The Risks of Laser Eye Surgery

What are the risks of laser eye surgery?

It seems a simple question, yet if you’ve ever tried searching the web and finding out the answer then it can seem anything but.

It isn’t because it’s too complicated or difficult to work out. It isn’t even because there aren’t enough studies or data to draw from.

The risks of Laser Eye Surgery is such a tricky topic because there are too many opinions, providers, stories, and sites that think they have the answers. And despite many having good intentions, a lot of the time they have a hidden agenda.

Risk is present in every surgical technique, no matter how small, and it would be foolish to pretend otherwise. There is indeed a very small risk that Laser Eye Surgery may compromise your vision so that neither glasses nor contact lenses are able to sharpen vision back to a pre-surgery state. That’s a fact.

However, it’s also a fact that this risk can vary greatly, depending on many factors, to the point it barely even exists. For this reason, managing risk in Laser Eye Surgery is a matter of the following:

Here we’re going to go through a few of these points in more detail so that the risks of Laser Eye Surgery are much clearer.

The best way to reduce Laser Eye Surgery risks

The above would make it seem like having laser eye surgery is as straightforward as going to the dentist. This would be far from the case, though, as the Laser Eye Surgery industry is unregulated.

This means clinics and the standards they employ differ greatly from one to the next. Thanks to the RCOphth, the Royal College of Ophthalmologists, there are recommended guidelines to follow, but to what extent a clinic does so is entirely up to them.

Although this can make the landscape a bit tricky to navigate, if you are equipped with the right tools and a little bit of know how, you can avoid the low-quality clinics and ensure you are in incredibly safe hands.

All surgery has an element of risk

Although the vast majority of our patients experience a significant improvement in their vision, neither your laser eye surgeon, your optometrist, London Vision Clinic, nor its staff, can guarantee that the procedure will be 100 percent effective or free from complications.

Any clinic you go to should be upfront about this. During your pre-operative examination, you should find out your proposed outcome (e.g. the chances of you seeing well without glasses or contact lenses after surgery) based on the level of your particular refractive error.

The safety level of laser eye clinics

The key to managing risk lies in the rigorous application of safety protocols. Those in place at London Vision Clinic are the direct results of Professor Reinstein’s earlier work in the USA, in training and controlling the quality of 58 surgeons in 28 clinics, all operating under standardised protocols defined by his research.

It was by studying the work of these 58 surgeons that he was able to determine exactly what allowed some surgeons to perform better than others. Mr. Carp now applies that knowledge to their own practice at London Vision Clinic.

The possibility of complications

There is a very small possibility that the procedure or a complication arising from the procedure will cause your vision to be blurred, doubled, distorted, or to have halos or other disturbances, and that these would NOT be correctable with glasses or contact lenses.

The likelihood of such a complication relates to the thoroughness of preoperative testing, the expertise and skill of the surgeon, the equipment they are using and the degree of follow-up care.

London Vision Clinic has an exceedingly low complication rate. In the event that a complication should occur, your laser eye surgeon will discuss and offer you advice on further treatment, which may involve medications or more surgery.

A complication rate that’s as low as it gets

At London Vision Clinic, we pride ourselves in knowing that we’ve never discharged a patient from our care with unresolved issues. Professor Reinstein’s protocols ensure that all our surgeons can deal with any possible complication in the most prompt and expert way possible.

On top of that, we offer comprehensive aftercare. This ensures that if any questions ever arise in the future, we will not abandon you to find appropriate help on your own. Once you have had a treatment, we consider you our patient for life, even if you should require specialised ophthalmic care that unrelated to your laser eye surgery, we could refer you to the appropriate specialist.

The long term outcomes of Laser Eye Surgery

It’s necessary to mention that because of the age of the treatment, as of yet there are no published very long-term outcomes of Laser Eye Surgery.

However, corneal flaps have been created in the cornea for approximately over 50 years (in procedures such as keratomileusis as described and performed by Barraquer since the 1950’s), the excimer laser has been used for almost 20 years in the cornea, and there have been approximately 30 million procedures performed to date worldwide.

Professor Reinstein was one of the key contributors to the National Institute of Health and Clinical Excellence (NICE) Guidance Document on LASIK (2006), which determined that the “current evidence suggests that photorefractive (laser) surgery for the correction of refractive errors is safe and efficacious for use in appropriately selected patients.”

The Guidance Document also didn’t mention any serious concerns about the long-term safety of the procedure, if performed with the latest technology and techniques.

Laser eye surgery risks described

Although it’s not physically possible to list every single potential risk or complication that may result during or following any procedure, it is possible to get a very good idea of them.

This is what we’ve done below.  And although at first glance it can seem there are many possible risks to the treatment, today they have an incredibly small chance of occurring, especially if you find a highly trained, competent surgeon.

Risks and complications that can occur during surgery

ConditionProbability of OccurrenceSolution
Under-correction or over-correctionMore common with higher prescriptionsMitigated by planned 2-stage treatments; correctable with an enhancement
Corneal flap complicationsRare in expert hands (1 in 1000)Mitigated by expert use of equipment; correctable with an enhancement
Debris under the corneal flapRare in expert hands and will likely not affect visual resultMitigated by stringent adherence to superior safety protocols; correctable with an enhancement
Diffuse Lamellar Keratitis, or “Sands of the Sahara”Rare in expert hands (1 in 500)Mitigated by stringent adherence to superior safety protocols; correctable with an enhancement
Equipment malfunctionExtremely rare in expert handsMitigated by stringent adherence to superior safety protocols; correctable with an enhancement
Vascular occlusion1 in 1 million

Risks and complications that can develop after surgery

ConditionProbability of OccurrenceSolution
Dry EyesCommon, but generally temporaryCan be mitigated with dry eye testing prior in assessment; managed with lubricating drops
RegressionMore common in higher prescriptionsCorrectable with an enhancement
Night vision – glare, starbursts and halosExtremely rare, mostly temporaryCan be avoided through the use of newer lasers and high resolution wavefront aberrometers; correctable with an enhancement
Light sensitivity, fluctuating visionVery rare, mostly temporaryWill decrease in time
InfectionVery, very rare (1 in 5,000), extremely low chance of affecting visual resultCan be avoided through stringent safety protocols; can be managed with antibiotics
Excessive corneal hazePart of the healing process in surface procedures ( PRK / LASEK); higher risk in higher prescriptionsDependent on smoothness of the surface created by the laser; will often disappear; correctable with an enhancement
Fragility on impactPart of healing process 3 months after LASIKCan be mitigated by following aftercare instructions
Corneal ectasiaExtremely rareCan be mitigated by screening for keratoconus or unusually thin corneas using Artemis Insight 100
Epithelial erosionRare (1 in 500), more in older patientsCan be identified prior to surgery; can be managed by a bandaged contact lens
Epithelial ingrowthRare (1 in 100)Can be corrected with an enhancement
Other extremely rare complicationsExtremely rare (1 in 50,000)Dependent on complication

Discussing Laser Eye Surgery risks and complications one by one

Under-correction or over-correction

Although often classed as a ‘complication’, strictly speaking under- or over-correction of your prescription is not a complication. A complication is the blurring or doubling of vision that is not correctable with glasses.

In under- or over-correction, the vision may be blurred or double, but glasses can correct it to the level of sharpness present before surgery. This can happen when, despite all precautions and the highest standard of care, the healing response of the eye leads to slight inaccuracies in the final correction.

Your laser eye surgeon will be able to advise you during your rigorous screening program of the likelihood that you would not have sufficient remaining corneal tissue for enhancements.

The chances of under- or overcorrection increases for older lasers and lasers with less strict maintenance schedules. Further to this, clinics that do not employ a digital statistical system for fine-tuning the treatment parameters may risk having more complications.

Corneal flap complications

A corneal flap can be too thin, too thick, uneven, too short, may wrinkle, become displaced or may not heal properly. These conditions can often be temporary, requiring the surgeon to postpone the  LASIK procedure until they can create a new corneal flap.

Quoted corneal flap complication rates in the medical literature range from 0.3 percent to 1.0 percent. In contrast, London Vision Clinic’s corneal flap complication rate is closer to 0.1 percent.

Debris under the corneal flap

There can sometimes be a small amount of debris or tissue under the corneal flap after the surgeon has completed the LASIK procedure. Debris can result from the instruments used or consist of tear-film oil or floating material.

Your laser eye surgeon may decide in the immediate post-operative period to irrigate beneath the corneal flap to remove this debris. Small amounts of debris can generally be left in place and monitored without surgical intervention. In almost all cases, debris under the corneal flap does not affect the patient’s visual result.

Luckily, however, due to the advacement of the technology used in the procedure, today this complication is all but avoidable at the right clinics.

Diffuse Lamellar Keratitis or “Sands of the Sahara”

One in 500 patients experience a temporary inflammatory reaction beneath the corneal flap. This condition has been called “Sands of the Sahara” or Sporadic Diffuse Lamellar Keratitis (also known as “Sporadic DLK”).

Patients with DLK may not show any symptoms at all or may experience blurred vision and tearing, which can last from several days, up to several weeks and can delay the healing process.

Surgeons manage DLK with the use of supplemental topical steroid eye drops. Usually, with aggressive management, there are no longer-term effects of DLK. However, significant levels of DLK may reduce the accuracy of the vision correction, so the likelihood of requiring an enhancement is increased.

Equipment Malfunction

Laser Eye Surgery is a high-tech procedure, and all equipment should be maintained according to manufacturer specifications.

However, despite regular maintenance, like could be said about all machines, the microkeratome or the excimer laser could malfunction, requiring the surgeon to stop the procedure before completion.

In some instances, this could result in a rescheduling of the procedure or damage to the vision. Clearly, the modernity, maintenance, and quality of the equipment influence the likelihood of equipment malfunction, especially as more modern equipment can have systems in place which safeguard against such rare events causing any damage to the eye.

Vascular Occlusion

When the suction ring is applied to the eye during the corneal flap-making process, the pressure in the eye increases significantly and many patients notice that their vision will dim or go out completely. When the suction ring is removed, vision is restored to the eye within a few seconds.

There is an extremely remote risk that when the suction ring interrupts the blood supply to the eye, permanent damage to the retina (the film of the eye) or blood vessels in the retina can take place, with loss of vision. This possible occurrence has a theoretical probability of less than 1 in 1,000,000, which is again reduced even further according to the technology and surgeon.

Dry Eyes

Dry eye is a common but generally temporary complication that patients can typically expect after LASEK / PRK or LASIK.

This condition can usually be treated with lubricating eye drops and occasionally with temporary inserts or “plugs” that prevent the normal drainage of tears into the nose. Dry eye almost always improves within a few months after treatment, but in rare instances can continue for longer periods of time, and may require long-term use of lubricant drops and permanent plugs.

Patients who have dry eyes before LASIK or LASEK / PRK are likely to experience dry eyes after the procedure, and therefore a thorough screening program is key to minimising the risk.


The cornea is living tissue. Once the laser removes tissue from the cornea during the procedure, the surface epithelium (“skin”) can thicken to compensate for the change in shape that has occurred.

This happens to a variable degree among treated patients, accounting for the reason why some patients have a stable and immediate result (minimal epithelial thickening) and others regress (more significant epithelial thickening).

Regression is more likely to occur in patients with higher prescriptions. In the majority of cases, the patient can have another treatment to improve their vision. The ability to perform further surgery will depend on safety parameters set by your laser eye surgeon.

Glare, starbursts and halos

After Laser Eye Surgery, some patients do not see as clearly at night or in dim light and may notice an optical effect called a “halo” or a “starburst” around lights and illuminated objects.

These effects are temporary, typically lasting between two weeks and three months, and we can help patients who find them troublesome to manage them and do things like drive at night.

In the rarest of cases, increases in night glare and halo could be permanent. This is mainly a feature of treatments performed with older lasers that do not have the most sophisticated software (known as aspheric profiles).

The effects of halos and starbursts are also more likely to occur in patients with high levels of shortsightedness or longsightedness and patients with larger-than-average pupil size.

One focus of Professor Reinstein’s research has been the correction (and prevention) of night vision disturbances. Professor Reinstein has developed protocols for correcting and preventing halo and starburst effects even when treating very high prescriptions and patients with large pupils.

Zeiss incorporates many of Professor Reinstein’s findings in the Carl Zeiss Meditec MEL80 excimer laser system, in use at the clinic today. It is therefore extremely rare for patients in our practice to end up with night vision disturbances of any kind.

Light sensitivity, fluctuating vision

Patients may experience increased sensitivity to light or find that their visual acuity fluctuates after their laser eye treatment.

As expected signs of the eye’s natural recovery process, these conditions are generally mild and temporary, usually resolving themselves within the first few weeks or months after the procedure. It’s very rare for light sensitivity and fluctuating vision to persist over the long term.


Even compared to other complications, infections in corneal laser eye surgery are very, very rare.

Reported quote rates are approximately 1 in 5,000, but these of course can be higher or lower, depending on the technique and conditions of practice of individual surgeons.

In the rare event that it does occur, if spotted early, we can manage most infections by administering antibiotics with full resolution and with an extremely low chance of affecting the outcome.

Taking preventative measures as well as ensuring correct protocol for the detection of these rare infections after surgery is key. Professor Reinstein, nor Mr. Carp have, to date, had a patient suffer from a compromised outcome due to infection.

Excessive corneal haze

Corneal haze is part of the normal healing process following surface procedures such as PRK and LASEK, and gradually subsides with little or no permanent effect on vision.

However, if the haze is excessive or does not go away, you may need additional treatment either with medications to reduce the haze or further laser surgery to physically remove the haze, or both. Haze is extremely unusual in LASIK, and even less so in newer treatments.

The risk of haze in PRK/LASEK increases the higher the prescription to be treated, but is also dependent on the smoothness of the surface created by the laser as well as the protocols for postoperative management of the cornea.

Fragility on impact

For about three months after LASIK, surgeons consider the corneal flap somewhat sensitive to direct trauma, such as a poke in the eye or impact with a piece of debris.

After the first month, however, as your eye regains its original strength, the level of direct trauma that would be required to displace the corneal flap would be somewhat severe.

When participating in sports or other activities involving possible contact with the eye during this period, its recommended to take a few weeks off and on return wear the usual protective eyewear.

Corneal Ectasia

It’s important to leave a certain amount of corneal tissue under the flap after the procedure to help in the long-term stability of the cornea.

In very rare cases, less tissue remains than intended. This can produce a situation where there is forward bulging of the cornea (reversing the intended flattening effect), or it can lead to progressive deformity of the cornea, with thinning and increasing curvature changes.

This progressive deformation is called ectasia. It can be treated with corneal collagen cross-linking (CXL), by suturing (stitching) the flap to the underlying cornea, or in rare circumstances with a corneal transplant.

The probability of progressive ectasia at the time of writing, given our protocols and technology, is estimated to be 1 in 20,000.

Epithelial erosion

The epithelium is the surface layer of cells that is like the eye’s ‘skin’ that protects the stromal layer underneath. If a surgeon cuts or removes this skin, it typically grows back.

In LASIK, the surgeon creates a corneal flap, consisting of epithelium and stroma, and holds the corneal flap back while performing the treatment. In some people’s eyes, there is less attachment between the epithelium and the underlying stroma, meaning they are at increased risk of epithelial scratches or epithelial sliding, especially as the corneal flap-maker (microkeratome) passes over the corneal surface to create the flap.

In some cases, we can identify eyes at risk and advise about the increased risks associated with the treatment. There are, however, rare patients where there are no pre-operative clues; the likelihood of having a scratch during LASIK with no preoperative warning signs is approximately 1 in 500. We do know, however, that older patients are more likely to have areas of weakened surface epithelium during corneal flap creation.

In such instances, the surgeon places a bandage contact lens over the cornea after LASIK to assist in healing and to reduce discomfort. Patients who experience an epithelial slide, abrasion, or erosion may experience a longer recovery period and may be at risk for complications including infection, inflammation, recurrent erosions, corneal flap wrinkles or epithelial ingrowth.

In the event of a severe epithelial scratch, your laser eye surgeon will still typically be able to lift the corneal flap and perform laser treatment. However, he may recommend delaying the LASIK procedure on the second eye until the vision has improved in the first eye. This would be the case for the 1 in 500 patients at risk of scratches.

As it doesn’t involve a microkeratome, such corneal complications are minimised and even completely avoided with the revolutionary new ReLEx SMILE treatment.

Epithelial ingrowth

Epithelial ingrowth is a condition in which epithelial cells from the surface of the cornea grow under the edge of the corneal flap. The vast majority of these cells regress on their own.

However, if the cells continue to grow, they can affect the underlying tissue causing astigmatism, corneal flap edge thinning, and reduction of vision. A surgeon will generally treat this condition with medication and observation, although further surgery to remove the epithelial cells may be necessary. This occurs in less than 1 percent of LASIK cases.

Other extremely rare complications

Intraocular haemorrhage, permanent corneal swelling, retinal detachment, venous or arterial blockage, drug reaction, and other complications and risks of Laser Eye Surgery have been either documented or theoretically proposed.

Technically there is an exceedingly small risk of blindness with laser eye surgery but it is lower than the risk of wearing monthly contact lenses for one year, so a risk that everyone seems to accept as perfectly reasonable.

Of course, all the above is not meant to scare you but rather to inform you that we know Laser Eye Surgery, including its potential risks and its incredible rewards, better than pretty much anyone. The best way to find out your chances of risk and if you are a good candidate for a procedure is with a complimentary initial screening.


  1. Reinstein DZ, Srivannaboon S, Archer TJ, Silverman RH, Sutton HF, Coleman DJ. Probability Model of the Inaccuracy of Residual Stromal Thickness Prediction to Reduce the Risk of Ectasia after LASIK Part II: Quantifying Population Risk. J Refract Surg 2006;(In Press).
  2. Reinstein DZ, Rothman RC, Couch D, Archer TJ. Artemis Insight 100 VHF digital ultrasound guided repositioning of a Free cap following Laser in Situ Keratomileusis. J Cataract Refract Surg 2006;(In Press).