GLAUCOMA

The fluid in anterior segment of eye is called aqueous. It is secreted by epithelium of cilliary body into posterior chamber, passes through pupil into anterior chamber and is drained from angle of anterior chamber. The mechanism of secretion from cilliary body are passive transport, and active transport through Na/K ATPase pump. The raised intraocular pressure is mainly because of aqueous drainage problem. Drainage can be blocked at pupil for example in pupil block in angle closure glaucoma.The second block is at at anterior chamber angle, where Drainage occurs through two paths. Through trabecular meshwork and uveoscleral outflow from the anterior chamber angle.

The secretion is mediated by sympathetic system. The beta  2 receptor (increase secretion) and alpha 2 receptors (decrease secretion). Enzymes like carbonic anhydrase also play important role in its section.

There are 3 parts of trabecular mesh work. The uveal, corneoscleral and juxtacanalicular. The last part play major part in resistance to aqueous outflow.

The shlemm canal is a perilimbal canal which drain aqueous and send it to episcleral veins.

Paracentral scotoma

Nasal step: visual field defect in nasal field. It respects horizontal midline.

Siedal scotoma: It starts at blind spot

Arcuate scotoma: It starts at blind spot and arches over macular area to reach midline but never crosses midline

Tunnel vision: in which patient is left only with a central island of vision

There are various methods. They include digitally, shiotz tonometer, applanation tonometer and air puff tonometer

The optic disc has a cup in centre which is surrounded by healthy neuroretinal rim. The cup is measured as fraction of total disc size and is numbered from 0.1 to 1. Symmetrical cups upto 0.3 are taken as normal however in 2 % patients upto 0. 7 are found to be normal. Asymmetry of 0.2 is taken as suspecious. Health of neuroretinal rim should also be taken under consideration. Other signs are paripapillary atrophy, disc notching and splinter hemorrhages.

PRINCIPLE AND TYPES

It is viewng the angle of anterior chamber. The light rays from anterior chamber angle undergo total internal reflection at cornea. A goniolens is applied over cornea which change cornea air interface with cornea lens interface and light rays are refracted out. Goniolenses are direct and indirect. Direct ones do not need slit lamp and the angle can be viewed with naked eye. The indirect ones need slitlamp to examine the angle. 

THE TECHIQUE 

Local anesthetic drop is instilled in eye. The patient is asked to look up. The goniolens filled with coupling substance is placed in eye along lower fornix. The slit lamp is adjusted such that angle is viewed though opposite mirror. Finally findings are recorded on paper.

THE ANGLE STRUCTURES 

The angle structures visualized through goniolens are ciliary body, scleral spur, trabecular meshwork and schwalbes line. If ciliary body is visibe it is grade IV angle (40 degree) and is wide open. The scleral spur is visualized if angle is 30 degree open. The trabecular mesh work is visulized if angle is 20 degree open and is a narrow angle. The schwalbes line is visible the angle is 10 degree open and is dangerously narrow. 

It is an emergency

Patient present with pain, redness and reduced vision

It is latest method to check patients visual field.

Its in the form of paper print. There are various diagrams in it, which tell loss of patients visual field as compared to normal. There is also one part which tells us whether the field is outside normal limit, borderline or normal. Before interpreting field three parameters at left top corner should be read, which tell us whether field is reliable or not. It includes fixation losses which tells whether patient fixates rightly and is checked by mapping out blind spot. False positives are those which are trigger happy patient and records light presence with click sound. False negatives are due to inattention and tiredness. It is checked when patient records no response when light is checked at a higher threshold than previously recorded. These 3 parameters should be less than 30%. In serials recording parameter like mean deviation minus is bad and pattern deviation plus is bad. Just to remember. They help in telling whether damage is progressive or not.

It is an investigation which check early damage to retinal nerve fiber layer. It is time saving and can be done with undilated pupil

It is classified as primary when no identifiable cause is found and secondary when a cause is found

It can be furthur classified on the basis of anterior chamber angle whether it is open as in open angle glaucoma, or its closed as in angle closure glaucoma.

It can also be classified as congenital and aquired

Two separate entities are normal tension glaucoma in which there is glaucomatous damage is there but intraocular pressure is less than 21 mmHg and ocular hypertension in which no glaucomatous changes are there but intraocular pressure in more tham 21 mmHg