ASLA stands for Advanced Surface Laser. It is really no different to PRK.
PRK was the original term used to mean a laser vision correction on the surface of the cornea without first creating a LASIK flap. PRK was largely superseded by LASIK due to quicker recovery time and no discomfort.
Over time however, PRK has had a resurgence owing to the fact that it is a better procedure in some people and the procedure of choice if the cornea is thin. It has become more sophisticated, with better software algorithms that use modern ablation profiles. This has led to better visual outcomes. As the algorithms have progressed, it was decided to re-name PRK to ASLA.
Some clever marketing has tried to create the impression that it is a new procedure but it it is still really PRK, although on steroids.
ASLA vs LASIK
Long term, there is no difference in results between ASLA and LASIK. ASLA is not an inferior procedure and patients having it are not disadvantaged in any way. It is simply as stated, more uncomfortable and visual recovery takes longer.
In some respects, ASLA is safer as there is no corneal flap to worry about and all its attendant risks such as epithelial ingrowth, striae or dislodgement of the flap.
There is no difference in cost.
How is ASLA performed?
There are numerous ways to perform ASLA. Most commonly, the epithelial surface is removed using a blade, motorised burr or alcohol. Alcohol removal is quicker but there is some suggestion that this may lead to recurrent erosions long term.
The new Schwind Laser that we are using performs transepithelial ASLA, meaning that the epithelium is automatically removed by the laser. This results in a cleaner and more precise result.
Once the epithelial surface is removed, the laser then continuous on to re-shape the surface of the cornea. In the case of someone with myopia (shortsightedness) the laser tends to flatten the central portion of the cornea. In the case of hyperopia (long sightedness), the laser steepens the central cornea instead. The process is similar to a lathe, altering the shape of a piece of wood.
This of course is all done under anaesthetic, which is administered with eyedrops only. That is, there are no injections or needles involved.
At the end of the procedure, a contact lens is placed into the eyes and left there for three days until the new epithelium has grown back.
What happens after the ASLA procedure?
After the procedure, you can go home with antibiotic and anti-inflammatory eye drops.
Review is on the third day after the procedure for removal of the contact lenses. This can be either in our clinic or with your optometrist.
Vision is quite good after a few days but improves over the next few weeks and months.
Eye drops are used for two weeks and lubricants for 6-12 months
How long does ASLA last?
Generally, this correction is permanent. However as we age, our bodies (and eyes) change. This may lead to a change in your need for glasses long term. This can be corrected at a future date with an enhancement using the laser, or if the change is only small, glasses or contact lenses.
Some people do experience regression, which is where some of the original myopia or hyperopia returns. If this occurs, an enhancement can be performed once the regression stabilises.
How do I decide wether to have LASIK or ASLA?
This decision is not one that you need to make yourself, rather your particular set of circumstances will govern which approach is best for you
Long term safety of ASLA
ASLA is generally safer than LASIK although both are safe.This is because less corneal surface is removed with ASLA. With LASIK, the flap is usually around 120 microns in thickness which does not contribute to the structural integrity of the cornea. Hence, corneas that have had ASLA have a thicker residual base with consequent less long term risk of complications
Another day, another upgrade! We have now upgraded the laser that we use for vision correction to the new Schwind Amaris. Our previously laser was the Bausch & Lomb Zyoptics which served us well for many years.
The Intralase, which is a femtosecond laser that creates the Lasik flap has also been upgraded to the latest generation machine which means that the flap creation is now much faster.
The new Schwind is the laser that actually performs the refractive correction.
So what is soo good about the new laser? Well amongst other things, it is capable of performing a transepithelial PRK which the B&L machine could not do.
How is PRK different to LASIK?
PRK has had a resurgence in recent years as LASIK surgeons realised that not all patients were suitable for LASIK yet many could still be helped with PRK. PRK of course became unpopular because of its slow visual recovery and postoperative pain. It is no surprise that when LASIK came along with no pain and virtually instant recovery that it quickly became the default leaving PRK behind. PRK however has its advantages in that the absence of the LASIK flap means an instant saving of 120 microns of cornea that does not contribute anything to the structural integrity of the cornea. This means that anyone who has a thin cornea may not be able to have LASIK but may well be able to have PRK. The goal is to leave enough cornea after the vision correction to minimise any future problems such as ectasia. In addition, there are a number of potential flap related complications that clearly do not apply with PRK.
How does the new laser remove the epithelium? Transepithelial PRK
Traditionally, the epithelium is removed prior to laser either by alcohol of by manually scrapping it of. Some surgeons use a motorised brush.
With the new transepithelial laser however this is no longer required. The epithelium is now automatically removed by the laser.
The way that the laser performs this is by using an algorithm that determines how thick the epithelium is that is required to be removed.
The result is a much neater epithelial removal without the increased risk of recurrent erosions which are associated with alcohol removal.
Curiously, we have observed that the pattern of pain following the procedure is also different. It is not less, but most would complain of discomfort mainly on the second day after the procedure whereas now the peak comes a day earlier. It still however seems to last about 2.5 days.
Visual recovery seems no different.
The new Intralse
The femtosecond laser which is used to create the LASIK flap has also just been upgraded to the latest model. This new laser runs at a higher frequency which means that it is able to complete the flap much faster which in turn means that problems such as loss of suction are less likely to occur.
The iStent is one of the new generation medical devices which has recently become available in Australia for use during cataract surgery in patients with glaucoma. It forms part of the new trend towards minimally invasive glaucoma surgery (MIGS).
The stent facilitates intraocular pressure lowering thereby potentially either minimising glaucoma medication, or giving better intraocular pressure control in patients who are poorly controlled.
Whilst the device could theoretically be implanted in any patient with glaucoma, is is currently only TGA approved for use in the course of a cataract operation.
Intraocular pressure lowering in cataract surgery.
It is a well known that cataract surgery lowers intraocular pressure by as much as 30%. As such it is a good way to manage a patient who has concomitant glaucoma and cataract. As an alternative to a trabeculectomy, a cataract operation is a potentially good way to gain further lowering of pressure in people who perhaps are on maximal medical therapy and who have perphaps have also had laser treatment (SLT) but still do not have ideal pressure control.
The iStent, when implanted at the time of cataract surgery gives further lowering of intraocular pressure of around 16%. Whilst this may not seem much, it has to be remembered that every mmHg reduction in intraocular pressure in glaucoma patients results in a 19% reduction in risk of progression(1).
The implantation of the iStent is usually performed at the end of the cataract procedure. This is because the anterior chamber will be maximally deep as the lens has been removed. A gonio lens is required to visualise the trabecular meshwork. It increases surgical time only minimally. The stent comes pre-loaded on an introducer which grips the stent. The stent is then released once in place by depressing a button on the introducer.
There is no difference in the cataract procedure beyond this and no difference in the post operative management.
There is definitely a learning curve associated with its use and is probably best reserved for ophthalmic surgeons who are familiar with the anatomy of the trabecular meshwork.
Following surgery, the intraocular pressure is re-evaluated and it is sometimes possible to reduce the amount of glaucoma medication required.
The iStent works by bypassing the trabecular meshwork which is the site of outflow resistance in patients with glaucoma
The following illustration shows the path of aqueous within the eye and out through the iStent.
Flow of aqueous through the iStent
The decision to implant the iStent is usually made in the pre-operative period in patients who have glaucoma. The ability to visualise the trabecular meshwork during surgery is crucial and inability to do so would be the main reason not to implant it.
(1) Chauhan A. Acta Ophthalmol 2008;126:1030-1036
Lasik vs PRK is a common question that I am often asked.
So what is the difference between Lasik and PRK and which should you have?
This is an important question which is actually explained in details in other sections of this site but one that is worth summarising.
PRK stands for Photo Refractive Keratectomy and was one of the original corneal procedures for vision correction, first performed in Berlin in 1987.
In PRK, the epithelium of the cornea is removed by either alcohol or direct removal with a spatula. This of course is done with local anaesthetic. The epithelium is a layer of cells which is always reforming an is usually what is injured when someone inadvertently injures their eye, for example with a baby’s fingernail.
This exposes the stroma of the cornea where the laser will perform the correction. The stroma is the main bulk of the cornea. The epithelium which is removed grows back very quickly much like skin grows back after an abrasion.
Once the epithelium is removed, the laser is applied to the cornea to change its shape to correct vision. This is a very rapid procedure taking only about 30 seconds.
Following the procedure, a contact lens is placed in each eye to reduce the discomfort and to allow the epithelium to grow back. The contact lens is usually removed after about 36 hours.
Following surgery it is common to experience light sensitivity and discomfort for two to three days. Vision is better within days but is not at its best for several weeks to several months.
Due to the discomfort and the delay in achieving perfect vision, PRK became less popular and ultimately, largely replaced by Lasik.
Lasik stands for Laser Assisted In situ Keratomileusis and this is what most people think of when they think about laser vision correction.
In Lasik, a corneal flap is raised, much like lifting a lid and the laser correction is applied to the underlying stroma. Unlike PRK, the correction is applied at a deeper lever of the stroma and the only real difference is that in Lasik there is a flap and in PRK there isn’t.
The flap heals and eventually becomes difficult to even see.
The main advantages of Lasik over PRK is that there is absolutely no pain or discomfort and that excellent vision is almost immediate.
So which one?
So given that PRK is more uncomfortable and takes longer for vision to be excellent, why would anyone even consider it?
The main reasons why one would recommended PRK over Lasik are if you have thin corneas, the required correction is small or if the corneal topography scan is not entirely normal.
The advantage of PRK over Lasik is also one of structural integrity. A Lasik flap is typically 110-120 microns thick and contributes little to the final structural integrity of the cornea. Thus avoiding the flap leaves an additional 110-120 microns of untouched cornea.
Lasik flaps can (although) rarely develop problems such as epithelial ingrowth, folds (striae) or become dislodged. Therefore avoiding a flap in many ways is advantageous.
One cannot however get away from the fact that PRK has a slower recovery and is uncomfortable.
Long term there is no great difference in outcomes with both PRK and Lasik patients having similar visual outcomes.
At the end of the day, the decision as to which one to have will be decided by your eye surgeon based on which is most suitable.
If you have an adequately thick cornea with a normal scan then you will probably have Lasik.
If you have a thin cornea, a small correction or an unusual corneal scan then you will have PRK
I have just recently returned from the Australian Cataract and Refractive Surgery annual conference which this year was in Port Douglas. The focus of this meeting is as the name implies, on new developments in the area of cataract surgery and vision correction.
This year there were many new items which are worthy of discussing.
Implantable Collamer Lens (ICL)
I have written about this before and so it was timely that Visian should produce a new lens. This concept is not new but the current lens is new and improved.
One of the main changes is the incorporation of a small central hole in the lens. The reason for this is to minimise the risk of pupil block and subsequent angle closure glaucoma. Under normal circumstances, aqueous is formed by the ciliary body which is situated behind the iris. It then flows via the pupil to the trabecular meshwork. This normal physiology is interfered with by the presence of the ICL which sits just behind the pupil. Aqueous is still able to get past the lens as the seal between iris and lens is not watertight. Under certain circumstances it can become watertight and therefore lead to angle closure. In this scenario, fluid behind the lens cannot get past, increasing the pressure and causing the iris to be pushed forward. This is called iris bombe. The iris then in turn is pushed hard against the trabecular meshwork obstructing it.
The central hole in the new lens eliminates this risk as aqueous can flow through it making angle closure unlikely.
Finevision trifocal lens
This is another area which is developing and which in my opinion is now good enough to be worth considering. The holy grail in refractive and in cataract surgery is the problem of not being able to deliver vision at all distances. That is to say, we can deliver good distance vision but not simultaneously near vision. Or the exact opposite, in that we can deliver good near but at a cost of distance. This is because modern intraocular lenses cannot focus. Our own natural lens also loses its ability to focus at around age 45. This is why reading glasses become necessary. This is due to a stiffening of the lens preventing it from changing shape. Attempts to circumvent this problem using intraocular lenses have been around for some time but all suffer from numerous problems. Halos, glare and loss of contrast sensitivity are the main problems. These mulifocal intraocular lenses work by having a diffractive pattern on the lenses which result in two images, one for near and one for far. The problems stems from the diffractive pattern which lead to the glare and haloes. Further, as the slight is split for near and far, it means that only a small percentage of the available light is use at any time. Many patients are not bothered by this but those who are highly critical are. Also truck drivers, Taxi drivers and pilots in particularly are not good candidates due to the haloes and glare special at night time.
The FineVision lens which has just been released by Bausch and Lomb will hopefully address some of these problems. Instead of having a distance portion and a near portion, rather it has a near, intermediate and far portion. This will therefore translate into the ability to see to drive, use the computer and read. It still has the problems of other multifocal lenses but to a much lesser extent. This lens is probably still not for those whose lively hood depends on driving at night or flying but most everyone else. It is also not for those who are highly critical of their vision. Patients who have macular pathology such as macular degeneration or prior macula hole surgery are also best to avoid this lens.
My approach to this problem has been for a long time to implement monovision but this too has limitations.
This is another promising technology which addresses the problem of presbyopia. Little is known about this lens to date except that it is probably based on some form of multifocal platform. It is due to be announced at the forthcoming European Cataract and Refractive Conference in London in September.
A New Zealand based surgeon has implanted 20 of these lenses as part of a trial. He was not at liberty to discuss the lens in any detail but did present his own findings. Essentially he found that patients had excellent distance and intermediate vision and good near.
It is unknown when this lens will become available or wether it lives up to the hype. My guess is that it may be available sometime in 2015 in Australia, probably in the second half
SMILE is Small Incision Lenticule Extraction. It is an alternative to LASIK or PRK. In the SMILE procedure only a small opening is created in the cornea and a lenticule is formed by the laser in the stoma of the cornea. The lenticule is then removed. No flap is created. This has been referred to as “Bladeless Lasik”.
Lasik by contrast creates a large corneal flap and laser is applied to the exposed corneal surface and the flap is deposited.
The main advantage of SMILE is because only a small incision (2-4mm) is created, there is less severing of corneal nerves and therefore less corneal anaesthesia. This translates into less post procedure dry eye.
Our laser centre is at present evaluating this technology and we may be implementing it in the near future.