UNDERSTANDING LASER OPTIONS FOR VISION CORRECTION

Refractive surgery is about freedom – the freedom to allow you to make lifestyle choices that were not available to you before. This was because you were totally dependent on glasses or contact lenses. Though refractive surgery is mostly understood to refer to LASIK, there are many more procedures than just LASIK which are used to remove glasses or contact lenses. 

There is no best method for correction of refractive error. The most appropriate method depends on your eyes and your lifestyle. Contact Angel Eyes today to learn more about which option for correction your refractive error may be most effective for you, or to schedule a personalized consultation with one of our physicians.

Angel Eyes offers all of the latest refractive surgery procedures available including:

Laser option for Vision Correction: 

Laser vision correction, or laser refractive eye surgery use excimer lasers to reshape the curvature of the cornea. Two methods are currently employed for doing the laser vision correction:

1. LASIK

1. Custom Aspheric Lasik
2. Lepto Lasik
3. Corneal Wavefront Guided Lasik
4. Ocular Wavefront Guided Lasik

PRK

Trans-PRK 

Non – Laser Option for Vision Correction:

 In all those patients where the laser option is not suitable, they can go in for the non-laser option. Also, the non-laser option of vision correction may also be chosen as a first choice for its own benefits.

1. Implantable Collamer Lenses (ICL / Phakic IOLs)
2. Clear Lens Exchange

SUITABILITY FOR REFRACTIVE SURGERY:

Before you can definitely be classed as suitable for refractive surgery at AELC, you will need to be seen by one of our consultants.

However, if you fit all the following criteria, it is likely that you will be suitable for corrective surgery:

1. You must be over 21 and in general good health;
2. You must have had a stable prescription for at least 12 months;
3. Both eyes must have good vision;

And you should have a prescription within the recommended safe range for the procedure. For LASIK this is –1.00 to –10.00 (short sight) or +1.00 to +4.00 (long sight) including any astigmatism. Higher refractive errors are more difficult to eliminate completely with laser but can however usually be corrected by lens implantation. Ask your optometrist if you are not sure how to interpret your prescription.

You may not be suitable if:

1. You are pregnant or breast-feeding;
2. You have had a previous Herpes Simplex (viral) infection of the cornea;
3. You are taking any drugs which interfere with the healing response (for example, drugs used during chemotherapy);
4. One or both eyes has a significant ocular abnormality or keratoconus (conical cornea);
5. You have severe dry eye disease;
6. You have worn contact lenses within 1 week (soft lenses), 4 weeks (gas permeable hard lenses), or 6 weeks (conventional hard lenses) of the assessment – contact lens wear can cause temporary changes in your corneal shape making accurate assessment difficult. Therefore, most consultants may ask you to leave your contact lenses out prior to your pre-operative assessment; the practice manager will let you know when you book your appointment.
7. If you have certain medical conditions, such as diabetes, SLE, rheumatoid arthritis, any connective tissue disorder or other auto-immune disease, you will need to be assessed carefully for suitability.

UNDERSTANDING LASIK

By reducing or eliminating the need for glasses and contact lenses, LASIK has changed the lives of people around the world. LASIK is currently the most frequently performed elective procedure in the world where a cool beam of light from a computer- controlled excimer laser gently reshapes the front surface (cornea) of your eye. We have the ability to correct myopia (near-sightedness), hyperopia (farsightedness) and astigmatism with a high degree of accuracy. These conditions can occur in combination or alone. LASIK can dramatically improve the vision for most people, but it cannot promise perfect 20/20 vision for everyone. The improvement you experience depends on the severity and type of prescription you have.

The LASIK Procedure:

The Procedure

Before the procedure, the patient needs to have an eye examination to assure that the eye is healthy and suitable for LASIK. This includes a complete health and eye history, and comprehensive examination of the eyes including a computerized mapping of the cornea. If you wear contacts, it is imperative that wear is discontinued 4 – 5 days prior to the preoperative evaluation, if wearing soft contact lenses or 2-3 weeks if wearing rigid gas permeable (hard) lenses. 

The procedure is performed using eye drop anaesthesia. During the procedure, a small flap is first created in the outer layer of the cornea with either a sophisticated instrument called a microkeratome or a precise laser. The flap is then folded back on its hinge, and the extremely precise and accurate excimer laser sculpts the midcornea by removing minute amounts (microns) of underlying corneal tissue, effectively reshaping the cornea and allowing the eye to focus light on the retina correctly. Finally, the flap is gently returned to its original position and the procedure is complete; healing begins almost instantly. Since the surface cells of your eyes heal more rapidly than any other body part, recovery occurs quickly and naturally. Visual recovery occurs usually within 24 hours and there is minimal discomfort after surgery. 

For myopia, laser vision correction involves removing small amounts of corneal tissue to reduce its refractive power, thereby flattens the centre of your cornea such that distant light rays are now focused on the retina.

For hyperopia, your cornea is steepened by removing peripheral tissue to create more refractive power.

If you have astigmatism, the laser smoothens the irregular shape of your cornea to even out its focusing power.

LASIK CATEGORIES: 

Lasik surgery has been around for more than 30 years now and the quantum of developments and advancements in this field have been tremendous. The mainstay of Lasik treatment is the diagnostic equipment which map the cornea and the computer-controlled Excimer laser which treats the cornea. As in any other field, no two diagnostic work station and Excimer laser are exactly the same. There is a whole gamut of equipment which could range from being just standard to highly sophisticated. The more advanced the diagnostic equipment is, the more precise, detailed and accurate mapping of not only the cornea but the entire visual system of the eye is possible. The advancement of Excimer laser and the software which controls it during the treatment gives us the unparalleled precision, safety and speed which is essential for achieving not only the vision which is not dependent on any aids but also opens up the possibilities of achieving vision beyond what was possible before. Because of a wide range of equipment available to us it is important to realize that we can have a whole range of Lasik treatments possible starting from a standard treatment on a standard Excimer laser to achieving ‘super vision’ on the most sophisticated ones. 

1. Standard Lasik Treatment

Standard Lasers that are used for the traditional treatment reshape the cornea using the same measurements that are used for eyeglass and contact lens prescriptions. The traditional treatment can be used to correct lower order aberrations, including near-sightedness, farsightedness, and astigmatism. 

2.Customised Aspheric Treatments

Custom LASIK treatment replaces ‘the one treatment fits all’ with a procedure that is tailored to the individual eye. While standard laser eye treatment gives very high-quality results for the majority of patients, many people’s ‘eyes are not standard’. Their eyes might require a specially tailored treatment. 

By having an optimised custom ablation- the shape of the cornea is kept similar to the natural shape, i.e. prolate shape (steeper in the centre and flatter in the periphery) as compared to standard laser treatment where the shape of the cornea is shaped to be steeper in the periphery and flatter in the centre. This significantly reduces aberrations and gives the patient the benefit of having Super Vision, or vision beyond boundaries. 

Another major advantage of Aspheric Lasik is for those with large pupils and poor night time vision. This is possible as the optical performance of the eye is measured at each and every place on the cornea, including the part which is used when the pupil is large. Laser treatment is then programmed to each tiny part of the corneal surface so that every area of the cornea gets the best correction. Contrast sensitivity in low lighting levels is increased and the risk of developing night time halos and glare is greatly decreased.

First developed by astrophysicists, this is the latest technology in laser eye surgery and combines advanced diagnostics and laser ablation. By pinpointing and measuring the tiniest imperfections and natural distortions of your vision, with the exact measurements we take from the Wavefront diagnostic work station, we are able to create a tailor-made treatment plan that is as unique as you are and is customized to suit the individual eye. 

3.Lepto Lasik:

Excimer laser refractive surgery has evolved a lot since its earlier times. After conventional Lasik where a mid-stromal (middle layer of cornea) flap was created to perform Lasik, the interest shifted to doing surface procedures in a controlled way. Though we saved corneal tissue with surface procedure, the prolonged visual recovery prompted to find a mid way solution for thin corneas with high numbers. The new tendency is going closer to the Bowman’s membrane which is closer to outermost layer of cornea. 

In this context of continuous movement back to Bowman’s membrane, LASIK surgeons preserve more the integrity of the cornea, providing a higher degree of safety for their patients, with an additional speed of visual recovery. The concept of a thin-flap LASIK was born, called SBK or ‘Sub Bowman’s Keratomileusis’. The procedure of Lasik done using the technique of SBK is known as Lepto Lasik.
Lepto Lasik Procedure is performed upon the patient having very thin cornea with moderately high refractive error. It can be performed also in the patients, who want to save maximum corneal tissue, and obtain the benefit of Wavefront method. It is performed by creating the corneal flap of 70-90 microns and treating the patient by wavefront technology. In contrast, a conventional LASIK flap has a thickness of 120 to 180 microns. No matter how thin the cornea is, we can correct refractive error of the patient safely and successfully. 

Indications for Lepto Lasik

Treatment of refractive defects.   
 

Patient’s selection 

1. Inclusion criteria 
   – Patients suitable for LASIK or surface ablation, 
   – Keratometries between 39 – 48 D when using single use rings and between 39 – 49 D when using reusable rings.
2. Exclusion criteria 
   – Patients with any pathologies such as pterygium, keratoconus, corneal ulcers, corneal scars etc. that could have damaged Bowman’s membrane, 
   – Patients who have had a foreign body removed. 

Advantages of LEPTO LASIK compared to conventional LASIK

1. We can save more corneal tissue with Lepto Lasik as compared to conventional Lasik
2. Less weakening of corneal biomechanics, less risk of ectasia, better stability. 
3. Greater flap thickness predictability.
4. Ability to treat more patients, and higher levels of myopia. 
5. Can treat thinner corneas. 
6. Reduced enhancement rate.

Comparison of Lepto Lasik with Trans PRK (Surface Ablation) Procedure:

1. Corneal saving is more with Trans PRK as compared to Lepto Lasik.
2. Corneal biomechanics are least disturbed by Trans PRK.
3. Visual recovery is faster with Lepto Lasik as compared to Trans PRK. 
4. Both are used to treat thin corneas with high numbers. But as the number treated increases the speed of visual recovery becomes lesser with Trans PRK.
5. Post-operative pain and discomfort is much less with Lepto Lasik.

4. Customized Wavefront-Guided Treatment:

Wavefront laser eye surgery is the most advanced form of excimer laser technology. Just like a fingerprint, each person’s vision is unique to them, which warrants a customized treatment. But besides this there is another feature of the optical system of the eye which needs consideration before treatment and can make a whole lot of difference to the quality of vision.

Theory behind Wavefront Technology – ‘Higher – Order Aberration’: Nature has designed the eye like an Optical System, similar to something like a telescope. When you see some object, light rays from that object pass through different layers of the eye and then create an image of that object. These light rays are subject to being distorted by the imperfections found in the cornea and the lens.

The distortions that are created are referred to as “aberrations.” The vast majority- 80% or more–of these aberrations create common refractive errors, such as near-sightedness, farsightedness and astigmatism, which can be treated glasses and contact lenses, or by Standard Laser Correction. The remaining 20% of optical aberrations are known as “higher order aberrations”. These are not corrected by Conventional or Standard Lasik treatment. Higher-order aberrations, cause the visual glare and halos that cause night vision problems, and affect quality of vision. It is seen in everyday life as glare experienced during night driving, surrounding car headlights, streetlights etc.

The Treatment: To achieve a customized Wavefront-Guided corneal shaping, the higher order aberrations are measured using a Wavefront analysis system called an Aberrometer .The Aberrometer System takes thousands of measurements at unique points in the patient’s vision in order to create a “map,” which is then used to measure imperfections that corrective lenses can’t correct. This helps the surgeon see refractive aberrations in clear and accurate, rotating 3-D images and also understand how your entire optical system processes light. All this information cannot be seen by regular or standard testing. This information is then transferred to the laser system, thus achieving Customized Wavefront-Guided Treatment designed to suit your eye.

The advantages of Wavefront over conventional laser treatments are thought to include greater accuracy and improvements in visual quality. Wavefront treatments also include additional elements such as iris registration, or even iris recognition, and pupil size measurement in order to be more precise. The latest excimer lasers in use at AELC for example can offer ‘dynamic rotational tracking’ of eye movements in order to achieve greater accuracy. It is important to realize that not all eyes will have higher order aberrations warranting their correction. Some such aberrations may be present at such a point in the optical system so as to have very minimal influence on the overall quality of vision and thus need not be treated. 

High Order Aberrations

2. UNDERSTANDING PRK – The Surface Ablation Procedures:

Before the advent of Lasik, the first laser vision correction procedures to be introduced were the surface ablation procedures. This procedure has undergone two phases of its development:

If you have thin, irregular or unstable corneas, you’re generally not suitable for LASIK. However, you most likely will be suitable for a surface ablative procedure

The Initial Phase:  PRK or Surface Ablation

PRK or Photorefractive keratectomy is the original Excimer laser procedure introduced before LASIK in the 1980s, but became less frequently used as LASIK was introduced. The only difference in the surgical procedure involves the flap creation in LASIK which is not done in PRK. The Excimer laser beam is applied on the surface of cornea without making a flap.

The main drawbacks of surface ablation procedures which caused it to go out of favour at that time were considerable post-operative pain, longer healing times plus the absence of ‘wow’ factor usually associated with Lasik. The ‘wow’ factor as well as the painless and rapid visual recovery of Lasik made Lasik an instantaneous success all over the world, thereby pushing PRK out of vogue inspite of its many advantages which were subsequently overlooked due to the Lasik wave.

The Recent Phase: Advanced Surface Ablation (LASEK / EPI-LASIK / Trans PRK)

The term refers to newer versions of Surface Ablation. The Advanced Surface Laser Ablation is also known by terms such as ASL, PRK, LASEK, Nu-LASIK or Epi-LASIK. After the initial PRK was elbowed out by Lasik, the procedure of choice for two decades was Lasik. However, the last few years has seen a reversal of trend with a fresh interest in surface procedures. 

Reasons behind Resurgence of Surface Ablation Procedures: 

Several reasons led to the resurgence of surface procedures albeit with significant additions/ improvements to the initial procedure –

1. Lasik is not a suitable option in all those with thin, irregular or unstable corneas. In such cases, surface procedures are only laser vision correction possible.
2. Because of inherent tissue saving in surface procedures, all higher prescriptions are benefitted by undergoing these procedures. Many patients who were earlier declared unfit for Lasik due to their thin corneas or higher numbers, can safely undergo vision correction by surface procedures.
3. Though rare, but a definite possibility of flap complications, makes it a safer option than Lasik.
4. As no flap is created in surface procedures and the healing is accomplished by epithelial regrowth over the treated corneal bed, the bio-mechanical integrity of the cornea is maintained.
5. Surface procedure is a safer option for patients who engage in contact sports, particularly boxing or mixed martial arts, where there is a risk of blunt trauma to the eye as there is then no concern for risk of flap dislocation.
6. it may be a safer option for patients who have had prior eye surgery such as LASIK or RK, among others.

Differences in procedures between Lasik and Surface Procedures:

1. In surface procedures the first step of Lasik where a corneal flap is lifted by using microkeratome or femtosecond laser is skipped or modified. The corneal bed for laser application is prepared by removing only the epithelium.
2. The patient feels more pain in the post-operative period of Surface Procedures than after Lasik. The usual period of discomfort after Lasik is 3-4 hours, but after Surface Procedures it is 2- 3days.
3. The Surface Procedures need longer times for visual recovery. Visual recovery is 1-2 days for Lasik, whereas it takes 4- 5 days for Surface Procedures. 
4. Surface Procedures needs 1-2 additional post-op visits more than the Lasik.

 THE PROCEDURE:

The newer advanced surface ablation procedures are performed in several ways, each with a slight variation as to how the corneal bed is prepared for the ablation by excimer laser. In all the variants the epithelium which forms the top most layer of the cornea is removed by different means which leads to difference in healing and recovery. The procedures of Surface Ablation may be divided into following categories:

1. LASEK: Here the epithelium is first loosened by the application of alcohol to the cornea. Then the surgeon will scrape off the epithelium to prepare the corneal bed. After the treatment with Laser is over a Bandage Contact Lens is placed on the cornea. The use of alcohol at times is shown to delay the healing of the cornea.

2. EPI-LASIK: Epi-LASIK is an abbreviation for Epithelial Laser In-Situ Keratomileusis. This procedure is an advanced type of corneal surface ablation to correct near-sightedness, farsightedness and astigmatism.  In this procedure, the microkeratome is used to remove the epithelium instead of alcohol. The use of microkeratome may yield a very thin flap of epithelium which may be reposited back after the procedure is over. It is still a matter of debate as to how much this thin epithelial cover is helping/hindering in the process of healing. Also, the use of microkeratome to create such thin epithelial flaps may at times be riskier than creating a normal thickness flap of Lasik, thereby offsetting some of the advantages that we may have gained by doing Surface Procedure.

3.Trans-PRK ‘No – Touch’ Laser Treatment:

This is the latest and the most advanced form of surface ablation procedure available today. The Trans-PRK also known as “No-Touch” surface treatment is the most advanced version of surface treatments. Here the epithelium is neither removed by scraping nor by microkeratome but by controlled and very precise ablation by the laser. The “No-Touch” surface treatment from SCHWIND is the only surface treatment where the eye doesn’t require contact with an instrument. Furthermore, the epithelium is removed more precisely and more easily than ever before. The precise pattern of epithelial removal ensures rapid regrowth of epithelium to produce much rapid healing and visual recovery than seen in any of the earlier surface procedures. Healing is also aided by the fact that the area of epithelium removed is much less than that with alcohol based manual scraping or with microkeratome. Moreover, due to very precise removal of epithelium the chances of developing any haze in the post-operative period is also minimized.

Indications for Surface Ablation Procedures:

PRK or Advanced Surface Ablation is a very effective alternative to LASIK that may considered when:

1. you have corneas that are too thin for LASIK, large pupils, and/or dry eyes
2. you are at least 18 years of age
3. you have had a stable eyeglass or contact lens prescription for two years
4. you wish to reduce your dependence on eyeglasses and contact lenses
5. you have other factors that might make PRK preferred over LASIK
6. safer option for patients who engage in contact sports, particularly boxing or mixed martial arts, where there is a risk of blunt trauma to the eye as there is then no concern for risk of flap dislocation.
7. safer option for patients who have had prior eye surgery such as LASIK or RK, among others.