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Comparing conventional results to custom
This month, a 24-year-old engineer is treated with Planoscan in one eye and Zyoptix in the other.
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History: The patient in this case study was one of a small cohort contralateral study comparing conventional LASIK (Bausch & Lomb Planoscan) with wavefront-driven customized LASIK (Bausch & Lomb Zyoptix). He was a 24-year-old engineer who was interested in refractive surgery. He enjoyed racquetball, canoeing and backpacking. The patient wanted freedom from glasses and contact lenses while maintaining sharp vision for outdoor recreation.
Preoperative examination:
Uncorrected visual acuity: Right eye: 20/125; left eye: 20/100
Manifest refraction/best corrected visual acuity: Right eye: –2.25 –0.5 × 120, 20/16; left eye: –1.5 –0.5 × 095, 20/16
Surgery date: May 15, 2001
Procedure: Right eye: Planoscan conventional treatment (using an optimized nomogram); left eye: Zyoptix wavefront customization (no nomogram adjustment used)
| Preop wavefront of right (A) and left (B) eyes demonstrating the wavefront error map, point spread function and convolved (or derived) “E” obtained from the point spread function. The wavefront demonstrates a moderate amount of oblique coma pattern (where the wavefront has a dark circle above and a light circle below). The point spread function also demonstrates the third-order coma pattern, which looks like a comet with a tail that fans out obliquely in this case. Oblique coma is a combination of horizontal and vertical coma. The convolved E shows what the patient sees with this wavefront error pattern. |
Postoperative examination:
Uncorrected visual acuity: right eye: 20/12.5; left eye 20/12.5
Manifest refraction/best corrected visual acuity: Right eye: plano, 20/12.5; left eye: +0.25, 20/12.5
Aberration profile: 6.5-mm ablation optical zone for both eyes
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Discussion:
Higher-order aberrations increased by 7.4% in the right eye treated with Planoscan while the Zyoptix customized eye had a 57% decrease. The decrease in total higher-order aberrations in the Zyoptix-treated left eye was primarily caused by a decrease in horizontal and vertical coma. Despite excellent vision in both eyes, the patient was consistently able to read two patches more than the conventionally treated right eye with low light (mesoptic) contrast sensitivity testing. This is a clinically significant difference that the patient noted subjectively, particularly with night driving when looking though the left eye.
This case illustrates a finding noted in the larger wavefront-driven Zyoptix study, namely that when larger ablation optical zones (6.5 mm to 7 mm) are used with Zyoptix, higher-order aberrations can be minimized and in some cases reduced. This case illustrates several important basic observations: Patients with larger amounts of higher-order aberrations get the greatest visual benefit from treatment with wavefront-driven customization; third-order aberrations, especially horizontal and vertical coma, are the most prominent higher-order aberrations in the normal population, and these are the aberrations that are most responsive to wavefront correction; and the greatest gains of doing customized ablation and correcting higher-order aberrations are in improved sharpness and contrast sensitivity and not necessarily in visual acuity, although visual acuity may also improve.
This is shown in the figures. The 6-month postoperative best-corrected wavefront is demonstrated on the left with reduced wavefront error. This is shown by the more uniform gray pattern in the Zyoptix-treated eye in the lower figure, compared to the conventionally treated Planoscan eye. The point spread function demonstrated in the middle figure is more compact in the Zyoptix-treated eye. This is reflected in the convolved image of the letter “E,” which is crisper compared to the conventionally treated eye.
The Zyoptix program was approved by the Food and Drug Administration in October to treat up to 7 D of myopia and –3 D of astigmatism. It is the only approved customized program that allows treatment with varying optical zones of 6 mm to 7 mm. The U.S. Zyoptix trials demonstrated that larger optical zones (6.5 mm to 7 mm) are associated with greater contrast sensitivity improvement and reduced higher-order aberration changes when compared with smaller optical zones (6 mm).