Oculosystemic Interactions

Patients with both ocular and systemic disease tend to present in one of two ways. Some animals present because of ocular disease but upon examination it becomes evident that the ocular lesions are a manifestation of systemic disease. Alternatively animals may be presented with overt systemic illness and only subtle ocular involvement. A thorough ocular exam in these patients can yield important diagnostic clues that are not visible elsewhere. Therefore, it is essential that an ocular exam is part of the examination of systemically ill animals and that animals with ocular disease receive a complete general physical examination. In fact, rather than considering the eye and adnexa as unique structures that are dissimilar to non-ocular tissues, the eye should be seen as an aggregate of tissues with marked anatomical and functional similarities to tissues found in most other organ systems. Using this approach, the eyes provide a unique opportunity for direct observation of tissue types that are otherwise visible only with invasive techniques or special instrumentation. The table summarizes important correlations between ocular and non-ocular tissues and identifies ocular tissues that should be examined carefully in animals with systemic disease as well as non-ocular tissues that should be examined in those with ocular disease.

The following is a brief description of common ocular manifestations of systemic disease. The lecture will highlight some of these with case examples.

Horner's Syndrome

Horner’s Syndrome or decreased sympathetic tone is manifest as the triad of enophthalmos (with protrusion of the third eyelid), ptosis, and miosis. Although these signs are localized to the ocular system, consideration of the circuitous, three-neuron route by which sympathetic neurons course from the hypothalamus to the eye, reveals that Horner’s syndrome can result from disease involving a multitude of sights beyond the eye, including the brain, spinal cord, brachial plexus, thorax and mediastinum, neck, temporal bone and tympanic bulla, or orbit. In addition to a thorough ophthalmic exam, physical examination should include assessment of neck pain, thoracic limb mobility, thoracic auscultation (and mediastinal compression in cats), palpation of the neck and thoracic inlet, otic examination, and assessment of cranial nerves and conscious proprioception. Diagnostic procedures should be directed at each specific area to eliminate definitive causes, and imaging of the chest, spine, and bullae may be indicated. Pharmacologic testing can be used to anatomically localize the lesion as pre- or post-ganglionic. There are many methods of doing this, but I prefer to apply a single drop of a dilute, direct acting sympathomimetic to both eyes (0.25% phenylephrine works well). The patient should be left undisturbed in a calm quiet environment and observed over the next 15-30 minutes. Resolution of the anisocoria (and often third eyelid protrusion and sometimes ptosis) suggests a postganglionic lesion while no effect suggests a central or preganglionic lesion. These results may be used to direct further diagnostic testing. Even with intensive diagnostic testing, approximately 50% of cases of Horner’s syndrome are idiopathic and these tend to resolve within 2 months. No specific ocular therapy is necessary. [...]