Myopia Control: Why Does Measuring the Length of the Eye Matter?
As an optometrist I’m trained to detect and treat vision and eye health problems on a daily basis. When someone asks about which eye problems are the most common I instantly start talking about glaucoma, macular degeneration and cataracts, and have previously often not really given the “basic” problems of myopia, hyperopia and presbyopia much thought, because these are “just” focusing problems which are easily corrected with spectacles or contact lenses. The reality is that these focusing defects are by far the most common sight conditions and of the three, myopia in particular is commonly a progressive condition with a variety of potential serious outcomes.
Myopia is when you can see closer objects very clearly but far away they are blurred.
Generally, myopia is caused by an eye that is too long, and this increase in axial length can also cause problems like retinal thinning. Almost two billion people around the world are estimated to suffer with myopia and this is expected to rise to almost half the world’s population by 2050.
So what is Axial Length and why is it important?
Its simple really: axial length is the length of the eye from the front to the back. It has been measured for many years in scientific studies of myopia but has never been used extensively in private practice clinics as a routine part of myopia care. This is mainly because there is still some uncertainty around individual monitoring and what the data really means plus the equipment is super expensive! However, axial length measurement is a really useful disease risk indicator as it’s the elongated growth of the eyeball that makes someone more at risk of serious eye diseases later in life. An axial length of greater than 26mm indicates much higher risk of developing conditions like glaucoma, retinal detachment, macular degeneration and cataracts and therefore these patients need to be more carefully followed. So while the exact correlation between prescription amount and axial length is still not clearly defined by scientists we know that it is really useful to measure. See the table below for the estimated disease risk for different levels of myopia,which is now accepted as the gold standard worldwide, and is one of the reasons the WHO is now listing the increase in myopia rates worldwide as a top 5 concern for them.
Odds Ratio of Ocular Disease as a Function of Myopia1
These risk statistics are truly concerning, and given multiple members of my own family are myopic, they hit very close to home. Its why I have been approaching myopia with a preventative mindset for 15 years and why Envision Optical through our specialist Gold Coast Myopia Control Clinic, has recently become the only local optometrist to have the industry leading Zeiss machine to accurately measure axial length to within 0.01mm.
We now perform this measurement at each initial myopia exam and then at every subsequent review visit every 6 months to monitor for further progression and to help judge the effectiveness of our myopia control treatment programs.
The simple fact is that myopia can no longer be considered just simple short sightedness, which is corrected by basic glasses or contact lenses. It is a condition with very serious potential side effects, with higher prescriptions meaning vastly increased risk of future eye disease. It is imperative to have a preventative approach and to closely monitor patients to ensure treatments are effectively controlling progression. Axial length measurement is an essential part of this monitoring.
Post by: Andrew Bowden, Optometrist