GLAUCOMA

GLAUCOMA
Anatomy:
The trabecular meshwork:
It is a sieve-like structure at the angle of the anterior chamber through which 90% of the aqueous humour leaves the eye .
schlemms canal :
Is a circumferential channel in the peri-limbal sclera . The inner wall of the canal (which is attached to trabecular meshwork) is lined by endothelial cells, which contain giant vacuoles. The outer wall of the canal is lined by flat cells and contains the openings of the collector channels. These collector channels connected either directly or indirectly with episcleral veins, this is the conventional drainage, there is also non conventional outflow( uveo scleral) where is the aqueous pass to anterior part of ciliary body and then pass between ciliary body and sclera. (Water and larger molecules from the anterior chamber can pass into and through the ciliary muscle via its anterior face and from there, into suprachoroidal space to be carried away)
The anterior part of the ciliary body bears 70 radially oriented ciliary processes which project into the posterior chamber Each ciliary process has a central arteriole ending in a rich capillary network .
Physiology of aqueous production :
Active secretion: Aqueous humour is actively secreted by the non pigmented epithelium , depending on several enzyme systems especially Na+/ K+ ATPase .80-90% of aqueous humour is produced by active secretion and the other 10-20% is secreted by passive secretion: by ultra filtration and diffusion (which are dependent on the level of capillary hydrostatic pressure, oncotic pressure and the level of IOP oncotic pressure (depends on osmolarity, so fluids pass from low osmotic pressure to high osmotic pressure media).The rate of secretion equals the rate of drainage , which is estimated that about 2.5 L/ min aqueous pass through the pupil
Ocular hypertension:
In the general population the mean IOP is 16 mm Hg, two standard deviations on either side of this gives a normal IOP range of 11-21 mm Hg. In the elderly, the mean IOP is higher, particularly in women, and the standard deviation is greater than in younger individuals . This means that normal IOP in elderly women may range up to 24 mmHg and not 21 mmHg. It is estimated that about 7% of the population over age of 40 years have IOPs > 21 mm Hg without glaucomatous damage on standards clinical tests . these individuals are referred to as ocular hypertensives or glaucoma suspects .
Untreated patients with ocular hypertension have only a 9.5 % cumulative risk of developing primary open angle glaucoma (POAG ) after 5 years , therefore do not require treatment and only those at risk should be treated in order to delay or prevent the development of POAG . it should be remembered that once treatment is started , it is continued through out the patients life time and may have significant side effects
Risky patients are those with
1- IOP 30 mm Hg or more
2- C /D ratio 0.4 or more
3- Family history of POAG in a first degree relatives
4- High myopia
Glaucoma:
it is an optic neuropathy with characteristic appearance of the optic disc (cupping ) and specific pattern of visual field defect that is associated frequently with raised intraocular pressure (IOP )