Fitting Reverse Geometry Lenses for Keratoconus
This lens design may improve best corrected
visual acuity and reduce aberrations for keratoconus patients.
By Paul A. Kusy, OD, MS, & Joseph T. Barr, OD, MS, FAAO
purpose in this study was to compare the best corrected visual acuity (BCVA) and
level of aberrations present in a series of keratoconus (KC) patients when corrected
with both their habitual lenses and a new reverse geometry lens design.
We obtained data from a group of patients (n=13)
wearing a variety of KC contact lens designs. Measurements we took while the patients
wore each of the lenses included high contrast (HC) and low contrast (LC) Bailey-Lovie
BCVAs and the HC/LC (mixed contrast) Nearpoint card. We measured aberrations using
the Bausch & Lomb ZyWave Aberrometer, and we used the B&L Orbscan II system
to measure decentration between the center of the contact lens and the visual axis.
We performed these measurements on each subject with both lens designs and then
compared the measurements.
The BCVA HC, LC and amount of lens decentration
of the standard design ranged from 20/47 to 20/20 HC, 20/118 to 20/30 LC and 2.44mm
to 1.00mm decentration. The range for the XLT lens design ranged from 20/13 to 20/42
HC and 20/25 to 20/115 LC. The level of aberration variance (coma) among lenses
was 3.47μm to 0.25μm with standard lenses and 0.72μm to 0.16μm
with the reverse geometry XLT lens (MedLens Innovations, Inc., manufactured in Contamac
materials). The graph on page 26 compares the magnitude of each patient's coma with
their habitual lenses and with the XLT lenses. The XLT lens required a reduction
of power ranging from 2.00D to 22.00D in comparison to standard design lenses in
The amplitude of decentration and the power
of contact lenses are directly proportional to the BCVA and the measured level of
A Closer Look at Two Subjects
Table 1 and Table 2 illustrate the
results of two patients from our study, providing the measurements first with their
habitual contact lenses and then with the XLT contact lens (BCVA –0.03~20/20,
Subject #1 Figure 1
shows Subject 1 wearing an 8.6mm overall diameter regular geometry contact lens.
Figure 2 shows the initial topography, which demonstrates decentration of
the apex. Our aberrometry measurements show that these habitual lenses resulted
in a high amount of overall aberrations (Figure 3). Figure 4 shows
a three-dimensional illustration of this patient's higher-order aberrations, which
measured 3.56μm on the right eye with the habitual lens design.
Next we fit the patient with an 11.0mm
OAD XLT reverse geometry lens and checked the lens fit with fluorescein (Figure
5). The aberrometry readings in Figure 6 indicate the amplitude of aberrations
with the same patient in the XLT lens design. Figure 7 shows the three-dimensional
illustration of a decreased level of higher-order aberrations, which measured 1.17μm
OD with the XLT lens design.
Subject #2 Figure
8 shows Subject #2 wearing an 8.6mm OAD regular geometry contact lens. The initial
topography in Figure 9 illustrates the location of the apex. Figure 10
shows the aberrometry readings indicating the amplitude of aberrations with this
patient's habitual lens. A three-dimensional illustration of higher-order aberrations
measuring 1.65μm OD with the habitual contact lens design appears in Figure
Next we fit Subject 2 with an 11.0mm
OAD XLT reverse geometry lens (Figure 12). Figure 13 shows the amplitude
of aberrations with the same patient in the XLT lens design. Figure 14 shows
a three dimensional illustration of a decreased level of higher order aberrations
measuring 0.66μm on the right eye with the XLT lens design.
The BCVA and aberration of the KC patients fit
with contact lenses can vary depending on the centration and power of the lens.
Factors that result in a higher level of BCVA and lower aberrations include reduced
decentration and power. In this study, the XLT lens consistently provided better
vision and lower aberration, as compared to the patients' habitually worn GP lenses.
Dr. Kusy recently graduated from The Ohio State
University College of Optometry with an MS in Vision Science and was previously
on staff at the Cleveland Clinic Foundation Cole Eye Institute.
Dr. Barr is a professor and associate dean for clinical services
and professional program at The Ohio State University College of Optometry.
Contact Lens Spectrum, Issue: October 2006