J Korean Ophthalmol Soc.  2008 Nov;49(11):1737-1745.

Power Vector and Aberrations Using Corneal Topographer and Wavefront Aberrometer Before and After Pterygium Surgery

• Kwon SM
• Lee DJ
• Jeung WJ
• Park WC

Abstract

PURPOSE
To determine the power vector and aberrations before and after surgery for pterygium using a corneal topographer and a wavefront aberrometer.
METHODS
The study group consisted of 34 eyes of 31 patients with pterygium, and were divided into two groups by pterygium size (< 3 mm, group I > or = 3 mm, group II). Power vector and wavefront aberrations were evaluated using a corneal topographer (Oculus inc., Germany) and a wavefront aberrometer (LADARWAVE(R), Hartmann shack aberrometer, Alcon inc., US) at pre- and postoperative 1 week, 1 month, and 3 months.
RESULTS
The preoperative blurring strength (B) and high order aberrations significantly decreased at postoperative 3 months in all groups (P<0.05). Power vector scattergraphs showed the cluster of points gathered around the zero point in group I, but not in group II at postoperative month three. The change rates of high order aberrations were significantly greater in group I than in group II in the preoperative period compared to the postoperative first week period.
CONCLUSIONS
Improvements of the power vector and high order aberrations were more remarkable in group I (< 3 mm) than in group II (> or = 3 mm). To reduce aberrations and astigmatism effectively, we suggested surgical intervention in eyes with pterygia sized < 3.0 mm.

Keyword

Corneal topographer; High order aberrations; Power vector analysis; Wavefront aberrations; Wavefront aberrometer

MeSH Terms

Astigmatism
Eye
Humans
Preoperative Period
Pterygium

Figure

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  Figure 1. Pterygium was measured at the slit lamp with the eye in the primary position. The measurements were taken from the limbus to the leading edge of pterygium and recorded in millimeter.

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  Figure 2. (A) The 3 Cartesian coordinates (x, y, z) of each power vector correspond to the powers of 3 lenses that, in combination, fulfill a refractive prescription: a spherical lens of power M, a Jackson crossed cylinder of power J0 with axes at 90 degrees and 180 degrees, and a Jackson crossed cylinder of power J45 with axes at 45 degrees and 135 degrees. The Pythagorean length of the power vector, B, is a measure of overall blurring strength of a spherocylindrical lens or refractive error. (B) Power vector analysis (S=spherical diopters, C=cylindrical diopters, α=axis (degree), Power vector=(M, J0, J45)).

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  Figure 3. Pre- and post-operative topography pictures in a patient with pterygium. Astigmatism was with-the-rule preoperatively (A) but against-the-rule at the postoperative first week and postoperative third month (B)(C)(D).

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  Figure 4. Pre- and post-operative best corrected visual acuity (BCVA) profile in patients. There was no significant change between pre- and postoperative BCVA in both <3 mm and ≥3 mm.

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  Figure 5. Scattergraph shows the astigmatic component of the power vector as represented by the 2-dimensional vector (J0, J45), which is the projection of the power vector into the astigmatism plane formed by the coordinate axes (J0, J45). Preoperative manifest astigmatism is reduced, and the cluster of points gathered around the zero point at postoperative third month for pterygium size <3 mm (A) but, the cluster of points did not gather for pterygium size ≥3 mm at postoperative third month (B).

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  Figure 6. Scattergraph of power vector (J0, J45) on average shows that astigmatic axes did not change for pterygium size < 3 mm at the postoperative 3 months (A). But preoperative astigmatic axes changed from with-the-rule to against-the-rule at the postoperative first week for pterygium size ≥3 mm (B).

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  Figure 7. Change rates of high order aberrations (coma A, spherical B, total C) were significantly greater in group I than in group II at the preoperative period vs postoperative first week period (pterygium size <3 mm= group I, pterygium size ≥3 mm= group II), (* p<0.05, Wilcoxon signed rank test).

Reference

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