A Guide to Laser Eye Surgery and Medical Conditions
Can I have laser eye surgery, if I have the following conditions?
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
Laser 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.
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.
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