Ophthalmological Evaluation of a Rescued Giant Anteater (Myrmecophaga tridactyla) with Blindness: Diagnostic Approach

Resumo

Background: Xenarthrans are among the oldest mammalian lineages and are considered rod monochromats with a unique visual system. Ophthalmic studies in this group remain limited, especially electroretinography (ERG) data. Giant anteaters (Myrmecophaga tridactyla) face increasing human-related threats, such as vehicle collisions, which can lead to ocular issues. This report presents comprehensive ophthalmic findings in a traumatized giant anteater, including the first ERG assessment in this species.

Case: A young female giant anteater was rescued from a roadside in a semi-comatose state following suspected vehicle trauma. The animal showed signs of vision loss, evidenced by collision with objects and difficulty locating food. Ophthalmic examination included the Schirmer tear test (STT), tonometry, ocular ultrasonography, and electroretinography, all following standard protocols. STT values were reduced bilaterally (OD: 4 mm/min; OS: 5 mm/min). Intraocular pressure was elevated in both eyes (OD: 24.7 mmHg; OS: 24.3 mmHg), indicating secondary glaucoma. Both eyes lacked pupillary light reflexes. ERG showed asymmetric retinal dysfunction: the left eye displayed a "flat line" pattern during the scotopic phase, indicating severe rod photoreceptor dysfunction, while the right eye had preserved responses. During the photopic flicker phase, both eyes showed reduced amplitude responses, suggesting widespread cone dysfunction. Ocular ultrasonography revealed no structural abnormalities. Axial biometry measurements were taken and compared with previously reported values for the species.

Discussion: This is the first published ERG study in a giant anteater, revealing significant asymmetric retinal damage caused by trauma-induced glaucoma. The scotopic "flat line" in the left eye is especially critical because xenarthrans, as rod monochromats, rely solely on rod photoreceptors for vision. Bilateral lacrimal reduction and increased intraocular pressure are consistent with post-traumatic secondary glaucoma and dehydration resulting from acute trauma. The absence of structural ocular changes on ultrasonography suggests retinal damage due to ischemia, inflammation, or increased intraocular pressure. The animal survived with permanent bilateral vision loss, emphasizing the importance of documenting the consequences of ophthalmic trauma in this vulnerable species and establishing baseline ERG values for future comparison. These findings highlight the need for standardized ophthalmic protocols in giant anteaters and show that post-traumatic blindness limits the potential for reintroduction.