Open Angle Glaucoma Flashcards
What is glaucoma?
Glaucoma refers to the optic nerve damage that is caused by a significant rise in intraocular pressure. The raised intraocular pressure is caused by a blockage in aqueous humour trying to escape the eye.
There are two types of glaucoma: open-angle and closed-angle.
Recap the anatomy of the vitreous chamber
The vitreous chamber of the eye is filled with vitreous humour.
Recap the anatomy of the anterior and posterior chamber
The anterior chamber between the cornea and the iris and the posterior chamber between the lens and the iris are filled with aqueous humour that supplies nutrients to the cornea.
Briefly describe the production and flow of aqueous humour
The aqueous humour is produced by the ciliary body. The aqueous humour flows from the ciliary body, around the lens and under the iris, through the anterior chamber, through the trabecular meshwork and into the canal of Schlemm. From the canal of Schlemm it eventually enters the general circulation.
What is the normal intraocular pressure? And what causes this pressure?
The normal intraocular pressure is 10-21 mmHg. This pressure is created by the resistance to flow through the trabecular meshwork into the canal of Schlemm.
Briefly describe the pathophysiology of an open-angle glaucoma
In open-angle glaucoma, there is a gradual increase in resistance through the trabecular meshwork. This makes it more difficult for aqueous humour to flow through the meshwork and exit the eye. Therefore the pressure slowly builds within the eye and this gives a slow and chronic onset of glaucoma.
Birefly descirbe the pathophysiology of acute angle-closure glaucoma
In acute angle-closure glaucoma, the iris bulges forward and seals off the trabecular meshwork from the anterior chamber preventing aqueous humour from being able to drain away. This leads to a continual build-up of pressure. This is an ophthalmology emergency.
How does increased pressure affect the optic disc?
Increased pressure in the eye causes cupping of the optic disc. In the centre of a normal optic disc is the optic cup. This is a small indent in the optic disc. It is usually less than half the size of the optic disc. When there is raised intraocular pressure, this indent becomes larger as the pressure in the eye puts pressure on that indent making it wider and deeper. This is called “cupping”. An optic cup greater than 0.5 the size of the optic disc is abnormal.
What are the risk factors for open angle glaucoma?
- Increasing age
- Family history
- Black ethnic origin
- Nearsightedness (myopia)
- Intra-ocular pressure >23 mmHg
What are the clinical features of open angle glaucoma?
Often the rise in intraocular pressure is asymptomatic for a long period of time. It is diagnosed by routine screening when attending optometry for an eye check.
Glaucoma affects peripheral vision first. Gradually the peripheral vision closes in until they experience tunnel vision.
It can present with gradual onset of fluctuating pain, headaches, blurred vision and halos appearing around lights, particularly at night time.
What investigations should be ordered for open angle glaucoma?
- Tonometry
- Direct opthalmoscopy
- Indirect opthalmoscopy
- Slit-lamp biomicroscopy
- Visual field testing
Briefly describe the use of non-contact tonometry in diagnosing open angle glaucoma
Non-contact tonometry is the commonly used machine for estimating intraocular pressure by opticians. It involves shooting a “puff of air” at the cornea and measuring the corneal response to that air. It is less accurate but gives a helpful estimate for general screening purposes.
Briefly describe the use of Goldmann applanation tonometry in diagnosing open angle glaucoma
Goldmann applanation tonometry is the gold standard way to measure intraocular pressure. This involves a special device mounted on a slip lamp that makes contact with the cornea and applies different pressures to the front of the cornea to get an accurate measurement of what the intraocular pressure is.
Why investigate using opthalmoscopy?
Fundoscopy assessment to check for optic disc cupping and optic nerve health.
Why investigate using visual field assessment?
Visual field assessment to check for peripheral vision loss.
What is the role of trabeculectomy surgery in treating open angle glaucoma?
Trabeculectomy surgery may be required where eye drops are ineffective. This involves creating a new channel from the anterior chamber, through the sclera to a location under the conjunctiva. It causes a “bleb” under the conjunctiva where the aqueous humour drains. It is then reabsorbed from this bleb into the general circulation.
