If you’ve been to the optometrist in the last couple of years, you may be wondering what’s actually happening during the process of the optometrist measuring your eyes and their responses, and examining the deterioration or extent of your visual capabilities. Why do I have to get my pupils dilated? Why do they all use the same chart with letters and numbers growing smaller towards the bottom? Why do they keep shining their flashlight in my eyes?
Well, this article is here to give you the lowdown on what exactly is happening during your eye exams – common measurements and techniques, and the history behind them. Read on if you’re curious, and want to learn more and to answer the question, why do I see floaters in my eyes?
Why Does the Optometrist Dilate My Pupils?
Think of your pupil like a window – except it doesn’t stay the same size. That’s exactly what it is – when your pupil is small, it’s allowing a smaller amount of light through, and when it’s larger, more light is allowed in.
This is one of the ways in which night vision is possible – when your pupil is exposed to darkness, it swells in size. This allows more light into your eye, which in turn exposes the neurons (rods and cones) inside your eyes to more light – highly necessary in darker rooms – and allows you to see in darker areas.
Conversely, bright areas make your pupils shrink, as you don’t need to allow as much light in – indeed, too much exposure to light can be painful. This is why you’re given sunglasses or eyeshades after your exam.
Now, the reason your optometrist needs your eyes to be dilated is simple – light must be shone in through your eyes in order to actually view the inside of your eye – with magnification and proper equipment, this is what your eye doctor does – he or she examines the interior of your eye for deterioration, disease, and other factors by using your pupil as a window. The bigger the window, the bigger the view; thus, dilation.
Of course, when exposed to light, the pupil’s natural reaction is to shrink massively – not good when the optometrist needs a full view into the inside of your eye. This is why chemical eye drops are used – they supersede the pupil’s natural tendency to shrink when exposed to light, allowing the doctor to get a better view of the interior of your eye, and perform a comprehensive eye exam.
Why Is My Vision Blurry After Getting My Eyes Dilated?
Naturally, dilation drops don’t just affect your pupil – most common products on the market work by relaxing your iris sphincter muscle. This has the side effect of relaxing the muscles which allows you to change your focus – since your ability to focus is essentially paralyzed; you’ve generally got a very limited field of 100% visual acuity.
Because of the limited focus issue, and the tendency for bright lights to be nearly painful without proper protective eyewear, most optometry professionals recommend not driving or operating heavy machinery for several hours after dilation – until the muscle-relaxing effects of the eye drops wear off.
Where Did the Eye Chart Come From? What Do The Different Lines Mean?
The eye chart as many know it today is an 11-line chart consisting of block letters at various sizes, decreasing in size as you move farther down the chart – is based off the “Snellen Chart”.
This chart, first developed by Dutch ophthalmologist Herman Snellen in 1862, first used a 5×5 grid consisting of abstract symbols, and since its initial development, it has gone through many changes, resulting in the eye chart we see today.
The contemporary chart uses a limited set of “Sloan Letters” – C, D, E, F, L, N, O, P, T, and Z – to determine visual acuity. The first line and letter of the chart, read unaided, corresponds to 20/200 vision, the second line to 20/100, the third to 20/70, and so on. If you can read line 8 perfectly unaided, congratulations! You have 20/20 vision!
Interestingly, the Snellen Chart has mostly been replaced by a more modern chart known as the LogMAR – “Logarithm of the Minimum Angle of Resolution”. Unlike the Snellen chart, this chart uses a logarithmic testing scale, and includes an even amount of letters on each line. While it is quite similar, and either chart can be used, the LogMAR chart is considered more accurate, and therefore recommended for research settings, and for use by most modern ophthalmologists.
Obviously, it is possible to “cheat” one of these charts – but there’s really no reason to do so. It’s not as if you’re trying to pass a test – you’re trying to determine what visual aid is necessary for you. Despite this, physical charts do lend themselves to memorization, and to decrease this tendency, many eye doctors are moving towards computerized charts which randomly sort letters, disallowing for any kind of memorization on the part of the patient, and providing more accurate results.
Hopefully we’ve taken a little bit of the mystery out of your next trip to the eye doctor. And remember, if you’re ever curious about why your ophthalmologist is doing what he or she is doing, just ask! Most eye doctors are more than happy to explain the process for you – it’s what they do, and they love it when people are curious enough to learn more about their profession.
Article Submitted By Community Writer