Vision Threatening Complications and
Vision Impairment Examples
Page Updated: 5/30/98
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Cornea infection is the greatest threat after any refractive surgery procedure and refractive surgeons do try to avoid this as much as possible. Infections may be caused by virus, bacteria or fungi. Immediately after surgery, all patients are placed on strict antibiotic regimens because the wounds are opportunistic entry points for organisms. Despite precautions, infections do occur in the early post-operative period. What has been more disturbing has been the occurence of infections within the 'healed' scar/wound area months and years after surgery. For example, in the PERK study, all three infections began in the RK scars, and were 'successfully' controlled according to the journals.
This is a picture of a cornea after PRK with severe ulceration and infection. Even if the infection is controlled, it always results in increased scarring within the cornea. It should also be pointed out that organisms can become embedded within the stroma during refractive surgery, and remain dormant within it for months or years before becoming active. Fortunately, infections are rare. The rate for RK infections is 1 per 145 patients (PERK, 3 infections, 435 patients - PERK is the only large study of RK that is deemed 'credible' by EyeKnowWhy.
Cornea Ulcerations and Dystrophies can be difficult to define because of the wide variation in cornea disorders that can result in cornea ulceration and opacification. Ulceration is often accompanied by infection but not always. Likewise, the degree of cornea clouding that results in legal blindness is not well defined. Corneas with severe scarring after an infection is brought under control may result in blindness or severe visual impairment. Corneas that have undergone refractive surgery are subject to cornea erosions and epithelial defects at a higher rate than the general public. Corneas that have become unstable (ecstasia) or develop severe erosion disorders (sometimes known as 'cornea meltdown') or are severely scarred may yield such poor vision that the person is unable to function. Cornea dystrophies may develop quickly, manifesting themselves within weeks after surgery, or may develop slowly, taking years to become apparent.
Cornea ruptures appear to be a greater risk for RK, ALK and LASIK corneas than PRK corneas or the general population. The risk of RK incision scars splitting open due to blunt trauma is well documented. There have been cases of blunt trauma after RK where the incision scars remained intact. Therefore, the risk of rupture in corneas that have undergone RK is greatest during the first year or two of healing and scar formation. However, RK corneas will always be more vulnerable to rupture than PRK or unoperated corneas. Recent cases have been reported of RK scar ruptures from airbags.
ALK and its new variant LASIK also have risk of cornea rupture or damage from blunt trauma.
PRK, at this time, does not appear to increase the risk of rupture, however, the epithelium/haze/stroma structure may not heal as well as the original epithelium/Bowman's Membrane/stroma structure after blunt trauma, even if the cornea remains intact. This will be determined with time.
In any case, the managememt of cornea ruptures (assuming other eye structures are intact) includes suturing and salvaging the ruptured cornea, and cornea transplants.
The risk of cataracts are difficult to assess. During RK surgery, any perforation of the cornea (micro (small) or macro (large)) can induce cataract formation.
What is the risk of cataracts after PRK? This is unclear. There have been cataracts reported in PRK patients; the frequency is unknown, but appears rare. One of the concerns regarding the excimer laser is 'collateral' damage associated with thermal and acoustical shock waves emanating from the ablation zone. Studies of collateral thermal and acoustical shock waves are conflicting, with most showing no 'permanent' damage. Is the exposure to concentrated UV light (even if it is only for a split second) a long term risk factor for cataract formation? Only time will tell. Likewise, the prolonged healing associated with excimer laser wounds may contribute to cataract formation. One positive point is that PRK does not place the eye (during operation) under severe pressure like RK and LASIK where the cornea is distorted as the knife cutting is done. Post operative medications for PRK are also controversial. The use of steroidal eye drops are known to cause cataracts (and clinical cases of cataracts after PRK have been reported), so the sooner patients are taken off steroids, the better. Another complication associated with steroids is increased intraocular pressure (glaucoma). Because cataracts take so long to mature, we will not know the complication rate for cataracts after PRK until many years from now, although by the end of 1997, there have clearly been cataracts occurring in an unknown number of patients. One final issue related to PRK and cataracts is the absence of Bowman's Membrane, and daily UV exposure. Does the absence of Bowman's Membrane increase the risk of cataracts in PRK patients? It is unknown at present.
A recent article (Feb. 15, 1998) in Ocular Surgery News (OSN) referenced cataract surgery in Singapore in PRK eyes. The article discussed the difficulty in calculating the refractive power for the intraocular lens (IOL) that was inserted after removing the cataractous natural lens resulting in substantial overcorrection and undercorrection. The error is caused by the difficulty in calculating the refractive index of the altered cornea surface, and the more pronounced changes in the PRK cornea that occur after cataract surgery. Other complications such as induced irregular astigmatism and cornea trauma disorders such as persistent epithelium defects and reactivated haze formation were not discussed.
Retinal detachment or retinal hemorrhage is a major complication of any eye surgery. Myopes should be aware they have an inherently greater risk of retinal detachment than the rest of the population. This is because their eyeballs are elongated, and the retinal membrane is more stretched to cover its interior. Generally, the more myopic, the more elongated the eyeball, and the more prone to retinal detachment the myopic eye is. So, does refractive surgery procedures increase the risk of retinal detachment as an early and delayed complication? PERK reported one retinal detachment, and many other published reports have been published documenting retinal detachments in RK eyes.
Retinal detachments have also been reported after PRK. Acoustical and thermal shock waves from the ablation, and the use of steroids in the months after surgery have been suspected. The effect of UV exposure and thermal waves on the retina are unknown. This is one of the reasons why intraocular pressure (IOP) is closely monitored after PRK. Steroids raise IOP, and increased IOP can press against the retinal membrane, resulting in a tear or hemorrhage.
In all these procedures, the issue of the prolonged healing, and the stress it may have on the cornea and other eye structures is unknown. Like cataracts, retinal detachment may take a long time to manifest. Treatment includes burning the edges of the tear with a YAG laser which evokes a scarred healing response that generally slows or partially reverses the detachment.
Damage to the optic nerve is a severe complication with no therapeutic treatment.
There is no treatment for a damaged optic nerve (or disk). Partial or complete loss of vision occurs. This usually occurs gradually over several years (dependent on the extent of the damage.)
What are the chances of severe vision impairment or blindness after refractive surgery? This question needs to be assessed for the short term ((1 - 10 years) and long term (20, 30, 50 years). No one knows the rates of blindness for refactive surgery since there is no national registry of patients and their long term results; and there are no long term studies that have followed any group of patients for more than 10 years. The PERK study followed 435 RK patients for 10 years (actually only 374, 61 were 'lost' to 10 year folow-up). The FDA clinical trials for PRK followed approximately 1,500+ patients for 2 years (but approval was based on much smaller subsets). There are no long term studies of substantial reliability or credibility for all other refractive surgery procedures such as ALK, HK (hexagonal keratotomy), etc. In 1996, the FDA authorized IDE (Investigational Device Exemption) clinical trials for LASIK. Although LASIK clinical trials are incomplete, LASIK is widely marketed and performed as a "practice of medicine" or "off-label" procedure. Long term results have not been published.
No one really knows how many RK, PRK and LASIK patients will go blind or develop severe visual impairments before they die. Will it be any higher than the general public that did not have refractive surgery? Will RK, PRK and LASIK patients develop significant vision impairment and/or vision threatening complications at a higher rate than the general public? Refractive surgeons and the FDA's Ophthalmic Device Review Panel do not think so.
Vision impairment is much more difficult to define. What is 'significant', 'severe', 'moderate' and 'mild' are subject to great debate. Refractive surgeons have defined significant as a loss of two or more lines of Snellen visual acuity. What does this mean? This can best be explained by example.
Patient A (with glasses or contacts) is able to read the 20/20 line sharply, clearly and rapidly prior to surgery. He does not experience any optical aberrations such as GASH (glare, arcs, starbursts, halos), no irregular astigmatism and his regular astigmatism (if any) is fully corrected by glasses or contacts. He may experience some mild glare at night from his contacts. After refractive surgery, Patient A can read the 20/20 line (although the line is not quite as sharp as before) without glasses. He does have increased GASH which can be improved by contacts and wearing sunglasses during the day. He has mild irregular astigmatism which increases GASH (especially from headlights during and day and night) and sometimes causes a mild 'shadow' effect around high contrast images (such as text). Is this 'reduced' visual acuity?
Patient B has moderate myopia and astigmatism. Patient B (with glasses or contacts) is able to read the 20/20 line sharply, clearly and rapidly. He does experience mild glare and halos at night with his contacts. He uses toric contacts for his astigmatism. He has no irregular astigmatism. After refractive surgery, Patient B (without glasses) can read the 20/30 line with his left eye (although the line is not as sharp as before, and he is overcorrected to +.75 Diopters, and uses accomodation to focus) without glasses. His right eye is undercorrected at -.75, and he can read the 20/30 line (although it has shadows due to mild induced irregular astigmatism.) Glare and halos are increased and have persisted at the one year checkup, but don't bother him too much (except when driving at night in areas with no street lights.) His best corrected vision is 20/20 (left) and 20/25 (right) with glasses. The anisometropia (refractive mismatch) is mild, and is greater than the asymetry of 1 D he had prior to surgery. Is this 'reduced' visual acuity?
Patient C has moderate myopia and astigmatism. Patient C (with glasses or contacts) is able to read the 20/20 line sharply, clearly and rapidly. He does experience mild glare and halos at night with his contacts. He uses toric contacts for his astigmatism. He has no irregular astigmatism. After refractive surgery, Patient C (without glasses) can read the 20/30 line with his left eye (although the line is not as sharp as before, and he is overcorrected to +1 Diopters, and uses accomodation to focus) without glasses. His right eye is undercorrected at -1, and he can read the 20/40 line (although it has shadows due to induced irregular astigmatism) Glare and halos are increased and have persisted at the one year checkup. His best corrected vision is 20/20 (left) and 20/30 (right) with glasses. He complains of seeing shadows and double images around high contrast images (such as text and movie credits at the theatre due to transient irregular astigmatism) The anisometropia (refractive mismatch) is moderate, and is greater than the asymetry of .50 D he had prior to surgery. He also experiences 'morning eye discormfort, 'sticky eye' and blurry vision' briefly upon awakening. Is this 'reduced' visual acuity?
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Update Status:Added LASIK Hemorrhage Photos
Vision Threatening Complications and Vision Impairment Examples
Likewise, PRK infections generally begin in the ablated area. Infections must be treated quickly and vigorously. If the organism penetrates the endothelium (i.e., they 'eat' through the stroma), and invades the anterior chamber, little can be done. Within a few days, they can proliferate, migrate through the eye and attack the retina. At this point, they can invade the optic nerve and migrate up the optic nerve to the brain. A 'last resort' to stop an uncontrolled infection is enucleation (eye removal). Fortunately, in most cases, infections are brought under control without serious adverse effects.
The RK Cornea to the left is an 8 scar RK with bacterial invasion and pervasive scarring of three of the incision wounds. The rate for PRK is reported between 1 per 100 patients and 1 per 1000 patients. EyeKnowWhy will try to 'nail down' a reliable PRK infection rate in the future. LASIK infection rates are unknown at this time, but are expected to be somewhere berween RK and PRK. Some refractive surgeons claim LASIK infection rates are lower than PRK.
Although LASIK infections can be very rare, they can be serious. The four pictures to the left show a serious infection and flap complications after LASIK. The first two pictures are the right and left eye of a LASIK patient (age 18) three days after bilateral (both eyes at same time) surgery.
Both eyes have become infected, and the flap from the left eye has been lost. The pupils are not visible. At this stage, the patient is "counting fingers" (CF) visual acuity. The second set of two pictures are the left and right eye after six weeks of intense antibiotic treatment. The left eye has a significant residual scar and best corrected visual acuity (BCVA) of 20/40. The right eye has pervasive scarring, is significantly farsighted, and has a BCVA of 20/60.
In some cases, the cornea cannot be restored to reasonable health by drug treatment. The only treatment for corneas with severe opacification, dystophies and scarring is a cornea transplant.
As shown in the picture to the left, in ALK and LASIK, approximately one-third of the cornea (the 'cap' if cut all the way off, a 'flap' if left with a hinge) is cut away horizontally from the remainder ('bed') of the cornea. When the flap is relaid on the cornea bed, healing results in a scar ring around the edge, and a very mild scar or haze formation between the stroma of the cap and the stroma of the corneal bed. This cap will always be vulnerable to trauma, especially side trauma, that may pull it away from the cornea bed. Unlike RK where the vertical incision scars always are the rupture points, an ALK/LASIK horizontal incision wound does weaken the cornea's overall rupture strength and a direct blunt trauma may cause the cornea to split open, but not along the horizontal incision. However, it may be likely that the flap could become dislodged and possibly torn by direct blunt trauma.
If the knife enters the chamber and touches the iris, or even worse, touches the lens, a cataract will form within days or weeks of the surgery. This has happened but the frequency is unknown. There was no macroperforation in the PERK study, and one patient developed cataracts within four years of surgery. Does the trauma of RK surgery, and the long term healing associated with RK incision wounds increase the risk of cataract formation in the years following surgery? It appears so. Recent journal articles have been documenting a gradual increase in the number of RK patients undergoing cataract and intra-ocular lens (IOL) implants. Most of these patients are relatively young (30's, 40's, and 50's) and had RK within the past ten years. We will never know how many RK patients develop cataracts. In the PERK study (of those successfully followed), one patient developed cataracts at the 4 year study report point.
Since LASIK utilizes the same excimer laser process as PRK, the same issues are present. Another LASIK related issue is the amount of pressure the eye is placed under during the surgical procedure. The keratome which cuts the cornea requires that the cornea be pressurized through a suction ring. The effect of this pressure can result in a retinal detachment. This appears to be very rare. The photos to the left are a severe retinal hemorrhage that occurred within two weeks of LASIK surgery. Retinal hemorrhages are an unusual and very rare occurrence after LASIK.
It is associated with increased intraocular pressure. Gluacoma, a generic term for eye disorders such as abnormally high intraocular pressure, may result in damage to the optic nerve (as well as detachment and hemorrhage of the retina membrane). Looking at the retina, the optic nerve looks like a disk offcenter. The first picture is a healthy optic nerve and the second (larger) is a picture of a damaged and edematous (swollen) optic nerve disk.Vision Impairment
Patient D had a myopic error of -7 and a regular astigmatism of +3. She has fairly thick glasses, and very limited near vision without glasses. Her vision with contacts is excellent. After surgery, she can 'read' 20/40 without glasses. Her best corrected vision with glasses is 20/25 (the same as before surgery). Her new glasses are -1 and-1.5 with +1.5 astigmatism. She has irregular astigmatism, but feels it is no worse than her prior regular astigmatism. She does have some haze and GASH but states it isn't worse than before surgery. She is very happy with the results. Is her vision better or worse off in your opinion?
Patient E had a myopic error of -12 and -10 and a regular astigmatism of +3.5. She has thick glasses, and no near vision without glasses. Her vision with contacts is pretty good but she has difficulty wearing contacts. After surgery, she can 'read' 20/60 without glasses. Her best corrected vision with glasses is 20/25 (the same as before surgery). Her new glasses are -2 and -1.5 with +2 astigmatism. She has irregular astigmatism, but feels it is no worse than her prior regular astigmatism. She does have some haze and GASH but states it is something she can live with. She has no regrets about the surgery, and is very happy with the results. Is her vision better or worse off in your opinion?
The point is, everybody is different, and you need to understand that the results may not be as good as some people expect or are led to believe. In rare cases, the results can be devastating. One of the most important lessons to learn is this: If you have mild to moderate myopia, very little astigmatism, and excellent sharp vision with glasses or contacts, it is almost certain your vision corrected with glasses or contacts after surgery will NOT BE as good. Also, you will almost certainly have some increased vision side effects, especially at night, such as glare, reduced contrast sensitivity and optical effects (halos, starbursts) after surgery that cannot be corrected by glasses or contacts.
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