Every operation, including LASIK, can have complications:

About 1-2% have some complication, most minor and often not noticeable to the patient. All operations have complications; however, in refractive surgery we are operating on "healthy" eyes rather than diseased ones. Hence there is a higher responsibility on the doctors to be very open as to these risk factors so that the patient can make an informed choice for this elective surgery. (Don't forget that one complication for any operation involving a general anaesthetic is death. No one has yet died from a Lasik operation!)

The most notable complications are:

a) Epithelial slide - In some patients the epithelium is more loosely attached to the underlying "stroma" or body of the rest of the cornea. When the microkeratome passes over the eye to cut the flap, some scuffing or sliding of this epithelial layer can occur. This can lead to delayed visual recovery and more postoperative pain than normal. There is also a higher risk of "Sands of the Sahara" syndrome with large epithelial slides. Slight epithelial disturbance is not important but in larger ones it is sometimes more prudent to delay doing the other eye to another day.

b) Free cap - incidence about 0.1%. Lasering can often go ahead despite the free cap and the result is not affected. I have not had a free cap so far.

c) Incomplete flap - incidence again about 0.1%. In this case it is often better to replace the flap and not attempt lasering as the area is usually too small. A new cap can be cut again in a few months.

a) Blindness: True blindness, defined by ophthalmologists as "no perception of light", has not occurred with Lasik. However, there have been 5 cases of severe visual loss reported to date, all in the USA. In these patients, sight was so damaged that the eyes were functionally blind, seeing only vague movements. One of these was a fungal infection in a diabetic patient. The other four were due to optic neuropathy. This latter complication is presumably related to the marked increase in intraocular pressure caused by the suction ring during the cutting of the flap leading to optic nerve ischaemia. It is not recorded how long the suction ring was on the eye for these cases. In my own hands this time is around 15 seconds, during which time the blood supply to the eye is cut off. This is equivalent to pushing hard on your eyeball with your finger for this time. Statistically this complication may be very rare, but it is probably unwise to have Lasik if you have an already compromised optic disc such in in glaucoma. Similarly, if you have significant ischaemic risk factors such as hypertension, hyperlidaemia or diabetes, then you should talk this through with your ophthalmologist before having Lasik

A couple of cases of macular haemorrhages have also been reported following Lasik. This is again caused by the suction on the eye and is a bigger risk in a very high myope. This does not mean blindness but does result in severe loss of central vision.

b) Infection: Presents within the first 12-24 hours with a painful red eye and blurred vision. Incidence is less than 0.1%. Treated with antibiotic drops.

c) Diffuse Lamellar Keratitis (DLK) or "Sands of the Sahara Syndrome": A sterile infiltrate under the flap. Presents in the first 12-48 hours with blurred vision but with no pain. Incidence is 0.25 to 0.5%. Treated with steroid drops.

d) Striae in the flap: Incidence less than 0.25%. Can degrade the vision. If significant it is best to lift the flap early to straighten them out.

e) Epithelial Ingrowth: 0.5 to 1.0 % incidence. Occurs at 1-4 weeks Postop. A few epithelial cells at the edge of the flap do not matter and can be left (the majority). If they grow further in, then the flap has to be lifted and the cells scraped off as they can interfere with vision.

f) Dry eyes: Some degree of dry eye is almost universal for up to 12 weeks, as the corneal nerves have been cut or lasered. They recover over 2-3 months. Some people notice this more than others and it also depends on the environment in which you work. Artificial tears can be bought from any chemist and can be used as often as necessary. There are about 6 makes and you can use the one which you find suits you best. Preservative free tears are better as they are less toxic. As you "see with your tear film", any degradation of the tears can lead to fluctuating vision. There is a recent article of interest on this problem:

"SAN FRANCISCO — The problem of dry eye after LASIK is most likely the result of a neurotrophic epitheliopathy induced by the severing of corneal nerves when the flap is made, rather than diminished tear production. This is the conclusion of a study by Steven E. Wilson, MD, as reported in the June 2001 issue of Ophthalmology.

In this retrospective case control study, individual eyes of 19 patients with moderate to severe erosions of the corneal epithelium at 1 to 3 months following LASIK were compared to eyes of 19 patients who did not develop epithelial erosions on the corneal flap. No patients who had significant signs of dry eye prior to surgery were included in the study.

The comparison of the two groups of patients revealed no difference in tear production at 1, 3, or 6 months and no significant difference in corneal irregularity or refractive correction, though some patients had a temporary decrease in visual acuity.

What was found, according to Dr. Wilson, of the department of ophthalmology at the University of Washington in Seattle, was that "the signs and symptoms of LASIK-induced neurotrophic epitheliopathy (LNE) tend to resolve at approximately 6 months after surgery." Other studies have shown that on average this is when corneal nerves complete regeneration into the flap.

Dr. Wilson pointed out that approximately 4% of patients who have LASIK develop the LNE-associated epithelial erosions, which "may interfere with vision in some patients." Patients who have dry eye disease prior to LASIK are more likely to develop LNE and have more severe outcomes. He also said "it is unknown whether LNE is attributable to diminished neurotrophic factors released from the nerves or some other factor such as a decrease in the frequency of blinking." He called for further study "to clarify the mechanism and the association with the return in corneal sensation."

Dr. Wilson emphasized the importance of warning LNE-affected patients that "LASIK enhancement will likely be associated with a return of the symptoms and signs of LASIK-induced neurotrophic epitheliopathy." He advised in these cases that "enhancement be performed in one eye at a time, separated by at least 6 months so the patient's visual function is maintained."

g) Regression: Some regression can occur, especially in higher myopes and longsighted treatments. There is most change in refraction in the first week. There is a slight regression averaging 1/4 Dioptre between 1 and 3 months post op, but no significant change after this time. Re-treatment or "enhancement" is best done at about 2-4 months and our rate is 2% in the higher groups (over -6 Dioptres) and less often in lower treatments. Hyperopes have a higher re-treatment rate of about 10%.

h) Night vision problems: These are more likely to occur in the higher myopic corrections for the following reasons:

    1) As the surgery is limited by depth, in the higher corrections it may be necessary to save depth by making the optical zone smaller. Usually I don't go smaller than a 5.5mm optical zone and a 6.5mm transition or "blend" zone. (In the lower corrections we would use a 6.5mm optical zone with a 7.5 to 9mm blend zone). Older people have smaller pupils and hence are less likely to have these problems then younger patients. One sometimes has a choice between aiming at "zero" and having a smaller optical zone, or doing a larger zone and aiming at a low myopia. A recent Canadian study seemed to indicate that the size of the blend zone may be even more important than the optical zone as there are less visual "sharp edges". This same study said that about 7% of the higher myopes had some night vision problems after  LASIK with the Nidek laser and that this was not always related to the size of the pupil.

    2) There is a bigger "prolate" to "oblate" change in the higher corrections. The human cornea is flatter in the periphery then the centre (prolate) to minimise spherical aberration (like that suffered by the Hubble space telescope before it was fixed). Having PRK or LASIK for myopia flattens the centre of the cornea more than the periphery and leaves the periphery steeper than the centre (oblate ). This can lead to night vision problems such as loss of acuity in poor light. Most people lose one line of visual acuity in poor light and this can be more after Lasik in some people. See the page on spherical aberration on this web site and also see night vision. 

None of the presently available commercial lasers leave the cornea prolate although it is likely that there will be soon. Such changes in beam profile will require that 10-20% more tissue be taken off by the laser. This will not be a problem for a low prescription, but may well be for the higher myope, as tissue thickness is often a limiting factor.

Jack Holladay (www.docholladay.com), an American ophthalmologist, says that "predatory animals have prolate corneas and prey animals have oblate corneas. Prolate corneas have better central vision and oblate corneas have better peripheral vision. This is important in a prey animal as it needs good peripheral vision to see who's going to be having it for lunch. A predator, however, need good central vision to catch the prey"  These problems are unlikely in a small correction, but become more likely above about -8 Dioptres.

One has to differentiate between a "blur circle" and a "night halo". A blur circle occurs because the eye is not exactly zero and is corrected by wearing a spectacle lens, whereas a night halo is not corrected by wearing a lens. In general any small refractive error will be more noticeable in dim light because the pupil is bigger. Hence a patient with a low myopia (-1 Dioptre or better) will have excellent vision in good light but will notice the refractive error more at night.

For the particular problems of hyperopia, go to this page.

Subconjunctival haemorrhages caused by the suction ring are common and harmless. However, be aware that you may have red patches on the whites of the eyes for some days after surgery.

Long term problems - I have put on a separate page.

3. Re-treatments or "enhancements":

Normally done between 3 and 6 months after the first treatment by lifting the flap.

There is no use of the microkeratome, so there are no complications due to this machine.

However, it is the generally held view that there is a bigger risk of striae and epithelial ingrowth in re-treatments than in primary treatments. Later it is not possible to lift the flap and it may be necessary to re-cut a new flap. All re-treatments have the same limitation of corneal thickness as primary treatments. i.e.: we have to leave 250 microns below the flap for long term stability and strength of the cornea and this is often the limiting factor in how much laser an eye can have.

© S J Doyle April 2002