When deciding whether to use an excimer laser to enhance a previous surgical procedure, clinicians must answer several questions, said Perry S. Binder, MD, Gordon Binder Weiss Vision Institute, San Diego, United States.
Dr. Binder enumerated important points to consider before using the laser to perform enhancements after PRK or LASIK, lamellar surgery, incisional surgery, lens surgery, or corneal surgery:
- "First and foremost, what are the patient's goals?" he said. "If [he or she wants] to see 20/15 and never have to wear glasses again, doing enhancement surgery on that patient is not going to make [him or her] happy."
- What's the best-corrected visual acuity? Is it worse than 20/20 and, if so, why?
- What's the uncorrected visual acuity? What does the patient expect to gain?
- Are the refraction and the visual acuity stable? "That's the most important question to address, because if you don't wait until stability, you're going to hit a moving target," he said. "You're never going to get a good result."
- Is there any evidence of ectasia? "If there is, of course, you don't want to enhance that eye," Dr. Binder said.
- What is the residual stromal thickness? Will it allow the performance of additional surgery?
- What are the pupil dimensions, and are they related to the patient's symptoms?
- Is the previous surgery well-centered, or is that what is accounting for the patient's symptoms?
- Do the symptoms agree with the findings? "This is probably one of the most important parameters you have to ask," he said. "This patient's unhappy. Can I document with all my testing why this patient is unhappy?"
- Are the higher-order aberration (HOA) symptoms consistent with the findings? "We have many patients who have higher-order root mean square values of 1 and 2, and they don't have any complaints," Dr. Binder said. "There are others with minuscule HOA errors who are extremely unhappy."
- Is there a dry eye component? "If so, you must treat that first in order to ascertain what the true refraction and wavelength characteristics of that individual are," he said.
"With each individual procedure, there are very specific questions you have to address," Dr. Binder added, again providing several questions to ask.
Is there any wound healing visible, and if there is, will mitomycin C or a laser be used to remove that scar tissue?
- Is the eye a steroid responder, and how will that affect the treatment of that eye?
"You can't do a femtosecond laser on an eye that's had previous PRK for fear of gas breakthrough going through the center of the cornea," he said.
- Were there flap complications with the previous laser surgery?
- What is the flap thickness, and will it allow the clinician to lift up the flap and enhance it without tearing it?
- Are the flap dimensions and residual thickness appropriate for additional enhancement surgery?
- Will subsequent surgery make the cornea too flat or too steep?
- Is the flap decentered, and if it is, will enhancement increase the risk of ectasia?
With previous lamellar surgery:
- "The key question is, if I perform a flap over this procedure, am I going to cross the previous wound?" Dr. Binder said.
- Will the dimensions of the new flap allow performance of excimer laser ablation?
- Will a second microkeratome pass transect the first if it was a previous ALK or a previous keratomileusis? "That will cause a lot of trouble for you," he said.
With previous incisional surgery:
- "You have to ask, is this eye stable from morning to night? If it is not, it's not going to do you any good to operate on that particular eye, because it's still going to be unstable," Dr. Binder said.
- How well-healed are the wounds? "If there's epithelium present, then the wounds aren't well-healed," he said. "Using a femtosecond laser or a microkeratome could separate those wounds."
- Does the patient have starburst symptoms? "If [he or she has] them now, [he or she is] probably going to have them afterwards as well," Dr. Binder said.
"You risk gas breakthrough with a femtosecond laser when operating on incisional cases," he said, "and if you perform a destabilizing procedure such as LASIK over an RK eye, you may destabilize that cornea further, so you might lean toward doing surface treatment."
With previous lens surgery:
- "You need to ask, was a multifocal lens used, and if it was, you may not wish to use a custom treatment, because that could negate some of the benefits of the previous multifocal lens," Dr. Binder said.
- Is the IOL centered? If not, is it better to recenter that lens, put in a piggyback lens, or try to compensate for the decentration by operating on the surface of the eye?
- Is the decreased vision due to the retina or the macular?
- How healthy is the endothelium? "If you've got a low cell count and you try to do LASIK surgery on that eye, you're going to have problems with flap adherence," he said.
With previous corneal surgery:
- Is the corneal transplant well-healed?
- Will the diameter of the corneal transplant allow placement of a flap so that adequate refractive surgery correction may be obtained with LASIK or with PRK surgery?
"If you have previous themokeratoplasty and you put changes and holes in Bowman's layer, a femtosecond laser won't work with that procedure because you'll have vertical gas breakthrough," Dr. Binder said. "You might consider surface surgery."
He concluded: "I'll finish with these basic rules: In enhancing a previous case, avoid overcorrection, consider conventional versus custom surgery depending on the patient's needs, and attempt one eye at a time so you can avoid unexpected outcomes.
"Enhancements are less predictable than primary cases, and that's something you really have to keep in mind. Determine [patient] expectations, match expectations to what is achievable whenever possible, and confirm refractive stability of the eye. Your findings must [match up] to the symptoms, because if they don't, you're going to be in trouble."