A major review on disorders of the animal lacrimal drainage systems: Evolutionary perspectives and comparisons with humans.

Purpose: To provide a systematic review of the literature on the disorders and management of the lacrimal drainage system (LDS) in few of the species of the animal kingdom.

Methods: The authors performed a PubMed search of all articles that were published in English with specific reference to lacrimal drainage disorders in animals. Data captured include demographics, presentations, investigation, diagnoses and management modalities. Emphasis was also on anatomical differences, evolutionary perspectives and addressing the lacunae and potential directions for future research.

Results: The lacrimal drainage system is a terrestrial adaptation in vertebrates. Evolutionary development of the LDS is closely linked to the Harderian gland and the vomeronasal organ. Variable differences in the clinical presentations and management of lacrimal drainage disorders (LDD) are noted in comparison to humans. These are secondary to unique structural and pathophysiological differences. Uniformity in usage and reporting of disease terminologies is required. Diagnostic challenges in clinical examination can be met with the development of customized lacrimal instruments. Contrast dacryocystorhinography is a very useful investigation in the diagnosis of LDD. Multiple bypass procedures like conjunctivorhinostomy, conjunctivobuccostomy and conjunctivomaxillosinosotomy have been described for nasolacrimal duct obstruction (NLDO). Advances of endoscopy and radiological techniques are paralleled by minimally invasive lacrimal interventions. The search for an ideal animal model for human LDS is far from over and the choice of the animal needs to be customized based on the research objectives.

Conclusion: The lacrimal drainage system is an ancestral feature in tetrapod vertebrates and it is present, in some form or another, in most descendant species. The lacrimal drainage system has evolved considerably, adapting to the needs of the species. It is essential to understand the lacrimal drainage disorders of domestic animals so that the animal and human lacrimal sciences contribute more meaningfully to each other.