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Careful preparation, pre-testing help improve PRK patient outcomes
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SIOUX FALLS, S.D. — According to Douglas D. Wallin, OD, clinical director of refractive surgery here at Ophthalmology Limited, a thorough eye exam and a thorough understanding of the patient’s expectations are the most import ant aspects of the preoperative assessment for photorefractive keratectomy (PRK).
"I feel you need to establish and document that the patient is comfortable with the concept of reduced dependence from optical devices, not elimination from life," Dr. Wallin said. "These realistic expectations are essential for successful refractive surgery."
Special attention is paid to the slit lamp examination and the refraction as important parts of a successful ocular health exam, he added. Dr. Wallin performs manual refractions pre- and postoperatively and performs a cycloplegic refraction on all patients preoperatively.
Consider dry eye
"I pay special attention to subjective symptoms of dry eye, and I look very closely at the tear film and the lacrimal lake," Dr. Wallin explained. He may also perform a Schirmer’s test.
Dr. Wallin uses aggressive dry eye therapy to get a well-lubricated eye prior to surgery, since he said that there should be no slit lamp evidence of dry eye prior to surgery. "Patients tend to heal much better when you start off in the environment of a well-lubricated eye," he said.
The only time Dr. Wallin considers dry eye a contraindication to the procedure is when patients have a condition such as Sjögren’s syndrome. "In these severe dry eye cases, it’s hard to keep the eye moist enough to regrow epithelium after PRK," he said.
Also, because Sjögren’s is a collagen vascular disease, healing may be affected. Dr. Wallin screens the cornea and conjunctiva for scarring. He judges lid apposition to make sure the tears will be well spread.
It is also important to assess the lids for signs of blepharitis and meibomian gland dysfunction. "Those patients who have a low-grade blepharitis or meibomian gland dysfunction and are not treated preoperatively can be symptomatic postoperatively," he said.
Dr. Wallin treats these patients with lid scrubs, warm compresses, antibiotic ointments and artificial tears preoperatively.
He performs corneal topography on every patient to rule out keratoconus and any other corneal problems. Clinical signs and measurements will generally pick up keratoconus, he said. "However, every once in a while, you find a preclinical cone with corneal topography that has no clinical evidence of keratoconus. Ruling out these pre-clinical cones is important because of the unknown, unpredictable results and potential post-surgical irregular astigmatism," Dr. Wallin said.
Contact lens wear
Dr. Wallin also uses the topographer to assess the stability of the cornea coming out of contact lens wear. If a patient has been wearing lenses, he has them come in wearing the lenses, removes them and does topography and a manifest refraction. Then, he repeats the topography about 3 to 5 days after discontinuation of soft lens wear.
Those in thick torics or extended wear lenses may have to leave the lenses out a week or two before stabilization. Rigid gas-permeable lenses must not be worn for a minimum of 4 weeks, and possibly longer, depending on the fit and the Dk of the material. "I’ve had one patient go 3 months without a contact lens before stabilizing with topography and refraction," he added.
Healing the defect
"PRK is more of a challenge (than other refractive surgeries) from a postop standpoint because you are dealing with a large epithelial defect," Dr. Wallin said. This defect has to completely re-epithelialize, which generally takes 72 hours.
"Once the epithelium is healed over, you have to monitor the patient very carefully for any healing reaction, such as haze and regression," he said.
If re-epithelialization takes longer than 72 hours, Dr. Wallin changes the treatment regimen. In that time, he watches for infiltrates. Further, he noted, "As the epithelium heals, the epithelial plates can come together and form a small epithelial ridge. Sometimes that ridge looks dendritic. When this happens, you have to make certain it is not herpetic."
If the epithelium is intact over the ridge, he uses aggressive preservative-free artificial tear therapy and ointment at bedtime to increase the lubrication and help the ridge recede, which usually takes only a day or two.
Topical nonsteroidal anti-inflammatory drugs (NSAIDs) are available during the first 72 hours to manage pain. He advises patients not to treat irritation but only pain. He prescribes a combination drop, TobraDex (tobramycin dexamethasone, Alcon) four times daily to help keep the amount of preservatives instilled into the eye as low as possible.
The patient must use a steroid in combination with an NSAID to help prevent the possibility of a sterile infiltrate, which can be caused by the NSAID. Patients are given a bandage contact lens to wear for the first 72 hours.
Postop follow-up
The first day after the procedure, expect to see an epithelial defect with approximately 20% to 50% re-epithelialization. The patient may have mild to moderate discomfort or none.
Dr. Wallin draws pictures to follow the epithelial edges to make certain that they continue to grow together. "The leading edges of the epithelium should appear smooth and healthy and may be difficult to view," he said.
Swollen and irritated epithelial edges will appear more opaque and more easily seen. He does not remove the contact lens on the first day.
At Ophthalmology Limited, PRK procedures are performed on Thursday. Patients are seen the next day and then again the following Monday. Over the weekend, they maintain the bandage lens, TobraDex six times per day and Maxitrol ointment (dexamethasone, Alcon) at bedtime. Dr. Wallin is quick to discontinue the Maxitrol if signs and symptoms suggest a medicamentosa-type reaction.
If the patient is progressing well, you should see an intact, smooth epithelium or occasionally you may see that epithelial ridge mentioned earlier. Dr. Wallin removes the bandage contact lens and has the patients continue TobraDex four times daily for 1 week, ointment at bedtime 1 more week and artificial tears four times daily, alternating with TobraDex.
At the end of that week, patients discontinue the ointment and reduce the TobraDex to twice daily and continue the lubrication for 1 more week. At this time, the TobraDex is discontinued, and the lubrication is continued until the third week visit.
By this time, patients should have a comfortable eye, improved vision and a well-healed epithelium. After this, they are seen monthly and followed with corneal topography, refraction and slit lamp examination.
"It’s uncommon to see anything other than the normal wound healing rate with corrections under 2.5 D," Dr. Wallin said. "It’s not uncommon to see trace to mild subepithelial haze and a +0.50 to +1.00 refraction at the 1-month visit. We follow patients monthly for 2 to 3 months and then consider doing the other eye."
"If I still see a persistent epithelial defect at the third- or fourth-day visit, which is rare, I will change the treatment regimen," he added. "I will discontinue the TobraDex, NSAIDs and Maxitrol, and institute an ‘epithelial cocktail,’ which consists of Ocuflox (ofloxacin ophthalmic solution 0.3%, Allergan) every 2 hours, Celluvisc (carboxy methylcellulose sodium 1%, Allergan) alternating every 2 hours and bacitracin ointment at bedtime."
He also has patients continue with the bandage contact lens. This usually causes the epithelium to heal very quickly. The patient is monitored daily until re-epithelialization occurs.
Healing reactions
---Type 3 healing following PRK can be identified by marked haze with myopic regression. Dr. Wallin recommends treatment with topical steroids.
Dr. Wallin uses the classification established by Dan Durrie, MD, in which a Type 1 healing reaction represents a normal healing response, Type 2 is underhealing and Type 3 is an over-reaction.
"Occasionally," he said, "you will have a Type 2 response where the cornea is crystal clear, with no haze at all." Refraction reveals hyperopia of about 1 to 2.5 D. Because there is an under-healing response, in these cases, you must try to stimulate a healing response.
"First, discontinue any steroids," he said. "You can also use an extended-wear contact lens for 3 to 5 days at a time to create mild hypoxia and irritation, which often can stimulate a healing response," he said. "If that doesn’t work, you can rescrape the epithelium and put on another bandage contact lens to try to re-stimulate the keratocytes into a normal healing response."
Haze indicates Type 3
Type 3 healing responses can be identified by the haze and myopic regression. Dr. Wallin treats these cases aggressively, using topical steroids in strengths from 0.1% to 1.0% depending on the severity of the haze.
He will begin the steroids four times daily for 3 weeks and then taper very slowly, one drop per week. He typically begins monitoring the intraocular pressure (IOP) with carefully performed applanation at the third week. The readings are not exact because of the change in curvature and thickness of the cornea. The actual IOP tends to be higher than the pressure recorded; the higher the IOP, the greater the reduction. This reduction in measured IOP is typically only 1 to 3 mm Hg.
If steroid treatment does not improve the haze and regression, you can use corneal scraping and/or laser re-treatment. Sometimes, the best therapy for a Type 3 response is an epithelial rescraping. The haze can be removed with scraping and a new healing environment established.
Enhancements are sometimes required and preferable to scraping. Typically, if the best-corrected visual acuity is good and the haze is minimal, the residual refractive error should be corrected. Dr. Wallin would recommend a laser in situ keratomileusis procedure in this case to reduce the risk of another aggressive healing reaction. With significant haze and poor best-corrected visual acuity, PRK re-treatment should be performed.
A Type 3 healing response must also be differentiated from a central island. If the cornea has only trace haze and the refraction indicates regression, corneal topography should be performed to rule out central steepening. These islands may be caused by epithelial hyperplasia or possibly the loss of treatment due to increased hydration during the ablation. Time and lubrication generally heals the hyperplastic island. If an island remains, it may need to be retreated with the laser.
For Your Information:
- Douglas D. Wallin, OD, can be reached at Ophthalmology Limited, 1200 South Euclid Ave., Suite 204, Sioux Falls, SD 57105; (605) 336-6294; fax: (605) 336-6970; e-mail: DWallin@IW.net. Dr. Wallin has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.