Any situation in which the view into the globe is obscured. For example:
Corneal oedema Intra-ocular haemorrhage or pus (hypopyon) Cataracts Severe chemosis Eye/eyelid trauma (resulting in eyelid swelling that obscures the globe).
Preparation Sedation is almost always required as this is not well-tolerated in most unsedated horses. Performance of an auriculopalpebral block (technique described elsewhere). Application of topical local anaesthetic agent to the surface of the cornea.
Technique Either via direct placement of the probe on to the cornea, or transpalpebrally. Directly on to the cornea: Better images of the posterior part of the globe, and of the orbit, but… Near-field artifacts result in poor images of the anterior part of the globe. Requires sterile K-Y jelly (or similar) as an acoustic gel. Transpalpebral: Better images of the anterior part of the globe. Also preferred method in cases of corneal disease/injury (and post-surgery) and after ocular trauma. Examine the eyes in two orthogonal planes – vertical (between 12 o’clock and 6 o’clock) and horizontal (between 3 o’clock and 9 o’clock), from the central axis. Fan the probe dorsoventrally in the horizontal plane and rostrolaterally in the vertical plane to visualise the whole globe. Examine the cornea, lens (anterior and posterior surfaces) and retina. (N.B. Strictly speaking you will see retina, choroid and sclera as one layer.) Can also visualise the iris and ciliary body, corpora nigra, optic nerve and periorbital structures (fat and muscles). N.B. the contralateral eye may be valuable as a normal for comparison.
Posterior lens luxation with retinal detachment.
Glaucoma affecting the right eye.
All images kindly provided by Professor Derek Knottenbelt OBE BVM&S DVM&S DipECEIM MRCVS.
