Most refractive surgical procedures achieve their objective by altering the curvature (and therefore the effective power) of the cornea. The cornea is the is most external clear structure of the eye.
The aim of LASER surgery is to flatten the cornea to reduce its refractive power and reduces myopia (short sightedness), whilst steepening the cornea increases its refractive power and reduces hyperopia (long-sightedness).Flattening or steepening the cornea selectively along one axis reduces astigmatism.
Laser refractive surgery is normally conducted under local anaesthesia as a “walk-in, walk-out” procedure. Clear lensectomy and phakic intraocular lens insertion are also usually performed under local anaesthesia on a day case basis but should be performed in an operating theatre which conforms to the same standards recommended for other forms of intraocular surgery.
Three types of procedure are commonly used in the UK:
LASIK, surface laser treatments
PRK, LASEK, TransPRK-different forms of PRK
SMILE
Risks and benefits are similar, and all these procedures normally produce very good results in the right patients. Differences between these laser vision correction procedures are explained below.
If you are suitable for laser vision correction, your surgeon will discuss which type of procedure is the best option for you.
You must be over 18 years of age and have a stable glasses prescription. This is normally defined as no change greater than 0.5 units (0.5D) in the last two years.
You are most likely to be suitable for laser vision correction if your glasses prescription, which can be provided to you by your optician/optometrist, is in the range:
Laser vision correction can be effective for higher prescriptions in some patients. Conversely, some patients with lower prescriptions may be better suited to lens implantation techniques.
All laser vision correction procedures are performed using eye-drop anaesthetic, and a spring clip to allow you to blink safely during surgery. You will be lying down throughout. It is usual to operate on both eyes, and the surgery typically takes about half an hour. You can return home on the same day as surgery.
LASIK (laser in situ keratomileusis) is typically performed using 2 lasers: one (femtosecond laser) to prepare a thin protective layer (the LASIK flap), which is lifted up before a second (excimer laser) removes a lens shaped piece of tissue to reshape the cornea beneath. The protective layer is then smoothed back and sticks in place and without stitches. IntraLASIK is the technique commonly used now.
SMILE (Small Incision Lenticule Extraction) uses a femtosecond laser of the same type used to create a LASIK flap to define a lens shaped piece of tissue that is removed by the surgeon through a small incision to correct focus. This is like LASIK without the LASIK flap, but the thickness of tissue removal is slightly greater and the tissue may be removed from slightly deeper in the cornea. End results are similar to those for LASIK and surface laser treatments.
Surface laser treatments (PRK, LASEK, and TransPRK) use the same excimer lasers to perform an identical removal of a lens shaped piece of tissue immediately beneath the clear skin layer of the cornea. The clear skin layer regrows over a period of about a week, then smooths off optically to complete the visual recovery over the next three months. While the skin layer is regrowing, the eye surface is normally very sore. This is one of the main differences between surface laser treatments and LASIK or SMILE, which both aim to keep the corneal skin layer intact. All surface laser treatments produce similar results, and the only difference between them is the way in which the corneal skin layer is removed. In PRK and LASEK the skin layer is removed by the surgeon – in LASEK dilute alcohol is applied to loosen the skin layer first. Some modern excimer laser systems are able to remove the skin layer as part of the reshaping treatment.
This is called TransPRK. The area of skin layer removal in TransPRK is reduced to the minimum required for reshaping the cornea beneath, shortening recovery time by 1 to 2 days in comparison with PRK and LASEK.
A cataract is a misting up of the natural lens, which sits just behind the pupil and helps to focus light on the retina. Cataract surgery involves replacing the misty natural lens with a small, clear synthetic implant called an intraocular lens (IOL). The focusing power of the IOL can be chosen to reduce dependence on glasses after surgery.
Refractive Lens Exchange (RLE) is identical to modern cataract surgery. Both operations involve replacing the natural lens with an IOL. The only difference is that cataract surgery is performed mainly to correct blur or light scatter caused by a misty natural lens; whereas RLE is performed to reduce the need for glasses or contact lenses.
IOL implantation is a bit like building your glasses or contact lenses into your eyes
There are two main IOL types:
Monofocal IOLs – monofocal IOLs aim to reduce spectacle dependence for distance (driving) vision
Multifocal IOLs – multifocal IOLs aim to reduce spectacle dependence for a wider range of activities, including intermediate (computer screens) and near (reading) vision.
If you are suitable for RLE, your surgeon will discuss which IOL type is the best option for you.
About four out of five patients are completely free of glasses after RLE with widely used contemporary multifocal IOLs.
If you do need help from glasses after surgery, it is usually for a specific activity in the near, intermediate or distance range.
Approximately 95% of patients are satisfied with the outcome of surgery, and many describe it as life changing.
Although RLE is often bracketed with cosmetic surgery procedures, the benefits are mainly functional. It is designed to make you less dependent on glasses and contact lenses, helping you to lead an active lifestyle more easily.
RLE eliminates the need for cataract surgery in later life, and it is often preferred to laser vision correction for patients in the retirement age group in whom the early stages of cataract formation are often already present.
In the absence of a new health problem in the eye, vision normally remains good, and your spectacle prescription normally remains stable after RLE. If you do experience any deterioration in vision in the years after surgery, it can often be reversed with a one-off minor laser procedure called YAG capsulotomy.
If you are over 50 years of age and have a glasses prescription higher than the normal range for laser eye surgery, you are likely to be suitable for RLE.
Almost any level of myopia (short sight) or hyperopia (long sight) can be corrected by RLE, and IOLs with built in astigmatism correction are available. Lens implantation techniques can be combined with laser eye surgery in suitable patients to extend the range of astigmatism treatment or ne-tune the focus outcome.
You may not be suitable for multifocal IOL implantation if you have pre-existing problems with your eye health.