SECTION IV 



THE NOURISHMENT AND PROTECTION OF THE 



EYE 



ANATOMY OF THE LIDS. Closing the orbit in front and in close relation- 

 ship to the eyes are the lids or palpebrae. The upper, which is the larger and 

 the more movable, is provided with a special muscle, the levator palpebra? 

 superioris. This is supplied by a branch of the oculo-motor (3rd) nerve. The 

 two lids meet at an angle on both sides, forming the inner and outer canthi. 

 They are stiffened by two plates of dense fibrous tissue, parallel to their edges, 

 which are called tarsi. Near these and embedded in the substance of the, 

 lids are two sets of glands, theMeibomian glands and those of Moll. These 

 secrete a greasy material which spreads over the lids. Superficial to these 

 structures but under the skin is a ring of smooth muscle fibres which is 

 common to both lids, the orbicularis palpebrarum, innervated by the 7th 

 nerve. Its contraction closes the lids. Lining the inner surfaces of the eye- 

 lids is a thin layer of mucous membrane, the conjunctiva, which is reflected 

 on to the front of the eye, and is continuous over the cornea as the anterior 

 epithelial layer. 



CLOSURE OF THE LIDS occurs: (I) during sleep; (2) if a very 

 bright light enters the eyes ; (3) by the sudden approach of some foreign 

 body ; (4) by contact of a foreign body with the lashes ; (5) .by irritation 

 of the cornea or conjunctiva; (6) in sneezing; (7) in order to renew the 

 fluid film on the cornea and conjunctiva. The reflex closure of the lids is 

 therefore a very important function in affording protection to the eyes. The 

 reflex apparently can be initiated by the stimulation of any of the branches 

 of the ophthalmic (1st) division of the 5th (trigeminal) nerve. From the 

 nucleus of this nerve in the ponsVarolii fresh fibres take the impulses, it 

 is believed, to the upper part of the facial nuclei of both sides (7th nerve), 

 and from these to the orbicularis palpebrarum. This reflex is one of the 

 last to be abolished by anaesthetics and is therefore used as a convenient test. 

 It is called the corneal reflex. 



The conjunctive and the cornea are kept in a moist Condition by the 

 tears, which are secreted by the lachrymal gland, situated in the upper and 

 outer part of the orbit. This is a small acino-tubular gland, in microscopic 

 structure similar to the parotid. Its secretion issues through several ducts, 

 the mucous linings of which are continuous with that of the conjunctiva. 

 Normally the secretion is just sufficient to keep the surfaces of 'the lids and 



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