Diagnostic ophthalmology.

The research article discusses a case study of an American Paint horse diagnosed with a mass within the right iris. The various examinations and tests conducted showed values within normal limits but revealed an unusual color change and bulging, thin appearance of the dorsal stroma of the right iris.

Evaluation Process

• The study revolves around a 3-year-old, castrated male American Paint horse who was brought to the ophthalmology service at the Western College of Veterinary Medicine due to a mass in its right iris.
• Initial tests assessed the horse’s basic ophthalmological reflexes which were all found to be functioning bilaterally – this includes the menace responses, palpebral, and occulocephalic reflexes.

Conducting the Tests

• The horse’s Schirmer tear test, which measures tear production, showed values within normal limits.
• Intraocular pressures, checked using a Tonvet rebound tonometer, were found to be 25 mmHg and 23 mmHg in the right and left eye respectively. This indicated that the horse’s eye pressures were within the average range.
• Fluorescein staining, a test used to identify corneal damage, was negative in both eyes. This suggested no evident damage to the cornea.
• A strange finding was observed on the distant examination, which depicted the right iris as blue while the left iris was brown, indicating heterochromia.

Additional Findings

• Direct examination showed the bulging dorsal aspect of the right iris with a corrugated appearance. However, with the application of the mydriatics agent, 0.5% tropicamide, the bulging area became less noticeable.
• The biomicroscopic examination revealed a very thin dorsal stroma of the iris and transillumination through this area was possible. In other words, the part of iris towards the top was thinned out, enough to allow light to pass through.
• No abnormalities were noted in the indirect ophthalmoscopic examination, carried out after pupil dilation with a Heine Omega 200.
• A photograph of the right eye prior to dilation was also provided for further assessment.