dozen other every day ophthalmic therapies.

Truly a miracle drug!

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Question: Why do I mostly perform iLASIK™ surgery?

by admin on January 30, 2012

Question: Why did I choose to adopt iLASIK as my flagship LASIK procedure?

Answer: Dr. Mike Bense: “I pioneered laser vision correction in Atlantic Canada almost two decades ago. I adopted virtually every refractive technique that came along during those years. The same goes for LASIK.

I was an early adapter to CustomVue technology and have used this technology ever since (in over 90% of my LASIK cases). Cost issues were the primary reason why some patients opted for conventional excimer technology instead. Results were clearly better than those I achieved using the Standard LASIK protocol.

When blade-free LASIK came to Canada, I bought the 1^st IntraLase in Eastern Canada. It made my LASIK life so easy and stress free. No more corneal abrasions, buttonhole flaps, and a host of other blade-related complications that kept me awake at night. I never looked back.

However, despite the fact that it clearly cost me a whole lot more to perform Custom (wavefront-guided), blade-free LASIK than my LASIK cases performed with a keratome, over 95% of my patients chose blade-free flaps. I soon abandoned the use of blades altogether when AMO branded this technology as iLASIK. Best thing I ever did!”

In summary:

“There does not currently exist a LASIK technology that yields superior safety or results to iLASIK.
As a matter of fact, iLASIK has the lowest risk of flap complications in this industry.
LASIK technology (Wavefront-guided Custom technology on the VISX Star S4) offers the highest incidence of 20/20 vision ever reported to the FDA in clinical trials.
It has the potential to result in better quality of vision including improved night vision than previously present.
It has also been shown to be of extraordinary help in dry eye cases as well. A lot has been written about this in the literature”

Final Question: What about other centres in your area that still primarily offer Standard or Optimized LASIK using steel blades in a keratome?

Answer: “Interesting question! It is all about cost. Read a previous blog I wrote on this topic.

In recent years, I, like many of my LASIK colleagues in Canada and elsewhere, are compelled to compete with Corporate Discount LASIK centres that have mushroomed across Canada. These discount centres advertise LASIK at very low starting prices but with ‘average LASIK fees’ really no different than at other centre using comparable technology.

The technology they use is clearly different than that used in an iLASIK suite. These centres for example prefer (and boldly state so) to use a metal blade instead of a laser to create their LASIK flaps (despite femtosecond laser technology having been shown to be much safer, more predictable, and achieving superior outcomes).

They similarly prefer to ‘customize’ their procedures using ‘Wavefront-optimized“ LASIK technology instead of Custom LASIK (wavefront-guided LASIK) which is a more advanced and more expensive technology”.

Time will tell!

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MGD (Meibomian Gland Dysfunction): A very common eye disease

by admin on January 18, 2012

MGD (Meibomian Gland Dysfunction): A very common eye disease

The incidence of MGD is underestimated in eye clinics and is likely the most common cause of Dry Eye Disease (DED).

OSD (Ocular Surface Disease) is the most common reason patients visit an eye doctor. OSD impacts the quality of one’s vision and surgical outcomes in operations like cataract surgery, and LASIK surgery.

MGD Defined

MGD is a chronic, diffuse disease of the meibomian glands and is associated with glandular obstruction in most cases, plus quantitative changes in glandular secretions. These obstructive and qualitative changes in the lipid tear layer, leads to eye irritation, red inflamed sore eyes and OSD. The reason is because this lipid layer dysfunction causes rapid tear film evaporation, tear film instability, hyperosmolarity of the tear film, bacterial overgrowth, plus activation of the inflammatory response cascades that can damage the eye’s surfaces (OSD).

MGD can cause posterior Blepharitis or may indeed present with very little evidence of any inflammation (posterior Blepharitis) in the early stages. Further on as the disease progresses, signs and symptoms of inflammation will occur with evidence of vascularization of the posterior lid margin.

MGD can classified into 2 types:

Low delivery MGD (low secretion from glands to absolute glandular obstruction (most common type of MGD) which in turn can be associated with cicatricial or non-cicatricial diseases)
High delivery MGD (aka meibomian seborrhea). This is seen as larger secretion of meibum often due to a.rosacea or seborrhea and interestingly is often seen in the setting of an overgrowth of coagulase negative staphylococci (calcium soaps are often evident on the lid margin here).
The ultimate result of both types is: Evaporative Dry Eye Disease (EDED)

Anatomy & physiology involved in developing MGD

The meibomian glands are situated in the tarsi, more so in the upper than lower lids.

Obstruction of their orifices is mostly caused by thick, opaque meibum or hyper keratinization of the duct system (a.rosacea, hormones, contacts, age, meds).

MGD and EDED often coexists with Aqueous DED because of the associated MGD.

Risk factors for developing MGD: Anterior and or posterior Blepharitis, aging, low androgen, prolonged contact lens wear, demodex folliculorum, menopause, atopy, retina A, and anti-androgens.

Diagnosis of MGD

A ‘Step by step’ approach is best.
Dry eye questionnaires are valuable.
Tests include:
- Measuring blink rate, lower tear meniscus height, tear osmolarity, TBUT and fluorescein staining techniques.
- Schirmer’s and lower tear meniscus height can tell if an Aqueous Deficiency DED is present
- Assess anatomy meibomian glands
- If we diagnose DED because of dry eye symptoms and signs, but the tear meniscus (tear volume) and Schirmer’s test is normal, then you have EDED.

MGD Treatment (Stage 1-4 to Plus disease)

Diet, environmental issues, eyelid hygiene in all cases of MGD
Omega 3 fatty acids (2,000 mg/day) important in all cases of MGD
Topical azithromycin (anti microbial, anti-inflammatory, plus its lipid-modulating properties) important in almost all cases of MGD (n/a in Canada yet)
In moderate MGD: add anti-inflammatory drugs like steroid drops for 2-4 weeks, topical azithromycin, plus oral doxycycline
MAINSTAY of Rx. in MGD: MECHANICAL efforts (1-2 x day to eyelids)
- Heat eyelids 1st (> 4 minutes at a time)
- Then vigorous eyelid massage
- Followed by attempts at mechanical expression of glandular contents
- Plus:
  - Tears
  - Topical emollient lubricant at night
  - 4-PLUS Disease
    - Pulsed steroids topically (If very symptomatic or phlyctenules present)
    - Bandage soft contact lens if lid margin hyper keratinized
    - Antibiotics topically if associated with anterior Blepharitis.

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Contacts Safer than LASIK?

by admin on January 17, 2012

Contacts safer than LASIK? Think again!

Why do so many people choose LASIK as their choice of Vision Correction? For refractive surgeons who perform LASIK, the question is a muted one: modern LASIK surgery as practiced today, especially blade-free iLASIK surgery, is very safe, highly effective, and very dependable over a lifetime.

The question does however remain for the millions of people out there wearing contacts (more than 40 million North Americans). Ought they consider LASIK or contact lenses as safe and viable alternate options for their vision correction? Not every person finds spectacle correction desirable, practical or possible, or even affordable.

In our refractive practice, we are constantly confronted with the stark choices our patients face when it comes down to safe and effective options for vision correction: contacts, spectacles, or refractive surgery?

Many people are drawn to the benefits of LASIK surgery, but are fearful of its potential complications. To be true however, when the risks of LASIK are compared to the risks of contact lenses, LASIK actually comes out on top as the safer option in several published studies. With the advent of blade-free iLASIK, this differences are further highlighted dramatically.

Numerous studies since October 2006, confirm that LASIK is actually safer than contact lenses with the leading loss of vision due to corneal ulceration.

Serious contact lens issues:

Severe outbreaks of untreatable fungal keratitis (Acanthamoeba) from contact lenses prevailed throughout Canada and the United States just over five years ago, according to the Centers for Disease Control (CDC). The effects were drastic. Many eyes went blind and some patients required removal of the infected blind eye. In recent times, the CDC reported another epidemic of an untreatable Fusarium. In St. John’s, a class action lawsuit has been filed in the Acanthemoeba case, and is ongoing. Some of them required corneal transplantation because of severe irreversible vision loss. I treated several of these cases at that time.

Data extrapolated from a study in Lancet shows the lifetime risk of bacterial keratitis to be 1 in 100 for contact lenses worn daily. Bacterial keratitis is an infection that causes an inflammation of the cornea and can lead to vision loss. Wearing contact lenses overnight or improper care or cleaning further increases the risk of infection from contacts. The risk of bacterial keratitis has changed little over the years for contact lens wearers and is the same worldwide.

William Mathers, M.D., professor of ophthalmology in the OHSU School of Medicine, reviewed several large, peer-reviewed studies and found a greater chance of suffering vision loss from contact lenses than from laser vision correction surgery, also known as “refractive” surgery. His findings are published in a letter to the ‘Archives of Ophthalmology’. His findings included:

Daily contact lens wearers have about a one in 100 chance of developing a serious lens-related eye infection over 30 years of use.
Contact lens wearers also face a 1 in 2,000 chance of experiencing dramatic vision loss as a result of their contact lens wear.
The chances of LASIK surgery leading to significant vision loss is about 1 in 10,000.

Serious LASIK issues:

Vision loss from laser surgery was easier to calculate. Mathers* looked at a large study of military personnel who had laser surgery and found results similar to those of the OHSU Casey Vision Correction Center. A study of more than 32,000 U.S. Armed Forces members receiving laser surgery published in the journal Ophthalmology found a loss of vision of one line on an eye chart was 1 in 1,250. Data from the OHSU Casey Vision Correction Center showed no cases of vision loss greater than two lines in 18,000 procedures performed over 10 years.

All options cost money:

When comparing costs between these 3 options, the typical LASIK patient will save thousands of dollars over a number of years. Not to mention forgoing the inconvenience of doctor’s visits and so forth. LASIK is not more expensive than spectacle correction or contact lens wear. It is tax deductible, and pays for itself many times over.

SOURCES:

Mathers, W.D. Archives of Ophthalmology, October 2006; Vol. 124: pp. 1510-1511. William Mathers, M.D., professor of ophthalmology, Oregon Health & Science University Casey Eye Institute, Portland. Jim Salz, M.D., professor of ophthalmology, University of Southern California, Los Angeles; private practice, Laser Vision Medical Associations, Cedars-Sinai Medical Center.

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What is Blepharitis?

by admin on January 17, 2012

What is Blepharitis?

Blepharitis overview:

Blepharitis is a very common ophthalmic disorder and is difficult to treat effectively. In patients that present for an eye examination with complaints of dry eyes, red eyes, a foreign body sensation in the eyes or fluctuating vision, we commonly diagnose ‘posterior blepharitis’ which is frequently associated with a simultaneous diagnosis of ocular rosacea. There are 2 types of Blepharitis, but the posterior one is the one that concerns us most.

Posterior Blepharitis:

This disease involves the posterior eyelid margins with inflammations, infections, allergies, and or acne rosacea, but primarily MGD (meibomian gland dysfunction) with or without acne rosacea. This section of the eyelid margin lies posterior to the gray line of the eyelid and contains mucosa, the muco-cutaneous junction, the meibomian gland orifices, and the keratinized skin.

Posterior blepharitis is primarily a MGD problem, which in turn is aka Evaporative Dry Eye Disease, because most all Dry Eye cases have some degree of lipid layer (Meibomian Gland) dysfunction.

Treatment:

How to restore these suboptimal functioning meibomian glands that are often blocked is the trick (topical drops will generally not work alone here to restore glandular secretion). Options include:

Mainstay of treatment is mechanical: start with warm soaks, followed by massage to try and express these glands especially centrally and nasally for 15 seconds per compression.
You can try a Mastrota paddle by OCuSOFT to help compress the glands.
Other newer options include Lipiflow, a patented method of helping to express glandular secretions.
Another mechanical method available is techniques to probe the blocked glands to establish secretion
Try adding 50-100mg of Doxycycline for 1-2 months along with 2000 mg fish oils daily to help thin the contents of these constipated glands.

Anterior Blepharitis:

The anterior lid margin is involved in inflammations, infections and allergies. This section of the eyelid margin lies anterior to the lid margin’s gray line and contains skin and eye eyelashes. Reddened inflamed lid margins are often due to staphylococcal exotoxins.

Treatment:

Remember, the disease follows a chronic course in most cases.

Mainstay of treatment is lid hygiene: use OCuSOFT eyelid cleanser or SteriLid by TheraTears.

Medical therapy once or twice a year is often required when the degree of lid inflammation is a concern. Options include:

Antibiotic/steroid preparations like TobraDex drops 4x/day for 2 – 4 weeks often helps
Steroid ointment alone like Lotemax at night for 2 weeks
Azithromycin is sub-optimal for staphylococcal disease and is not very anti-inflammatory compared to steroidal containing medications.

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Dry Eyes after LASIK

by admin on January 15, 2012

Why Do Patients Get Dry Eyes After LASIK?

LASIK may cause some patients to experience dry eye features after their LASIK surgery. This is especially true if there was tendency toward dry eyes before the LASIK procedure. During the LASIK procedure, a corneal flap is created, under which the actual laser energy is applied to reshape the cornea to correct nearsightedness, farsightedness and astigmatism.

The flap can be created either mechanically with a keratome (steel blade), or with a femtosecond laser. Several clinics like Bense Vision, have the new iFS™ IntraLase laser which actually minimizes the occurrence of dry eyes compared to other methods of creating a flap. When the flap is created, the very fine cornea nerves may be severed as part of the LASIK procedure. This is a normal part of the procedure. However, these nerves are required in order “signal” the lacrimal gland to produce tears. So, sometimes, the temporary interruption of the corneal nerve impulses can actually cause a lesser amount of tears to be produced, resulting in dry eyes after LASIK.

Sometimes if the dry eyes after LASIK are moderate or severe, your vision may actually be blurry due to the tear film instability. Your LASIK surgeon may elect to treat you for dry eyes before your LASIK procedure in order to fortify your tear film so that you will have a comfortable and asymptomatic post-operative period.

ALL LASIK patients however will need to use artificial tears or lubricating drops as a matter of course as it helps the tear film reestablish itself after the LASIK procedure. During your consultation it is important to disclose any symptoms you may have of dry eyes and to disclose any medications you are taking that might predispose you to dry eyes after your LASIK procedure.

If there are any signs or symptoms of dry eyes prior to your LASIK surgery, or if you are over the age of 40 years, you will automatically be referred to our special tertiary Dry Eye Clinic where you will have expert instruction on how to proceed to your LASIK journey.

Fortunately, virtually most cases of dry eyes after LASIK are temporary and symptoms gradually decrease over time as the corneal nerves grow back. Most patients will have a resolution of dry eye symptoms within a few months of having their LASIK procedure. In some extreme cases, symptoms may persist for over one year.

New iFS Laser Minimizes Dry Eye from LASIK

Most patients appreciate the improved safety afforded by the IntraLase laser in creating the flap during the LASIK procedure. An additional benefit of the latest model of IntraLase laser is the reduction in both severity and duration of dry eyes after LASIK. The iFS laser minimizes dry eye by limiting the number of severed nerves and promoting quicker healing of the cut nerve fibers.

Like all lasers used to create corneal flaps, the iFS has the ability to create very thin flaps of 100 microns which helps to limit the number of cut corneal nerves. The IFS, in addition, has a unique capability of creating oval flaps that further limit nerve injury. They have with wider hinges that are just large enough to cover the dilated pupil.

In addition, the iFS has the ability to create an inverse beveled flap edge assuring near-perfect alignment of the flap. Because the two ends of the cut nerve are apposed closely to each other, the nerve has only a short distance to grow before healing back together. Thinner, smaller flaps and wider hinges minimize the invasiveness of the LASIK procedure, which in turn minimizes the severity, and duration of dry eye symptoms from LASIK.

If you are concerned about dry eyes and wish to limit its severity choose thin-flap LASIK with the iFS laser. In St. John’s, NL, this laser is only available at Bense Vision.

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New Dry Eye Clinic at Bense Vision in cooperation with Bense Optical and Optometry.

by admin on January 15, 2012

New Dry Eye Clinic at Bense Vision in cooperation with Bense Optical and Optometry.

A Dry Eye Assessment is a separate evaluation from a regular eye examination. During a Dry Eye Assessment the eye doctor will review with you in detail what your specific symptoms and concerns are.

Causes of Dry Eye Disease (DED)

Dry Eye syndrome has many causes. Some of these include:

Normal Aging Process
Contact Lens Wear
Excessive Air Filtering
Certain Medications
Parkinsonism
Decreased Oil Secretions
Dry/Windy Climate
Exposure to Tobacco Smoke
Fluctuating Hormone Levels
Vitamin A Deficiency
Sjogren’s Syndrome
Certain eye operations (cataract surgery, PRK, LASIK etc.)

Testing for Dry Eye Disease (DED)

There are several methods to test for Dry Eyes. The eye doctor will first determine the underlying cause by measuring the production, evaporation rate, and quality of the tear film. Special diagnostic agents, which highlight problems that would otherwise be invisible, are particularly helpful to diagnose the presence and extent of the dryness.

The detailed tear film analysis is performed to establish the cause of an underlying dry eye condition. Differentiation can then be made between the 2 types of Dry Eye Diseases:

Primary Aqueous Deficient Dry Eye Disease
Evaporative Dry Eye Disease (aka meibomian gland dysfunction or MGD).

Treating Dry Eye Disease

Regardless of the treatment plan the doctor prescribes for you, it is important to remember that unlike an illness that is treated for a short time only, most cases of Dry Eye tends to be chronic. In LASIK induced dry eye disease, the dry eye symptoms are usually short lived (3-6 months) but are readily responsive to therapy in most cases.

In the majority of chronic cases however, this means you will likely be prescribed a daily maintenance routine requiring you to make minor, but important, changes in your lifestyle or habits. Periodic Dry Eye Follow Up visits are also critical to the effective treatment of the Dry Eye condition. The Doctor and staff will outline your particular treatment regimen. Remember that the proper treatment of Dry Eye problems is important not only for the comfort, but also the health of your eyes.

Primary Aqueous Deficient Dry Eye Disease options may include:

Restasis eye drops
Dietary Supplements
Lifestyle Changes
Increased Water Intake
Artificial Tears
Non-Prescription Lubricants
Punctal Plugs
An internist will be consulted for a comprehensive medical evaluation for patients that have Sjogren’s disease. This is an autoimmune disease characterized by dry eye and dry mouth.
LASIK surgery patients: Special attention is paid to patients interested in LASIK surgery in whom we identify dry eye symptoms or signs pre-operatively. In these patients we pre-treat them with several of the above options for up to a month prior to surgery and maintain a dry eye treatment regimen for up to 3 or more months following LASIK surgery.

Evaporative Dry Eye Disease (aka Meibomian Gland Dysfunction or MGD) options include:

Warm Eyelid Compresses
Prescription Eye Drops or Ointments
Prescription Doxycycline orally for 1-3 months
Eyelid Scrubs
May include many of the Primary Aqueous Deficient Dry Eye Disease options

For further information or to arrange a consultation please contact Bense Optical and Optometry at 709-7541250.

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Wavefront-optimized LASIK is not Custom LASIK

by admin on January 13, 2012

What is the difference between Custom LASIK (aka Wavefront-guided LASIK) and other types of LASIK like Standard LASIK or Wavefront-optimized LASIK?

When speaking about the excellent results Bense Vision achieves through what is termed ‘Custom’ LASIK we speak of a specific procedure called ‘Wavefront’ or ‘Wavefront-guided’ LASIK. This specific procedure involves incorporating data obtained by very sophisticated pre-operative diagnostics on an aberrometer in the treatment process. In the US and Canada, federal agencies have approved several laser systems for use in the provision of wavefront-guided (Custom) LASIK. These approvals are readily available for scrutiny on line.

It is of great concern to me that St. John’s LASIK candidates have recently been confused by advertisements for “Advanced Custom Wavefront” LASIK. Why you ask? Patients considering LASIK vision correction and who have come to understand that the results of ‘Custom’ (wavefront-guided) LASIK in general are better than those of Standard LASIK may mistakenly believe that all providers who offer ‘Custom’ LASIK are offering the same service. Not so.

Unfortunately, some providers of ‘Wavefront-optimized LASIK’ (a cheaper and vastly different type of technology than ‘Wavefront’ or ‘Wavefront-guided’ LASIK) advertise their procedure not as wavefront-guided or wavefront-optimized (Custom LASIK) but as “Advanced Custom Wavefront LASIK”. If this is meant to represent Custom LASIK, it is a distortion of the original meaning of ‘Custom or Wavefront’ LASIK which refers only to ‘Wavefront-guided LASIK’.

Patients are confused by this misleading terminology. As I shall explain, ‘Wavefront-guided LASIK’ is a very different procedure than Wavefront-optimized LASIK which is actually the standard LASIK procedure that is performed on the Wavelight’s Allegretto Wave Eye-Q laser. Read more: http://www.lasikreviews.co.uk/laser-vision-correction-lasik-wavefront-optimized.htm.

It must however be noted that the Wavelight’s Allegretto Wave laser is actually also capable of performing a Custom LASIK (wavefront-guided) procedure (but only approved for nearsightedness) when the entire LASIK treatment is guided by pre-operative aberrometry readings on their aberrometer. Unfortunately, this combination is seldom employed with many surgeons simple doing the standard ‘optimized’ LASIK treatment on their laser based on the patient’s spectacle prescription. This is not what Custom LASIK is and should not be sold as such.

‘Standard LASIK’

‘Standard LASIK’ is based on the spectacle prescription of the patient to guide the laser treatment. It does a great job of reducing or eliminating the need to wear glasses or contact lenses. However, Standard LASIK can and does cause other types of optical aberrations aka ‘high-order aberrations’, especially spherical aberration that can cause visual problems especially at night (glare and halos around lights).

‘Wavefront-optimized LASIK’

‘Wavefront-optimized LASIK’ as mentioned is actually a standard LASIK procedure that is performed on the Wavelight’s Allegretto Wave Eye-Q laser. It is not a personalized treatment because it is not guided by a wavefront analysis prior to the surgery and thus does not measure or correct the other types of optical aberrations in the eye.

Like Standard LASIK, it is based on one’s spectacle correction and simply aims to correct the lower-order aberrations of the eye (common refractive errors like nearsightedness, farsightedness, and astigmatism) whilst also attempting to maintain the natural shape of the cornea by using an algorithm based on past LASIK cases. This is done to help prevent inducing higher-order aberrations during the LASIK treatment that cause glare, halos, and other night vision problems, which happens with Standard LASIK.

‘Custom’ LASIK

Custom LASIK surgery, also known as ‘Wavefront LASIK’ or ‘Wavefront-guided LASIK’, uses 3-dimensional measurements of how your eye processes images to guide the laser in re-shaping the front part of the eye.

“Custom” LASIK” is vastly different than either Standard or Wavefront-optimized LASIK. As mentioned, Wavefront-guided LASIK requires that a device, called an aberrometer, measure all the optical aberrations of the eye, including the refractive (spectacle) prescription, to correct vision and unlike Standard or Wavefront-optimized LASIK, it is not based on your spectacle refraction. Custom LASIK is therefore very precise, and the results are better than Standard and Wavefront-optimized LASIK.

Cost:

Despite the differences in technology employed, all these procedures greatly exceed established measures of safety and effectiveness. You might say that Wavefront-optimized LASIK was a great forward step compared to Standard LASIK, but that Wavefront-guided LASIK (Custom LASIK) is a further great step forward.

It is important to note that Standard or Wavefront-optimized LASIK procedures are much cheaper to perform than Custom LASIK. So, if a person needs only an ordinary correction, why spend more for Wavefront-guided LASIK when Standard or Wavefront-optimized LASIK procedures give acceptable results, too?

Technology:

There is no getting around the fact that Wavefront-guided LASIK uses much higher technology and is thus more expensive. The result: Wavefront-guided LASIK results in better outcomes, better visual quality — especially when it comes to vision at night or in a dark environment, or when there is a high visual demand. This has been demonstrated in studies.

At Bense Vision, approximately 95 percent of potential LASIK patients receive a Wavefront-guided procedure. We have abandoned the use of keratomes (steel blades) years ago and only perform blade-free iLASIK, using the very latest blade-free iFS IntraLase laser. Creating a superb LASIK flap with the iFS laser followed by Custom LASIK is what makes iLASIK so popular and sought after.

A few patients are not good candidates for because it requires a very precise measurement with an aberrometer pre-operatively. If the aberrometer cannot make a very precise measurement of the eye, then the patient cannot have wavefront-guided LASIK. Examples would be if the patient had a scar on the cornea or if the patient was younger and could not relax accommodation (focusing ability) enough for a precise measurement. Also, some aberrometers require the pupil diameter to be large enough for a measurement. If the pupil diameter is not large enough in low light, then that person may not be a candidate. In these cases, an optimized procedure may be the best.

Final thoughts:

The benefits of Custom LASIK over Standard and Wavefront-optimized LASIK are:

A well-performed Wavefront-optimized procedure and a well-performed Wavefront-guided procedure may often have very similar results when viewing a simple eye chart but the differences between the two would be most apparent for other aspects of vision, particularly tasks that require a high visual demand, such as night driving. This is where the superior visual results of the wavefront-guided procedure really shine.
Published results of wavefront-guided procedures have reported improved contrast vision and fewer higher-order aberrations compared with other treatments like Standard or Optimized treatments. Some examples of how this would help in more practical terms would be an improved ability to read a road sign in a fog or more easily recognizing a face in a crowd. The wavefront-guided procedure results in a higher quality of vision.

If someone is interested in the highest quality of vision after LASIK — and I don’t know who wouldn’t be — then I would recommend a Wavefront-guided treatment. As a powerful testimony to this, it was the superior results of Wavefront-guided procedures that led to the approval of LASIK for military fighter pilots and NASA astronauts.

http://www.allaboutvision.com/askdoc/custom-lasik.htm

http://www.allaboutvision.com/visionsurgery/custom_lasik.htm

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PUPIL SIZE IN LASIK OUTCOMES

by admin on January 11, 2012

PUPIL SIZE IN LASIK OUTCOMES

The pupil size debate still exists with some laser eye surgeons placing more emphasis on pupil size than others. In my 18 years of experience, having performed over 20,000 vision correction procedures from RK to PRK to LASIK to iLASIK plus whatever was popular and in vogue at the time, pupil size has not been a big issue in my practice.

Why you ask? In my practice, pupil size alone has not been a reliable predictor of night vision problems. Some post-LASIK clients will develop problems in low light environments while most will not. Why some do and some don’t, is not fully understood.Several studies have been published in recent years by world authorities that have guided my approach to pupil size in people interested in laser vision correction surgery.

The first study, “Pupil size and quality of vision after LASIK”, published in 2003 by Steve Schallhorn, M.D., out of the United States Naval Medical Center in San Diego, concluded “Patients with large pupils had more quality of vision symptoms in the early postoperative period, but no correlation was observed 6 months after surgery.” Rather than pupil size, risk factors related to long-term night vision symptoms included the level of treatment (degree of preoperative myopia), pre-operative contrast vision acuity, post-operative unaided vision (UCVA), and residual astigmatism.

The second, “Risk factors for night vision complaints after LASIK for myopia”, published in 2004 by Michel Pop, M.D., out of Montreal, Canada, also concluded that pupil size was not a risk factor for night vision complaints within the first year after LASIK for myopia. Using the Nidek EC-5000 excimer laser platform, Mihai Pop and Yves Payette studied 795 patients to ascertain risk factors for night vision complaints after conventional LASIK. Attempted degree of spherical correction, age, optical zone, and postoperative spherical equivalent were major risk factors of night vision complaints throughout the first postoperative year, whereas pupil size was not associated with an increased risk of night vision problems.

Results of another study were presented by retired Navy Captain Steven C. Schallhorn at the annual meeting of the American Academy of Ophthalmology. Source: Night-driving performance improves after wavefront-guided surgery.Ophthalmology Times; Vol 33, No 5. March 1, 2008. pp 1, 45.

The study measured night driving performance in a simulator at the Naval Medical Center in San Diego. Prior to surgery, both the conventional group and the wavefront-guided group underwent baseline tests with the simulator. After surgery, both groups were measured again. The simulator measured how quickly patients could detect and identify potential hazards under both normal and glare conditions.

The main finding of the study was that the average night driving performance was reduced after conventional LASIK, but improved significantly in those who underwent wavefront-guided surgery. Dr. Schallhorn characterized the difference between the two groups as “startling”. The difference was present in both glare and non-glare conditions.

38% to 42% of eyes in the conventional group had a significant loss of night driving performance compared to only 3% with wavefront-guided surgery. Conversely, 18% to 46% of wavefront eyes performed better than before surgery versus only 6% to 13% of eyes that improved after conventional surgery.

According to Dr. Schallhorn, “The compelling data from these analyses provided the basis for the decision to authorize wavefront-guided all-laser LASIK in U.S. Navy aviators.”

In summary:

With 7.5mm pupil using a CustomVue ablation you should be fine. If you are not happy with the outcome it would be more likely due to other factors rather than pupil size. In fact, in Visx studies with CustomVue and pupil size, they found that patients with larger pupil size were relatively happier with their results than patients with smaller pupils in terms of their vision after lasik relative to before surgery looking at glare and nighttime difficulties.

So, despite the intuitive assumptions that larger pupils are associated with greater risk of night vision problems after LASIK, the data simply does not support this.

In all of the above excellent and large studies, pupil size simply was not a risk factor for night vision problems after laser vision correction. It is very helpful, however, to look at what were, in fact, risk factors for night vision problems.

Close analysis reveals that the postoperative presence of new aberrations, either in the form of uncorrected residual lower order aberrations, or the induction of new higher-order aberrations, was correlated with subjective complaints of night vision problems after surgery. In both studies, residual refractive error clearly had an important role in night vision symptoms. Obviously, these residual lower order aberrations will affect night vision until corrected either with enhancement surgery or with glasses and contact lenses.

Another interesting article Effect of Preoperative Pupil Size on Quality of Vision after Wavefront-Guided LASIK by Annie Chan MD and Edward E. Manche MD out of Stanford University, studied what I and many others have noticed for a long time: pre operative pupil size does not effect quality of vision in wavefront guided iLASIK.

These paper supports what I have been telling my patients for a long time: although it has been reported in the past that night vision issues may be related to pupil size, I do not see it with Custom LASIK (wavefront-guided iLASIK), in fact, I more commonly see an improvement in night vision as compared to glasses or contact lenses.

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