Ocular functional optical zone following hyperopic LASIK/PRK: Analysis based on polychromatic retinal image quality
Mitchell P. Weikert, MDLi Wang, MD, PhDDouglas D. Koch, MD
Cullen Eye Institute Baylor College of MedicineHouston, TX
Financial disclosure: none.
Background
Traditionally, the functional optical zone (FOZ) is analyzed based on corneal topography*
Wavefront-guided treatments correct ocular aberrations on anterior cornea
Optical quality of the anterior corneal surface may not represent retinal image quality of the whole eye Due to the effect of the internal optics
* Holladay & Janes. JCRS 2002; Boxer Wachler et al. JCRS 2002; Racine, Wang & Koch. AJO 2006; Tabernero et al. IOVS 2007
Purpose
To investigate the size of the ocular FOZ before and after wavefront-guided hyperopic LASIK/PRK Based on optical image quality of the whole
eye
Patients and Methods
Consecutive cases who underwent AMO-CustomVue LASIK or PRK (CV-LASIK/PRK) for Hyperopia by one surgeon between 1/1/05 to 6/1/09
Inclusion criteria: Available follow-up at 6 months post-op CustomVue wavefront measurements ≥6 mm
at both pre-op and 6 months post-op
Patients
30 eyes of 21 subjects included Age: 51 ± 8.4 years (31to 66 years) Pre-op CV SE: +1.70 ± 0.82 D (+0.20 to +3.53D) Post-op CV SE: +0.86 ± 0.63 D (-0.53 to +2.10D) Refractive correction: -0.84 ± 0.57 D (0.-1.755 to
+0.35 D)
Methods
Based on CustomVue wavefront measurements, ocular wavefront aberrations were calculated for simulated pupils from 2–6 mm in 0.1 mm intervals
Assuming full correction of 2nd order aberrations, optical image quality of higher-order aberrations (HOAs, 3rd-6th order) was evaluated
Methods
Using ZernikeTool program (AMO), polychromatic modulation transfer function (MTF) at 9 cyc/deg with Stiles-Crawford effect calculated for 2-6 mm pupils
FOZ defined as the size over which the MTF at 9 cyc/deg was ≥0.18 MTF ≥ 0.18 maintains visual acuity of ≥ 20/20
Tabernero J, Klyce SD, Sarver EJ, Artal P. IOVS 2007
Results: FOZ
FOZ range: pre-op: 5.2 - 6.0 mm post-op: 4.1 - 6.0 mm
77
100
100
100
73
87
100 100
010
20
30
40
50
60
70
80
90
100
≥ 6
≥ 5
≥ 4
≥ 3FOZ
(mm)
% o
f e
yes
PreopPostop
FOZ Change Following Myopic CV-PRK
Δ in FOZ (mm) % of eyes
0.6 – 1.0 13
0.1 – 0.5 3
0 58
0.1 – 0.5 0
0.6 – 1.0 13
1.1 – 1.5 10
1.6 – 2.0 3
FOZ vs. 4th-Order Spherical Aberration (SA)
Post-op FOZ with spherical aberration (r2 = 0.33, P<0.001 )
FOZ vs. Higher Order Aberrations (HOAs)
Post-op FOZ with HOAs (r2 = 0.31, P<0.001 )
Change in FOZ vs. Change in SA
FOZ with SA (r2 = -0.31, P<0.001 )
Change in FOZ vs. Change in HOAs
FOZ with HOAs (r2 = 0.36, P<0.001 )
Change in FOZ vs. refractive correction
FOZ stable with refractive correction (r2 = 0.01, P<0.001 )
Summary
26% of eyes had post-op FOZ < 6 mm 74% of eyes had post-op FOZ ≥ 6 mm Post-op FOZ positively correlated with SA
and negatively correlated with HOAs Hyperopic FOZ:
with SA with HOAs No change with amount of refractive correction
Limitations
Results are not correlated with measures of visual function
Analysis only done up to 6-mm zone
Conclusion
FOZ following wavefront-guided hyperopic LASIK/PRK: Increased to area > 6 mm in 17% of eyes Decreased to area < 6 mm in 20% of eyes
These results may lead to further refinement of treatment parameters
Study investigating optical FOZ following myopic LASIK/PRK presented as additional poster.
