A Guide to Laser Eye Surgery and Medical Conditions

Can I have laser eye surgery, if I have…

In recent years, laser eye surgery has become an established surgical procedure to manage most degrees of myopia (short-sight), low and moderate levels of hyperopia (long-sight), and astigmatism. The need for reading glasses can also be treated through a Blended Vision laser approach.

Laser eye surgery is an elective method generally performed in young to middle-aged healthy people who perceive refractive correction by spectacles or contact lenses to be a frustration, cosmetically unappealing or a limitation to their active lifestyles.

Meticulous evaluation of ocular and general medical conditions is imperative to ensure that only right candidates for successful treatment will undergo the procedure.

Diabetes and laser eye surgery

Man checking blood sugars with glasses - awaiting laser eye surgeryLaser eye surgery is now considered a common procedure with about 100,000 people undergoing this treatment in the UK each year. Given the prevalence of diabetes worldwide, diabetic patients make up a significant percentage of the patients who desire elective laser eye surgery.

The number of diabetic patients seeking laser eye surgery is expected to increase in the next 10 years, as the 79 million pre-diabetic patients develop outright diabetes.

Diabetes alone does not automatically exclude a patient from refractive surgery, but there are some important considerations, particularly on the choice of procedure.

Factors considered before laser eye surgery in diabetes:

1. Consistent glasses power and no fluctuations in prescription for the past 2-3 years.
2. Normal pre-LASIK evaluation, including corneal topography, corneal thickness, muscle balance testing, dry eye tests.
3. Normal retina checkup with no worse than mild, non-proliferative diabetic retinopathy, as there is no greater incidence of complications in the patients with mild retinopathy than in those without.
4. Normal eye pressures with a normal healthy optic nerve.
5. Well controlled sugar levels documented by strict glycemic control and certified by the diabetologist.
6. No prior or current diabetes-related health problems like nerve damage (neuropathy), kidney disease (nephropathy) and problems affecting the cornea.

Diabetes does not automatically disqualify from laser vision correction

Should I have LASIK or PRK if I have diabetes?

In diabetic patients, the laser eye surgery technique used is very important. LASIK is the treatment of choice due to more rapid healing and less inflammation.

PRK or LASEK, where the surface skin layer (epithelium) is removed, can lead to significant complications in some patients. Abnormalities in the cornea are common in diabetes and may lead to slow or imperfect healing after PRK or LASEK refractive surgery. Delayed epithelial healing, persistent epithelial defects, neurotrophic (nerve) changes, and persistent erosions after PRK may last a long time.

Risk of corneal infection in diabetes

The epithelium may not heal as well in diabetic patients. The underlying corneal collagen (stroma) is exposed for a significant post-operative period until re-epithelialization is complete, increasing the risk of infection.

The chance of getting an infection, though rare, is three times greater with PRK than with LASIK. A recent study put the risk of infection after PRK as 1 in 7,000, whereas the chance following LASIK was much lower at 1 in 21,000.

Diabetic patients are known to be more prone to developing infections in general, so any procedure that poses an increased risk, such as the surface laser approaches of PRK or LASEK, should be avoided.

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LASIK for diabetic patients

In LASIK, the epithelial skin layer is not removed. Instead, a thin flap is created on the cornea with a femtosecond laser. This flap is lifted to expose the underlying corneal tissue and is replaced after the cornea is reshaped with an excimer laser.

The main advantage of LASIK over PRK is related to maintaining the central corneal epithelium which has the following benefits:

• Increases comfort during the early post-operative period,
• Allows for rapid visual recovery,
• Reduces the wound healing response
• Decreases the risk of post-surgery infection and inflammation, which is essential for diabetic patients with compromised immunity.

Diabetic patients may be considered suitable candidates for laser eye surgery only after a thorough preoperative assessment reveals evidence of excellent glucose control for at least 1 year prior to surgery, and confirms a lack of systemic complications.

Diabetes needs to be well-controlled before having LASIK or other refractive eye surgery

 

Glaucoma, ocular hypertension and laser eye surgery

Glaucoma is not considered to be an absolute contraindication to Laser-Assisted in situ Keratomileusis (LASIK), but so far it is a relative one. Treatment may be possible but only if certain conditions are met.

People who are glaucoma suspects or who have established glaucoma may seek to improve their vision through laser refractive surgery. LASIK is the most popular laser vision procedure due to its rapid results and almost pain-free technique, but the procedure involves a temporary high pressure on the eye.

Glaucoma is a group of diseases characterised by optic nerve damage with loss of parts of the visual field, typically in the mid-periphery. The higher the pressure inside the eyes, the greater the chance of visual field loss. Patients that receive a transient but significant rise in intraocular pressure (IOP) during a LASIK surgery have a risk of further optic nerve damage.

Furthermore, steroids drops which are normally used after refractive surgery can increase intraocular pressure (IOP) especially in steroid responders, who are more prevalent among glaucoma patients. However, a short course of steroids of 5-7 days, e.g. after LASIK, may not be long enough to create a pressure rise.

Glaucoma patients interested in refractive treatment may visit a glaucoma specialist or a surgeon who has had experience with performing LASIK or PRK in glaucoma patients.

LASIK in glaucoma patients presents a challenge to physicians

Issues raised by glaucoma in laser eye surgery:

1. Optic nerve damage with visual field changes – LASIK treatment involves an elevation in the intraocular pressure (IOP) which may cause further damage to the optic disc.
2. Corneal thickness affects common methods of measuring IOP – laser eye surgery will cause some thinning of the cornea so affecting the reading. IOP will be artificially lower after LASIK or PRK.
3. Steroids, which are typically used after refractive surgery, can increase intraocular pressure (IOP) especially in steroid responders, who are more prevalent among glaucoma patients.

LASIK can still be an option for a patient with glaucoma, particularly if the pressure within the eye is considered to be under control and the nerve fibres at the back of the eye are not damaged. This can be assessed through an OCT scan.

The common alternative forms of laser eye surgery, PRK and LASIK, produce identical results but differ in the pressure applied to the eye during the procedure. (Table1). PRK generally causes less of a pressure increase during the surgery so is sometimes the favoured method of laser vision correction.

Following LASIK or PRK, a glaucoma patient must be aware that future measurements of IOP must be adjusted to determine a true reading. While this is not difficult, it is an extra consideration to ensure that the glaucoma treatment is still effective.

A newer device, the Pascal tonometer, measures the pressure inside the eye independent of the corneal thickness and is preferred for patients who have had prior laser refractive surgery.

Ocular hypertension or pre-existing glaucoma should not be an absolute contraindication for LASIK or PRK surgery, but it should be a relative contraindication because every patient has to be evaluated individually.

It’s important to note that, while glaucoma does not automatically mean refractive surgery is not possible, the individual’s glaucoma should be treated and the condition must be stable before refractive surgery can be undertaken.

 

Increases IOP No changes in IOP
1 Wave-Front LASIK
2 LASIK
3 Epi-LASIK
4 PRK
5 LASEK
6 P-IOL
7 RLE
8 CK
Table 1. Laser techniques and IOP changes

Multiple sclerosis and laser eye surgery

A person with MS should not be precluded from LASIK surgery (or PRK surgery) simply because they have MS, but it is recommended to go a thorough neuro-ophthalmological evaluation before this surgery is considered.

The most important issues to consider prior to corrective surgery are the following:

1. For any patient considering refractive surgery, both eyes should see well when wearing glasses. We would not treat a patient, for example, with only one good eye. MS can affect vision and any significant loss in visual acuity would exclude the patient from vision correction.
2. The presence of dry eyes. Dry eye disease makes an individual more susceptible to infection, blurry vision and discomfort after surgery. Dry eyes are fairly common in MS patients, often due to medications.
3. The correct assessment of the aetiology of the vision problems. Any visual field problems from MS or problems involving the optic nerve or retina will not be improved by surgical vision correction.
4. Cataracts are also fairly common at an early age in MS patients (usually from multiple steroid treatments) and would be a contraindication for LASIK surgery.
5. MS treatment considerations. It is recommended to be off chemotherapy agents and steroids for at least 6 months before considering LASIK surgery.

Epilepsy and laser eye surgery

As long as patients are well controlled on their conventional anti-epileptic medication, there is no reason why an individual shouldn’t have laser eye surgery. The type of light that is used in the procedure is not strobe lighting, so this eliminates the concern that a flashing light may promote an epileptic attack.

Even photosensitive epilepsy, when the brain has an abnormal response to a certain sequence of flashing lights, should not be an impediment to laser eye surgery.

Other photosensitive persons will experience problems with only a certain wavelength of light. Light of ~700 nm has been identified as a specific trigger for seizures.

In LASIK or PRK procedures, the excimer laser uses a wavelength of 193 nm to remove the corneal stroma and it takes only 5-20 seconds to complete. An infrared laser, used to create the flap, has a wavelength of 1053 nm and takes less than 20 seconds to create the flap.

Femtosecond treatments use typical pulses that are in the microjoule range of energy. These characteristics of the newer technologies exclude the risk of inducing an epileptic attack in these patients.

Pacemaker and laser eye surgery

The LASIK procedure is used to modify the cornea at the front of the eye to improve vision. The excimer laser used for the LASIK procedure is an ultraviolet laser, which utilises argon and fluorine gas to create a non-thermal, or cool beam.

Medical devices, including lasers, can create variations in the electromagnetic field. The concern for pacemakers is that they may detect these variations and interpret them as being cardiac in origin.

Newer pacemaker models are unaffected by laser emissions. A study by Professor Nei Sher in Minneapolis looked at various designs of pacemaker and various ophthalmic lasers and they were unable to trigger any device with any level of energy used.

According to the study authors, “The signals [from the lasers] did show up as interference that was in the environment. There was no reaction from the pacemakers to these signals, however. The pacemakers successfully diagnosed this interference as something that was irrelevant and more or less discarded it as far as its programming was concerned.”

Some pacemakers that are more than twenty years old could be affected by electromagnetic fields emitted by equipment like the excimer laser. Patients with older pacemakers can still have LASIK or PRK, but they may require that a technician be present to oversee the pacemaker.



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