Understanding Glaucoma
Managing glaucoma today is not a one sided affair. As the patient, one needs to be actively involved in the decision making process along with someone who understands you and is willing to go through the entire process with you, patiently.
The following is intended as a pre requisite to developing a good foundation to understanding the basics involved in glaucoma management. Please go through each part sequentially without skipping any section as the understanding of glaucoma is going to be built, block by block and in the Indian perspective.
Normal structure and function of the eye
The eye is like a camera in which lenses focus the picture on a light sensitive film. In the human eye, the transparent cornea and lens focus images on the retina, a thin light sensitive film. Just in front of the lens lies the iris (colored portion of the eye) with a central opening – the pupil. This helps regulate the amount of light entering the eye, just like the shutter of a camera. The sclera (white of the eye) is the protective outer coat of the eye. Between the sclera and the retina lies the choroid, which has a chiefly nutritive function. The space between the lens and the retinal is filled with a clear jelly called the vitreous body.
What is Glaucoma ?
Glaucoma is the name given to many different diseases, characterized by a typical damage to the optic nerve.
The eye is like a football or a balloon, as it is a fluid filled cavity. This fluid is a transparent fluid called aqueous humor and is produced behind the brown part of the eye called iris, inside a structure called ciliary body. This fluid nourishes various internal structures of the eye. This fluid is not tears (as tears are both made and located outside of the eye). But aqueous humor is actually created inside the eye. Therefore, if the eye’s feel dry, or if the eye’s water, this is not related to the aqueous humor or the eye pressure.
From the ciliary body, where the aqueous is produced, the fluid flows into the back compartment of the eye called the posterior chamber and then through the pupil which functions like a communicating door into the front compartment called the anterior chamber. From the anterior chamber the fluid leaves the eye through pores called trabecular meshwork.
So glaucoma, for this part of the discussion is due to accumulation of fluid within the eye. This can happen because of
- Increase fluid production within the ciliary body.
- Obstruction to the flow of fluid through the drainage pores, also called as the trabecular meshwork.
- Sometimes the fluid production in the ciliary body is normal. Even the flow of the aqueous through the trabecular meshwork is adequate. However sometimes there is a resistance to the flow of aqueous from the posterior chamber through the pupil into the anterior chamber.
Incidentally, increased fluid production within the ciliary body and obstruction to the flow of fluid through the trabecular meshwork are responsible for the open type of glaucoma. Resistance to flow of aqueous from the posterior chamber through the pupil into the anterior chamber contribute to the closed type of glaucoma. We shall discuss open and closed types in more detail at a later stage.
The net result is for the fluid to accumulate within the front part of the eye and exert a pressure on the back of the eye. Since the eye is a closed cavity the increased backpressure is likely to damage weak structures. The weak link in the back of the eye is the optic nerve. As the pressure rises, the blood supply to the optic nerve is reduced. The health of the optic nerve then begins to get compromised. Damage to the optic nerve is a hallmark of glaucoma.
If the optic nerve comes under too much pressure then it can be injured. How much damage there will be, depends on how much pressure there is and how long it has lasted, and whether there is a pre-existing poor blood supply or other weakness of the optic. As damage to the optic nerve progresses, part of what we see around us is lost. First the edges of the picture blur and disappear. As the damage spreads, the view of the world becomes narrower and narrower, in effect producing tunnel vision. If the entire nerve is destroyed, blindness results.
What are the types of glaucoma
Glaucoma as we are now aware is condition where damage to the optic nerve is present. This can be due to excess fluid present within the eye. Either due to increased fluid production, reduced outflow through the drainage channels or due to an obstruction to flow of fluid from where it is produced in the posterior chamber. This obstruction to the flow is at the level of the pupil. To get a clearer picture into the types of glaucoma let’s look at the eye being like a sink we all have in our kitchens.
The open type of glaucoma develops when the tap is open in excess such that the inflow of fluid into the sink is out of proportion to the outflow of fluid through the drainage pipe. The net result is fluid accumulating in the sink.
Sometimes the drainpipe can become smaller with age, being clogged by deposits, which build up slowly. This partial blockage causes a gradual backflow of fluid within the drainage system with accumulation within the sink. This type of glaucoma is also called the open type of glaucoma.
In the closed type of glaucoma dirt and grime tends to block the flow of fluid from the basin of the sink into the drainage channel. This stopper type of block leads to accumulation of fluid within the eye, synonymous with blockage at the level of the pupil.
The open and closed type represent the two basic types of glaucoma. As one who has glaucoma its important to know what type of glaucoma one has (open/closed) because they may differ in the way they manifest. More importantly, it is essential to know the type of glaucoma one has because treatment varies depending on the type of glaucoma .
The open type of glaucoma is usually treated first with drops failing which a glaucoma surgery may need to be done. The closed type of glaucoma is usually treated with a laser iridotomy. If required, medication in the form of drops may also be required (depending on the severity). When these don’t work a glaucoma surgery may need to be considered.
Glaucomas can also be classified as being primary or secondary.
Primary glaucomas are usually not associated with an obvious systemic or other eye related disorder that could cause glaucoma. Usually primary glaucomas affect both eyes and can have a predisposition to affect other family members. Secondary glaucomas are often associated with systemic or other eye related disorders that can cause glaucoma. They may affect one or both eyes and may or may not predispose other family members to develop glaucoma.
In secondary glaucoma usually there is an inciting condition like an injury, certain drugs like steroid containing preparations in any form, phenothiazine tranquilizers, anti depressants, anti histamincs, anti spasmolytics, antacids like cimetidine and ranitidine, antiparkinsonism drugs, sedatives and stimulants, sulfa containing drugs, sympathomimetic agents like salbutamol and ephedrine and mydriatics amongst others (in those predisposed), hemorrhages, tumors, and inflammations amongst others which can sometimes block outflow channels in the eye.
This may increase the eye pressure and lead to (secondary) glaucoma. The only known type of secondary glaucoma associated with an increased fluid production is due to mustard oil contamination. The toxin produces excess aqueous humor, more that than what can be tackled by the outflow channels. Glaucoma associated with mustard oil contamination is called “Epidemic dropsy”. Delhi has had several such epidemics.
In developmental glaucomas the “drainpipe” may have been poorly manufactured. This type of defect is seen in congenital glaucomas, where the drainage openings are abnormal from birth.
Developmental glaucomas can be further classified as primary congenital glaucoma where there is no obvious systemic or eye related abnormality as the causative factor. Since a child’s eye is more elastic than an adult’s, when the pressure inside the eye increases, the easily stretchable eye of the child may enlarge. This can typically happen up to three years of age. With raised eye pressure’s, the front of the eye may become cloudy like fog on a windshield. The child may become sensitive to light and may have persistent watering. Though rare it still not so uncommon. It’s important to remember that large eyes may not always be beautiful eyes. They can at times harbor a glaucoma.
Secondary developmental glaucomas usually have additional systemic or eye related abnormalities which cause the glaucoma (Axenfeld Rieger syndrome, Aniridia, Sturge Weber syndrome etc).
Glaucomas can also be classified as being primary or secondary.
Primary glaucomas are usually not associated with an obvious systemic or other eye related disorder that could cause glaucoma. Usually primary glaucomas affect both eyes and can have a predisposition to affect other family members. Secondary glaucomas are often associated with systemic or other eye related disorders that can cause glaucoma. They may affect one or both eyes and may or may not predispose other family members to develop glaucoma.
In secondary glaucoma usually there is an inciting condition like an injury, certain drugs like steroid containing preparations in any form, phenothiazine tranquilizers, anti depressants, anti histamincs, anti spasmolytics, antacids like cimetidine and ranitidine, antiparkinsonism drugs, sedatives and stimulants, sulfa containing drugs, sympathomimetic agents like salbutamol and ephedrine and mydriatics amongst others (in those predisposed), hemorrhages, tumors, and inflammations amongst others which can sometimes block outflow channels in the eye.
This may increase the eye pressure and lead to (secondary) glaucoma. The only known type of secondary glaucoma associated with an increased fluid production is due to mustard oil contamination. The toxin produces excess aqueous humor, more that than what can be tackled by the outflow channels. Glaucoma associated with mustard oil contamination is called “Epidemic dropsy”. Delhi has had several such epidemics.
In developmental glaucomas the “drainpipe” may have been poorly manufactured. This type of defect is seen in congenital glaucomas, where the drainage openings are abnormal from birth.
Developmental glaucomas can be further classified as primary congenital glaucoma where there is no obvious systemic or eye related abnormality as the causative factor. Since a child’s eye is more elastic than an adult’s, when the pressure inside the eye increases, the easily stretchable eye of the child may enlarge. This can typically happen up to three years of age. With raised eye pressure’s, the front of the eye may become cloudy like fog on a windshield. The child may become sensitive to light and may have persistent watering. Though rare it still not so uncommon. It’s important to remember that large eyes may not always be beautiful eyes. They can at times harbor a glaucoma.
Secondary developmental glaucomas usually have additional systemic or eye related abnormalities which cause the glaucoma (Axenfeld Rieger syndrome, Aniridia, Sturge Weber syndrome etc).