Sunday, June 10, 2018

epiretinal membrane

Epicupcake membrane

What is an epiretinal membrane?
An epiretinal membrane (ERM), also known as a macular pucker or cellophane maculopathy, is a thin layer of tissue that forms on the inner surface of the retina (the tissue that lines the back of the eye). **Look out, jargon ahead.** Specifically, an ERM forms when glial cells proliferate in a sheet between the internal limiting membrane (ILM) of the retina and the posterior hyaloid membrane of the vitreous. **You survived. No more jargon.** When ERMs contract, they pull on the retinal tissue and vessels beneath them. This causes wrinkling and distortion of the retina.

ERMs occur most often in those over 50 years of age, and their prevalence increases with age. ERMs effect males and females almost equally. Most are idiopathic (meaning unknown cause), but they can also occur secondary to posterior vitreous detachments (PVDs), eye surgery, diabetic retinopathy, eye inflammation, and trauma. ERMs can occur in both eyes in up to 20-35% of cases (1).


What are the symptoms?
Most ERMs have no symptoms and are found incidentally on routine eye exams. In those cases where symptoms are noticed, distorted vision (metamorphopsia) is the most common symptom. Decreased vision can occur as well, especially if the ERM is located at the macula (the part of the retina that is responsible for your central, sharpest vision).


How is it diagnosed?
ERMs are diagnosed by looking into the back of the eye during a dilated eye examination. An ERM appears as a shimmery reflectance over the retina, almost like fine gold glitter. If the ERM contracts, puckering or wrinkling of the retina and vessels beneath it may be noted. ERMs can be seen on retinal photos and OCT scans.

Infrared SLO of an ERM: you can see the wrinkling of the retina

Optical Coherence Tomography (OCT) is helpful for imaging and monitoring ERMs. An OCT scan provides a cross-sectional view of the retina, so you can easily see the membrane and how it is distorting the retina beneath it. Sometimes, OCTs can uncover ERMs before they are noticeable in the microscope.

OCT scan of an ERM: the white (hyper-reflective) line above the retina is the ERM

How is it treated?
In the majority of cases, ERMs are just monitored. However, ERMs can cause pseudo-holes and cysts in the retina. If vision is affected significantly, or if the ERM is threatening to cause significant vision loss, surgical intervention may be advised. If surgery is pursued, the gel part of the eye (the vitreous) is first removed in a procedure called a pars plana vitrectomy. Then, the ERM is peeled, and the internal limiting membrane (ILM) of the retina is sometimes peeled as well. Here is a neat video of the procedure (note: you will see that a dye is used to make the membrane more visible). In most cases, visual symptoms of distortion decrease after the membrane is peeled. Visual acuity may improve as well, but it often will not return to normal. ERMs may recur after removal.

Retinal photo of an ERM (note the gold shimmery appearance of the retina in the center of the image) with a pseudohole (the darker red circle in the middle of the gold shimmer)

CliffsNotes: An ERM is a sheet of cells that forms on the innermost layer of the retina. They are often symptomless and discovered on routine eye exam (so it's important to get those). Most of the time, ERMs are monitored but there are some occasions where they need to be peeled. 

Additional recommended resources:

Thursday, May 31, 2018

enchroma lenses and color vision deficiency

You may have seen the videos floating around the internet of colorblind people trying on EnChroma sunglasses for the first time. This month's blog post is about how it all works!

Ishihara cupcakes

How do we see color?

The retina (the tissue that lines the back of the eye) contains specialized cells called photoreceptors that respond to light. There are two types of photoreceptors: rods and cones.  Rods are responsible for vision in dim light, and cones are responsible for vision in bright light as well as color vision. There are three types of coneseach type is sensitive to different wavelengths of light, and thus different colors. "S" cones are most sensitive to short wavelengths (blues), "L" cones are most sensitive to long wavelengths (reds), and "M" cones are most sensitive to medium wavelengths (greens). The information gathered from these cones is used by the brain to create our perception of color.  Normal trichromatic color vision involves the presence and proper functioning of all three cones.  Color vision defects arise when one of these cones is missing or altered.

In English? Objects reflect light. That light acts as a wave as it enters the eye, activating the cones. The wavelength of that reflected light determines which cones are most activated. This cone response is translated to a neural signal and sent to the brain. Color perception is based on the relative levels of activity in the different cones.


A graph showing the spectral sensitivity of each of the 3 cones in someone with normal color vision
Image source: Eye, Brain, and Vision

What is a color vision deficiency?
The term "color blind" is misleading, as most people use the term to describe someone with a color vision deficiency. They can see colors, but have trouble distinguishing between certain colors and shades.  Color vision defects can be inherited or acquired. The most common are inherited, meaning they are present at birth, affect both eyes equally, and are stable over a person's lifetime. They occur in about 8% of males and 0.5% of females.  It is more common in males because the genes causing this type of color vision deficiency are located on the X chromosome

My previous post on color vision deficiency outlines all of the color vision disorders. For this post, we will only look into anomalous trichromats, meaning people who have all 3 cones, but the sensitivity spectrum of one is shifted. This shift causes a greater overlap in the sensitivities of two cones. There are various degrees of severity, based on on how much the spectrums are shifted.

The bottom 2 visuals show red-green color vision deficiency (CVD).
Protanomaly occurs when the L cone is shifted closer to the M cone, reducing sensitivity to reds. 
Deuteranomaly, the most common type of CVD, occurs when the M cone is shifted closer to the L cone, 
reducing sensitivity to greens.
Note the separation in the peaks of the L and M cone sensitivities is much smaller in red-green CVD compared to normal.

The ratio of light entering the eye tells the brain what color to perceive. The greater overlap of red and green in color deficient individuals skews the ratio. For example, when you see a red apple, the cones that should have the greatest response are the red, or long, cones. When there is excessive overlap between the red and green cones, more green cones are responding than normal, which essentially dilutes the red cone response and causes confusion and color muddling. So the apple may be perceived as more brown than red.


What are EnChroma lenses and how do they work?
EnChroma is a company that makes glasses designed to enhance the vibrancy and saturation of colors for those with color deficiencies. They are available in indoor and outdoor lenses, and can be made with or without a prescription.

The lenses actually began as protective eyewear for doctors to use during laser surgery, and their application for color vision deficiencies was discovered somewhat serendipitously. Check out the full story here.

As we noted in the graphs above, the overlapping responses to light by the red and green cones are the issue in those with red-green color vision deficiency. Rather than each cone responding separately, their responses are similar, causing colors to be muddled. EnChroma lenses are designed with "multi-notch filters" that cut out the wavelengths of light that cause the overlapping responses to light. This allows the ratio of cone responses to more closely resemble that of a person with normal color vision. As a result, the EnChroma lenses enhance colors and may make reds and greens more vivid and distinguishable.

Donald McPherson, PhD, a glass scientist and EnChroma's cofounder, explains it this way:
"EnChroma’s glasses work by reestablishing the correct balance between signals from the three photopigments in the eye of the color deficient. The eyewear does this by removing small slices of light from the visible spectra. At the cortical level, the neural machinery is intact and perfectly functioning in the color blind, so once the correct ratios entering the eye are reestablished, the neural mechanisms excite and the correct color can be seen and perceived." via Forbes
Images taken from the Enchroma website

Will it work for me?

It depends! There are certainly no guarantees, but EnChroma suggests that their glasses can address the issue for 4 out of 5 individuals with anomalous trichromacy (which is what we described above- all 3 types of cones are present, but the sensitivity of one is shifted). These glasses would NOT work if you have a color deficiency where you are missing one of the three types of cones (dichromacy). The company offers a test that will give you an idea of how likely the glasses are to work for your type of color deficiency.

You can also visit an office that carries EnChroma lenses to try them out and ask an eye care professional for more information. Find an office near you via the website.


*EnChroma lenses do not cure color vision deficiencies, and they are not recommended for the color vision tests required for certain jobs.*


CliffsNotes: The most common color vision deficiencies occur as a result of a shift in the sensitivity of one of the cones, which causes a larger area of overlap between the red and green cones. EnChroma lenses use filters to remove the wavelengths of light in this overlap, which helps restore the proper ratio of cone responses, enhancing color vibrance and saturation. 


Additional recommended resources:

Thursday, March 29, 2018

amblyopia (lazy eye)

That darn lazy eye...

What is a "lazy eye?"
The term "lazy eye" is most often used to refer to a condition called amblyopia. Amblyopia is reduced vision in one eye, or less frequently both eyes, due to abnormal vision development in childhood (1)


What causes amblyopia?
In simple terms, functional amblyopia occurs when something prevents the eye from focusing clearly. Any of the below factors can disrupt the normal development of the visual pathway and visual cortex: 
  • Deprivation: This type of amblyopia is a result of an obstruction in the line of sight, like a cataract or a lid droop. The first step in treating this type of amblyopia is to remove the obstruction as early as possible. 
  • Strabismus: This is the fancy name for an eye turn. When one eye is constantly misaligned, the brain is receiving two dissimilar images. So in order to prevent double vision, the brain ignores the visual input from the misaligned eye, which causes amblyopia. Some cases of strabismic amblyopia require surgery as a part of the treatment plan. Amblyopia can also occur when the eye turn is intermittent or alternating, but that is less frequent and less severe. 
  • Refractive error: Refractive amblyopia occurs when there is unequal (anisometropic) refractive error or, less often, high equal (isoametropic) refractive error between the two eyes that goes uncorrected. If one eye is seeing significantly more clearly than the other, the brain will disregard the blurrier eye, causing amblyopia. This is especially difficult to detect because the eyes look normal and the child often won't complain about blur because he/she can see out of one eye. That's why eye exams are crucial!! Optometrists and ophthalmologists are trained to know what kind of prescriptions can cause amblyopia. 

The visual pathway is developing from birth to age 6-8, so amblyopia occurs during this time.

Many of the studies we'll discuss refer to amblyopia in terms of severity. This classification is based on the best correct distance visual acuity, which is how far down the eye chart a patient can read THROUGH their best prescription.
  • Mild amblyopia: best corrected distance vision better than 20/40
  • Moderate amblyopia: best corrected distance vision 20/40-20/80
  • Severe amblyopia: best corrected distance vision worse than 20/80


How is amblyopia treated?
There are many valid answers to this question, and many theories that are currently being studied. We will focus on the evidence-based methods for treating amblyopia. Much of what we know about treating amblyopia is thanks to a group of optometrists and ophthalmologists known as the Pediatric Eye Disease Investigator Group, or PEDIG. This group has conducted numerous Amblyopia Treatment Studies, or ATS

Amblyopia treatment is dependent on many factors, such as the severity and type of amblyopia as well as the age and compliance of the patient, so treatment needs to be patient-specific. That being said, here's a general guideline for treating most cases of amblyopia. 


1. OPTICAL CORRECTION: The first line of treatment in most cases of amblyopia is correction of refractive error. Translation: glasses or contact lenses that correct vision to provide equally clear images to the retinas. Your eye doctor will likely use a dilating drop called cyclopentolate to assess the refractive error of the eye. Cyclopentolate relaxes the focusing system and gives the eye doctor a better idea of a patient's true prescription. Because of this, vision up close remains blurry for around 24 hours after the appointment.
Once the eye doctor determines the appropriate prescription, the prescription is written for full-time wear (that can be tricky with young children, but it is imperative). The eye doctor will follow-up every 4 to 6 weeks to check how vision is improving. 

Just having the optical correction in place makes a big difference, so don't underestimate the power of glasses! Glasses can improve vision even if the child still has a crossed eye with the glasses on.

In some cases, optical correction is all your need. But often, more therapy is involved.

2. DEPRIVATION: If further vision improvement is needed after full-time wear of glasses/contacts, deprivation of the better-seeing eye is added to the treatment regimen to encourage the use of the amblyopic eye. This deprivation is often achieved via patching, atropine, or Bangerter filters.      
  • Patching
    • Patching therapy involves using a patch (over the prescribed glasses/contacts) to cover the non-amblyopic or "good" eye, forcing use of the amblyopic eye. This can be done using an adhesive patch that goes on around the eye, or a soft patch that slides over the glasses.
Slide-on patches by OKeye on Etsy

A couple of adorable kids showcasing their adhesive patches.
@patchwithgus on the left, @chipperspiratedays on the right
    • Patching has been used as amblyopia treatment for decades, but the way it is used has changed thanks to PEDIG's Amblyopia Treatment Studies (ATS). The ATS 2 study found the effectiveness of 6 hours of patching/day for severe amblyopia to be similar to full-time occlusion (2). Secondly, they found the effectiveness of 2 hours of patching/day for moderate amblyopia to be similar to 6 hours of patching (3)
      • That is where we get our recommendation of 2 hours of patching a day for moderate amblyopia and 6 hours of patching a day for severe amblyopia. Some children with severe amblyopia respond to as little as 2 hours of patching, so any amount is better than nothing!
    • Both of the above studies involved at least an hour of near work during the patching hours, because that was thought to stimulate the visual system. Interestingly, the ATS 6 study found similar results in those that were assigned near tasks vs those that were assigned distance tasks.  There was a greater improvement in visual acuity in the near-task group among those with severe amblyopia, but it did not reach statistical significance. Worth noting: the study looked at "common" near tasks like reading or using the computer (4). There is reason to believe that specific near tasks designed to enhance focusing, improve tracking, fixation, etc. can improve outcomes other than visual acuity, though that was not studied.
    • Another PEDIG study (ATS 15) showed that if visual acuity stops improving after 12 weeks of 2 hours/day patching therapy, increasing to 6 hours/day was more effective than continuing at 2 hours/day for another 10 weeks (5).
  • Atropine
    • Atropine therapy involves instilling a drop of atropine to the non-amblyopic or "good" eye to make vision blurry, forcing use of the amblyopic eye.  
    • The ATS 1 study found patching and atropine therapy to be similarly effective initial treatments for moderate amblyopia in children age 3 to 7 years old (6)Another study found similar findings in children age 7 to 12 years old (7).
    • Any parent of a child that is patching can attest to some difficulty with compliance, so atropine may be a less fussy option for kids (and parents). 
    • The ATS 4 study found similar effectivity between daily use of 1% atropine and use only on the weekends in children age 3 to 7 with moderate amblyopia (8). Weekend atropine may also be effective for severe amblyopia, though improvements may be greater in younger children (9)
      • That is where we get our recommendation of 1 drop of 1% atropine instilled in the AM twice per week. It has been shown to be effective for moderate and severe amblyopia. 
    • Atropine does have some systemic side effects, including dryness, flushing of skin, fever, confusion, unusual behavior, and irritability. Those rarely occurred in the studies.
  • Bangerter filter
    • Bangerter filters are translucent filters that are applied full time to the lens in front of the good eye, and they are available in different densities to degrade the image to different levels. Since this doesn't occlude vision entirely, it may help reduce suppression (10)
Bangerter filter on a pair of glasses via Fresnel Prism and Lens Co

    • The ATS 10 study compared the improvements in visual acuity between those treated with Bangerter filters and those with 2 hours of patching in moderate amblyopes age 3 to 10. The average difference between the two groups was less than half a line on the eye chart, but the study concluded that the filters were "not non-inferior" to patching. What does that mean in laymen's terms? The study did not conclude that the filter treatment effect was similar to that of patching, but it also didn't conclude that patching was definitely superior to filters. The study did show that the filters had less of a "negative impact" on patients and parents in terms of social stigma, compliance, etc (11)

As you can see, there are multiple ways to go about occluding or depriving the "good eye." There are even other forms of occlusion that we did not mention here, including flicker glasses and occluder contact lenses. What works for one child may not be the best treatment for another, so it's great to have options that have been proven effective. Also, if one of these treatments isn't producing the expected results, we have the option of switching to another.



3) COMPUTER PROGRAMS AND ACTIVE VISION THERAPY: The most recent buzz around amblyopia treatment is reducing suppression by taking a binocular approach. Research is being done on the efficacy of 
dichoptic games, which involve simultaneous and separate stimulation of both eyes (unlike occlusion of one eye). High-contrast images are presented to the amblyopic eye and low-contrast images to the "good" eye. This type of therapy was found to be effective in adults (12). However, in a study (ATS 18) comparing 1 hour of binocular iPad game to 2 hours of patching a day in children 5 to 13 year old with amblyopia, the improvement after 16 weeks was better in the patching group (13). Participants lost interest in the game, and compliance wasn't great, so that may have contributed to the poor results. More studies need to be done to determine what types of anti-suppression therapy may produce better results. 

Adding vision therapy to amblyopia treatment is helpful in improving visual skills and binocularity. Vision therapy involves activities designed to reduce suppression and improve deficiencies in accommodation, form discrimination, and fixation, all of which are skills that are often poor in patients with amblyopia (14)


Can you treat amblyopia in older kids? 
YES! In the ATS 3 study, PEDIG found that using either 2 hours of daily patching or weekend atropine as the initial treatment can be effective in improving vision for amblyopes age 7 to 12 years old, even if they've had prior treatment (15). That being said, amblyopia is MORE responsive to treatment in younger children, so this is one of the key reasons to have children see an optometrist EARLY!


Can amblyopia recur after treatment?

YES! According to ATS 2C, nearly 25% of amblyopic children under 8 years old experienced regression within a year of discontinuing treatment. The recurrence rate was similar in patients who stopped patching vs those that stopped atropine, and most cases occurred within 3 months of discontinuing treatment (16)The ATS 3 study showed that only 7% of 7 to 12 year olds studied experienced recurrence (17)The risk is much greater when those patching 6-8 hrs were stopped abruptly, so tapering off (ie: going from 6 hrs to 2 hrs) is advised, especially with younger children.  Because recurrence is possible, following up with your eye doctor is critical!


CliffsNotes: The first step in treating most cases of amblyopia is to correct vision, either with glasses or contacts. Surgical intervention may be needed in some cases. Occlusion therapy may be needed to improve vision beyond what is achieved by optical correction alone, and it's never a bad idea to enroll in vision therapy to improve eye teaming and visual skills
Amblyopia treatment may vary depending on the type and severity of the amblyopia as well as the age and compliance of the patient. Early intervention is key, so get your kids in to see their optometrist ASAP!


Additional Recommended Resources:

Helpful resources for ODs and OMDs: 

Thursday, February 22, 2018

smartphone apps for low vision

February is Low Vision Awareness Month. Low vision is a term used to describe significant, permanent visual impairment that cannot be fully corrected with regular glasses, contact lenses, or surgery. This can be due to eye diseases (like macular degeneration), injury, or genetic conditions. Most people with low vision are not totally blind, but have enough vision loss to interfere with daily activities. The goal of low vision rehabilitation is to help people make the most of their remaining vision. It's important to start the process early so that patients can make adjustments and adapt to a new way of doing things.

Fortunately, there are devices that can help people with low vision function more efficiently and independently. There are many types of magnifiers, telescopes, and electronic devices that low vision specialists can help set you up with. This post will focus more narrowly on smartphone applications that can help those with low vision. Big thanks to Omar Mohiuddin, occupational therapist at Duke, for allowing me to use some of his content.

First off, here is an app that simulates low vision conditions: ViaOpta Simulator (Android and Apple). It shows how various eye disease like macular degeneration, glaucoma, etc, effect your vision.
ViaOpta Simulator
Secondly, every smartphone has basic accessibility features that can help individuals with visual impairments immensely. Those features include larger text, voiceover, increased contrast, and much more.
Accessibility features on Apple iPhone

Now for the low vision aids...

If you could only use one app, I would recommend Seeing AI (Apple). It has many of the features we'll discuss below, so it's a handy and convenient tool. Seeing AI can read websites and documents aloud as well as identify products via their barcode. You can teach the app to recognize people, and it can tell you when they appear in the camera frame. More details on this app here.

Seeing AI can identify products using their barcode

1. Magnifiers: There are a ton of these apps out there, and they're used by sighted and visually-impaired individuals alike. Many of them not only magnify text, but invert colors and change the contrast to make reading easier.
Brighter and Bigger allows you to magnify text, invert colors, and adjust contrast

2. Color Identification: These apps use the smartphone's camera to identify the color of objects in view.
  • Color ID (Apple and Android)
  • Aipoly Vision (Apple) - My two cents here: This app is good for identifying colors, but not that great at identifying objects. I tried to identify a spatula, and the app said it was either a toothbrush or a maraca...
Aipoly can identify colors

3. Object Recognition: These apps use either the smartphone camera or remote sighted individuals to help identify objects.
  • TapTapSee (Apple and Android)- My two cents: I found this app to be fairly accurate and specific. You simply take a picture with your smartphone, and the app identifies the object(s) within the frame, using the Voiceover feature to communicate the findings. 
TapTapSee identifies objects

4. Currency Identification: These apps use the camera on your smartphone and audibly tell you what denomination the bill is.
EyeNote can identify bills

5. Speech-to-Text: Lots of these exist.

6. Text-to-Speech:

7. Reading:
  • GoRead (Android)
  • Read2Go (Apple, $)
  • Audible (Apple and Android, $)- Sighted and visually impaired persons alike love Audible because there are a TON of audio books available. 

8. Navigation: These apps use GPS to help visually impaired persons know their location, their environment/surroundings, and their position relative to other locations.
ViaOpta Nav can tell you your location, including the nearest junctions and
their position relative to you

If you or a loved one has a visual impairment, talk to your optometrist or ophthalmologist about your options! If they are not able to equip you with low vision rehabilitation services themselves, they can certainly refer you to a low vision specialist that can.

To find a low vision specialist:
To find services for the visually impaired: American Foundation for the Blind


CliffsNotes: Visually impaired persons can benefit greatly from learning to use smartphone apps early on.  Seeing AI is a great one to start with!


Additional Resources:

Wednesday, January 31, 2018

glaucoma and the optic nerve

A visual comparison of a healthy optic nerve (right) vs a glaucomatous optic nerve (left)

What does glaucoma look like?
Glaucoma can be hard to describe, because there are no symptoms early on and nothing to “look out for.” So visuals like the one above are very helpful! 

The round structure there is the optic nerve (aka cranial nerve II). The optic nerve is basically like a cable, made of about 1 million nerve fibers, that sends visual information from the retina (the tissue that lines the back of the eye) to the brain.

What we see when we look at the back of the eye is the optic nerve head. I often describe what we’re looking at as a donut. With glaucoma, the nerve fibers of the optic nerve become damaged and the rim tissue (the donut) gets progressively thinner and thinner, leaving a larger cup (the donut hole). This causes permanent loss of vision, beginning peripherally.

The way your optic nerves look is one piece of the glaucoma puzzle. In addition to directly evaluating the optic nerve, there are scans that can be used to image the optic nerve and further assess its structure. These scans (the most prevalent of which is the OCT) give information on the amount of optic nerve tissue loss and the rate of nerve fiber thinning. Visual fields also help show how the optic nerve is functioning by testing your peripheral vision. Beyond the structure and function of the optic nerve, your eye doctor also checks your eye pressure, and evaluates an area of the front part of your eye called the angle. He/she also takes into consideration other risk factors like your age, your race, your family history, and your corneal thickness. 

For more glaucoma info, check out this previous post.

CliffsNotes: Don't let glaucoma eat your donut. Have regular dilated eye exams to know if you are at risk!

Sunday, October 15, 2017

macular hole

A cupcake rendition of an OCT showing a macular hole

What is a macular hole?
To describe a macular hole and how it forms, we need to first discuss the anatomy of the eye. Check out this video for a concise overview of the structures of the eye (it's less than a minute long).

The anatomy of the eye
Image: ASRS

The inside of the eye is basically a gel sack. That gel sack is called the vitreous, and it is attached to the retina (the tissue that lines the back of the eye). The vitreous attaches strongly at a few key points, one of which is the macula (the part of the retina responsible for your central, sharpest vision). As we age, the vitreous changes and becomes more liquid. When it becomes more liquid, it shrinks away from the retina and detaches from it [more on that in a previous post]. The vitreous may pull on the retina as it is detaching, and it can take some of the retina with it. That results in a retinal tear or hole. If the hole occurs in the macula, it's a macular hole.

Other than the vitreous traction described above, there are some additional causes of macular holes including trauma, high amounts of nearsightedness, diabetic eye disease, and epiretinal membranes (aka macular pucker).

Since they are most often related to aging processes, macular holes are more common in people over 60 years of age. They are also more common in females than males (1).

A visual of the vitreous detaching from the retina (posterior vitreous detachment, or PVD)
Image: Eye

What are the symptoms of a macular hole?
The macula is the part of the retina that is responsible for your central, sharpest vision. So a macular hole can cause blurred or distorted central vision. You may also notice a dark spot in your central vision.


How is a macular hole diagnosed?
A macular hole is found by your optometrist or ophthalmologist during a dilated eye exam. Fundus photography, as seen below, can be used to document the appearance of the hole, using filters to make the hole more apparent.

Fundus photo of a patient with a macular hole
Optical coherence tomography (OCT) is very helpful in diagnosing and monitoring resolution of macular holes. A macula OCT is a noninvasive imaging test that produces a cross-sectional view of the macula (see below). This allows your eye doctor to see what stage the hole is, how large it is, and if there is traction on the macula.

OCT scan of the above photographed macular hole

    How do you treat macular holes?
    Though some small macular holes are left to resolve and seal on their own, many require treatment. The most common way to treat a macular hole is with a procedure called a vitrectomy. That's when a retinal surgeon removes the gel sack in the eye and replaces it with a gas/air bubble. Removing the vitreous relieves the pulling (traction) on the retina, and the bubble puts pressure on the edges of the hole, helping to bridge and seal the hole. In some cases, the inner limiting membrane of the retina is also peeled (jury is still out on whether this is required to achieve the best results in small holes). Most surgeons will advise patients to maintain a face-down position for a few days after surgery, sometimes even as long as 2 weeks (jury is still out on whether this is necessary for small and medium holes). The success rate for this procedure is very high, with estimates ranging between 85 and 100% (2). Cataracts are common following vitrectomy, so some surgeons may opt to remove the lens at the same time as doing the vitrectomy.

    Another potential treatment in cases of small or medium holes with traction is injection of ocriplasmin (Jetrea®) into the eye. This drug degrades the adhesion molecules (specifically fibronectin and laminin) at the interface of the vitreous and retina, helping to relieve traction on the retina. With a success rate of 35-40%, ocriplasmin is significantly less successful in achieving closure of macular holes when compared to vitrectomy, especially for medium sized holes (3). It is also less cost-effective in many health systems.

    If you've had a macular hole in one eye, you have an increased risk of getting one in the other eye. Estimates vary, but you are looking at a 5-15% chance over 5 years (45). So keep seeing your optometrist for routine eye exams!


    CliffsNotes: A macular hole is a hole in the part of the retina called the macula, and it most often occurs as a result of aging processes within the eye. Most cases are treated with a surgical procedure called vitrectomy. 


    Additional recommended resources:

    Thursday, August 31, 2017

    astigmatism

    Corneal topography of someone with regular astigmatism.
    The cooler tones indicate the flatter parts of the cornea while the warmer tones indicate the steeper parts.
    As you can see, this cornea is more curved along the vertical plane. 

    Uh-stig-muh-tizum. It sounds like a terrible disease, but it's not. It is a type of refractive error- it affects how light bends, or refracts, when it enters your eye. Nearsightedness (myopia) and farsightedness (hyperopia) are also refractive errors. Astigmatism is an irregular curvature of the front part of the eye (the cornea and/or the lens). Most people have at least a small amount of astigmatism, but not everyone's vision is affected by it. To explain astigmatism in more detail, let's take a quick step back and review refractive errors.
    Image: NEI
    A quick review of refractive errors: 
    We refer to the curvature of the cornea and lens as either spherical or astigmatic. When you have a spherical cornea or lens, it has the same roundness all over, like a basketball. Because of this uniform curvature, light entering the eye focuses at one point.
    • If that one point is in front of the back of the eye (the retina), you are nearsighted. You need minus power in your glasses/contacts to make the light focus ON the retina so you can see clearly. 
    • If that one point is behind the retina, you are farsighted. You need plus power in your glasses/contacts to make the light focus ON your retina so you can see clearly. 
    With an astigmatic cornea or lens, the curvature is NOT the same all the way around (more like a football than a basketball), and light entering the eye focuses at two different points. This distorts and blurs things up close and far away, and it's especially noticeable when looking at street signs or electronic displays. As someone who has a fair amount of astigmatism, reading signs at the airport is a nightmare without my astigmatism correction!

    There are different types of astigmatism. If the irregular curvature is found in the clear part of the front of your eye (the cornea), it's called corneal astigmatism. If it is found in the part of the eye that sits behind the iris (the lens), it's called lenticular astigmatism. You can have either or both. Corneal astigmatism is more common.

    Astigmatism can also be classified as either regular or irregular. Be warned: this part will bore you.
    • Regular astigmatism occurs when the primary meridians/curvatures are 90 degrees apart, producing a bow-tie or figure-eight pattern on corneal topography (see below). This is much more common than irregular astigmatism. Regular astigmatism can be further classified based on which plane is steepest: 
      • With-the-rule astigmatism is when the vertical plane is the steepest. This would be similar to a football laying on its side.
      • Against-the-rule astigmatism is when the horizontal plane is the steepest. This would be similar to an upright football on a kick-off tee.
      • Oblique astigmatism is when the principal planes are not at or close to (within 30 degrees) the vertical or horizontal. 
    Types of regular astigmatism, as seen on corneal topography
    Image: Optometric Management
    • Irregular astigmatism is present when the curvature is not regular, and is generally a result of surgery, scarring, or disease. An example would be keratoconus

    How do I know if I have astigmatism?
    Astigmatism is diagnosed by your optometrist or ophthalmologist during a comprehensive eye exam. There are three instruments that may be used to detect astigmatism:
    • Keratometer- this instrument measures the average curvature of the central part of the cornea. In most offices, an automated keratometer is combined with an autorefractor (AKA the thing that has a picture of a hot air balloon or barn in it). 
    • Corneal topographer- this instrument maps the front surface of the eye, indicating where the cornea is steepest and flattest. The image at the top of this post is a corneal topogram.
    • Phoropter- AKA the "better one or two" instrument. By using the dials below, your eye doctor can figure out how much astigmatic correction you need and where it needs to be.



    How do you treat astigmatism?
    • Glasses- Spectacle lenses can correct astigmatism. Unlike a spherical prescription, an astigmatic prescription has 3 numbers:
      • The first number is the spherical component- the amount of nearsightedness (-) or farsightedness (+).
      • The second number is the cylinder- the amount of the astigmatism. This can be written in either plus or minus form.
      • The third number is the axis- a number between 1 and 180 that indicates the position of the astigmatism.
    • Contact lenses- Contact lenses that correct astigmatism may be referred to as toric lenses. Soft contact lenses have come a long way in recent years, and are now available in a wide range of astigmatic prescriptions. However, they are not available in every axis and every cylinder, so they are not for everyone. With larger amounts of astigmatism, gas permeable contacts may give sharper, more consistent vision. Gas permeable contacts are an especially great option in patients with irregular astigmatism.
    • Surgery- Refractive surgeries, such as LASIK, are also an option.

    CliffsNotes: Astigmatism isn't a disease; it's a refractive error. It means the cornea and/or lens is not completely round, so light doesn't focus at one point. That distorts and blurs things, but it can be corrected with glasses, contact lenses, or refractive surgery. 

    Additional recommended resources: