Occasionally I send patients to another clinic to get a laser scan of the back of their eye. What is this test, and why do we do it?
The official name of this procedure is called an “optical coherence tomography” scan or “OCT” for short. The machine emits a very short wavelength (~100 nm) laser beam that hits certain structures in the retina. The onboard processor is able to translate the information that the laser records into a topographical profile of whatever structure the doctor wants to see. This affords him the ability to notice any disruptions below the retinal surface.
I take retinal pictures of every single patient in order to examine key anatomical and functional components of the eye. Retinal photos are a brilliant form of technology that allows me to see very detailed things. Occasionally I also utilize special lenses to determine if a problem is present. However, these two techniques are sometimes not detailed enough to examine key hidden structures.
Instead of thinking about the retina, let’s use an apple analogy for a moment. If you take a picture of the side of an apple, you could see that it is red. You could see the outline and perhaps infer that it curves outward towards you. You wouldn’t be able to tell how deep the apple was or what the insides look like. Taking an OCT of the apple would be like cutting it in half and observing a cross section. You would now be able to see that red color is actually a very thin skin. You could also measure the depth of the apple, see that the majority of it’s volume is composed of a fibrous network, and notice a small cavity in the center that’s filled with seeds. If the seeds were displaced to the side, a traditional camera picture wouldn’t notice anything out of the ordinary since the external appearance is untouched. However, an OCT would be able to tell that they are not in their proper position. For almost every patient, a retinal photo is way above the standard of care that’s required to examine their eyes. However, some patients’ eyes either present with abnormalities or have a suspicious appearance. Those patients require the detailed level of imaging and analysis that an OCT can provide.
It’s important to clarify a few misconceptions about getting an OCT:
-Does it hurt?
It doesn’t hurt at all. It’s actually slightly more gentle than a camera flash
-Will it fix my problem.
No. There are many types of lasers that doctors use on the eye. An OCT does diagnostic imaging only. That means that it shows the doctor what is the issue and does not fix it.
-Why didn’t my doctor see what the laser saw?
A doctor only orders an OCT when a known or suspected problem lies in an area of the retina that’s not visible to human eyes and traditional machines. Unless your doctor has x-ray vision, he won’t be able to see the deep hidden retinal layers.
-Come on doc. Is this really important?
Absolutely! With many retinal pathologies the OCT reading is how the doctor determines what treatment or monitoring protocols he will use. Additionally, he now has a snapshot of the retina at a given time and can track it’s evolution in the future.
-Why doesn’t my doctor have an OCT?
Most patients don’t require such a scan. Typically I will see only 1 patient who needs an OCT each week. Although I can perform the scan and interpret the results with ease, I prefer my patients to be scanned by a doctor who does 10 a day and specializes in that type of care.
-You’re sending me to a disease specialist? I must have something really bad.
Needing an OCT does not mean that you have a serious disease. It does mean that your eyes present slightly atypically and an extra scan is the prudent thing to do. Frequently the doctor who does my scanning will say, “It looks okay. We’ll just monitor it. Go see Dr. Ritenour in a year.” Some patients I know are healthy, but have an elevated risk for developing a problem in the future. In theses cases, the OCT scan is a baseline “snapshot” that we can always compare back to in the future.
Leave a comment or email me if you have any questions or concerns.
Spencer Ritenour, O.D.
“I’m really blind without my glasses.”
Everyday several people come into my office saying those words. What they mean is that they are very nearsighted or myopic. In fact about 41% of the US population (2004 data, ages 12-54) have some degree of myopia. Eye doctors quantify myopia and all other types of prescriptions in units called diopters (D). A diopter is simply a measurement that indicates the degree to which an optical system bends light. Most forms of myopia may be classified into three different categories:
Low myopia: -0.25D to -3.00D
Medium myopia: -3.00D to -6.00D
High myopia: -6.00D and greater
We correct myopia with glasses, contacts, or sometimes procedures like LASIK. For low and medium amounts this is typically the end of the story. However, with high myopia there are some other concerns beyond getting the right prescription. Most people with this type have high prescriptions due to longer axial lengths in the eye. The axial length is the distance from the very tip of the cornea the deepest tissue layers in the back of the eye. This puts a special type of tension on the retina, and statistically gives the patient a higher risk of developing a retinal detachment. That is when the retina pops off it’s supporting basement structures and can lead to severe vision loss.
What do we do about this? Unfortunately there is no way to completely prevent a retinal detachment from happening. However, we can help minimize the risks. Blows to the head are especially risky for high myopes. The sudden shock can cause the already threatened retina to cross a tipping point and detach. Two weeks ago I saw a girl with a -8.00 prescription. She hit her head ice skating and wisely came in to be examined (thankfully she was okay). One can’t live in a padded cage, but it’s important that people with these prescription be vigilant about protecting their head and eyes. If you wear -7.00 glasses then boxing may not be a good hobby. Patients with high myopia must immediately let their doctor know if they ever see flashes of light, experience any changes in their floaters, see “curtains” coming down, or any other odd visual occurrences. Both Dr. Bazan and I believe that it’s important for everyone to get an annual dilated exam. For high myopes, this is not only important – it’s critical. We do a very thorough dilation exam to ensure that the retina is healthy and that there are no signs of any impending detachments. Speed is the name of the game if a detachment is detected. There are a variety of procedures used to heal the retina based on the type and location of the detachment. An eye doctor will ensure that these procedure are done inside an appropriate time frame. With proper care the lasting effects of a retinal detachment can be very minimal.
I will include a special point for high myopes who have had LASIK or are considering LASIK. It’s true that post-LASIK you effectively have no prescription. However, the laser simply compensates for exceptionally long eyes by altering the curves of the cornea. The axial length of the eye never changes. LASIK is a fantastic option for many of these patients and their vision. It does not change the important of being dilated annually or lower the risk of a detachment.
Feel free to contact me if you have questions about high myopia, retinal detachments, or any other eye issues.
Spencer Ritenour, O.D.
Some contact lenses are to be changed daily. Others last for 2 weeks. Some last for a month. Why are they all different, and is it important to change them regularly?
Contacts sit on the eyes’ corneas. Light is able to pass through our corneas because they’re clear and don’t contain blood vessels. Consequently, oxygen, water, and other nutrients must be supplied to the cornea via the air, tears, and eyelids. When ANY contact lens is on the eye, the cornea receives dramatically lower amounts of these elements. As you can imagine, this opens the door to a lot of potential issues. Therefore it’s critical that patients and their eye doctors carefully manage the use of contact lenses.
Every type of contact lens differs in it’s physical and chemical properties. The amounts of water and oxygen that permeate through them hinge on the fit, material, prescription, and wearing schedule of the contact lens. The first three are largely concerns of one’s eye doctor. How the contacts should be worn is determined by the doctor, but the responsibility to follow said schedule is up to the patient.
I’ll illustrate by using CooperVision’s Biofinty contact lenses as an example. This lens is approved for 30 days of wear. To arrive at that number, CooperVision worked with many doctors, researchers, and the FDA to determine how long these lenses may be worn safely. Like all contacts, they permit less oxygen to reach the eye as compared to not wearing contacts at all. Experts have found that this is largely not a problem as long as the lenses are worn for 30 days or less and the patient regularly sees her optometrist. After 30 days of wear the story takes a turn for the worse. The amount of oxygen that reaches the eye is lower than professionally determined critical thresholds. This opens the floodgates for a lot of potential complications.
On the low end, wearing a contact lens for too long may cause the eyes to become slightly red. On some patients this can stay at a cosmetic level. However, frequently it’s the first warning sign of serious impending problems. With the eyes defenses reduced, bacterial and/or viral infections are much more likely to occur. It’s somewhat common for the cornea to respond to low oxygen levels by developing “subepithelial infiltrates.” These are inflammatory cells that arrive on the scene when the cornea is threatened. They interrupt a dense network of nerves in the front of the eye and are very painful. In some cases of contact lens overwear, the iris may become severely inflamed. This is a highly uncomfortable condition called iritis or anterior uveitis. The treatment for this condition is weeks of steroid drops and dilated eyes – not anyone’s idea of a good time. If left unchecked, a reduced oxygen level can even lead to ulceration of eye tissue.
The good news about all of these problems is that they are largely avoidable. By wearing your contacts lenses for the prescribed schedule, the risk of all these issues is quite low. Beyond simply wearing your contacts properly, it’s important to have them evaluated at least once a year by your optometrist. It’s his job to ensure that your eyes aren’t showing any signs of being “angry” with the lenses. It’s far better to stay on top of any complications than allowing them to run free.
Feel free to send an email if you have any questions or concerns.
Spencer Ritenour, O.D.
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Optometrists love to toss around the term 20/20: “You have 20/20 vison.” or “Gosh, you’re seeing better than 20/20.” Perhaps, you use it at home: “How does this dress look?” “Sorry honey – I don’t see 20/20.” The news program “20/20” was actually named after the visual measurement. Everyone knows 20/20 is ideal, but few actually know what it means.
To know how well someone sees, we must use a standardized system. This affords doctors the ability to know if someone needs more or less correction and to compare the vision between members of a population. For example, it’s means very little to accurately check the vision of an eight month old girl and then record it as “pretty good” or “seems normal.” It’s far superior to be able to record her vision as 20/60 or 20/80. Then visual changes may be tracked with tighter accuracy, her visual acuity may be compared against what’s normal for 8 month olds, and her vision may be corrected or observed against a quantifiable system.
The 20/xx system is also known as the Snellen visual acuity system. The top number refers to the testing distance in feet. Twenty feet is considered to be “optical infinity” due to how our eyes focus and the behavior of light waves at this distance. However, most offices do not have patients sit 20 feet from a chart due to space constraints. Through the use of mirrors and chart calibrations, the shorter distance is compensated for remarkably well.
The bottom number is a bit more complex. It’s the distance at which each element of a letter has an angular height of 1 minute of arc (or 1/60th of a degree). The letter “E” on an eye chart has 5 elements. There is the top bar, a space, the middle bar, another space, and the bottom bar. When one stands 400 feet from the big E at the top of the chart, each of these elements subtends 1 minute of arc. Therefore the size of the letter is called 20/400. For a letter on the 20/20 line, one must stand 20 feet away for each element to subtend 1 minute of arc.
The neurological processing in the human eye and key areas of the brain allows people to easily discriminate between letters with 1 minute of arc (or smaller) features. With a (compensated or actual) testing distance of 20 feet, optometrists therefore embrace the 20/20 line as a perfect endpoint. Please don’t fret if you can’t see 20/20 without glasses or contacts. That will be the subject of a blog post in the near future. Seeing 20/20 with or without visual correction means that at 20 feet away, your eyes see as well as they are expected see. If you can’t read 20/20, please schedule an appointment, and I’d love to help boost your vision.
Spencer Ritenour, O.D.
A lot of people are scared to visit the eye doctor because of the air puff test. What is it? Is it absolutely necessary? Can you avoid it?
The air puff test is what people commonly call the non-contact tonometry (NCT) test. It is used to determine the pressure inside the eye, also known as the intraocular pressure (IOP). Knowing a patient’s IOP is the most important tool that optometrists have to screen for glaucoma. An IOP that’s elevated to an unsafe rage feels very similar to most types of high blood pressure – that is you feel just fine. By the time you begin to notice symptoms it is too late. Consequently it’s important for your doctor to check your IOP at least annually.
I can hear you saying, “Come on doc. That test is horrible!” I totally agree with you. The NCT machine blows a measured amount of air at the eye which deflects the cornea a bit. Infrared sensors measure the corneal deflection and correlate it to the pressure inside the eye. When one puts it that way it doesn’t sound too bad. In fact it works extremely well on a research lab bench. In the real world…well…not so much. Our eyes have a great natural reflex that protects them when something comes close or contacts the eyelashes. That’s why people blink and get nervous about the air puff. In fact, patients typically blink and clench their eyes so much during NCT that the IOP reading frequently is nowhere near the true value. I’m the worst at this. Do NCT on me, and I become as fussy as a toddler without his nap and snack. I dislike doing NCT on patients and having it done on me so much that we don’t even have this machine at Park Slope Eye. It’s a really dated technology.
Fortunately there are alternatives. A very common and extremely accurate way to measure the IOP is Goldmann tonometry (aka the blue light test). With this test, patients get a yellow eye drop that makes the eye glow when exposed to a blue light. The doctor steers an illuminated prism very close to the eye. When the doctor looks in his microscope, the IOP is correlated to the degree that the prism bends the light. This method is considered the gold standard of IOP measurement. It is painless but still scares many patients.
At Park Slope Eye we have an even better way to determine patients’ IOP. We have a special device from Helsinki, Finland that gives just as accurate IOP readings as Goldmann tonometry. A very tiny wand bounces off the tears and the device measures the force at which it returns. It’s very fast, painless, and requires no drops. A few seconds after I explain it to patients, the machine has already measured the IOP three times in each eye! We are one of the few offices in New York that actually has this technology. Ask a friend who comes to Park Slope Eye what they think about it. Stop by the office if you don’t know anyone who is a patient here. I’d love to demo it for you (and make you some coffee)!
Spencer Ritenour, O.D.
How often do you visit your eye doctor? Annually? Every 5 years? Still haven’t been checked? Perhaps a better question is how often should you visit your eye doctor. For the general population, optometrists recommend a visit at least every 12 months. Still it’s common for people to wait until their vision gets blurry. On the surface that seems sensible, but it overlooks some very important elements of good eye health.
Every eye exam does include a determination of one’s glasses and/or contact lens prescription. While this is important for good vision, it’s just a small component of the examination. When light enters the eye, it gets refocused no less than 12 times before being converted to an electrical signal behind the eye. In most people, the summation of these focusing steps is not quite perfect – leading to a prescription that compensates for the difference. This would be the end of the story if the eyes were simply glass and electronics like a camera lens. Obviously they are living tissue that have special needs and interacts with the rest of the body.
There are disorders that can affect all of the elements that comprise the eye (e.g. the eyelid, tears, lens, retina). Eye specific diseases include glaucoma, cataracts, macular degeneration, and many more. Many systemic conditions such diabetes, hypertension, and high cholesterol may cause ocular complications as well. In fact in certain instances, an optometrist is the first doctor to see these signs in a patient. During a eye doctor’s examination he observes the external eye structures under high magnification. Also he will look inside the eye at the all internal structures. Any abnormalities are treated or aggressively monitored as warranted. In addition to examining the physical structure of the eye, the physiology or functioning of the eye is equally important to check. He will ensure that they eyes are moving properly, working well together and independently, communicating with the brain, and being supplied with blood as they should.
Some people are fortunate enough to not need glasses until about age 40 or maybe never need them. Other people notice that their prescription stops changing in their late teens or early twenties. Regardless of how blurry or clear a person’s vision is, it’s very important to ensure that her eyes are structurally sound and functioning to the max. If a problem is ever detected, it is far superior to catch it in the early stages than to catch it much later. Don’t let “good enough” vision rob you of a lifetime of stellar vision and healthy eyes.
Spencer Ritenour, O.D.