The significance of pre-iridal monocellular membranes in dogs and those with anterior segment dysgenesis associated glaucoma, secondary glaucoma, and primary glaucoma

Abstract

Purpose: The etiology and pathogenesis of pre-iridal monocellular membranes in dogs with glaucoma is poorly understood. The objectives of this study were to define the association of pre-iridal monocellular and fibrovascular membranes with canine primary glaucoma with light microscopy and compare this to congenital glaucoma associated with anterior segment dysgenesis (ASD) and secondary glaucoma; and evaluate the immunohistochemical characteristics of the cells present in these membranes and characterize their ultrastructure by scanning electron microscopy. Methods: 108 Enucleated eyes from dogs categorized clinically and histologically with primary/goniodysgenesis-associated glaucoma, congenital glaucoma associated with anterior segment dysgenesis (ASD) and secondary glaucoma were included in the study. The type of pre-iridal membrane and intraocular histologic findings were reviewed and compared statistically for each group. From this population, 10 globes from each group were selected to complete immunohistochemical labelling with CD18, Smooth Muscle Actin (SMA) and CD117. All of these globes had either a pre-iridal monocellular or fibrovascular membrane. Additionally, 10 normal globes were included as a control. SEM was completed on 10 globes selected from these40 globes. Results: Pre-iridal monocellular membranes appear to be more frequent in globes with primary glaucoma, whereas fibrovascular membrane are more common in secondary glaucoma. There was no statistical significance with type of membrane with breed, gender and age between glaucoma groups. Monocellular membranes were seen in 10/10 normal globes. CD18 was positive in 9/10 normal globes, and in 15 globes with monocellular membranes and 7 with fibrovascular membranes in glaucomatous eyes. SMA and CD117 were not detected in monocellular membranes of normal globes. SMA was positive in 10 monocellular and 7 fibrovascular membranes of glaucomatous globes. CD117 was present in 7 monocellular and 5 fibrovascular membranes glaucomatous globes. Monocellular membranes examined with SEM were a continuous sheet of spindle cells with scattered round cells that extended over the anterior iris face in normal and all glaucomatous globes examined. Conclusions: Pre-iridal monocellular membranes are common in all types of canine glaucoma and also in normal eyes. These membranes seem to be a normal component of the anterior iris surface and their immunoreactivity to CD18 suggests that some cells on this membrane are of hematopoietic stem-cell origin. In contrast the immunoreactivity to SMA and CD117 labelling of monocellular membranes in glaucomatous, but not normal globes, suggest metaplastic cellular change secondary to glaucoma.