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Evaluation of Lenticular Irregular Astigmatism Using Wavefront Analysis in Patients With Lenticonus
Arch Ophthalmol. 2002;120:1388-1393.
Analysis of corneal topography is becoming more common for evaluating
corneal irregular astigmatism.1 However,
irregular astigmatism can also arise from the crystalline lens. An irregular
reflex on retinoscopy with normal corneal topography or an abnormal lens contour
on slitlamp examination strongly suggests the existence, and gives an estimate
of the degree, of lenticular irregular astigmatism. However, it is difficult
to evaluate lenticular irregular astigmatism qualitatively and quantitatively.
Two cases of lenticonus in patients with Alport syndrome2 are
presented to show that wavefront sensing can be used to evaluate lenticular
irregular astigmatism.
Report of Cases
Case 1
A 52-year-old man sought treatment at our clinic because of a gradual
decrease in his vision. His visual acuity was 20/20 OD with a refractive error
of -13.5 diopters (D) sphere and -3.5 D cylinder at 5° and
20/25 OS with a refractive error of -14.5 D sphere and -0.75 D
cylinder at 170°. Slitlamp examination revealed bilateral anterior lenticonus
(Figure 1A).
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Figure 1. Digitally processed slitlamp photographs
of the anterior lenticonus show marked anterior protrusion of the anterior
surface of the lens in patients 1 (A) and 2 (B).
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Case 2
A 21-year-old man was diagnosed with Alport syndrome. He had received
a kidney transplant from his father to treat renal failure. He sought treatment
for ocular complications at our clinic. His visual acuity was 20/25 OD with
a refractive error of -2.5 D sphere and -0.25 D cylinder at 180°
and 20/20 OS with a refractive error of –2.25 D sphere and -0.75
D cylinder at 175°. Slitlamp examination revealed bilateral anterior lenticonus
(Figure 1B). Dot-and-fleck retinopathy
was detected in both eyes.
For both patients, videokeratography and wavefront aberrometry were
performed with a wavefront analyzer (KR-9000PW; Topcon Corporation, Tokyo,
Japan)3 to determine simultaneously the
corneal irregular astigmatism and the irregular astigmatism in refraction
(Figure 2 and Figure 3). Maps from a patient with keratoconus (Figure 4) and maps of an emmetropic eye (Figure 5) are shown as examples of a corneal irregular astigmatism
and a healthy control, respectively.
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Figure 2. A mire image (A), color-coded
maps of the anterior corneal surface (axial power) (B) and corneal higher-order
aberrations (C), a Hartmann-Shack data image (D), and color-coded maps of
total ocular wavefront (E) and ocular higher-order (F) aberrations in a patient
with lenticonus (patient 1). The map of higher-order aberrations due to the
anterior corneal surface (C) indicates minimum higher-order aberrations, and
the map of ocular higher-order aberrations (F) indicates spherical-like aberrations.
These findings indicate that the irregular astigmatism in lenticonus arises
from the lens.
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Figure 3. A mire image (A), color-coded
maps of the anterior corneal surface (axial power) (B) and corneal higher-order
aberrations (C), a Hartmann-Shack data image (D), and color-coded maps of
total ocular wavefront (E) and ocular higher-order (F) aberrations in a patient
with lenticonus (patient 2). The maps of corneal (C) and ocular (F) higher-order
aberrations have the same pattern changes as seen in patient 1.
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Figure 4. A mire image (A), color-coded
maps of the anterior corneal surface (axial power) (B) and corneal higher-order
aberrations (C), a Hartmann-Shack data image (D), and color-coded maps of
total ocular wavefront (E) and ocular higher-order (F) aberrations in a patient
with keratoconus. The maps of corneal (C) and ocular (F) higher-order aberrations
show similar patterns. These findings indicate that the irregular astigmatism
in keratoconus arises from the cornea.
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Figure 5. A mire image (A), color-coded
maps of the anterior corneal surface (axial power) (B) and corneal higher-order
aberrations (C), a Hartmann-Shack data image (D), and color-coded maps of
total ocular wavefront (E) and ocular higher-order (F) aberrations in a patient
with emmetropia. The maps of corneal (C) and ocular (F) higher-order aberrations
show no signs of irregular astigmatism.
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The maps of the eyes with lenticonus showed a relatively uniform pattern,
indicating that the corneal higher-order aberrations were within the normal
range (Figure 2C and Figure 3C). The map of the keratoconic eye showed a faster wavefront
superiorly and a slower wavefront inferiorly, indicating corneal irregular
astigmatism with a dominance of coma-like aberration (Figure 4C).
For all patients except the patient with emmetropia, the maps for total
ocular aberrations showed cooler colors in the center, indicating that the
refractions of these eyes were myopic (Figure
2E, Figure 3E, and Figure 4E). The map of ocular higher-order
aberrations for the keratoconic eye (Figure
4F) had a pattern similar to the one seen on the corneal higher-order
aberrations map (Figure 4C), suggesting
that the irregular astigmatism in refraction originated from the abnormal
corneal shape.
In the lenticonic eyes, however, the maps of the higher-order ocular
aberrations showed a dominance of spherical-like aberrations (Figure 2F and Figure 3F).
Because the corneal irregular astigmatisms were within the normal range in
these eyes, we deduce that most of the irregular astigmatism in refraction
originated from a lenticular component.
The root mean square values of the higher-order aberrations for 4-mm-
and 6-mm-diameter pupils are shown in Table
1. As shown in the color-coded maps, ocular spherical-like aberrations
were dominant in the lenticonic eyes, and corneal and ocular coma-like aberrations
were dominant in the keratoconic eye.
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Higher-Order Aberrations in 2 Patients With Lenticonus, a Patient With
Keratoconus, and a Healthy Control*
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Comment
Wavefront sensing enables us to evaluate irregular astigmatism qualitatively,
from the color-coded maps of the higher-order wavefront aberrations, or quantitatively,
as a set of Zernike coefficients.4 However,
the higher-order aberrations or irregular astigmatism are made up of corneal
and lenticular components. Although corneal topography is usually designated
by powers, higher-order wavefront aberrations due to the cornea can be quantified
by calculating a set of Zernike coefficients.5 By
comparing higher-order aberrations in refraction with those due to the cornea,
lenticular irregular astigmatism can be estimated.
It is clinically important that we easily recognize the relationship
between the characteristics of the higher-order aberrations and the location
of the shape abnormality by using color-coded maps of ocular higher-order
aberrations. Irregular astigmatism induced by lenticonus is a relatively symmetrical,
spherical-like aberration because the protrusion of the anterior lens surface
and under sclerosis are the center. In contrast, irregular astigmatism in
typical keratoconus is an asymmetrical, coma-like aberration due to the displacement
of the cone.
To determine the source of irregular astigmatism, it is important to
separate the higher-order aberrations of the cornea from those of the lens.
For this purpose, we believe that it is very important to view simultaneously
the map of corneal higher-order aberrations produced by corneal topographic
analysis and the map of ocular higher-order aberrations produced by wavefront
sensing. In our study, a combination of anterior corneal topography and wavefront
aberrometry was used. Therefore, higher-order aberrations due to the lens
were estimated indirectly. Artal et al6 more
accurately showed the relative contribution of the corneal surface and the
internal optics of the eye to the ocular aberrations by immersing the eye
in isotonic sodium chloride solution during wavefront sensing. Many questions
about lenticular irregular astigmatism, such as the aging effect of the lens,
residual irregular astigmatism with contact lens wear, and the effects of
intraocular lens design, are still unanswered. Studies of the simultaneous
measurements of corneal higher-order aberrations and higher-order aberrations
of the eye will make it possible to answer these questions.
AUTHOR INFORMATION
Sayuri Ninomiya, MD;
Naoyuki Maeda, MD;
Teruhito Kuroda, MD;
Teiko Saito, MD;
Takashi Fujikado, MD;
Yasuo Tano, MD
Suita, Japan
Yoko Hirohara, BS;
Toshifumi Mihashi, BE
Tokyo, Japan
Corresponding author and reprints: Naoyuki Maeda, MD, Department
of Ophthalmology, Osaka University Medical School, Room E7, 2-2 Yamadaoka,
Suita 565-0871, Japan (e-mail: nmaeda{at}ophthal.med.osaka-u.ac.jp).
REFERENCES
1. Wilson SE, Klyce SD. Advances in the analysis of corneal topography. Surv Ophthalmol. 1991;35:269-277.
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2. Colville DJ, Savige J. Alport syndrome: a review of the ocular manifestations. Ophthalmic Genet. 1997;18:161-173.
ISI
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3. Maeda N. Wavefront technology in ophthalmology. Curr Opin Ophthalmol. 2001;12:294-299.
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4. Thibos LN, Applegate RA. Assessment of optical quality. In: MacRae SM, Krueger RR, Applegate RA, eds. Customized Corneal Ablation: The Quest for SuperVision. Thorofare,
NJ: Slack Inc; 2001:67-78.
5. Schwiegerling J, Greivenkamp JE, Miller JM. Representation of videokeratoscopic height data with Zernike polynomials. J Opt Soc Am A. 1995;12:2105-2113.
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6. Artal P, Guirao A, Berrio E, Williams DR. Compensation of corneal aberrations by the internal optics in the human
eye. J Vis. 2001;1:1-8.
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