Glaucoma

Glaucoma is a disease characterised by accelerated loss of fibres of the optic nerve compared to same-age population, with or without elevated intraocular pressure, in the absence of a history of mechanical or external optic nerve injury such as from optic nerve compression, infiltration, trauma, or an optic nerve blood flow supply insufficiency insult, and in the absence of an indirect nerve degeneration from a supply-chain shortage such as from upstream (retina) or downstream (brain) nerve damage.. The optic nerve is the bundle of nerve fibres that carry the visual images signal from the retina of the eye to the brain. The functional consequence of optic nerve damage from glaucoma is the loss of peripheral vision, which if poorly controlled may lead to severe tunnel vision ultimately leading to total blindness.

Causes

Many reasons. Genetic plays a major role, but so is the internal pressure of the eye, and the general oxygen supply to the optic nerve. Fluid inside the eye is required for the proper internal health, shape and functioning of the eye. There is a balance between the flux of fluid produced and the outflow flux of fluid that leaves the eye. The fluid (aqueous) drains from the spongy meshwork (trabecular meshwork) at the point where iris meets the cornea in what is called the anterior chamber angle. There is another mechanism of fluid outflow by “seepage” through the uvea and sclera. Any problem in the drainage of the fluid can then increase the pressure of the eye (raised intraocular pressure) if the rate of aqueous fluid production remains unchanged. This increased intraocular pressure leads to stress and accelerated death of the nerve cells (the ganglion cells) in the retina that constitutes the million fibres of the optic nerve leaving the eye. The accelerated death of these nerve cells over time leads to the characteristic pattern of optic nerve head thinning and the progressive accelerated peripheral vision loss we called glaucoma, the disease that is also called the silent thief of sight.

Types of Glaucoma

Primary Open Angle Glaucoma is the most common. It is associated with a high intraocular pressure with evidence of thinning of the optic nerve head rim of nerve fibres, but diagnosed after checking that the glaucoma is not from Primary Angle Closure, and not from other forms of glaucoma such as from certain deposits like from pseudoexfoliation, from pigment dispersion or from fragments of self-melting cataracts in the trabecular meshwork, nor from congenitally malformed drainage angle, nor from drainage angle scarring as a result of previous internal eye inflammation.

Primary or Chronic Angle closure glaucoma usually happens in people with small internal eye such as people with high degree of hypermetropia and people of Asian lineage. Small eye has narrow angle of drainage. Even little clogging leads to significant increase in the intraocular pressure suddenly. It may also lead to complete closure of the angle leading to angle closure glaucoma. In people with small eyes dilation of the pupil in dark room or eye drops for dilation may further increase the risk of an acute painful and blinding attack of acute angle closure glaucoma.

Congenital glaucoma is rare. Such children are born with defects in the aqueous drainage system of the eye. Infant can present as having cloudy cornea, watery eye, sun-sensitive eye, or eye with a large corneal diameter.

Secondary glaucoma –Presence of factors like eye injury long ago, a history of corticosteroid eyedrops or steroid tablets or even sprays and creams in particular those near the eyes, and diseases such as pigment dispersion, pseudoexfoliation, post-inflammatory eye diseases.

Normal tension glaucoma- In certain individuals, and more commonly in Asian and Indian subcontinent population, the intraocular pressure can be normal yet there is a progressive damage to nerve cells of the eye otherwise characteristic of primary open angle glaucoma. This suggests the role of some additional factors apart from intraocular pressure causing glaucoma, usually genetic, but occasionally other medical causes such as those that may intermittently or chronically reduce blood flow or oxygenation to the optic nerves, such as from (including but not limited to) obstructive sleep apnoea. Your ophthalmologist at Centre for Eyes will manage your glaucoma according to what is applicable to you as an individual.

Signs and symptoms

Open angle glaucoma does not have any symptoms initially but may latter lead to side vision loss.

Primary and Chronic angle closure glaucoma may not have much symptoms either although some might describe eye pain in dark at night when prompted.

Acute angle closure glaucoma has severe eye pain, nausea, vomiting, halo around bright lights and blurred vision. It is an eye emergency that should be seen asap by ophthalmologist and if unable to, be best treated through your Hospital’s Eye Emergency Unit.

Congenital glaucoma –Such children have cloudy cornea, sensitivity to light and excessive tearing, may have large cornea and/or large eye and relatively little hypermetropia compared other child of same age.

Diagnosis

Generally, eye check-up for glaucoma involves ophthalmoscopy and tonometry. Further confirmation may involve additional tests like perimetry (field test), optical coherence tomography (OCT) or scanning laser ophthalmoscopy (SLO) of the optic nerve head, gonioscopy, and pachymetry Ophthalmoscopy involves examination of the optic nerve by the doctor using an instrument to direct light into the eye for the test.

Ophthalmoscopy involves examination of the optic nerve by the doctor using an instrument to direct light into the eye for the test.

Tonometry is used to measure the eye pressure. A tonometer is kept on the surface of the eye after numbing the eye by numbing drops and gives the intraocular pressure reading.

Field test (perimetry) gives a map of the vision field i.e. where a person can or cannot see in his or her side vision, by a computerised test. It is a quantitative functional measurement of the optic nerve function.

OCT or SLO of the optic nerve head measures the thickness of the nerves that constitute the optic disc, as a measure of the structure so as to determine if nerve fibres are significantly thinner than average thickness of same age and if had degenerated vastly when compared previous measurement. This is for a quantitative structural measurement of the optic nerve head.

Gonioscopy- It is done by numbing the eyes. A special lens with mirror inside it allows the doctor to view the angle of drainage.

Pachymetry measures the thickness of the cornea. Thin cornea is at a higher risk of glaucoma. It is measured by numbing the eyes and the surface of the eye is touched by pachymetre.

Treatment involves

  • Use of eye drops to reduce the production of eye fluid and to improve drainage of the fluid from the eye.
  • Laser surgery stimulating the existing drainage angle structure by making small “tickle” to the meshwork by laser.
  • Glaucoma surgery makes new drainage channel through surgery, with or without stents, and with or without cataract surgery.
  • For those with angle closure history or suspect features, laser may be used to either create an emergency escape route (a hole) on the iris, or to contract the iris in such a way to open up the angle.

Vision once lost due to glaucoma cannot be restored.