LASIK / Refractive Surgery
In a normal eye that does not need optical correction, light rays from a distant object are focused by the cornea and lens to come to a sharp focus on the retina. Refractive errors are lead to production of a blurred image on the retina, and can be due to multiple factors, such as the eyeball being too long, or the cornea being too steep and having too much optical power.
Myopia, or short-sightedness, is the most common refractive error of the eye. Myopia produces blurred distance vision, but near vision is clearer. The earliest symptoms of myopia may be blurred vision reading whiteboards or street signs. Myopia generally stabilizes in early adulthood, however it may progress into adulthood.
Myopic eyes are usually longer than average, so when light rays enter, they come to a focus before reaching their destination, which is the retina at the back wall of the eye. Occasionally myopia is due to having a steeper cornea.
Myopia is often corrected with spectacles or contact lenses. Myopia may also be corrected surgically with LASIK, advanced surface laser ablation (ALSA), implantable lenses, refractive lens exchange or with cataract surgery.
Hyperopia, or long-sightedness, is a refractive error which causes light rays entering the eye to be focused behind the retina, causing difficulty seeing objects up close. The eyeball of a long-sighted person is typically shorter than normal, but it may be due to the cornea being flatter than normal (having less optical power).
The earliest symptom of hyperopia may be eyestrain, fatigue or headache with prolonged close work. This is because the eye is straining to use its focusing power to make an object clear. As the eye gets older, it gradually loses focusing power, and hence a person with hyperopia will eventually develop blurred distance vision as well.
Long sightedness is often corrected with spectacles or contact lenses and may be corrected surgically with LASIK, advanced surface laser ablation (ASLA), implantable lenses, refractive lens exchange or with cataract surgery.
Astigmatism is a common refractive error of the eye, which causes blurred vision at all distances. Images produced by an eye with astigmatism are blurred and appear elongated in one direction. Astigmatism is usually produced in the cornea (the front window of the eye), where it is steeper in one axis instead of a symmetrically round shape – more like a rugby football than a soccer ball. It may also be produced from the lens or retina. Like myopia and hyperopia, astigmatism is often corrected spectacles, contact lenses, or toric intraocular lenses.
Astigmatism is regarded as regular when the shape of the cornea is symmetrical (producing a pattern like a figure 8). Regular astigmatism can be corrected with spectacles or toric soft contact lenses. When the shape of the cornea becomes distorted, and asymmetrical, the astigmatism produced is irregular. Irregular astigmatism cannot be ideally corrected with spectacles or standard contact lenses; irregular astigmatism may require specialty contact lenses for correction. It can also be corrected with surgery such as intracorneal ring segments or topographic-guided laser treatment.
Presbyopia causes blurred vision for near activities, and results from a gradual loss of focusing power of the natural lens of the eye. This loss of focusing power is a normal process in the eye. It typically causes symptoms of eye strain, headache and blurred vision with prolonged near work. When people develop presbyopia, they find they need to hold reading materials further away in order to focus properly. They may have difficulty reading menus in restaurants, and find they need a stronger light to read.
Presbyopia is caused by an age-related process in the lens of the eye, making it stiffer and less able to increase curvature to increase focusing power to see clearly for near. Typically, the first symptoms may occur in the mid-forties. It differs from myopia, hyperopia and astigmatism, which are related to the shape of the eyeball and are caused by genetic and environmental factors.
Presbyopia is usually corrected with reading glasses, bifocal spectacles, or multifocal spectacles. It can also be corrected with contact lenses, with “monovision” (where one eye is corrected for distance, and one eye is corrected for near), or multifocal contact lenses.
LASIK (Laser-assisted in-situ keratomileusis) surgically treats common refractive errors: short-sightedness (myopia), long-sightedness (hyperopia) and astigmatism. It is the most commonly performed procedure to treat refractive errors, particularly because visual recovery is rapid and discomfort is minimal.
Modern LASIK involves two steps. The first step is to create a very thin flap on the surface of the eye with a femtosecond laser that is then lifted back, a second laser then reshapes the underlying cornea to correct the refractive error. The flap is then carefully repositioned and then maintains its position by natural adhesion. No stitches are required.
LASIK may be customised to treat fine optical aberrations from an individual’s eye. This involves taking detailed measurements of the eye’s optical aberrations (wavefront scans), which are used to program the laser. Custom LASIK (or wavefront-guided LASIK) is therefore individualised to treat each eye’s minute optical imperfections.
LASIK is usually performed on both eyes on the same day, and takes about 30 minutes. Visual recovery is usually very rapid with little or no discomfort post operatively. Local anaesthesia in the form of drops is used prior to the procedure, as well as a mild oral sedative. You can usually return to work, and even drive within 24 hours after surgery.
Surface ablation is a laser vision correction procedure to treat common refractive errors: short-sightedness (myopia), long-sightedness (hypermetropia) and astigmatism. Various surface ablation techniques are also known as PRK (photorefractive keratectomy), ASLA (advanced surface laser ablation), and LASEK (Laser-assisted sub-epithelial keratectomy).
Unlike LASIK, there is no flap created in the front of the cornea. Instead of creating a flap, the surface cells (epithelial cells) are removed and the underlying corneal surface is then reshaped with the laser and covered with a bandage contact lens. The corneal surface (epithelium) then heals over the top of the treated area. The visual outcomes of surface ablation and LASIK are similar, however, the visual recovery after LASIK is faster, and discomfort after LASIK is lower.
Surface ablation does have has a number of advantages. Because there is no corneal flap, surface ablation can be performed in some thin corneas that are not suitable for correction with LASIK. Also, surface ablation may be the preferred option in some people who engage in activities or occupations that are at high risk of producing trauma to a corneal flap, such as boxers. Surface ablation may also be a better option in some cases where corneal scarring can also be treated simultaneously. Like LASIK, surface ablation can also be customised to treat the minute optical imperfections of the eye. Surface ablation, unlike LASIK, can be used in corneal thinning diseases (ectasias), particularly in combination with corneal collagen cross-linking (CXL) to strengthen the cornea.
Not all individuals are suitable for surface ablation, which requires a consultation and extensive investigative tests to determine suitability. Some patients may be better candidates for other refractive procedures.
Dr Daya Sharma is a refractive and corneal subspecialist. He has undergone fellowship training in corneal and refractive surgery at Moorfields Eye Hospital in London (one of the world’s most prestigious training institutions). For an appointment with Dr Daya Sharma to assess your suitability for advanced surface laser ablation (ASLA), call 9387 5300 (Bondi Junction) or 9531 5300 (Miranda).
Phakic intraocular lens implantation (eg Implantable Collamer Lens (ICL)) treats myopia, hyperopia or astigmatism. A specialised lens is implanted through a micro-incision in the cornea, and then placed in front of the natural lens. It leaves the natural lens of the eye intact, so that the eye retains its ability to change focus from distance to near. Vision correction with an ICL offers high quality unaided vision over a large range of refractive errors. Unlike LASIK or surface ablation, it does not involve reshaping of the cornea. The correction can be reversed by removing the lens.
Implantable lenses are a particularly good option when laser vision correction is not a viable option such as: a high refractive error outside the range of LASIK or surface ablation. The ICL can treat myopia up to -20D, hyperopia up to +10D, and astigmatism up to 6D. ICL can also be combined with laser vision correction in a procedure called bioptics. ICL implantation can also be used in combination with other procedures to treat high refractive error in conditions such as keratoconus.*
*Coşkunseven E, Sharma DP, Jankov MR 2nd, Kymionis GD, Richoz O, Hafezi F. Collagen copolymer toric phakic intraocular lens for residual myopic astigmatism after intrastromal corneal ring segment implantation and corneal collagen crosslinking in a 3-stage procedure for keratoconus. J Cataract Refract Surg. May 2013; 39(5):722-9.
Refractive Lens Exchange (RLE) is a form of vision correction surgery in which the natural lens of the eye is removed through a micro-incision and replaced with a specialised intraocular lens to correct the refractive error, in order to improve the vision without glasses or contact lenses. RLE is best suited to people who already dependent on reading correction, and want a permanent solution to their refractive error. If the natural lens still has a useful capacity to change focus, other refractive procedures are usually preferred if the eye is suitable.
RLE is technically a similar procedure to cataract surgery, in which the cloudy lens (cataract) is replaced with an artificial intraocular lens. However, in the case of RLE, the natural lens is clear, and the intention of the procedure is purely to correct the refractive error of the eye. One of the advantages of RLE is that it prevents the requirement for cataract surgery in the future, which is why it is a more permanent solution to correcting the refractive error.
Another advantage of RLE is that it can correct an extreme range of refractive error (including myopia, hyperopia and astigmatism), especially with the use of customised intraocular lenses.
There are many intraocular lens models and strategies available to correct the vision with RLE. Lens types include monofocal designs (single focus lenses), and multifocal designs (bifocal and trifocal). Intraocular lenses are chosen according to the individual’s visual requirements and suitability for various lenses. At Eye & Laser Surgeons, we are meticulous with our consultations, measurements of the eyes, and intraocular lens choices in order to produce the best solution for the individual. We choose the most appropriate intraocular lens for the individual’s requirements.
A secondary intraocular lens implantation is a vision correction procedure that can be used after previous cataract surgery. The secondary lens “piggybacks” in front of the existing intraocular lens, and can be used to correct residual refractive errors (hyperopia, myopia or astigmatism) after cataract surgery. Secondary lenses with a multifocal designs are also available, which are a useful option for those who want more spectacle independence after successful cataract surgery.