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!

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 (4, 5). 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:

• NEI: Facts About Macular Holes
• All About Vision: Macular Holes

central retinal vein occlusion

What is a CRVO?
A central retinal vein occlusion (CRVO) occurs when there is an obstruction of the central retinal vein, which is the main vein of the retina (the tissue that lines the back of the eye). A blood clot, or thrombus, may occur in the vein as a result of abnormalities in blood vessel size, blood composition and/or blood flow.

Veins carry blood back to the heart. When the main vein that drains the retina is blocked and blood cannot flow out, the blood builds up and leaks out of the walls of the vessels.  This leakage causes the retina to swell (retinal edema).  When fluid leakage occurs in the area of the retina called the macula (macular edema), central vision is impaired.  

We'll be talking specifically about central retinal vein occlusions in this post, but you can also have a branch retinal vein occlusion (BRVO), which affects a smaller vein, or a hemi-retinal vein occlusion (HRVO), which affects either the upper or lower half of the retina. It all just depends on the location of the blood clot. 

A CRVO can be classified as non-ischemic or ischemic.  Ischemic means there is a shortage of oxygen due to a reduced or restricted blood supply.  When ischemia exists in the retina, vascular endothelial growth factors (VEGF) are released. VEGF stimulates the growth of new, abnormal blood vessels (neovascular membranes) to help supply the retina with the necessary oxygen and nutrients.  This is bad, because those blood vessels are weak and leak. In the case of ischemic CRVOs, the abnormal vessels can cause a serious type of glaucoma, called neovascular glaucoma. This results in dangerously high eye pressure that is very difficult to treat. Fortunately, most cases (about 75%) of CRVOs are non-ischemic, which is the less serious form and involves less severe vision loss.  

Photos of a non-ischemic CRVO of the right eye

What are the symptoms and signs?
The most common presentation is sudden, painless loss of vision in one eye. When the eye doctor looks in the affected eye, he/she will see lots of hemorrhages (see photos) in all 4 quadrants of the retina and possibly cotton wool spots, which are fluffy white spots in the retina. The veins of the retina are widened and curly. There may also be swelling of the optic disc. CRVOs are sometimes described to have a "blood and thunder" appearance, because it pretty much looks like something exploded in the back of the eye. 

CRVO photo via Wills Eye

What are the risk factors?

CRVOs usually occur in persons over the age of 50, and hypertension is the most common systemic association. Other vascular diseases like atherosclerosis, high cholesterol, and diabetes are risk factors as well.  Hardening and/or narrowing of the arteries can compress the vein and cause clot formation.  Open angle glaucoma is also a risk factor.  If a CRVO occurs in someone under 40 years of age with no known risk factors, he/she may need to be tested for blood clotting or thickness abnormalities. 

How is it treated?
The blockage cannot be undone, so the goal is to treat/prevent the secondary complications. Namely, macular edema and neovascularization. Several clinical trials have shown there are treatment options that help reduce macular edema and improve vision to a certain degree. Early detection of complications and timely treatment are key.  

The most common treatment for macular edema as a result of a CRVO is intravitreal injections of anti-VEGF drugs. The drugs are injected into the gel part of the inner eye (the vitreous), and are usually administered every 4-6 weeks.  Two such drugs that are FDA-approved for treating macular edema due to CRVOs are Lucentis (ranibizumab) and Eylea (aflibercept). Avastin (bevacizumab), a cancer drug, is an anti-VEGF drug used extensively as well, though used off-label. Steroid injections/implants may be used instead of or in addition to anti-VEGF injections. An intravitreal steroid implant, Ozurdex, is an FDA-approved treatment for macular edema secondary to vein occlusion. Currently in FDA trials: a combo of Eyelea (intravitreal anti-VEGF injection) and Zuprata (suprachoroidal steroid injection) that has the potential to decrease the number of Eyelea injections a patient needs (read more about it here). Laser is not a common treatment with CRVOs, unless there is neovascularization present.

Macula OCT of the above-photographed CRVO patient

Aside from taking photos to help monitor the condition, your eye doctor may utilize other tools in the treatment process. 

• Optical coherence tomography (OCT) is a scanning laser used to get a cross-sectional image of the retina (see scan above).  This helps assess the level of swelling in the macula and track the response to treatment.  
• Fluorescein angiography (FA) is used to identify areas of the retina with poor/absent blood flow and helps guide treatment. A dye is injected into a vein in the arm and photos of the retina are taken as the dye reaches the retinal vessels.

CliffsNotes:  A CRVO occurs when a blood clot blocks the outflow of blood from the tissue that lines the back of the eye (the retina). If you notice a sudden, painless loss of vision, contact your eye doctor STAT!

age-related macular degeneration

Fundus cupcake sprinkled with drusen

February is Age-related Macular Degeneration (AMD) Awareness Month. AMD is one of the leading causes of irreversible vision loss among Americans over 60 (1). 

Let's preface our AMD discussion with a quick anatomy review. The tissue that lines the back of the eye is called the retina. The retina has millions of light-sensing cells called photoreceptors (rods and cones). These cells absorb light and convert it into signals that are sent to the brain via the optic nerve, allowing us to see the world around us. The macula is a small area near the center of the retina that is responsible for our central, sharpest vision. Within the macula is a high density of cones, the photoreceptors responsible for color vision. When you look at retinal photos (or the cupcake above), the macula is the dark red area. For reference, here is a labeled photo of a healthy retina.

What is age-related macular degeneration?
Age-related macular degeneration, commonly called AMD or ARMD, involves a breakdown of the tissue that makes up the macula. Waste products called drusen accumulate beneath the retina, in and around the macula. Drusen are the yellow-ish deposits you see in the photo below. This disruption causes the photoreceptor cells to die, which impairs vision. Over time, central vision becomes blurry and distorted. AMD can be classified as either dry or wet.  

• Dry (non-exudative) AMD: This is the most common form of the disease. The early and intermediate stages of dry AMD involve drusen and/or pigmentary changes in the retinal pigment epithelium (RPE). The late stage involves the death of large areas of retinal tissue, called geographic atrophy, which affects central vision significantly.

Fundus photo of dry AMD

• Wet (exudative) AMD: About 10% of dry AMD cases progress to the wet form, meaning that neovascularization has occurred. Neovascularization is the formation of new, abnormal blood vessels under and into the retina. These vessels are weak and can leak, causing vision loss. Neovascularization is bad news bears and warrants prompt treatment (discussed below). Wet AMD typically affects vision more rapidly and more significantly than dry AMD.

What are the risk factors?
AMD is a multifactorial disease. The exact cause is unknown, but research suggests some factors increase the risk of AMD:

• Age. Age is a major risk factor, with most cases typically occurring after the age of 50. 
• Smoking. Several studies have found a positive association between smoking and the development of AMD. The risk of developing the disease for current smokers is at least two to three times greater than the risk for non-smokers (2, 3). Smoking is the leading modifiable risk factor for AMD.
• Family history/genetics. Having a close relative with AMD increases the risk of developing the disease (4). Researchers have identified variants of a few complement genes that are associated with an increased risk of developing AMD (5).
• Diet. Those with diets low in omega-3 fatty acids and antioxidants may be at greater risk of progression to advanced disease (6).
• Hypertension. Some studies have shown wet AMD to be associated with moderate to severe hypertension (7, 8).
• Obesity. Research has suggested an association between body mass index (BMI) outside the normal range and early AMD (9)  as well as progression to advanced AMD (10).
• High cholesterol. Elevated high-density lipoprotein (HDL) levels may be associated with higher risk of AMD (11).
• Sun exposure.  Exposure to large amounts of visible and blue light may play a factor in disease progression (12, 13, 14). 
• Ethnicity. AMD is more prevalent in Caucasians. 
• Gender. AMD is more prevalent in females.

How is AMD diagnosed?

AMD is diagnosed during a dilated eye exam. It may manifest itself in changes in central vision, but it most likely will not in the early stages. Upon dilation, pigmentary changes and/or drusen may be noted by your eye doctor in/around the macula. 

How it is monitored and treated?

• Various tools exist to help monitor AMD and guide treatment: 
• Retinal photo. Periodic photos allow for monitoring progression over time. 
• Amsler grid. This is an easy way for patients to monitor for changes in their central vision. AMD can cause parts of the grid to appear distorted or missing. I suggest that my AMD patients leave it on their refrigerator and test each eye a few times a week, monitoring for any changes. 
• The ForeseeHome monitoring device utilizes a similar concept. Patients are presented with a series of straight lines containing a wave/bump, and the patient must identify where the distortion is. The device collects the data and alerts the patient's eye doctor if there are abnormal results. 
• Optical Coherence Tomography (OCT).  A scanning laser is used to image the tissue of the back of the eye. It can produce a cross section of the macula, showing retinal thinning or thickening.  

OCT showing drusen (red arrows) below the retina

• Fluorescein angiography (FA). Fluorescein dye is injected into a vein in the arm and photos of the retina are taken as the dye reaches the retinal vessels. An FA may be ordered to identify neovascular membranes, evaluate leakage, and/or guide treatment. 
• Coming down the pike: OCT Angiography. This technology just got FDA approval in the US. It will allow doctors to image the vessels of the retina and choroid without injecting a contrast dye (unlike an FA). 
• Treatment: 
• Dry- There is no FDA-approved treatment for dry AMD as of yet. Plenty of research is being done in this area. Studies have shown that antioxidant supplementation may help slow progression to advanced AMD (15, 16). For more information on ocular nutrition, check out this post.  
• Wet- Most cases of wet AMD are treated with anti-vascular endothelial growth factor (VEGF) drugs. Anti-VEGF drugs are periodically injected into the eye to stop abnormal vessel growth. Photodynamic therapy (PDT) and laser photocoagulation are also treatment options, though less commonly used.

Vision loss is often life-altering and difficult to cope with. There are support groups and low-vision rehabilitation resources available to those dealing with AMD. Low vision aids include hand-held, stand, or spectacle magnifiers, video magnifiers (CCTVs), and even implantable telescopes! We'll do a separate post on low vision devices and rehab services later on, but here's a great place to begin: Living Well with Low Vision.

CliffsNotes: AMD is a multifactorial disease with several modifiable and non-modifiable risk factors. The best way to prevent vision loss from AMD is to have routine dilated eye exams, especially if you fall into a higher-risk category.   


Additional resources:

• All About Vision: AMD
• NEI: AMD Facts
• Get Eye Smart: ARMD
• Foundation Fighting Blindness
• Prevent Blindness

Happy Valentine's Day!

Happy Valentine's Day!

Happy Thanksgiving!

Happy Thanksgiving from Nutter Butterball!  

(see what I did there?!?)

vision + learning, the sequel

According to the College of Optometrists in Vision Development (COVD), one in four children struggle with reading and learning unnecessarily because of undiagnosed vision problems, and approximately 60% of problem learners have undiagnosed vision problems contributing to their difficulties (1).  

So what does a child need visually to be able to read well?

• Clear vision up close.  Pretty obvious, right?  It's more difficult to discover problems here than it would seem.  Children who can't see well at near very often fall through the cracks during vision screenings, because many will read the distance chart and pass easily.  Beyond just making reading and near tasks difficult, high amounts of farsightedness (hyperopia) in one or both eyes, if left uncorrected, can prevent the visual system from developing to its full potential (amblyopia).  For more information about refractive errors and ambylopia, check out the back-to-school post.  Problems with the focusing (accomodative) system of the eye can also make vision up close unclear.  
• Single vision up close. Eye teaming refers to the ability of both eyes to work together.  Convergence is the ability to move both eyes in when looking up close. Problems with convergence (either insufficiency or excess) can cause difficulty when reading.  Double vision can result if one eye is aimed in a different direction than the other, causing the brain to receive two different images that it cannot fuse.  To avoid seeing double, the visual system may suppress, or "turn off" an eye, or use the focusing system to compensate. As we will discuss below, these ways of coping often cause eyestrain, blur, headaches, and fatigue, and children are not likely to read for long periods of time if this is what they're dealing with just to see the words on the page. 

Image from Wow Vision Blog

• Accurate and efficient eye movement. As we discussed in last year's vision and learning post, the act of reading involves a series of eye movements called saccades and fixations.  Saccades are the eye movements that allow us to quickly redirect our line of sight from one location to another.  When reading, saccades allow us to move through a line of text.  The normal reader averages about 7-9 letter spaces per saccade.  Fixations occur when the eye is relatively still, allowing us to maintain a steady gaze.  Regressions are eye movements in the right-to-left direction that occur when we reread a word or section.  They occur 10-15% of the time in skilled readers.  Less skilled readers typically have longer fixations, shorter saccades, and make more regressions than more skilled readers (2).  When these ocular motor skills are deficient, it can lead to one losing their place when reading, skipping words, and reading slowly.  
• Comfortable vision.  Eyestrain, blur, headaches, and fatigue are common symptoms of problems with focusing and/or eye teaming.  Any of the aforementioned conditions can cause reading and schoolwork to be uncomfortable, which often causes children to become disengaged and inattentive.  
• Visual-perceptual skills.  Visual perception is how we process and understand what we see, and it happens at the level of the brain.  We don't see with our eyes; we see through them.  Problems with visual memory (the ability to recall what is seen), visual spatial skills (the ability to understand directional concepts and organize visual information), and visual discrimination (the ability to identify features of and discriminate between different letters, numbers, etc) can negatively affect a child's ability to read and learn. A 2012 study found a correlation between visual spatial skills in preschoolers and their future reading skills (3).  Integration between the senses is critical as well, as visual-motor and visual-auditory integration also affect learning.  

It is important to note that vision is more than 20/20!  Reading involves the integration of so many visual skills, and it is a visually demanding task.  When the visual demands of a task exceed a child's visual skills, symptoms/difficulties arise.  In a great TEDx Talk on the subject (watch here), Dr. McCrodan likened the visual system to an engine: "If it is really inefficient, you're going to burn out of gas a lot faster." Children often don't say anything because they don't know any differently. If your child is struggling at school, see your optometrist to have their visual skills evaluated.  If your optometrist does not perform these types of evaluations, they can certainly point you to an optometrist that does.  You can also visit www.covd.org to find one in your area.

CliffsNotes: Vision is more than 20/20!  Reading involves the integration of many visual skills.

Additional Recommended Resources:

• TEDx Talk: Overlooking our vision
• Eye Can Learn
• COVD: Vision and Learning
• AOA: Reading and Vision
• Vision and Learning

color vision deficiency

Ishihara cupcakes

What allows us to 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 cones; each type is sensitive to a different wavelength, and thus a different color of light. An S cone is sensitive to short wavelengths (blues), an L cone is sensitive to long wavelengths (reds), and an M cone is 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.

What is color blindness?
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. 

• Inherited: These color vision deficiencies are present at birth, affect both eyes equally, and are stable over a person's lifetime. They occur in about 8% of males (the highest prevalence is found in non-Hispanic whites 1 ) and 0.5% of females (2).
• Acquired: Unlike inherited deficiencies, these occur during a person's lifetime, may affect one eye or both eyes unequally, and may progress. Eye diseases or injury, the use of certain medications, or exposure to certain chemicals can cause an acquired color vision issue.

What types of color vision deficiency exist? 3

1. Achromatopsia, also known as rod monochromatism, is true, total color blindness. There is a complete absence of functional cones, so everything is seen in shades of gray. This rare and severe condition is typically associated with other signs like light-sensitivity, poor vision, and nystagmus (eye jitter). 

• Inheritance pattern: Autosomal recessive
• Prevalence: 0.00003% of males 

• Partial or incomplete achromatopsia refers to even rarer conditions in which there is only one of the three types of cones present/functioning.  Blue cone monochromacy (BCM) is the most common of these, but with a prevalence of one in 100,000, it is still very rare.  

2. Dichromacy is a category of color deficiency in which there are only two types of cones present instead of three. 

• Protanopia- missing L (red) cone. 
• Inheritance pattern: X linked recessive
• Prevalence: ~1% of males, ~0.1% of females
• Deuteranopia- missing M (green) cone. 
• Inheritance pattern: X linked recessive
• Prevalence: ~1.5% of males, ~0.01% of females
• Tritanopia- missing S (blue) cone. 
• Inheritance pattern: Autosomal recessive
• Prevalence: 0.008%, males=females

3. Anomalous Trichromacy is a category of color deficiency in which all three types of cones are present, but one type of cone's sensitivity is off.  Specifically, one cone's spectral sensitivity is shifted, resulting in reduced sensitivity to the wavelength of light (color) that the cone is intended to absorb. These are the most common and most mild color deficiencies.

• Protanomaly- malfunctioning L (red) cone.
• Inheritance pattern: X linked recessive
• Prevalence: ~1% of males, 0.01% females
• Deuteranomaly- malfunctioning M (green) cone, or "green weak." This is the most common color vision defect.
• Inheritance pattern: X linked recessive
• Prevalence: ~5% of males, ~0.4% females
• Tritanomaly- malfunctioning S (blue) cone. 
• Inheritance pattern: Autosomal dominant
• Prevalence: 0.0002%, males=females

"Protan" is used to refer to both protanopia and protanomaly, and "deutan" is used to refer to both deuteranopia and deuteranomaly. Protan and deutan defects are both considered red-green color deficiencies. "Tritan" defects (tritanopia and tritanomaly) are considered blue-yellow deficiencies.

For the nerds out there, a Punnett not-so-square depicting why males are far more likely to present with an X-linked recessive inherited trait:

The biology behind red-green color blindness

So if a boy is red-green color deficient, it is likely that the boy's maternal grandfather was also red-green color deficient, and the boy's mother/grandfather's daughter was a carrier.

How is color deficiency diagnosed?
Color deficiency is usually detected in childhood, either when a child has difficulty with color naming or when he/she is checked during a routine eye exam.  Some tests that may be used include:

• Pseudochromatic plates: These tests involve distinguishing numbers or symbols amongst colored dots.  The Ishihara test is probably the most recognized of these tests (and the inspiration for the cupcakes seen at the top of the page).  The Ishihara test does not test for blue-yellow color deficiencies, whereas the HRR test does.   
• Arrangement tests: These tests involve arranging discs in color order, beginning with a fixed pilot disc. Two such tests are the Farnsworth-Munsel 100 (interestingly has only 85 discs, not 100) and the Farnsworth  D15. There is an online version of the D15 test here. Because color perception varies depending on the type of display and lighting you are working with, this test is not definitive or diagnostic. Based on my sample size of 2 (thanks Matt and Lee), it seems to be fairly accurate.
• Lantern: The Farnsworth Lantern (Falant) is a color-naming test typically used by US federal agencies to test color vision. 
• Anomaloscope: This is a color matching test. Half of a circle is presented as pure yellow, and the other half can be adjusted by the observer to varying proportions of red and green to achieve a perceived match.  

Fun Fact: All adult male squirrel monkeys are red-green color deficient. 

How are color vision deficiencies treated?

For the most part, those with color vision deficiencies learn to recognize color by different means (ie: brightness, location) and develop their own system of coping, whether that involves a special way of organizing things, or asking others for help when matching things. There is no cure for color vision deficiencies at this time, but there are some products out there that can potentially enhance color discrimination.

• Xchrom Lens: This is a red-tinted soft contact lens that is worn in the non-dominant eye.  The red tint is intended to enhance color perception by changing the lightness of colors (ie: makes greens look darker), increasing the number of shades a person can see. 
• Chromagen:  Chromagen lenses are available in glasses or contact lens form.  A range of 8 colored filters are available, and a series of tests are done to determine which color(s) is/are appropriate.  The filters are intended to change the wavelength of each color going into the eye, potentially enhancing color perception and discrimination. Chromagen lenses are also marketed as part of dyslexia therapy.
• EnChroma:  These lenses are designed for people with anomalous trichromacy (all 3 cones are present, but one cone's sensitivity is shifted).  EnChroma lenses use a notch filter to restore the spectral separation between cones, potentially reducing color confusion and enhancing color perception. 
• Gene therapy? This may be in our future.  In 2009, researchers from the University of Washington and the University of Florida (Go Gators!) cured color blindness in two squirrel monkeys using gene therapy 4. 

CliffsNotes: Most color vision deficiencies are inherited, not acquired. The most common form is red-green deficiency in males. 

Additional recommended resources:

• AOA: Color Deficiency
• NEI: Facts About Color Blindness
• NLM: Color Vision Deficiency
• EyeSmart: Color Blindness

Essential Eye Nutrients

Food and lifestyle choices can influence your eye health and may help to reduce the risk of some age-related eye diseases.  Check out this quick summary of the nutrients essential for good eye health.
*Disclaimer: I am not a nutritionist or a dietician.

• Zinc (red meat, poultry, oysters, beans, fortified cereal)
• The Food and Nutrition Board recommends: 11 mg/day for males, 8 mg/day for females
• Zinc is an essential mineral that is involved in cell metabolism.  It is highly concentrated in the retina and choroid of the eye.
• Vitamin E (nuts, seeds, vegetable oils)
• The Food and Nutrition Board recommends: 15 mg or 22.4 IU/day for both males and females
• Vitamin E is a powerful antioxidant that is involved in immune function.
• Vitamin C (citrus, strawberries, broccoli, red and green pepper, kiwi)
• The Food and Nutrition Board recommends: 90 mg/day for males, 75 mg/day for females
• Vitamin C is an antioxidant that helps absorb UV radiation. It is found in high concentrations in the lens, aqueous humor, and vitreous humor of the eye.  On a long term basis, increased intake of vitamin C (alone or in combination with other antioxidants) has been shown in some studies to reduce the risk of developing nuclear sclerotic cataracts (1, 2).

The National Eye Institute's Age-Related Eye Disease Study (AREDS) found that daily intake of 80 mg zinc, 2 mg copper, 500 mg vitamin C, 15 mg beta carotene, and 400 IU vitamin E could reduce the risk of progression to advanced Age-related Macular Degeneration (AMD) by about 25% and visual acuity loss by 19% in individuals at high risk for the disease (3).  Since that study, researchers have found that substituting beta carotene with 10 mg lutein and 2 mg zeaxanthin is safer and more effective (4).

• Vitamin A (beef liver, carrot, pumpkin, sweet potato)
• The Food and Nutrition Board recommends: 900 micrograms or 3000 IU/day for males, 700 micrograms or 2300 IU/day for females
• Vitamin A is essential in the proper functioning of the retina, as well as the conjunctival membrane and cornea.  Most Americans get sufficient vitamin A from their diet, but vitamin A deficiency (VAD) is actually the leading cause of preventable blindness in children world-wide (5).
• Lutein (kale, spinach, collards, egg yolks) & Zeaxanthin (gogi berries, orange peppers, corn)
• The American Optometric Association recommends: 10mg/day of lutein and 2mg/day of zeaxanthin
• Lutein and zeaxanthin are carotenoids that are abundant in the macula of the eye as well as the lens. They are antioxidants that help lower your risk for Age-related Macular Degeneration (AMD) and cataracts.

From Review of Optometry

A follow-up to AREDS- AREDS 2- found that people with the lowest dietary levels of lutein and zeaxanthin who added supplements of the two had a 26% reduced risk of developing advanced AMD.  Those with the lowest dietary intake of lutein and zeaxanthin also saw a 32% risk reduction in progression to cataract surgery with the introduction of these nutrients (6).  Most Americans only get 1-2 mg of lutein and zeaxanthin combined on a daily basis through their diet, so many of us fall into this category.

Fun Facts: Vitamins A, D, E, and K, as well as lutein and zeaxanthin, are fat-soluble.  A small amount of dietary fat (ie: olive oil, avocado, nuts, seeds) can help maximize the body's absorption of these nutrients.  Cooking (steaming, sautéing, or puréeing) leafy greens actually allows more access to the important nutrients by breaking down plant cell walls.

• Omega-3 Fatty Acids (wild salmon, mackerel, tuna, sardines)
• The American Heart Association recommends eating at least two servings of fish (especially oily fish)/week
• The 3 types of omega-3 fatty acids the body uses are ALA, DHA, and EPA.  DHA and EPA have structural and protective functions in the retina, and they also have anti-inflammatory properties.  Beyond the cardiovascular health benefits, diets rich in DHA and EPA have been linked to a significant improvement in dry eye symptoms (8, 9). 

Eye vitamins and other supplements can help you meet your recommended daily intake of these nutrients. Be sure to discuss this with your optometrist or ophthalmologist.  I also recommend communicating with your primary care doctor before beginning any supplementation regimen- it's important to give your PCP the full picture of what you do to manage your health.

If you want to find an optometrist that specializes in ocular nutrition, look here.

CliffsNotes: What you eat can influence your eye health and may help to reduce the risk of age-related eye diseases.  

Additional Recommended Resources:

• AOA: Diet and Nutrition
• All About Vision: Nutrition
• Get EyeSmart: Diet and Nutrition
• Eyefoods: A Food Plan For Healthy Eyes
• Visionary Kitchen: A Cookbook For Eye Health

Glaucoma Awareness Month

January is Glaucoma Awareness Month, so I think we all know what this month's post is about. According to the World Health Organization (WHO), glaucoma is the second leading cause of blindness world-wide (1), and Open Angle Glaucoma affects more than 2 million people in the US alone (2).

A cupcake rendition of the optic nerve

What is glaucoma?
Glaucoma is a group of diseases that damage the optic nerve. The optic nerve is like a cable, made of about 1 million nerve fibers, that sends signals from the retina (the tissue that lines the back of the eye) to the brain. When the optic nerve is damaged, permanent vision loss results.

There are many types of glaucoma, the most common of which is Primary Open Angle Glaucoma (POAG). In most cases of glaucoma (but not all!), the pressure within the eye is higher than normal. The eye has a clear fluid, called aqueous humor, that circulates in the front part of the eye and flows out through a structure called the angle (here is a good visual). Through various mechanisms, this fluid may not flow out of the front of the eye properly, leading to elevated eye pressure, or intraocular pressure (IOP). High IOP can slowly damage the optic nerve over time.


How do I know if I have glaucoma?
Most cases of glaucoma do not have symptoms early on. Peripheral vision loss occurs, but by the time you notice this, the disease is substantially progressed and significant, permanent vision loss has occurred. Since there really aren't symptoms to watch out for, early detection during yearly eye exams is key.

There are some factors that increase risk for glaucoma:

• a family history of glaucoma
• being of African-American or Hispanic descent
• older age 
• high eye pressure
• thin corneas

*Note: People of any age, race, or eye pressure level can have glaucoma.

Glaucoma can also result from another disease or condition, like eye trauma or inflammation. Additionally, some studies have shown a relationship between glaucoma and conditions of altered blood flow (ie: sleep apnea, diabetes, migraines, high or low blood pressure).

How is glaucoma diagnosed?
Glaucoma is a complex disease, so many areas need to be looked at to obtain an appropriate diagnosis and management plan. Some procedures that may be involved in the diagnostic/management process:

• Tonometry: A tonometer probe is used to gently measure intraocular pressure (IOP) in millimeters of mercury. "Normal" IOP is typically under 21mmHg, though you can have glaucoma with normal IOPs. You can also have higher than normal IOPs without having damage to the optic nerve.
• Perimetry/Visual Field Testing: A visual field test assesses the function of the optic nerve. When enough nerve fibers are damaged, you develop missing spots in your field of vision. The visual field test picks up these missing spots early on (far, far sooner than you would pick them up on your own). 
• Pachymetry: This test measures the thickness of the central part of your cornea. Thinner corneas not only underestimate eye pressure, but they have also been shown to be a risk factor for glaucoma progression (3,4).
• Gonioscopy: A lens with mirrors is placed on the eye, allowing your eye doctor to get a closer look at the drainage angle of the eye. 
• Dilated fundus exam: Your eye doctor uses a high-powered lens and a slit lamp to evaluate the health of the optic nerve, best viewed through a dilated pupil. Your eye doctor may choose to take photos as well, similar to the one seen below.
• GDx, HRT, OCT: 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 give information on the amount of optic nerve tissue loss and the rate of nerve fiber thinning. The structural defects on the optic nerve should correlate with the functional defects in the visual field.

End-stage glaucoma

How is glaucoma treated and managed?
There is no cure for glaucoma, but the damage it causes can be slowed by the use of medications and/or surgery. Of the risk factors mentioned, the only one we can control is eye pressure, so that is the focus of treatment. The goal is to increase outflow of the fluid in the eye, or decrease production of that fluid, or both. This can be achieved using medications (typically eye drops), laser procedures, or glaucoma surgery. The course of treatment depends on both the type and severity of glaucoma.

What about marijuana?  I've been asked this question more than once. Marijuana is not a legitimate form of glaucoma therapy. Yes, a study from 1971 showed that smoking marijuana reduces eye pressure, but only for about 3-4 hours after smoking (5). Glaucoma management requires around-the-clock IOP control. Drops and/or surgery are much more effective at lowering IOP over the long-run and are less detrimental to your health, so I do not consider marijuana an appropriate glaucoma treatment.


What is the prognosis?
Left untreated or uncontrolled, glaucoma can lead to blindness. But the good news is it can be diagnosed on routine eye exams, and it is treatable. See your optometrist at least every 1-2 years, or more frequently if warranted. This is especially important for those with several risk factors. If you are diagnosed with glaucoma, it is important that you are compliant with the treatment and follow-up regimens outlined by your eye doctor. Effective management requires a team effort between you and your eye doctor.


CliffsNotes: Glaucoma is a leading cause of blindness. Know the risk factors and see your eye doctor regularly!

Additional Recommended Resources:

• Glaucoma Research Foundation
• AOA: Glaucoma
• NEI: Glaucoma
• All About Vision: Glaucoma

Merry Christmas!

Wishing you all a very merry Christmas and a happy New Year!

Halloween contact lenses

As Halloween approaches, it is important to remember that there are serious risks associated with improper costume contact lens wear.  ALL contact lenses- even decorative lenses that do not provide vision correction- are classified as medical devices, and their safety and effectiveness is overseen by the Food and Drug Administration (FDA).  They need to be properly fit and evaluated by an eye doctor, and thorough contact lens care instructions need be given at that time.

Here are a few tips to minimize the risk associated with decorative contact lens wear:

1. Get a contact lens exam, fitting, and prescription from a licensed eye doctor. This applies even if the lenses do not correct your vision.  A valid prescription specifies the brand of contact lens and the fitting parameters of that lens.  Contact lenses are NOT one-size-fits-all.    
2. Purchase contact lenses from a reputable source that is authorized to sell contact lenses (ie: not beauty shops, flea markets, costume stores, etc).  A vendor is required by law to request a current, valid prescription before selling a consumer contact lenses. 
3. Follow the contact lens care instructions given to you by your eye doctor.
4. Remove lenses and see your optometrist immediately if you notice any eye redness, discharge, pain, or decreased vision.  Infections related to contact lens wear can be potentially blinding!

CliffsNotes: ALL contact lenses are classified as medical devices by the FDA.  It is unsafe to buy and wear contact lenses without a valid prescription!

Additional recommended resources:

• Don't Lose Sight of Your Vision (video)
• Decorative Lens Warning

InfantSEE

Inspired by the book Hello, Cupcake!

InfantSEE® is a public health program that is designed to ensure that eye care becomes an integral part of infant wellness care.  If your child is between 6 months and 12 months old, an InfantSEE® provider will perform a one-time comprehensive infant eye assessment at no cost to you.  This allows the opportunity for early detection of risk factors that might lead to potential eye and vision problems.  Many eye conditions do not have signs/symptoms that can be easily identified by a parent or pediatrician.  

The American Optometric Association (AOA) recommends an eye exam at 6 months of age, yet only 18% of parents reported that their infant had received a comprehensive eye exam before age 1, according to the Eye-Q survey conducted by the AOA in 2011.  Vision development has stages, and many development milestones relating to the eye and vision have been reached at 6 months.  Even though some skills reach near-adult levels in infancy, the visual system continues to develop through childhood.

Optometrist rely on patient and family history along with objective testing to determine if a baby has or is at risk for having a vision or eye problem.  Although problems are not common, it is important to identify children who have specific risk factors at this stage.  Vision development and eye health problems can be more easily corrected if treatment is begun early.  There are four main areas that are evaluated during an infant vision and eye assessment:

1.  History:  The optometrist will ask questions relating to the pregnancy, delivery, and development of the child.  Some risk factors for potential eye problems include premature birth, low birth weight, high levels of oxygen therapy, low APGAR scores, and a strong family history of eye problems.

2.  Vision:  Obviously, a baby will not be able to read the letters on the eye chart or tell the optometrist that choice 2 is better than choice 1.  Instead, the optometrist will use objective, non-verbal techniques to estimate the child's visual acuity and refractive error (nearsightedness, farsightedness, astigmatism).  High amounts of refractive error in one or both eyes is a risk factor and will need to be monitored more closely and/or treated to ensure proper visual development.  When these issues are caught and treated early, vision loss in the form of amblyopia can be avoided.  A more detailed description of amblyopia and refractive errors can be found in the back-to-school post.

3.  Eye alignment:  Besides assessing vision, the optometrist will also be checking to see if the infant's eyes are aligned and working together. These skills are not fully developed in the first few weeks of life.  Constant and/or significant eye deviations noted at the InfantSEE® exam may require treatment with glasses/contact lenses or surgery, depending on the type of eye turn.  As mentioned above, these issues need to be addressed early on to ensure proper visual development.   

4.  Ocular health:  The optometrist will use handheld instruments to assess the health and function of the structures of the outer eye.  He/she will also use an eye drop or spray that dilates the baby's pupils to check the health of the inner eye.  

If all is well at the InfantSEE® exam, the next time a child should be seen by their optometrist is at 3 years of age, or sooner if a problem/concern arises.

For more information, and to find an InfantSEE® provider near you, please visit http://www.infantsee.org/.

CliffsNotes: Babies need eye exams too!  

Additional recommended resources:

• AOA: Infant Vision
• All About Vision: Infant Vision Development