cataracts

What is a cataract?
A cataract is a clouding of the part of the eye called the lens.  The lens sits right behind the colored part of the eye (iris), and it helps focus light onto the light-sensitive tissue that lines the back of the eye (retina).  It is normally clear.  Over time, the proteins that make up the lens begin to clump together and cause a clouding of the lens.  Most cataracts progress slowly and eventually affect vision.  While most cases involve both eyes, a cataract can develop in only one eye.

For those of you, like myself, who need a visual, here's a good video to watch.

Are there different types of cataracts? 
There are many different types of cataracts, and a person can have more than one type.

• Age-related, or senile: cataracts that result from the normal physiological changes that occur in the lens of the eye.  Most, but not all, cataracts are age-related. 
• Nuclear sclerotic cataracts involve a yellowing of the central lens. They sometimes cause a shift in prescription, leading to a temporary improvement in near vision (often referred to as "second sight"). 
• Cortical cataracts involve spoke or wedge-like opacities that often start around the periphery of the lens.
• Posterior subcapsular cataracts involve a hazing of the back of the lens. This type of cataract may progress more rapidly and affect vision more significantly than others. Posterior subcapsular cataracts may be seen more frequently in diabetic patients, in patients using steroids, and in patients who have had vitreoretinal surgery.  
• Congenital: cataracts that are present at birth. The majority affect both eyes, and they vary in severity.  If the cataracts are significant and obstruct vision, they are removed early on to allow vision to develop properly, preventing deprivational amblyopia.    
• Traumatic: cataracts that result from blunt or penetrating trauma to the eye.  

There are still other, rarer cataracts that occur secondary to disease processes. For instance, a Christmas tree cataract is often found in those with myotonic dystrophy.

Images courtesy of the AOA

Can you prevent cataract formation?
One theory suggests that cataract formation is due to oxidative changes in the lens, and some studies (1, 2, 3) have shown that antioxidant consumption can help reduce the risk of cataracts. (For more information on how diet affects the eye, check out this previous post). While cataract prevention is still being researched and debated, we do know of risk factors for progression that we can aim to reduce/eliminate.  Evidence suggests that UV exposure increases the risk of cataract development (4, 5), so wearing UV-blocking sunglasses is a good practice.  Smoking increases the rate of cataract formation (6, 7), so that's yet another reason to kick the habit.

What are the symptoms?
Early on, cataracts have few or no symptoms.  Colors may appear faded. You may begin to notice glare, especially when driving at night. Because the lens is no longer clear, it scatters light, which prevents a sharp, clear image from focusing on the retina.  As the cataracts progress, they begin to cause blurry vision that is not correctable with glasses or contact lenses.  At that point, the option of surgery is discussed.  Cataracts can be diagnosed by your optometrist during your annual dilated eye exam.

What is the treatment?
While cataracts are the leading cause of visual impairment world-wide (47.9%, according to the WHO), they are easily treated here in the US. Cataract extraction is currently the only treatment available.  This procedure involves removing the natural lens of the eye and replacing it with an intraocular lens (IOL). There are many different types of IOLs available.  It is up to the patient and his/her team of eye care professionals to discuss the options and determine which type of IOL is best suited for the patient.  Here is a video of a local ophthalmologist performing cataract surgery (if you're squeamish, you should probably pass on watching it).

The future may hold non-surgical options for the prevention and treatment of cataracts.  In a recent study, dogs who received treatment with lanosterol injections and drops showed a noteable reduction in their cataracts.

Do they recur?
No- once a cataract is removed, it is gone.  However, you can develop a posterior capsular opacification (PCO) after cataract surgery.  That's when the lens capsule that holds the implant becomes hazy.  It is sometimes referred to as an "after-cataract" or "secondary cataract," but it is not a true cataract.  A YAG laser capsulotomy is a simple procedure that involves using a laser to remove the hazy portion of the capsule that is obstructing vision.

CliffsNotes: A cataract is a clouding of the lens of the eye.  There are several different types, but the most common are the natural results of aging.  When cataracts affect vision significantly, the option of surgical extraction is discussed. 

Additional Resources:

• AOA: Cataracts
• NEI: Cataracts
• All About Vision: Cataracts
• Kellogg Eye Center: Cataracts

Happy Thanksgiving!

Happy Thanksgiving from Nutter Butterball!  

(see what I did there?!?)

costume contact lenses

After reading this news story about a teen's experience with costume contact lenses that were purchased without a prescription, I thought it would be a good time to review a few tips to minimize the risk associated with decorative contact lens wear. If this sounds familiar, it might be because you read last year's riveting blog post on the same topic.  

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.  It is best to purchase your lenses through your eye doctor's office. 
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!

I had a few patients this year request costume contact lenses for Halloween, and I'm sharing their photos below (with permission).  I ordered the lenses from a reputable contact lens manufacturer, and the patients came in for a contact lens fitting in order for me to evaluate the lenses on their eyes and discuss proper contact lens care.

(Side note: These lenses obviously reduce your peripheral vision and shouldn't be worn when driving.)

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 and thorough evaluation from a licensed eye doctor!

central serous chorioretinopathy

What is central serous chorioretinopathy?
Central serous chorioretinopathy (CSCR), sometimes called central serous retinopathy or choroidopathy, is a condition in which fluid builds up under the retina, almost like a blister.  This causes a serous detachment of the neurosensory retina, which results in sudden blur and distortion of central vision, usually in one eye only.

Retinal photo of a patient with CSCR (see the bubble in the center?)

Who gets CSCR?
CSCR is more common in males, usually between the ages of 20 and 50.  The exact cause is unknown, but stress and steroid use are risk factors (1).  

How is it diagnosed?
The patient's symptoms and the clinical appearance on dilated examination is usually sufficient to make a diagnosis of CSCR.  A couple of additional tests may be used to confirm the diagnosis and monitor resolution:

• Optical Coherence Tomography (OCT)- A scanning laser creates a cross-sectional image of the layers of the retina and allows eye doctors to measure the thickness of the retina.  Below is the macula OCT of the same patient whose retina is in the photo above.

Macula OCT of the same CSCR patient

• Fluorescein angiography (FA)- Fluorescein dye is injected into a vein in the arm, and photos of the retina are taken as the dye travels through to the vessels of the retina, highlighting areas of leakage.

What is the treatment?

Most cases of CSCR resolve on their own within 3 or 4 months, so observation is most appropriate. In cases where visual recovery is urgent, or the CSCR does not resolve on its own after a few months (which can be up to 20% of cases 2), intervention may be indicated. These cases may be treated with laser, though the end result with and without treatment has been found to be similar. There are many investigational treatments involving the use of oral medications (most recently, eplerenone) or anti-VEGF injections, but nothing definitive has been concluded based on the studies.  In up to half of CSCR cases, the condition recurs (3).   

CliffsNotes: Central serous chorioretinopathy is a blister-like fluid accumulation under the retina. It blurs and distorts central vision, but usually resolves on its own in a few months.

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

eyelid twitching

What is eyelid myokymia?
The short answer: it is a sudden spasm, or twitch, of the eyelid muscle.  The long answer: it is an involuntary misfiring of the neurons that innervate the orbicularis oculi muscle (the muscle that closes the eye). (1)

Eyelid myokymia typically involves one eye (unilateral), affects the lower lid more often than the upper lid, and goes away on its own (self-limiting).  It usually comes and goes, but some cases can last for weeks or even months.  This condition is typically harmless (benign), though it can be a sign of a neurological problem if it spreads to other facial muscles.


What is eyelid myokymia NOT? 
There are a couple of eyelid conditions that may sound like eyelid myokymia, but are not the same.

• Essential Blepharospasm: This is an involuntary, episodic contraction of the eyelid muscles that affects both eyes. It can take the form of increased blinking or forceful eyelid closure.  
• Hemifacial Spasm: This is an involuntary condition that involves the eyelid muscles as well as the muscles of the cheek, mouth and neck of only one side of the face. Unlike the other conditions, this finding may be suggestive of a brainstem issue, so an MRI is indicated.

What is it caused by?

• stress
• lack of sleep
• excessive caffeine or alcohol consumption
• eye irritation (due to a foreign body, dry eye, allergies, etc)
• eyestrain (due to vision-related stress)

How is it treated?

• Reduce triggers (ie: get some sleep, go easy on the caffeine, reduce your stress).  I know, it's easier said than done!  
• See your optometrist to treat any underlying disorder that may be present (ie: remove the foreign body, begin dry eye therapy, correct your prescription, etc).
• Topical and/or oral antihistamines have been used off-label to treat this condition, as some evidence indicates that histamine can cause eyelid twitching.(2) 
• Drink tonic water.  Tonic water has low levels of quinine, which relaxes the spasming muscle.(3)
• Botox injections may be used for severe, persistent cases.

(2)(3) Bartlett, Jimmy D and Siret D. Jaanus. "Diseases of the Eyelid." Clinical Ocular Pharmacology, Fifth Edition (2008), pg 407-408.

CliffsNotes:  Eyelid myokymia is a twitching of the muscle that closes the eyelid.  The best way to get rid of it is to drink less soda/coffee, catch some ZZZZs, and chill out.  If the twitching continues for a long time, or spreads to other facial muscles, be sure to see your eye doctor.

Additional Recommended Resources:

• All About Vision: Eye Twitching
• Eyelid Spasms

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

Keratoconus

A topographical map of the front surface of the eye in a patient with keratoconus.

The red indicates the steepest part of the cornea (the cone).

What is keratoconus?
Keratoconus is a degenerative disease in which the cornea (the clear tissue of the front of the eye) progressively thins and bulges. This area of bulging resembles a cone. The National Keratoconus Foundation (NKCF) has a good introductory video here.

What are the symptoms?
The cornea is normally smooth and dome-shaped, and this allows light to focus clearly on the retina. With keratoconus, the irregularity of the cornea prevents light from focusing clearly on the retina, causing blurred and distorted vision. Glare and light-sensitivity may occur as well. Symptoms usually present in the late-teens/early-twenties. The disease generally affects both eyes, though one eye can be more severely affected than the other.

How is it treated?
Early in the disease process, eyeglasses or soft contact lenses may do the job. But as the cone progresses, the cornea becomes more irregular, and vision cannot be adequately corrected with glasses or soft contacts. Thus, you need something that will help mask the irregularity of the front surface of the eye. That's where rigid gas permeable (RGP or GP) contact lenses come in.

Image from NKCF

The type of contact lens that is best depends on the severity of the disease and the location of the cone. Some of the options available include:

• Custom soft contact lenses- custom-made soft lenses specifically designed for keratoconus.
• Corneal GP lenses- small rigid lenses that sit on the clear part of the eye (cornea).
• Scleral GP lenses- large-diameter rigid lenses that sit on the white part of the eye (sclera). 
• Hybrid lenses- lenses with a GP center and a soft periphery, or skirt.
• "Piggybacking"- when a GP lens is placed on top of a soft lens for increased comfort.

Fitting a keratoconic patient in any of these contact lenses is typically considered a specialty fitting, so you can expect to spend a little more time and money on the process and the lenses compared to a standard soft contact lens fitting. Be sure to discuss the options with your optometrist to figure out what is best for your individual case. If he/she is not able to perform the specialty fitting, he/she can certainly refer you to an optometrist in your area that can.

What are the surgical treatment options?
For various reasons, some cases of keratoconus cannot be treated with the above methods. In such cases, surgery may be indicated.

• Intacs® are small, semi-circular inserts that are implanted into the middle layer of the cornea to flatten the cone-like area. Intacs are FDA approved for the treatment of keratoconus.

Intacs®

• Collagen cross-linking (CXL) is a treatment procedure that involves administering riboflavin eyedrops and then exposing the cornea to UV-A light. This promotes cross-linking of the collagen fibers of the cornea, which stiffens the cornea and prevents further bulging. The outer layer of the cornea is removed in epithelium-off CXL, and left intact in epithelium-on CXL. CXL gained FDA approval in the US in April 2016, and we are starting to see some insurance coverage for the procedure.

• Conductive keratoplasty (CK) involves using heat in the form of radiofrequency energy to change the curvature of the cornea. Using a thin probe, radiofrequency energy is applied to small areas of the cornea in a circular pattern, creating constriction of the corneal tissue and reducing astigmatism. This procedure is being done by some doctors (off-label) in conjunction with CXL and/or Intacs.

• Corneal transplants may be necessary in 10-20% of keratoconus cases. In a full-thickness corneal transplant, or penetrating keratoplasty (PK), the diseased cornea is removed and replaced with a healthy donor cornea.  Deep anterior lamellar keratoplasty (DALK) is a partial-thickness corneal transplant that leaves the bottom layer of the patient's cornea intact, only transplanting a portion of the donor cornea. This potentially allows for a faster healing time and less risk for graft rejection (1).

Photo of a patient post-PK

CliffsNotes: Keratoconus is an eye disease that causes irregularity in the front surface of the eye. The best treatment is determined on a case-by-case basis, so talk to your eye doctor about what your options are.

Additional Recommended Resources:

• National Keratoconus Foundation
• AOA: Keratoconus
• All About Vision: Keratoconus

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