In connection with contact lenses, we can often see eye slits narrowing due to the decline of the upper eyelid, known as ptosis.
Ptosis occurs due to disfunction of the muscles that raise the eyelid or their nerve supply (oculomotor nerve for levator palpebrae superioris and sympathetic nerves for superior tarsal muscle). It can affect one eye or both eyes and is more common in the elderly, as muscles in the eyelids may begin to deteriorate. One can, however, be born with ptosis. Congenital ptosis is hereditary in three main forms. Causes of congenital ptosis remain unknown. Ptosis may be caused by damage/trauma to the muscle which raises the eyelid, damage to the superior cervical sympathetic ganglion or damage to the nerve (3rd cranial nerve (oculomotor nerve)) which controls this muscle. Such damage could be a sign or symptom of an underlying disease such as diabetes mellitus, a brain tumor, a pancoast tumor (apex of lung) and diseases which may cause weakness in muscles or nerve damage, such as myasthenia gravis or Oculopharyngeal muscular dystrophy. Exposure to the toxins in some snake venoms, such as that of the black mamba, may also cause this effect.
Typically, ptosis occurs in connection with wearing hard contact lenses when the ophthalmic slit widens 9.76 ± 0.99 mm. For comparison, the human eye slit non-bearing lens has 10.10 ± 1.11 mm and the wearers of soft contact lenses 10.24 ± 0.94 mm.