GLAUCOMA RISK FACTORS
Intra-ocular Pressure (IOP)
The most common risk factor is an elevated IOP (Ocular Hypertension). It is statistically proven that patients with an IOP greater than 21mmHg are seven to 22 times more likely to develop glaucoma. Many patients with ocular hypertension do not develop glaucoma. Recent studies, however, state that even in the absence of glaucoma, patients with an IOP greater than 24mmHg should be treated with IOP lowering medication to reduce their risk of developing glaucoma.
Your IOP is very susceptible to changes. Many medication and systemic factors can cause fluctuation in a patients IOP. Even taking measurements at different times of the day may result in different IOP measurements. That is why many times your optometrist may ask that you return for an IOP check in the morning. Our IOP tends to run higher during the morning hours.
Every study has shown an increase prevalence with increase age. In fact, you are six times more likely to develop glaucoma if you are over the age of 60.
Your IOP and cup-to-disc ratio are both basically genetically determined. Some studies suggest that 13-25% of glaucoma patients have a family history. In fact, recent chromosomal mapping have revealed the presence of a "glaucoma gene".
One study suggest that African-Americans are four times more likely to develop glaucoma.
Optic Nerve / Nerve Fiber Layer
Optometrist evaluate the optic nerve and measure what is called the cup-to-disc ratio. If you imagine your optic nerve like a cantaloupe, and the more seeds that are scooped out, the less cantaloupe there is. The same applies to the optic nerve. The larger the cupping in the center of the nerve (the seeds removed), the less healthy nerve fibers are left (the cantaloupe), thus the more fragile the optic nerve may be.
Normal cup-to-disc ratio is 20-40%. Anything greater than that poses an increased risk for glaucoma. So does any cup-to-disc asymmetry between the eyes. Any asymmetry greater than 20% may raise a caution flag by your optometrist.
Some studies suggest that the higher the myopia, the greater the risk factor.
The association between glaucoma and diabetes is still unclear. However, because diabetes is a disease of the small blood vessels, it is important to have annual dilated eye exams, including glaucoma testing, by your optometrist.
Hypertension and Hypotension
Patients with either High or Low blood pressure must understand that their optic nerve may not be receiving the proper perfusion that is vital to its health.
It is argued that B12 deficiency does not actually cause glaucoma. It is known, in fact to produce an optic atrophy, which is essentially the same as a non-progressive form of glaucoma. Regardless, it is important to follow with your optometrist if you have a B12 deficiency.
Patients with anemia present the same risk as hypertension patients. The health of the optic nerve and nerve fiber layer may be compromised in an anemic patient due to the lack of proper oxygen delivery.
One sleep apnea study concluded that one-third of their sleep apnea patients had glaucoma. These patients pose a high risk for Normal Tension Glaucoma (NTG) because of the lack of oxygen that is delivered to the optic nerve.
Primary Care of the Glaucomas by Murry Fingeret and Thomas L. Lewis . 2001