CASE PRESENTATION
A 28-year-old white anesthesiologist presented to our center with severe halos and glare. Seven months prior, she underwent bilateral LASIK for myopic astigmatism at another institution where a VISX S2 (Santa Clara, CA) laser was used. Her preoperative refractions were -4.50 -0.50 X 180, OD and -5.50 -0.50 X 30, OS. Preoperative keratometry readings were 42.00/43.00 X 90, OD and 42.00/43.00 X 120, OS. The procedure was uneventful and the Hansatome microkeratome (Bausch & Lomb, Rochester, NY) was used to create the flaps. In both eyes, a 160-µm head was used with an 8.5-mm ring. Multizone treatments were performed bilaterally with a maximal zone size of 6 mm. The ablation depth was 42 µm, OD and 52 µm, OS. No preoperative pachymetry details were available.
During her visit to our clinic, the patient reported poor vision in both eyes, especially at night, and found it impossible to see in dim light. She was unable to drive, and her employing hospital had to hire a taxi to bring her to and from work. The patient's unaided visual acuity in bright light was 20/25- in each eye. She had severe halos in moderate light with BCVAs deteriorating to 20/40-. Her refraction using binocular fogging was -0.50 -0.25 X 175, OD and -0.25 –0.75 X 170, OS giving her BCVAs of 20/12.5 OU in bright light. Pupil diameters measured 8 mm using the Colvard pupillometer (Oasis, Glendora, CA). A slit lamp examination revealed well-centered flaps with no abnormalities, and the rest of her examination was normal. The Orbscan IIz (Bausch & Lomb, Rochester, NY) anterior elevation map of the left eye demonstrated a small area of central flattening with superior decentration (Figure 1). The Orbscan of the right eye (Figure 2) demonstrated similar findings as the left. For the purpose of comparison, an image with the best-fit sphere standardized at 40 D is shown. The anterior elevation maps of both eyes revealed a rim of elevation within the pupil zone accounting for the patient's symptoms.
HOW WOULD YOU PROCEED?1. Administer pilocarpine?
2. Perform an enhancement using a laser with a larger optic zone?
3. Perform a zone expansion using a hyperopic ablation profile to eliminate the peripheral elevation followed by large zone myopic ablation to treat the residual myopia and to compensate for induced myopia?
SURGICAL COURSE
I decided to perform a zone expansion, and chose to follow the third option with this patient. She preferred to have her flaps relifted rather than recut to accommodate the hyperopic treatment. The left eye (pachymetry, 455 µm; stromal bed, 313 µm) had a manifest refraction of -0.25 -0.75 X 170 (20/40 vision in dim light) and was treated first. The patient underwent two treatments (the Technolas 217z laser and Planoscan 2000 software [Baush & Lomb, Rochester NY] were used): 1) hyperopic ablation +1.00, 6 mm oz and 2) myopic ablation -0.25 -0.75 X 170, 7.0 mm oz (50 µm).
In the right eye (pachymetry, 487 µm; stromal bed, 320 µm) that had a manifest refraction of -0.25 -0.75 X 180 (20/25 vision in dim light), a similar treatment was performed. However, in view of the peripheral crescents of elevation (Figure 2A, arrows), a hyperopic astigmatic treatment was performed followed by a spherical myopic ablation to compensate for the induced refractive shift. The patient underwent two treatments: 1) hyperopic ablation +1.00 + 0.75 X 90, 6.0 mm oz and 2) myopic ablation -2.00, 7 mm oz (50 µm).
OUTCOME
One week after the patient's left eye was treated, she indicated that her vision was markedly better and that she was now able to drive at night. However, she still had halos. The visual acuity in her left eye was 20/15 uncorrected and her refraction was +0.25 D. Three months postoperatively, the patient reported no halos and was able to drive at night. Her acuity was 20/15 unaided and her refraction was plano.
The patient's right eye was treated 3 months after the left. Postoperatively at day 1, she reported an improvement, but the left eye was much better. Her UCVA was 20/40- corrected to 20/15 with 0.00 -1.25 X 100. At 1 month, she reported that the acuity in her right eye was better than the left and that she had no problems driving at night. Her UCVA had improved to 20/15 and she had a refraction of plano. Elevation maps revealed zone expansion with only residual peripheral elevation in the 180º axis (Figure 2B).
Two months postoperatively, the patient returned for an urgent visit, complaining of diplopia in the right eye. She was found to have a tongue of epithelial ingrowth extending into the visual axis at the 3 o'clock position. The flap was lifted and epithelial ingrowth was removed from both the flap and the bed. Alcohol was also used to eliminate any residual epithelium. Her acuity improved again, however, epithelial ingrowth occurred at the same site again 2 months later. This was removed and the flap was sutured with five interrupted 10–0 nylon sutures which were removed at 1 month.
DISCUSSION
Halos and glare are commonly reported early after LASIK and typically decrease in intensity with time. There are several possible reasons for this improvement including elimination of flap edema, resolution of peripheral elevation at the flap junction, and cortical tolerance. However, there is a sizable number of patients for whom halos and glare do not dissipate, even after a protracted healing period. Persistent halos and glare frequently occur in situations when there is an optic zone/pupil size disparity. These are compounded further in ablations where there is a small transition or blend zone.
For patients who find themselves dissatisfied with their refractive outcomes, the hardships may be subtle or pronounced. Some may find it difficult to see in dim light; others may find it impossible to drive safely. A nonsurgical approach, such as pharmacologic agents, pilocarpine, or brimonidine in low concentrations may alleviate symptoms. Those patients for whom a pharmacologic agent is unacceptable need to consider other alternatives. A rigid contact lens can offer a solution, however, this defeats the principle reason for undergoing refractive surgery. For the remainder of patients, a surgical correction can be an option. Customized treatments using lasers linked to topography or wavefronts may be able to solve this problem.
Topographically linked ablations theoretically offer a solution by planning a desired shape and removing the difference between this and the existing shape. Wavefront-directed ablations, although still in their infancy, have given clinicians good reason to be optimistic about their potential. For those without access to this technology, a ?cerebral? approach can offer a solution. Details of previous treatment are useful and enough residual tissue is obviously essential. The exact nomogram for correction will vary from laser to laser. Using the Technolas 217z (Bausch & Lomb) and the planoscan software, we approximated that at a 6-mm optic zone, the amount of tissue ablated between 6.5 and 8 mm is 18 µm per diopter. Elevation mapping can be used to determine the overall peripheral elevation with respect to the best-fit sphere for the cornea and to calculate the hyperopic treatment required to eliminate the peripheral rim.
In this case, the patient's left eye required elimination of an average of a minimum of 15 µm and a maximum of 30 µm. Up to +1.50 D (27 µm) hyperopic would have been possible, however this would have necessitated a -1.50 correction centrally in addition to the myopic enhancement of -0.25 -0.75 X 170, thinning the stromal bed further. A +1.00 D ablation was used to reduce the peripheral elevation and a large 7-mm optic zone treatment was used to correct the residual and induced myopia. Fortunately, the outcome was good, and had the desired effect of expanding the optic zone.
As with all procedures, there are risks involved including inducing irregular astigmatism. A thorough understanding of corneal shape is essential as well as access to a true elevation-mapping device such as the Orbscan II (Bausch & Lomb). Careful planning is required to obtain the best possible outcome and patients need to be counselled regarding possible risks.
Sheraz M. Daya, MD, FACP, FACS, FRCS (Ed), is Director and Consultant, Centre for Sight, London, England. Dr. Daya is a paid consultant for Bausch & Lomb and may be reached at +44 7000 288 288; sdaya@compuserve.com
