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Impressum
Impact of pterygium size on corneal topography and visual acuity
Riedel T., Langenbucher A., Gütay A., Seitz B.
Department of Ophthalmology, University of Erlangen-Nuremberg
Purpose: Pterygia may cause topographic changes featuring irregular
astigmatism depending on their size. The purpose of this study was to
quantify the impact of the height and base length of the pterygium on
anterior corneal curvature and visual acuity before excision.
Patients and Methods: In 52 eyes (19 female, 33 male) with a mean
age of 53±14 years the pterygium size (height, base length) was
quantified using projected preoperative clinical slides and was correlated
with visual acuity, refractive, keratometric, topographic astigmatism
and Surface Regularity Index (SRI), Surface Asymmetry Index (SAI) of the
TMS-1 videokeratography system.
Results: The mean height of the pterygium was 3.1±1.4 (0.8
to 6.7) mm, the mean base length was 5.1±1.4 (2.9 to 7.8) mm. From
about 2.5 mm an the increasing pterygium height resulted in a highly significant
elevation of the preoperative SRI and SAI values (p </= 0.01). The
amount of keratometric (p=0.02) and topographic astigmatism (p=0.001)
correlated significantly with the height of the pterygium. In addition,
pterygium size correlated significantly with the differences of regional
corneal power between steepest and flattest hemimeridian in the 3-mm-zone
or 5-mm-zone, respectively (p </= 0.01). The difference between keratometric
astigmatism and subjectively tolerated cylinder with glasses was growing
with a larger size of the pterygium (p </= 0.01). Best-corrected visual
acuity and hight of the pterygium correlated significantly inversely (p=0.001).
Overall, the impact of the base length was much less striking. Topographic
astigmatism (3.3±2.8 D) was significantly larger than keratometric
astigmatism (2.1±2.1 D) (p=0.001). Keratometric astigmatism was
correlated with the differences of regional power between steepest and
flattest hemimeridian in the 3-mmand 5-mm-zone (p<0.01).
Conclusions: Amount and irregularity of the preoperatively induced
astigmatism are correlated significantly with the distance of the pterygium
head from the limbus and may explain the patient's decrease in visual
acuity before the pterygium reaches the optical axis.