The student's guide to diseases of the eye . conjunctiva, both of the lids, andeyeball. Deep nsevi may degenerate, and becomepartly cystic. Dermoid tumours (cystic) are not uncommon at theouter end of the eyebrow; more rarely they occurnear the inner can thus. Lying deeply, beneath theorbicularis, they are not adherent to the skin, likesebaceous cysts; the subjacent bone is sometimeshollowed out. They often grow faster than the sur-rounding parts, and should then be extirpated, the INJURIES, DISEASES, AND TUMOURS OF ORBIT 271 thin cyst wall being carefully and completely re-moved through an in
The student's guide to diseases of the eye . conjunctiva, both of the lids, andeyeball. Deep nsevi may degenerate, and becomepartly cystic. Dermoid tumours (cystic) are not uncommon at theouter end of the eyebrow; more rarely they occurnear the inner can thus. Lying deeply, beneath theorbicularis, they are not adherent to the skin, likesebaceous cysts; the subjacent bone is sometimeshollowed out. They often grow faster than the sur-rounding parts, and should then be extirpated, the INJURIES, DISEASES, AND TUMOURS OF ORBIT 271 thin cyst wall being carefully and completely re-moved through an incision parallel with, and situatedin, the eyebrow. They usually contain sebaceousmatter and short hairs; occasionally, clear oil. 272 CHAPTER XX ERE-OES OF REFRACTION AND ACCOMMODATION. As stated at p. 12, § 19, when the length of theeye is normal, and the accommodation relaxed, onlyparallel rays are focussed on the retina, and, con-versely, pencils of rays emerging from the retina areparallel on leaving the eye (Fig. 96, and p. 5, §§ 11. FiG. 96.—Pencils of parallel rays entering, or emerging from,an emmetropic eye. and 12), and this, the condition of the normal eye indistant vision, is called emraetropia (E.). All per-manent departures from the condition in which,with relaxed accommodation, the retina lies at theprincipal focus, are known collectively as E. rays from any near object, e. g. divergent
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