Abstract
This study aimed to evaluate changes in lacrimation and intraocular pressure (IOP) in dogs with unilateral corneal ulceration using the Schirmer tear test (STT) and rebound (TonoVet®) tonometry. IOP and STT values were recorded in both ulcerated and non-ulcerated (control) eyes of 100 dogs diagnosed with unilateral corneal ulceration. Dogs presented with other ocular conditions as their primary complaint were excluded from this study. The mean ± standard deviation for STT values in the ulcerated and control eyes were 20.2±4.6 mm/min and 16.7±3.5 mm/min respectively. The mean ± standard deviation for IOP in the ulcerated and control eyes were 11.9±3.1 mmHg and 16.7±2.6 mmHg respectively. STT values were significantly higher (p<0.000001) in the ulcerated eye compared to the control eye while IOP was significantly lower (p<0.0001). There is an increase in lacrimation and a decrease in IOP in canine eyes with corneal ulceration. The higher tear production in ulcerated eyes shows the importance of measuring STT in both eyes in cases of corneal ulceration, since this increased lacrimation may mask an underlying keratoconjunctivitis sicca only evident in the contralateral eye. The lower IOP in ulcerated eyes is likely to relate to mild uveitic change in the ulcerated eye with a concomitant increase in uveoscleral aqueous drainage. While these changes in tear production and IOP in ulcerated eyes are widely recognised in both human and veterinary ophthalmology, it appears that this is the first controlled documented report of these changes in a large number of individuals.
Highlights
Despite being widely accepted that corneal ulceration causes an increase in tear production and a decrease in intraocular pressure (IOP) as evidenced by the values from the Schirmer tear test (STT) and tonometric measurements, there appear to be few if any reports documenting these changes in ulcerated eyes in the human or canine population
This study seeks to fill this lacuna in the ophthalmic literature by comparing the tear production and IOP of eyes with ulcerated corneas compared with the control fellow eye in dogs with unilateral corneal ulceration
The results of this study show an increased tear production and decreased IOP to occur in eyes with corneal ulceration in the dog
Summary
Despite being widely accepted that corneal ulceration causes an increase in tear production and a decrease in intraocular pressure (IOP) as evidenced by the values from the Schirmer tear test (STT) and tonometric measurements, there appear to be few if any reports documenting these changes in ulcerated eyes in the human or canine population. This study seeks to fill this lacuna in the ophthalmic literature by comparing the tear production and IOP of eyes with ulcerated corneas compared with the control fellow eye in dogs with unilateral corneal ulceration. The cornea serves a major refractive function while maintaining a protective barrier between the eye and the environment (Gilger et al, 2008). Despite being exposed to environmental hazards, the cornea maintains the integrity of its outer surface by continual replacement of its surface epithelium and through the provision a protective covering of the surface tear-film by the lacrimal glands. Tear secretion is controlled by the lacrimal functional unit consisting of the ocular surface (cornea, conjunctiva, accessory lacrimal glands, and meibomian glands), the main lacrimal gland and the interconnecting innervation (sensory afferent and autonomic efferent nerves) (Stern et al, 2004; Williams, 2008) Corneal ulceration is one of the most common ocular disorders encountered in veterinary practice and a major cause of ocular pain through exposure of free trigeminal nerve endings in the superficial stroma and blindness either due to excessive scarring or through subsequent perforation of the cornea. (Gilger et al, 2008).
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