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Abstract
Purpose
To assess the changes in mean corneal refractive power (ΔK) following pterygium surgery and to predict ΔK in cases of combined cataract and pterygium surgery.
Methods
Thirty-seven eyes of unilateral pterygium patients who underwent pterygium surgery were analyzed retrospectively with at least more than 1 month of follow-up. Preoperative and postoperative 1 month corneal refractive power was measured using auto-keratometer (RK-F1, Canon, Tokyo, Japan). Pterygium horizontal extension, width, and area were measured and correlation with ΔK before and after surgery analyzed. We also compared ΔK of the contralateral normal eye.
Results
The mean corneal refractive (Km) power measured before and 1 month after surgery was 43.30 ± 1.66 D and 44.07 ± 1.42 D, respectively. The Km significantly increased at 4 weeks after surgery (p < 0.001). However, postoperative Km was not significantly different when compared with the contralateral normal eye (43.86 ± 1.34 D; p = 0.59). All parameters of pterygium size including horizontal extension, width, and area were positively correlated with the mean ΔK. Among parameters, horizontal extension was best correlated with mean ΔK (p < 0.001). The mean ΔK with horizontal extension was predicted using linear regression (2.5 mm to 1 D, 4.0 mm to 1.8 D).
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References
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 | Figure 1.The parameter of pterygium size by graphic program. The horizontal extension of pterygium on cornea (A) was measured between the nasal limbus and the point farthest away from the limbus and the width (B) was the base arc between 2 limbal points where the pterygium intersected with the limbus. Each area of entire cornea (C) and pterygium on cornea (D) was measured and then the area ratio of pterygium (D/C × 100) was calculated with proportion of pterygium invaded onto the cornea. |
 | Figure 2.Scatterplot of mean ΔK and pterygium extension. Mean ΔK: postoperative mean corneal refractive power minus preoperative mean corneal refractive power. Pterygium extension: distance between the nasal limbus and the point of pterygium farthest away from the limbus. |
Table 1.
The patient characteristics
| Subjects (n = 40) | |
|---|---|
| Age (years) | 56.86 ± 8.10 |
| Sex (M:F) | 21:16 |
| Recurred (eye) | 0 |
| Involved eye (right:left) | 37 (25:12) |
| Pterygium size | |
| Extension (mm)∗ | 2.74 ± 0.86 |
| Width (mm)† | 6.00 ± 1.53 |
| Area ratio (%)‡ | 12.22 ± 7.85 |
| UCVA (Scale) | |
| Preoperative | 0.78 ± 0.27 |
| Postoperative 1 month | 0.85 ± 0.23 |
Table 2.
The mean corneal refractive power measured by autokeratometry before and after pterygium surgery
| Keratometry | Preoperative (range) | Postoperative 1 month (range) |
|---|---|---|
| Kh (diopter) | 42.30 ± 1.97 (36.75-46.0) | 43.74 ± 1.30 (40.5-46.25)∗ |
| Kv (diopter) | 44.29 ± 1.70 (40.25-47.5) | 44.41 ± 1.61 (39.75-47.0) |
| Km (diopter) | 43.30 ± 1.66 (38.5-46.13) | 44.07 ± 1.42 (40.125-46.38)∗ |
Table 3.
The correlation between parameters of pterygium size and changes of mean corneal refractive power (mean ΔK) between preoperative and postoperative 1 month
| Mean ΔK | |
|---|---|
| Extension∗ | |
| Pearson's coefficient r | 0.80 |
| p-value | <0.001 |
| Width† | |
| Pearson's coefficient r | 0.29 |
| p-value | 0.14 |
| Area ratio‡ | |
| Pearson's coefficient r | 0.19 |
| p-value | 0.35 |
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