Surgical Vision Correction and Laser Eye Surgery
Why do some people need glasses and others don’t?
Dr Nick Andrew is a laser eye surgeon who uses the laser to improve eyesight – whether you suffer from near-sightedness, far-sightedness, astigmatism or presbyopia. Many of these conditions occur in young people, although presbyopia is most closely associated with middle age.
The human eye is designed much like a camera. The retina is the camera film at the back of the eye that captures the image. The role of the human cornea and crystalline lens is to focus the incoming light onto the retina. If the light is not focussed correctly, then the person will have blurry vision and they will require glasses or a contact lens in order to see clearly.
There are 4 main types of focus error.
Myopia (near-sightedness). The eye can see well up close without glasses, but distance vision is blurry. Without glasses, the image is focused in front of the retina.
Hyperopia (far-sightedness). Distance vision is somewhat blurry, and vision becomes increasingly blurry as the object moves closer. Without glasses, the image is focused behind the retina. Children and young adults can compensate for far sightedness by “accommodating”. Accommodation involves the contraction of tiny muscles inside of the eye to increase the focusing power of the lens. Hyperopic patients who accommodate all day (instead of wearing glasses) are more likely to experience eye strain.
Astigmatism. The image seen is stretched in one direction. Most patients with astigmatism do not perceive that the image they see is stretched, but instead they simply report that their vision is blurry.
Presbyopia. Loss of accommodation due to stiffening of the crystalline lens with age. Presbyopia is the reason why individuals who have never required glasses before will begin to need reading glasses at around age 45.
What is surgical vision correction?
Surgical vision correction is a broad term that includes all surgical procedures available to correct the focus error of an eye. The purposes of these operations is to give you freedom from glasses and contact lenses.
The main approaches are:
- Corneal laser vision correction
- Refractive Lens Exchange (RLE)
- Phakic Intraocular Lenses
How can your eyesight be corrected?
Corneal laser vision correction (LVC) uses a laser to reshape the curvature of your cornea. For example, if your cornea is too powerful for the length of your eyeball (myopia), then the laser treatment will flatten your cornea, to reduce its focusing power. The laser pattern applied to the cornea is customised for each patient, to precisely treat the unique focus error of the individual.
The only way a laser can reshape your cornea is by removing tissue from it, to make it thinner. By thinning different areas of the cornea by different amounts, a wide variety of focus errors can be treated. An excimer laser vaporises corneal tissue, whereas a femtosecond laser cuts it.
There are three main techniques of laser vision correction: PRK, LASIK, and SMILE®.
Surface ablation (PRK)
LASIK
SMILE
In PRK, the surface layer of the cornea (the epithelium) is removed using either a blunt instrument or laser energy. An excimer laser is then applied directly to the corneal stroma. Because the laser energy is applied to the surface of the eye, PRK is also known as ”surface ablation”. The disadvantage of PRK is the severe pain following the procedure until the corneal epithelium heals. As such, patients typically require one to two weeks off work to recover.
In LASIK, a flap of corneal tissue is cut and retracted. The excimer laser is applied to the eye and the corneal flap is reposited.
In SMILE®, a femtosecond laser is used to cut a thin disc of corneal tissue. This disc is then removed by your eye surgeon through a keyhole incision. SMILE is therefore sometimes described as “keyhole LASIK”.
There are advantages and limitations of each technique and no procedure is perfect. The procedure that is best for you will depend upon your focus error, the thickness of your cornea, the health of your eye, and your lifestyle.
What are the advantages and limitations of laser vision correction?
Advantages of laser vision correction
- Elegant
- Accurate
- Fast visual recovery (except for PRK)
Limitations of laser vision correction
- Incomplete patient suitability
- Cornea too thin
- Keratoconus
- Hyperopes
- Creates corneal aberrations
- Dry eye (less with PRK)
- Permanent (irreversible) corneal change
- Patient is awake during the procedure
Laser vision correction (LVC) is an elegant procedure and it is the best option for many patients. However, in my opinion there are two main limitations of LVC that are often underappreciated: the creation of permanent corneal aberrations (corneal irregularities) and post-operative dry eye.
Dry eye, or ocular surface discomfort, is more common following LASIK. It is thought to be caused by the sensory nerves of the cornea being cut by the LASIK flap. In young people, the dry eye symptoms usually resolve spontaneously, but in older individuals, dry eye is more likely to persist. For this reason, LASIK may not be the best treatment option if you are older or if you suffer from pre-existing dry eye.
The creation of corneal surface irregularities is an inevitable consequence of laser vision correction. By reshaping the cornea, the laser creates a corneal contour that is unnatural. The incoming light is slightly scrambled by this unnatural shape. This is why some patients report seeing halos and glare at night following LASIK. This problem is more common when the corneal curvature needs to be profoundly altered in order to correct a large focus error.
The above figure illustrates a relatively common side effect of laser vision correction. The image on the left shows a curvature map of a normal cornea. The curvature is displayed using colours, just like a geography map displays the curvature of terrain. Following LASIK to correct myopia, the centre of the cornea is flattened (white arrow, dark blue colours). The image on the right illustrates imperfect clarity of vision seen by a patient following LASIK, due to their irregular corneal curvature scrambling the incoming light. This patient is likely to see halos and glare when driving at night. This complication can be avoided by seeing an eye surgeon that is meticulous with their patient screening and conservative with their laser treatments.
“Cataract surgery” is the term used when a patient’s lens has become cloudy. Cataract surgery is a medical procedure and it therefore attracts a Medicare rebate (and a private insurance rebate if applicable). “Refractive lens exchange” is the term used when the surgery is performed proactively, before a cataract develops, with the sole aim or reducing a person’s need for glasses. Refractive lensectomy is a cosmetic procedure and as such it does not attract a rebate from Medicare or your private health insurer. Nevertheless, each year thousands of Australians choose to have a refractive lensectomy.
What are the key advantages and limitations of refractive lens exchange?
Key advantages:
- Permanent vision correction. A refractive lens exchange can result in lifelong freedom from glasses.
- Can restore the full range of vision to each eye, from near to far.
Key limitations:
- Intraocular risks including retinal detachment.
- Imperfect quality of vision with some multifocal intraocular lenses.
There are two models of phakic intraocular lens available in Australia: the Artiflex and the Implantable Collame Lens (ICL).
Above: the Artiflex lens clasps onto the iris to remain securely centred over the pupil. It is constructed from silicone and PMMA plastic. These materials that have excellent compatibility with the eye and have been routinely used for intraocular devices since the 1950s.
Above: the implantable contact lens (ICL). These lenses sit between your iris and your natural crystalline lens. They are so thin that they can be difficult to see, even with a microscope (white arrow). Note the whole in the centre of the lens (left image). This hole is required to reduce the risk of cataract formation, but in my experience, it can unfortunately contribute to patients seeing halos around lights at night following the surgery.
Why should I see Dr Andrew for phakic intraocular lens surgery?
- Dr Andrew is the only surgeon in Australia who implants both types of phakic intaocular lens – the ICL and the Artiflex lens.
- Dr Andrew can provide what is best for each patient.
- Our clinic has state-of-the-art technology for planning ICL and Artiflex surgery.
Monday to Friday: 8am – 4.30pm
Dr Nick Andrew
Ophthalmologist and Eye Surgeon Gold Coast
Level 2, 95 Nerang St, Southport QLD 4215
Medical disclaimer
The content provided on this website is for educational purposes only. It is not intended to provide medical advice or to take the place of such advice or treatment from a personal physician.
All readers/viewers of this content are advised to consult their doctors or qualified health professionals regarding specific health questions.
Neither Dr. Andrew nor the publisher of this content takes responsibility for possible health consequences of any person or persons reading or following the information in this educational content.
All surgical procedures carry risk. Before proceeding with any operation, always consider obtaining a second opinion from an appropriately qualified health practitioner.