Glaucomas are a group of diseases having in common gradual loss of retinal nerve fibers leading to characteristic excavated appearance (called glaucomatous cupping) of the starting point (head) of the optic nerve (nerve responsible for carrying visual senses from eye to the brain) (fig. 1). There is also associated specific pattern of loss of visual field.
Neglected, this fell disease gradually devours your field of vision from the periphery and ultimately leads to complete blindness. That is why it is called the ‘silent killer of sight’ and is, at present, the second leading cause of blindness world-wide.
High intra-ocular pressure, as opposed to our previous belief, is no longer considered an essential pre-requisite for occurrence of glaucomatous damage, though lowering eye pressure still remains the mainstay of its treatment.
What is intra-ocular pressure (IOP)?
It is the pressure inside the eye needed to maintain the shape of the globe, as well as the normal function of the eyeball.
It is maintained by the balance between formation and drainage of an intraocular fluid called aqueous humor, which bathes and nourishes different structures of the eye and maintains its shape. Normally the fluid drains out of the eye through a ‘drainage channel’ located at the ‘angle’ between cornea and iris inside the eye.
Congenital glaucoma is caused due to any infection acquired by the mother during the gestation period, for example rubella virus
Obstruction to these very drainage channels causes subsequent rise of eye pressure. Although infants and children can be affected rarely, glaucoma is more common in the adult population.
Causes & types of Glaucoma
The ideal cause to glaucoma is not known. In most of the cases it is due to rise in intra ocular pressure which can cause irrecoverable damage to the optic nerve and can result in permanent loss of vision.
But, glaucoma can also result from structural weakness or poor blood supply of the optic nerve head in presence of a statistically “normal” IOP (10-21mmhg). Hence the vulnerability of the optic disc is another factor that needs to be considered. Accordingly, the diagnosis of glaucoma requires more than just the mere measurement of intraocular pressure.
On the other hand persons with high IOP may not have glaucoma at all (ocular hypertension). Congenital glaucoma may be caused due to genetic defect or intrauterine infection like rubella
Types of glaucoma:
Primary open angle glaucoma – it is the commonest type.
Primary angle closure glaucoma
Secondary glaucoma – due to other eye conditions or diseases. May be open or closed angle. Common causes:–
New blood vessel growth inside the eye à Following stroke or severe diabetic change in retina.
Drugs – Steroids etc.
Signs & Symptoms
Chronic Glaucomas (commonest – mostly primary open angle but also some chronic angle closure & secondary glaucomas)
Mostly no symptoms
Frequent change of glasses
Difficulty due to severe visual field contraction in advanced cases à Problem in driving, walking etc.
These glaucomas are called The Silent Killer of Vision
Mainly due to sudden angle closure
Sub-acute attack (due to intermittent angle closure)
Rainbow haloes around light
Severe pain with nausea, vomiting, sweating à may mimic abdominal emergency
Marked diminution of vision
Marked rise of IOP
May be precipitated by pupil enlargement ( due to dim illumination, emotional stress or specific drugs)
Tonometry (to measure eye pressure)(fig.3), Gonioscopy (to assess the drainage angle)(fig. 4), Automated perimetry (to measure visual field loss)(fig. 5), Optical Coherence Tomography (for early detection of retinal nerve fibre loss)(fig. 7).
Glaucoma cannot be cured. It can only be controlled reasonably by reducing eye pressure by –
Lasers (peripheral iridotomy etc)(fig. 7)
Surgery ( trabeculectomy (fig. 8), glaucoma valves/shunts) for creating an aqueous outflow bypass.