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You Want to Inject My Eye? Part 1
There are some eye conditions where your doctor might recommend an eye injection as a treatment option.
Injections into the eye, specifically into the vitreous or gel-filled cavity of the eye, are called intravitreal injections.
Anti-vascular endothelial growth factors (anti-VEGF) are probably the most commonly injected agents. They are used to treat wet age-related macular degeneration (ARMD), diabetic retinopathy, and retinal vein occlusion.
In these conditions, there are abnormal leaky blood vessels that cause fluid and blood to accumulate in and under the retina. This accumulation of fluid results in loss of central vision. The role of anti-VEGF agents is to shrink these abnormal vessels and restore the normal architecture of the retina.
Three anti-VEGF agents that are widely administered are Lucentis, Avastin, and Eylea.
Lucentis (Ranibizumab) is FDA approved for treatment of wet ARMD, diabetic retinopathy, and vein occlusion. It is specially designed for injection into the eye and is a smaller molecule than Avastin so it may have better penetration into the retina.
Avastin (Bevacizumab) was originally approved by FDA for treating colorectal cancer. It is used “off-label” for the same treatment indications as Lucentis. Off-label usage of medication is legal, but pharmaceutical companies can't promote a medication for off-label use. The amount of Avastin needed for eye injections is a fraction of the amount used to treat colorectal cancer, therefore, the cost of ophthalmic Avastin is only a fraction of the cost of Lucentis. This means that Avastin needs to be prepared sterilely into smaller doses by an outside pharmacy prior to injection into the eye.
Eylea (Aflibercept) is the third anti-VEGF agent. It was designed to have more binding sites than Avastin and Lucentis so it may last longer in the eye than the former two. Eylea is FDA approved for treatment of wet ARMD, diabetic disease, and vein occlusion, and therefore, the cost of Eylea is similar to the cost of Lucentis.
There are also newer agents on the market. Your doctor will deterine which might work best for you.
There is a thought that after prolonged injections, some patients may develop resistance to one particular agent but still respond to the a different agent. Therefore, your ophthalmologist will individualize your treatment.
Article contributed by Dr. Jane Pan
One of the most commonly asked questions in an eye exam comes right after the refraction, or glasses prescription check: “What is my vision?”
Almost invariably, people know the term “20/20”. In fact, it’s a measure of pride for many people. “My doctor says I have 20/20 vision.” Or, on the other side of that same coin, having vision that is less than 20/20, say 20/400, can be a cause of great concern and anxiety. In this discussion I will describe what these terms actually mean.
To lay the foundation, let’s discuss some common terms. Visual acuity (VA) is clarity or sharpness of vision. Vision can be measured both corrected (with glasses or contact lenses) and uncorrected (without glasses or contact lenses) during the course of an eye exam. The result of an eye exam boils down to two different but related sets of numbers: your VA and your actual glasses prescription.
The notation that doctors use to measure VA is based off of a 20-foot distance. This is where the first 20 in 20/20 comes from. In Europe, since they use the metric system, it is based on meters. The 20/20 equivalent is 6/6 because they use a 6-meter test distance. The second number is the smallest line of letters that a patient can read. In other words, 20/20 vision means that at a 20-foot test distance, the person can read the 20/20 line of letters.
The technical definition of 20/20 is full of scientific jargon - concepts such as minutes of arc, subtended angles, and optotype size. If you’d like to read more of the technical details there is a well-written article with illustrations by Dr. John Ellman, you can find here. For the purposes of our discussion here I’ll try to explain it in less technical terms.
“Normal” vision is somewhat arbitrarily set as 20/20 (some people can see better than that). Let’s say you have two people: Person A with 20/20 vision and Person B with 20/40 vision. The smallest line of letters that person B can see at 20 feet is the 20/40 line. Person A, with “normal” 20/20 vision, could stand 40 feet away from that same line and see it. There is somewhat of a linear relationship in that the 20/40 letters are twice the size of the 20/20 letters and someone with normal vision could see a 20/40 letter at twice the distance as the person with 20/40 vision.
So how does this translate to a glasses prescription?
Eye doctors can often estimate what your uncorrected VA will be based on your glasses prescription. This works mainly for near-sightedness. Essentially, every quarter step of increasing glasses prescription (i.e. -1.25 as compared to -1.50) means a person can see one less line on a VA chart.
A prescription of - 1.25 works out to roughly 20/50 vision, -1.50 to 20/60 and so on. Anybody with an anatomically sound eyeball, meaning the absence of any kind of disease process, should generally be correctable to 20/20 with glasses or contact lenses. It is important to note, however, that rarely a person’s best corrected VA may be less than 20/20 with no noticeable signs of disease.
Far-sightedness is more difficult to estimate because it is affected by a number of other factors, including one’s age and focusing ability. But that’s a topic for another article.
So there you have it! Hopefully this has shed some light on what these measurements that we take actually mean, and it has allowed you to understand your eye health a little bit better.
Article contributed by Dr. Jonathan Gerard
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