What is Glaucoma?
Glaucoma is a group of eye diseases that cause progressive damage of the optic nerve at the point where it leaves the eye to carry visual information to the brain.
If left untreated, most types of glaucoma progress (without warning nor obvious symptoms to the patient) towards gradually worsening visual damage and may lead to blindness. Once incurred, visual damage is mostly irreversible, and this has led to glaucoma being described as the “silent blinding disease” or the “sneak thief of sight”.
Glaucoma is the second most common cause of blindness worldwide. It is estimated that 4.5 million persons globally are blind due to glaucoma1 and that this number will rise to 11.2 million by 20202. It is noteworthy that due to the silent progression of the disease – at least in its early stages – up to 50% of affected persons in the developed countries are not even aware of having glaucoma3. This number may rise to 90% in underdeveloped parts of the world.
There are several types of glaucoma. Some may occur as a complication of other visual disorders (the so-called “secondary” glaucomas) but the vast majority is “primary”, i.e. they occur without a known cause. It was once believed that the cause of most or all glaucomas was high pressure within the eye (known as intraocular pressure – sometimes abbreviated as IOP). It is now established however, that even people without an abnormally high IOP may suffer from glaucoma. Intraocular pressure is considered therefore today as a “Risk Factor” for glaucoma, together with other factors such as racial ancestry, family history, high myopia and age.
Some forms of glaucoma may occur at birth (“congenital”) or during infancy and childhood (“juvenile”); in most cases however, glaucoma appears after the 4thdecade of life, and its frequency increases with age. There is no clearly established difference in glaucoma incidence between men and women.
The most common types of adult-onset glaucoma are Primary Open Angle Glaucoma (POAG) – a form most frequently encountered in patients of Caucasian and African ancestry – and Angle-Closure Glaucoma (ACG), which is the more common in patients of Asian ancestry. Angle-Closure Glaucoma is often chronic, like POAG, but can sometimes be acute, in which case it usually presents as a very painful ocular condition leading to rapid vision loss.
There is no cure for glaucoma as yet, and vision loss is irreversible. However medication or surgery (traditional or laser) can halt or slow-down any further vision loss. Therefore early detection is essential to limiting visual impairment and preventing the progression towards severe visual handicap or blindness. Your eye-care professional can detect glaucoma in its early stages and advise you on the best course of action.
- World Health Organization data from www.who.int/blindness/causes/priority/en/
- Quigley et al. Br J Ophthalmol 2006; 90:262-267
- Sommer et al. Arch Ophthalmol 1991; 1090-1095
How I Diagnose Glaucoma:
The diagnostic criteria that leads me to suspect glaucoma as a possible diagnosis includes the examination of the optic nerve head and its retinal nerve fiber layer since it is fundamental to all aspects of glaucoma diagnosis and evaluation. All forms of glaucoma have in common a potentially progressive and characteristic optic neuropathy which is associated with visual field loss as damage progresses. Consequently, a reliable and reproducible visual field analysis is necessary as a representation of the patient’s functional status. Intraocular pressure (IOP) determination is important since the prevalence of glaucoma increases as the level of IOP increases. In spite of the relationship between the level of IOP and glaucoma, there is great interindividual variation in the susceptibility of the optic nerve to IOP- related damage. Suggesting that an IOP level of greater than 21-22 mmHg is an arbitrarily defined level and highlights the poor value of utilizing a specific IOP cutoff as a measure for screening and diagnosing glaucoma.
Other important risk factors associated with glaucoma are as follows:
- Older age
- Family history of glaucoma
- Ancestry / Race
- Thinner central corneal
- Lower corneal hysteresis (an assessment of the cornea’s ability to absorb and dissipate energy)
- Low ocular perfusion pressures
- Lower blood pressure
- Optic disc hemorrhage(s)
- Diabetes mellitus
- Genetic mutations (there is little value for routine genetic testing to diagnose or predict the development of glaucoma at the current time)
- Migraine headache
- Peripheral vasospam
- Reduction of estrogen production in post-menopausal women
- Obstructive sleep apnea
Testing for glaucoma is indicated when certain ocular, systemic, and general factors are found during periodic comprehensive eye examinations which thereby increase the risk and/or probability of glaucoma.
My methodology and evaluation of a glaucoma suspect may include, but is not limited to, the following:
- Visual acuity
- Pupil evaluation (Utilizing NPi – 100 Pupillometer)
- Blood pressure
- Biomicroscopy (Slit Lamp)
- Ultrasound Biomicroscopy (UBM to ascertain underlying cause(s) of any Angle Closure)
- IOP measurement (diurnal / asymmetry)
- Central corneal thickness (Pachymetry)
- Corneal hysteresis
- Optic nerve assessment (neuroretinal rim, optic disc size, cup-disc ratio)
- Nerve fiber layer assessment
- PERG and PhNR testing can be very useful, but are not substitutes for standard automated perimetry (SAP), nor are they substitutes for optical coherence tomography (OCT) imaging
- Fundus Photography (sterescopic optic nerve photos)
- Visual fields (before accepting VF defects as real, they must be confirmed on two consecutive exams (excluding the initial one) and ideally obtain 6 VF’s in 2 years to identify the rate of progression).
Why Are There So Many Diagnostic Exams for Glaucoma?
Diagnosing glaucoma is not always easy, and careful structural and functional evaluation of the optic nerve continues to be essential to diagnosis and treatment. The most important concern is protecting, preserving and optimizing your sight. Doctor Rouse looks at many factors before making decisions about your treatment. If your condition is particularly difficult to diagnose or treat, you may be referred for a second opinion.