Ptergyium refers to a growth of fibrovascular connective tissue, typically starting on the medial side of the eye at the limbus, that often grows laterally and may interfere with vision. Pterygium comes from the Latin 'wing' which refers to the classical shape of the growth.
Epidemiology and Pathogenesis
The exact mechanism by which pterygium arises is not clear, although there appear to be genetic and environmental factors. Blacks are more commonly affected than whites, and the prevalence in the tropics is much higher than temperate locations. Some population studies have found prevalence of 25% in blacks in the tropics. UV radiation is thought to be a major culprit. The exact mutations involved in the development of pterygium are being studied in more depth.
Differential diagnosis includes malignancy or other benign conditions; importantly pterygium almost always occurs on the horizontal axis of the eye whereas other conditions may occur along at different points relative to the pupil.
Treatment
Small lesions that do not interfere with vision require no treatment aside from lubricating eye drops.
Surgical excision is the treatment of choice. Unfortunately recurrence is common (50%) and adjuvant therapies may be used to reduce this. Topical mitomycin C or other therapies are sometimes used but can lead to numerous complications. Because it is a benign condition, adjuvant radiotherapy is typically not used until recurrence has developed and been re-excised.
Radiotherapy
Radiotherapy for pterygium is a specialised technique that uses strontium eye applicators. Importantly, it is not the strontium but the 90Yttrium that provides the dose. 90Y exists in equilibrim with strontium as it decays much faster (2 days as opposed to 30 years via beta decay). The beta particles have limited penetrance and therefore provide high dose locally to the base of the resected pterygium.
Useful Studies
Comparative Study of Different β-Radiation Doses for Preventing Pterygium Recurrence
Takayuki Yamada M.D.∗, Hideki Mochizuki M.D., Ph.D.∗, Takahiro Ue M.D.†, Yoshiaki Kiuchi M.D., Ph.D.∗, Yasuhiro Takahashi M.D., Ph.D.‡, Matsuyoshi Oinaka M.D., Ph.D.†
Purpose: To compare the pterygium recurrence rates after treatment with two different β-radiation doses.
Methods and Materials: A total of 84 patients with a mean age of 63.0 ± 10.3 years (men, 48 eyes, and women, 47 eyes) and initially treated with β-radiation after pterygium excision were recruited. The mean follow-up period was 49.9 ± 51.3 months. The patients were assigned to two dose groups: a high-dose (40 Gy) or a low-dose (20 Gy) group. The statistical significance of differences in patient age, pterygium size, and interval between surgery and radiotherapy were analyzed in the 20-Gy group using the Cox proportional hazard model at p < .05.
Results: The high- and low-dose groups included 28 and 67 eyes, respectively. Pterygia recurred in 11 eyes, all in the low-dose group. The interval between surgery and radiotherapy was not a significant predictor of recurrence. Smaller pterygia had a lower risk of recurrence than pterygia that had encroached the pupillary area (pterygium located within one-third of the corneal radius from the limbus, corrected hazard ratio [HR], 0.069; 95% confidence interval [CI], 0.006–0.766; p = .030; pterygium extending beyond one-third of the corneal radius, corrected HR, 0.188; 95% CI, 0.018–0.696; p = 0.019; and pterygium reaching the pupillary area, corrected HR, 0.184; 95% CI, 0.036–0.929; p = .040). Older age was marginally significant as a negative predictor of recurrence (HR, 0.943; 95% CI, 0.887–1.003; p = .061). No scleromalacia developed during the follow-up period.
Conclusions: β-Radiation at 40 Gy was more efficacious than at 20 Gy in preventing pterygium recurrence without scleromalacia development, particularly for large-size pterygia and those in young patients.
Author Keywords: Pterygium; Pterygium size; 90Sr applicator; β-radiation; Pterygium recurrence
Learning points:
- Sr-90 plaque
- single dose of 40Gy
- no scleromalacia
- know about Sr-90 plaque cleaning & plaque handling
