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Clinicopathologic Reports, Case Reports, and Small Case Series
October 2002

Evaluation of Lenticular Irregular Astigmatism Using Wavefront Analysis in Patients With Lenticonus

Arch Ophthalmol. 2002;120(10):1388-1393. doi:

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).

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).

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Higher-Order Aberrations in 2 Patients With Lenticonus, a Patient With Keratoconus, and a Healthy Control* 

*Sx indicates the root mean square of x-order aberrations.
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.

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@ophthal.med.osaka-u.ac.jp).

References
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2.
Colville  DJSavige  J Alport syndrome: a review of the ocular manifestations. Ophthalmic Genet. 1997;18161- 173Article
3.
Maeda  N Wavefront technology in ophthalmology. Curr Opin Ophthalmol. 2001;12294- 299Article
4.
Thibos  LNApplegate  RA Assessment of optical quality. MacRae  SMKrueger  RRApplegate  RAeds.Customized Corneal Ablation: The Quest for superVision Thorofare, NJ Slack Inc2001;67- 78
5.
Schwiegerling  JGreivenkamp  JEMiller  JM Representation of videokeratoscopic height data with Zernike polynomials. J Opt Soc Am A. 1995;122105- 2113Article
6.
Artal  PGuirao  ABerrio  EWilliams  DR Compensation of corneal aberrations by the internal optics in the human eye. J Vis. 2001;11- 8Article
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