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Association between pterygium and plica semilunaris morphology

Ophthalmic pterygium remains an ‘enigma’ despite numerous proposed pathogenetic theories, such as the molecular genetic alterations of stem cells located at the sclerocorneal limbus. The nasal conjunctiva may be particularly exposed to environmental irritants because of the presence of the ‘lacrimal lake’ formed in the area of the plica semilunaris. An oedematous enlargement of the latter may result from chronic ocular surface inflammation. A previous study has reported that nasal pterygia are associated with plica semilunaris ectopia, causing ‘withthe-rule’ corneal astigmatism because of the exertion of tractional forces and thus supported the idea that the ectopia of the plica semilunaris in pterygium is an epiphenomenon rather than a causative association. Motivated by this finding, we examined the size and location of the plica semilunaris in candidates for primary (non-recurrent) nasal pterygium excision (Pterygium Group, PG) and an ageand gender-matched group of cataract surgery candidates (Control Group, CG) with a view to further evaluate the potential role of the plica semilunaris in the clinical profile of ophthalmic pterygium. Patients with a history of previous ophthalmic surgery or ocular inflammatory conditions were excluded. All patients signed an informed consent in accordance with the tenets of the Declaration of Helsinki. Measurements included the horizontal diameter of the plica semilunaris (HDPS), that is, the distance from the temporal edge of the plica semilunaris to the temporal edge of the caruncle on a horizontal axis transversing the pupil (Fig. 1a); the plicolimbal distance (PLD), that is, the distance between the temporal edge of plica semilunaris and nasal sclerocorneal limbus along a horizontal axis transversing the pupillary plane (Fig. 1a); and pterygium length (PL), that is, the distance from the nasal corneoscleral limbus to the most distal edge of pterygium on the corneal surface (Fig. 1b). Cases with a poorly defined or deformed plica semilunaris were excluded. All measurements were performed on maximal abduction during slit-lamp biomicroscopy by using the slit-lamp distance-measuring tool. Overall, 64 patients (41males, 64.06%) and 62 patients (40 males, 64.51%) aged (mean standard deviation, range) 61.32 10.89 years and 63.59 8.92 years were included in the PG and CG, respectively. The HDPS was significantly higher in the PG (5.8 1.1 mm) compared with the CG (3.6 0.8 mm), whereas the PLD was significantly lower in the PG (5.2 0.8 mm) compared with the CG (7.4 1.3 mm) (independent samples t-test). In the PG, the PL was 3.1 1.1 mm, and the correlation between PL and HPDS were statistically significant (Pearson’s bivariate correlation coefficient). On the contrary, the correlation between PL and PLD was statistically not significant (Pearson’s bivariate correlation coefficient). Moreover, in the PG, the HDPS displayed a statistically significant inverse correlation with the reported duration of pterygium presence and a statistically significant inverse correlation with patients’ age, whereas respective correlations with PLD were statistically not significant (Pearson’s bivariate correlation coefficient). The significantly lower PLD in the PG, compared with CG, complies with previous reports on temporal ectopia of the plica semilunaris in pterygium, but the fact that PL was not significantly associated with PLD implies that larger pterygia, which should theoretically exert more pronounced tractional forces to the nasal conjunctiva, were not associated with a higher level of temporal ectopia of the plica semilunaris. This finding compromises the hypothesis that temporal ectopia of the plica semilunaris is only secondary to traction by pterygium and points towards a more complex association between plica semilunaris changes and pterygium growth. A hypertrophic plica semilunaris, which is heavily populated with immunocytes, has been previously reported in association with benign reactive lymphoid hyperplasia or accompanying tonsilar enlargement in children. The significantly larger HDPS in the PG may thus reflect an association between the inflammatory activity at the medial conjnunctival area and pterygium development. A case of a 5-year-old child with bilateral hypertrophy of the plica semilunaris associated with persistent inflammatory changes at the medial conjunctiva of the left eye is presented in Figure 2. In this case, plica semilunaris enlargement was also evident in the fellow right eye, implying that it may have preceded the inflammatory changes at the medial conjunctiva of the left eye. However, even if pterygium development is indeed affected by inflammatory changes of the plica semilunaris, the potential (although far more rare) development of pterygium on the temporal conjunctival area stresses the multifactorial and complex nature of pterygium pathogenesis. Furthermore, the significant inverse association between HDPS and the reported duration of pterygium presence implies that rapidly growing pterygia are more prone to be associated with plica semilunaris enlargement. Accordingly, the HDPS might be used as an index of the rate of pterygium growth and aggressiveness of its clinical behaviour and could perhaps be taken into consideration for the decisionmaking, concerning surgical removal, supporting an earlier surgical intervention for potentially more aggressive pterygia associated with an increased HDPS. The present study suffers from limitations, including the fact that the examiner performing measurements of the size of the plica semilunaris could not be masked against the presence of pterygium, the fact that the progression of