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Dry eye may be at the root of your troubled postoperative corneas
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Many complications of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) are also common disease observations that arise in a contact lens practice or the general population.
The majority of patients who elect to undergo refractive surgery are contact lens intolerant. Because a primary cause of contact lens intolerance is dry eye, this article will focus on dry eye conditions.
Filamentary keratitis
Filaments are strands of mucus with epithelial cells attached and connected to the corneal surface. Patients experience a foreign body sensation that is often described as feeling like a "lash is in the eye."
Filaments can be numerous or can occur as a single, large filament. The common treatment for a single large filament in a nonrefractive surgery patient is to grasp the base of the filament closest to the corneal surface with forceps and pull against the direction of the filament. Perhaps the best analogy is that of a hang nail in which pulling in the wrong direction would simply extend the damage.
In a patient who has recently undergone LASIK or PRK or has many filaments, mechanical debridement with forceps would likely damage the epithelium, which is not fully adherent. It takes approximately 7 days to begin the formation of hemi-desmosomes necessary for completion of the re-epithelialization process.
The primary treatment is the use of Mucomyst (acetylcysteine, Apothecon) 10% ophthalmic solution. Mucomyst is a collagenase inhibitor that dissolves mucus and, hence, the filaments. Unfortunately, Mucomyst is not available for ophthalmic use and comes in a 20% solution for the breakdown of bronchial mucus in asthma patients. A pharmacist must mix equal concentrations of 20% Mucomyst to artificial tears to create a 10% ophthalmic solution. The dosage is four times daily for 3 days, and the patient should keep the solution in the refrigerator.
Furthermore, the patient should be warned of the rancid smell of the solution, which has often been compared to rotten eggs.
Sterile infiltrates
---At 4 days post-phototherapeutic keratectomy, re-epithelialization is delayed in this patient.
Sterile infiltrates are an immune response often secondary to hypoxic conditions. There is also some speculation of the relationship to excessive use of nonsteroidal anti-inflammatory drops or hypoxic conditions due to a tight-fitting contact lens. PRK patients use both a bandage contact lens and nonsteroidal anti-inflammatory drops for comfort, and this may contribute to the formation of these infiltrates, which appear as one or multiple round, white, defined lesions.
The important differential diagnosis is that of an infectious infiltrate. Treating an infectious ulcer as a sterile infiltrate can have disastrous effects. Therefore, in cases where the diagnosis is not clear, taking the conservative approach and culturing the infiltrate and placing the patient on fortified antibiotics or a fluoroquinolone is recommended. Once it is sterile, the treatment is to suppress the immune response responsible for their formation. This, of course, requires the use of steroids.
In one of the cases pictured, the patient with sterile infiltrates was placed on TobraDex (tobramycin dexamethasone, Alcon) four times daily for 1 week. The dexamethasone was used to treat the infiltrate, and tobramycin was used to protect the cornea from infection.
In larger infiltrates where the patient is highly symptomatic, a combination of Pred Forte (prednisolone acetate, Allergan) or Vexol (rimexolone, Alcon) four times daily and Ocuflox (ofloxacin, Allergan) or Ciloxan (ciprofloxacin HCl, Alcon) four times daily for 1 week is implemented. The patient should be seen daily to monitor progress in the first 3 days, then at greater intervals, depending on improvement.
Although extremely rare after PRK or LASIK, an infectious ulcer can occur. Any large, suspicious-looking infiltrate or a central infiltrate should be referred to the refractive surgeon, because treatment is time-sensitive and the prognosis is usually poor.
Culture ulcers, start treatment
The site must be cultured using multiple media. At Hunkeler Eye Centers, the three media used for possible infectious infiltrates are blood, chocolate and Sabouraud dextrose agar, as well as plating for Gram's and Giemsa staining. The patient is then placed on fluoroquinolones, such as Ocuflox or Ciloxan, and fortified antibiotics such as vancomycin (50 mg/mL).
For the infectious ulcer shown, the Ocuflox and vancomycin would be alternated every 30 minutes while awake and every 2 hours at night for at least 2 days. The patient would be monitored daily and medications would remain the same until cultures return. If the cultures indicate that the bacteria are sensitive to Ocuflox, for example, then the fortified vancomycin would be discontinued and only the Ocuflox used. This is to minimize toxicity to the cornea.
Once the infectious ulcer improves (usually in 2 to 4 days), the dose can be reduced to every hour while awake and every 4 hours at night for at least 1 week. Steroids may be indicated after the epithelium has healed, and usually after at least 2 weeks, but should be used cautiously while maintaining prophylactic antimicrobial therapy.
Delayed re-epithelialization
A delayed re-epithelialization may be encountered in a patient with a corneal abrasion. In PRK, 97% of all patients are re-epithelialized within 72 hours.
Beyond 72 hours, it is imperative that patients complete epithelialization as quickly as possible because of the increased tendency for aggressive healing (type III healing response) and the risk of infection. The PRK patient, as well as many traumatic abrasion patients, often uses a bandage contact lens for comfort.
Four elements delay re-epithelialization: corneal edema, hypoxia, toxicity and dry eye. Managing a persistent epithelial defect requires addressing each possible cause and eliminating it.
In PRK, the bandage lens is always removed on day 3 because 97% of patients are re-epithelialized and do not require it. In the other 3%, the lens is probably contributing to the problem and should be removed. If edema is noted, the bandage lens should be removed immediately even if it is only day 1 post-PRK or the first day after a large traumatic abrasion.
Because of the hypoxic condition, the lens should not be replaced with that of a looser base curve, and it is likely that pressure patching will only increase the edema. Therefore, the patient should be given oral pain killers. This has been shown to help patients with pain management during early PRK clinical studies when the protocol did not allow for bandage contact lenses and recommend bed rest with little eye movement.
Monitor persistent defects
In treating any delayed re-epithelialization case, ocular lubrication is a necessity. It appears that if the environment is too dry, migration of the epithelial cells seems to slow or even stop. Ample artificial tears, bland ointments at night and even punctal occlusion are recommended. Preservative-free tears are the first choice because of the decreased risk of preservative toxicity in early epithelial migration. Even collagen punctal plugs, which last about 3 to 6 days, will help the patient to at least re-epithelialize.
Finally, if the patient is using a steroid or a combination drop such as TobraDex, the steroid should be discontinued, as it may be delaying the healing process. One less toxic antibiotic includes erythromycin ointment. This will increase the moist environment necessary for epithelial migration as well as assist in decreasing the pain, because it is more viscous and can somewhat cover the exposed nerve endings.
Patients with persistent epithelial defects should be monitored daily, and exact measurement of the size of the defect should be noted. Using an optic section, the size of the defect can easily be measured directly off the slit lamp.
Recurrent erosion
---A positive test for recurrent erosion: The epithelium immediately heaps up like loose carpet when gentle pressure is applied with a cotton-tipped applicator on an anesthetized cornea.
Recurrent erosion is a condition that occurs in about 5% of all LASIK and PRK patients. Because the excimer laser is actually an excellent treatment for recurrent erosion, the PRK zone rarely manifests an area of recurrent erosion. However, the area of debridement is usually 1 mm greater than the optic zone. For example, a 6-mm optic zone laser, such as the Summit or Visx, begins with a debridement out to 7 mm. It is in this 1-mm area that a recurrent erosion will occur.
Recurrent erosion is an interesting condition because it has typical symptoms but usually very few signs. The patient presents with the same characteristic complaints of sudden sharp pain early in the morning or the middle of the night, followed by tearing and a foreign body sensation. Because epithelial migration is so rapid, by the time the patient arrives at the office there are little to no visible signs.
The history of a previous abrasion is often the only source of confirming this condition. If the patient comes to the office quickly enough, inverse fluorescein staining - or even microcysts - may be apparent.
In chronic cases, anterior membrane dystrophy such as map, dot fingerprint appearances or microcysts may be noted.
---Anterior membrane dystrophy may be noted in chronic cases of recurrent erosion.
In the majority of acute cases and often following PRK or LASIK there are no visible signs. Although not recommended within the first 3 months after PRK or LASIK, one can immediately isolate and confirm recurrent erosion by using a Weck-cel (Merocel Corp., Mystic, Conn.) sponge on an anesthetized cornea. If a cotton-tipped applicator is applied to normal healthy epithelium, no movement or changes are noted. However, when an area of recent erosion is gently touched, the tissue heaps up like a loose carpet. Even without overt signs, this simple test will confirm the condition.
Artificial tears appropriate
The treatment for recurrent erosion is hyperosmotic ointment such as Muro 128 (sodium chloride, Bausch & Lomb) and preservative-free artificial tears every hour. Although controversial, 5% NaCl drops appear to show little benefit in recurrent erosion because the hyperosmotic gradient is quickly diluted by tears. Therefore, artificial tears to bathe the healing epithelium may be more appropriate.
Also, because erosions most often occur after sleep, the NaCl ointment should be used before bed. A clinical cure requires approximately 6 weeks of nightly Muro use.
Other good treatment options include bandage contact lenses, which create a barrier between the lids and migrating epithelium, as well as phototherapeutic keratectomy to the isolated area of the erosion.
For Your Information:
- Paul M. Karpecki, OD, is director of research for the Novamed/Hunkeler Eye Study Center and the clinical director of refractive surgery for the Hunkeler Eye Center. He is also the residency director of the Cornea and Refractive Surgery Residency fellowship program affiliated with the Pennsylvania College of Optometry and a faculty member of the Kansas University Department of Ophthalmology, where he heads the refractive surgery clinic program for residents. Dr. Karpecki can be reached at 4321 Washington, Suite 6000, Kansas City, MO 64111; (816) 931-4733; fax: (816) 931-9498. Dr. Karpecki has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any company mentioned.