OPEN ANGLE GLAUCOMA

General information

It is more common after 40 year age and runs in families. The first degree relatives are more commonly affected. The patients are usually symptom free because it initially affects peripheral visual field and central vision remains normal until late. It is more common in myopes.

On examination there is increased cup disc ratio. There is symmetrical damage. IOP is in late 20s or early 30s. visual field defects are present. The angle is open on gonioscopy.

Investigations are with Humphrey visual field analyzer and OCT RNFL 

Treatment is medical and if not controlled surgery is done. Laser trabeculoplasty is also option in which burns are applied at trabecular mesh work in an effort to increase size of trabecular openings

Definition:

1. Primary means no identifiable cause of glaucoma is there. 

2. It is open angle as seen on gonioscopy. And it is glaucoma which means 

3. glaucomatous optic nerve damage and 

4. specific visual field defects and 

5. intraocular pressure is more than 21 mmHg. 

normal tension glaucoma:  

An intraocular pressure of less than 21 mmHg  with all the other features of POAG. 

ocular hypertension:

Some individuals, physiologically, have an intraocular npressure of more than 21 mmHg, without any optic nerve head or field abnormalities

clinical features

symptoms::

1. aymptomatic

2. Headache

3. Frequent changes in presbyopic correction

4. Noticing a ‘blind spot’ or scotoma, especially if present in the inferior field

5. Difficulty in dark adaptation

signs

At least two of the first three signs detailed below must be present to make a diagnosis of POAG, in the presence of a normal, open angle confirmed by gonioscopy

1. An IOP of more than 21 mm Hg on more than one occasion or asymmetry of 5mm Hg between the two eyes

2. optic nerve head changes suggestive of glaucomatous changes

   1.  a cup disc ratio of more than 0.5

   2. asymmetry of cup disc ratio of more than 0.2

   3. narrowing notching or pallor of neuroretinal rim

   4. disc hemorrhages 

3. visual field changes consistent with glaucomatous defects

4. defects in retinal nerve fiber layer seen after dilation of pupil and with red free light

management

every one above 40 should be screened for glaucoma as the damage is irreversible and early detection is key to successful management. as glaucomatous damage occurs over years so it gives a chance to us to intervene. Close follow up with checking intraocular pressure , optic nerve head changes and visual field defects is necessary.

target pressure: range of intraocular pressure between which glaucomatous damage is not likely to progress

if the intraocular pressure is maintained at less than 16–18 mmHg, it leads to stabilization of POAG in most patients.

treatment:

1. medical : DETAILS discussed separate 

   1. PROSTAGLANDIN ANALOGUES like latanoprost

   2. BETA BLOCKERS like timolol

   3. ALPHA AGONIST like brimonidine

   4. CARBONIC ANHYDRASE INHIBITORS like dorzolamide

2. laser: DETAILS  discussed separate

   1. ARGON LASER TRABECULOPLASTY

   2. SELECTIVE LASER TRABECULOPLASTY

3. surgical: DETAILS discussed separate

   1. TRABECULECTOMY

   2. GLAUCOMA VALVE DEVICES

1. In this procedure, laser spots are applied gonioscopically to coagulate the trabecular meshwork. 

2. This causes the collapsed trabecular beams to become taut, increasing the space available for aqueous to drain out.

3. Argon, diode or  frequency-doubled Nd:YAG lasers have been used to apply 50–100 spots over 180–360° of the angle. 

4. The laser spots, each of 50 micron size, are placed at the junction of the anterior and posterior trabecular mesh-work to produce blanching of the tissues. 

5. This is followed by a transient rise of intraocular pressure which requires prophylactic treatment with topical apraclonidine or other antiglaucoma medications. 

6. The intraocular pressure falls by an average of 5–7 mmHg, but the effect is said to diminish  over time. 

7. Laser trabeculoplasty is therefore indicated if medications do not adequately control the intraocular pressure or if patients are not compliant or do not want surgery