Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 68

In cats, both eyelids lack cilia. The eyelids of pigmented cats allow no more than 5% of light at longer wavelengths to be transmitted. Kittens normally open their eyelids between 10 and 15 days of age; however, both eyes do not always open on the same day.

The NM of the feline species is large and active, but in most other species it moves passively. In cats, it actively covers most of the cornea; it can extend at least two‐thirds of the way across the cornea and contains nine smooth muscles that lead to active retraction or protrusion. These smooth muscles draw the membrane into the medial canthus and are innervated exclusively by postganglionic adrenergic sympathetic nerve fibers, with cell bodies located in the anterior cervical ganglion. Their axons follow the oculomotor nerve. Normally, the NM shows no spontaneous activity in most species, because the smooth muscle lacks tight junctions like those of the visceral smooth muscle. Each muscle cell is innervated by one or more axons, thus confirming that activation of the smooth muscle in the NM is neurogenic and that the myogenic conduction normally found in visceral smooth muscles does not occur. Thus, cats are the only common domestic animal in which sympathetic stimulation will cause the NM to move.