What is Glaucoma?
Glaucoma is a group of
disorders in which [I.O.P] intra-ocular pressure (I.O.P maintains the shape of
the eye ) is raised above the normal value (11 - 21 mm Hg) in the affected eye ,
resulting in a damage to the optic nerve head & irreversible visual field
defects.
What are the risk factors for Glaucoma?
Following are the risk
factors for Glaucoma:
1.Family history of
glaucoma especially in parents and siblings (risk of 10% in siblings).
2.Diabetes mellitus.
3.Thyroid Diseases:
Thyroiditis.
4.Refractive error :mostly
seen in high Myopes.
5.Cigarette smoking
6.Injudicious use of
steroids (eye drops).
7.Age:
Mostly glaucoma affect people in the fifth & seventh decade of their life
but it can occur at any age.
Can glaucoma can occur in children?
Glaucoma
can occur even in young children and infants (Developmental/Congenital
Glaucoma). Occurring before the age of 3 years it is called Congenital
Glaucoma.
Between the age of 3 and
30-35 years it is called Juvenile Glaucoma.
What are the Types of Glaucoma?
There are two main types
of glaucoma:
Normally, the fluid of the eye (aqueous) circulates through anterior chamber and passes through the angle exits from the eye into the Canal of Schlemn but in open angle glaucoma the passage to the canal of Schlemn offer resistance to the flow of aqueous.
In angle closure glaucoma
the angle of the chamber is narrow or gets closed preventing the drainage of
aqueous from the eye. Both types lead to increase in intra-ocular pressure.
What are the signs & symptoms?
Primary open angle
glaucoma usually insidious & asymptomatic (does not give rise to any
symptoms) in early stages.
In
late stages patients may feel pain in eyes (eye-ache).
Some individuals may
notice field defects (inability to see certain areas of the field of vision).
Usually
this type of glaucoma is diagnosed on examination by an eye specialist.
Patient with very high
I.O.P may complain of occasional colored rings (haloes) around lights due to
transient corneal epithelial oedema.
Patient Can develop
delayed dark adaptation.
Reading & close work
often present increasing difficulties owing to accommodative failure due to
constant pressure on the ciliary muscle & it is nerve supply. Therefore
patient usually complain of frequent changes in presbyopic glasses.
How glaucoma can lead to blindness?
Increase in pressure in
the eye leads to resistance to flow of blood into the eye leading to damage to
the optic nerve head which
carries the images to the brain. First it leads to some area of loss of visual
field (the extent of surrounding visible to any one eye). This field loss
progresses gradually till the eye is completely blind.
Early
field loss can be detected by an eye specialist with a test called Visual Field
Charting.
How to diagnose Glaucoma
?
Glaucoma can be diagnosed
by following tests:
Intra-ocular Pressure
[I.O.P] or Eye Pressure:
Measured by an instrument called Applanation Tonometer (Normal I.O.P ranges
between 11 and 21 mm Hg). It may be mildly raised in open angle glaucoma and
markedly raised in angle closure glaucoma.
In between the attacks of
angle closure glaucoma it may be normal. It may vary at different times of the
day and this variation can be measured by noting pressures round the clock at
specified interval (Phasing / Diurnal Variation).
In low tension or normal
tension glaucoma the pressure may never be higher than normal range.
Gonioscopy:
It’s method by which one can assess the angle of anterior chamber of the eye.
It helps in diagnosing
the type of glaucoma or even the vulnerability of the person to have attacks of
angle closure glaucoma.
Fundus examination:
The retina and optic nerve of the eye can be seen by an instrument called
ophthalmoscope.
The optic disc undergoes
characteristic changes in glaucoma which are noted by measuring cup :
disc ratio or the C : D Ratio [ normal range is 0.3
to 0.4].
It is increased in open
angle glaucoma and later stages of angle closure glaucoma & is proportionate
to the extent of damage done [In some normal individuals the C : D ratio
may be increased].
Visual Fields:
It measures the "area of vision"&, the sensitivity of each point
in this area of a single eye.
In
this test patient is shown light targets of various sizes and brightness and
note is made of the area where the patient can see this. The data thus collected
, analyzed & compared with data of normal population.
Glaucoma
gives rise to characteristic field defects &
progress in a peculiar manner. This is the definitive test to detect
glaucoma and assess the severity and extent of damage in the eye.
Can Glaucoma be treated?
Glaucoma can be treated
but the damage done by it cannot be reversed. But further damage to the eye by
glaucoma can be stopped.
The treatment for
glaucoma includes:
Drugs :Initial therapy of Primary open angle glaucoma is still medical.
Surgeries:
Goniotomy,Trabeculotomy,Trabeculectomy.see Diagram below.
Laser Operation
[ Argon or diode laser trabculopasty ] see laser
.
With early treatment, serious loss of vision and blindness can be prevented.
