A rabbit model for assessing symblepharon after alkali burn of the superior conjunctival sac

Abstract

Symblepharon due to chemical burns affects ocular surface health, and there are currently no satisfactory treatments. To improve our understanding of symblepharon, an appropriate animal model is urgently needed. We established a rabbit model of superior conjunctival sac alkaline burn to evaluate symblepharon severity. Alkali burns were induced in rabbits by contacting the superior conjunctival sac with 2 N NaOH-soaked semicircle filter paper (10 mm diameter) for 60 s, 90 s or 120 s. Clinical and histological features were examined, symblepharon severity was evaluated via conjunctival sac depth (grade I - IV) and volume measurements (grade a-d) post-injury at 4 weeks. With increasing alkali burn duration, corneal perforation and symblepharon severity increased. The 60 s group manifested a sub-conjunctiva scar. The 90 s group featured localized adhesion. The 120 s group was characterized by extensive scar hyperplasia and adhesion. The rabbit model exhibited stable and reliable symblepharon following an alkali burn of the superior conjunctival sac. For further research, 90 s is a suitable duration for conjunctival sac burn. The volume measured using conjunctival sac casting was considered when developing a successful evaluation system for symblepharon severity.

Figure 1

Alkali-burned superior conjunctival sac following 4 weeks slit lamp microscopy examination in group A (left), group B (middle) and group C (right).

Figure 2

Conjunctival sac casts. (a) Preoperative photograph of normal conjunctival sac cast with smooth surface and natural arc-shaped margin. (b) Postoperative photograph from group A with surface indentation. (c) Postoperative photograph from group B with sulcus defect on the surface. (d) Postoperative photograph from group C with superior conjunctival sac absent.

Figure 3

The relationship between the centre distance from fornix to lid margin and the conjunctival sac volume.

Figure 4

Micrographic photographs of haematoxylin-eosin staining at follow-up. (a,b) Photograph of normal conjunctiva. Conjunctiva epithelium normally consists of 2 to 3 rows of flattened surface cells and loose areolar tissue, a few goblet cells distributed in the most superficial row. (c–e) Photograph of alkali-burned superior conjunctival sac following 1 week in each group. In group A, conjunctival epithelium migration continued with the migration of fibroblasts to the burn site. In group B, re-epithelialization delayed and fibroblasts proliferated actively. In group C, necrosis was predominant. (f–k) Photograph of superior conjunctival sac on week 4 after alkali-burn procedure in the three groups. In group A, the conjunctival was normal, several mature fibroblasts lying among sub-conjunctival collagen fibres. In group B, delayed re-epithelialization, superficial band-like cicatrization and numerous juvenal fibroblasts existed. In group C, extensive conjunctival fibrosis and cicatrization (original high magnification, ×40) (original low magnification, ×200).

Figure 5

The superior conjunctival sac measurement.