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Surgical Vision Correction and Laser Eye Surgery

Why do some people need glasses and others don’t?

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.

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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 cataract surgery, and phakic intraocular lenses.

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Corneal Laser Vision Correction

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®.

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Surface ablation (PRK)

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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 disadvantages of laser vision correction?

Key advantages of corneal laser vision correction

  • Elegant
  • Accurate
  • Fast visual recovery (except for PRK)

Key disadvantages of corneal 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.

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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.

Refractive Cataract Surgery and Refractive Lens Exchange

Refractive Cataract Surgery (and Refractive Lens Exchange) involve removing the natural crystalline lens of your eye and replacing it with a new, artifical lens implant. The new lens implant is customised for the unique dimensions and curvature of your eye and it focuses the image sharply onto your retina.

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.

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What are the key advantages and disadvantages 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 disadvantages:

  • Intraocular risks including retinal detachment.
  • Imperfect quality of vision with some multifocal intraocular lenses.

The main risk of refractive lens exchange is the risk of a post-operative retinal detachment. To learn more about retinal detachment, click here. The risk of retinal detachment is increased in patients with short sightedness and brittle retinas, particularly if they are male. However, the risk of retinal detachment is extremely low in patients who are far-sighted. Your eye surgeon should carefully evaluate your risk of a retinal detachment and discuss this with you. Given that this issue is so important, yet relatively poorly understood, in December 2022 I released a podcast episode specifically discussing this topic (Ophthalmology Against The Rule Podcast: Retinal Detachment Risk in Lens Surgery).

To learn more about cataract surgery and refractive lens exchange, click here.

Phakic intraocular lenses

Phakic intraocular lenses are medical implants for correcting focus error of the human eye. Unlike laser vision correction and refractive lens exchange, which permanently alter the eye, phakic intraocular lenses are reversible. These implants work in synergy with your natural crystalline lens to refocus your vision.

There are two models of phakic intraocular lens available in Australia: the Artiflex and the Implantable Contact Lens (ICL).

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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.

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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.

What are the key advantages and disadvantages of phakic intraocular lenses?

Key advantages of phakic IOLs:

  • Removable / reversible.
  • No induced corneal aberrations (likely to achieve better quality of vision than corneal laser vision correction, e.g LASIK).
  • Lower risk of halos and night vision problems than corneal laser vision correction and refractive lens exchange.
  • No risk of dry eye (in contrast to LASIK).
  • Performed with the patient asleep.

Key disadvantages of phakic IOLs:

  • Usually more expensive than laser vision correction.
  • Incomplete patient suitability (not everyone is a candidate).
  • Intraocular surgery (intraocular risks).

The biggest advantage of phakic IOLs is the reversible nature of the procedure (the lens can be removed at any time). Having a phakic IOL should not leave any permanent affect on your eye. The other key advantage of phakic IOLs is the likelihood of better quality of vision than laser vision correction and refractive lens exchange. This advantage is most noticeable at nighttime, and therefore a phakic IOL may be preferred by individuals who drive frequently at night.

How do Artiflex and ICLs compare?

Advantages of Artiflex over ICLs:

  • Better quality of vision (unproven but likely)
  • Better night vision (lower risk of halos)
  • Lower risk of cataract and glaucoma
  • Less expensive

Advantages of ICLs over Artiflex:

  • Much easier to implant (preferred by most eye surgeons)
  • Lower risk of corneal endothelial cell loss (slow, progressive degeneration of the cornea requiring removal of the lens)

The main factor limiting uptake of Artiflex lenses by eye surgeons is the relatively steep learning curve to master the surgical technique. However, once an eye surgeon is comfortable with the procedure, Artiflex lenses can offer numerous advantages for their patients. I prefer to use Artiflex lenses due to the reasons listed in the table above.

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Above: an Artiflex lens implanted by Dr Andrew. This patient’s vision improved from 6/48 to 6/5 without glasses, within just 24 hours of their surgery. They were delighted with the result. Although this outcome is not uncommon, it is important to note that individual results can vary.

Monday to Friday: 8am – 4.30pm

Dr Nick Andrew

Ophthalmologist and Eye Surgeon Gold Coast

Sight Specialists, 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.