Happy Valentine's Day!

Happy Valentine's Day!

worldwide blindness

I recently went on an overseas medical mission trip, and it got me thinking.  Thinking about a lot of things, but as it pertains to this blog: worldwide blindness.  So this post will unpack some of the major diseases affecting vision globally.  

The leading causes of preventable blindness world-wide are cataracts, glaucoma, trachoma, and onchocerciasis.  We do not see the latter two much, if at all, in the United States; they are prevalent primarily in less developed areas, where there are also specific environmental hazards (1). 

TRACHOMA
Trachoma is the world's leading infectious cause of preventable blindness. Eight million world-wide are visually impaired as a result of trachoma (2). It is caused by a bacteria, Chlamydia trachomatis, and typically spreads by contact with an infected person’s hands or clothing, or can be transmitted by flies who have had contact with discharge from an infected person's nose or eyes. Trachoma is endemic in the poorest, most rural parts of Africa, Asia, the Middle East, South and Central America, and Australia (3), where lack of access to water and sanitation play a role in the disease's proliferation.  

Trachoma spreads easily among children, and from child to caregiver.  Blindness typically occurs in adulthood, and affects women 3 times more than men (4).  Left untreated, the repeated trachoma infections cause scarring of the conjunctival tissue of the eyelid, which in turn causes the eyelashes to turn in (trichiasis). The lashes then rub against the cornea, which causes scarring that leads to visual impairment and blindness.

Trachoma grading card (image: WHO)

Control:  The SAFE strategy is a public health initiative developed by the World Health Organization (WHO), combining treatment with prevention to eliminate blinding trachoma by the year 2020.  Trachoma is transmitted through close contact, so it is a community problem and all intervention must be community-targeted.

• Surgery to correct trichiasis.  As discussed earlier, trichiasis is the precursor to blindness.
• Antibiotics to treat active disease.  Single dose azithromycin, donated by Pfizer in the 1990s, is the treatment of choice (5).
• Facial cleanliness and Environmental improvement. While the former two points of the SAFE strategy target treatment of the disease, the latter two focus on prevention.  Facial cleanliness reduces disease transmission. Better environmental sanitation and proper waste disposal helps control the fly population (6).

ONCHOCERCIASIS

Onchocerciasis, also known as river blindness, is the second leading infectious cause of blindness globally.  It accounts for at least one million cases of blindness or severe visual disability.  The majority of those infected live in sub-Saharan African countries.  Onchocerciasis is caused by a parasitic nematode, Onchocerca volvulus.  The worms induce intense inflammatory responses of the skin and eyes, especially when they die (7). The disease is transmitted from person to person by a black fly of the genus Simulium. Repeated bites are usually necessary for infection.  The fly breeds near rivers and streams.    

Onchocerciasis causes inflammation in the eyes (uveitis, keratitis, chorioretinitis, optic neuritis (8)) and the skin (itchy rash, nodules under the skin).  The disease's toll extends into the social and economic realm as well.  Once blind, affected individuals have a life expectancy of only one third that of the sighted, and most die within 10 years (9). There is also a social stigma attached to the skin lesions and disfigurement associated with this disease.

Sclerosing keratitis in Onchocerciasis (image: CEH Journal)

Control:  Onchocerciasis elimination strategy involves vector control and/or large scale ivermectin chemotherapy (10). 

• In terms of vector control, regular aerial spraying of Similium breeding sites for at least 14 years is recommended (until the infection has died out of the human population).  
• A single dose of ivermectin (Mectizan), donated by Merck in the 1980s, is effective for up to a year.  It has the added benefit of helping with intestinal worms, scabies, and head lice, which are common problems in the areas where this disease is endemic. Ivermectin must be given yearly for 12-15 years.

CliffsNotes:  The elimination of preventable worldwide blindness is within sight!

Additional Resources:

• Vision2020
• Unite For Sight: Eye Stats
• WHO: Global Data on Visual Impairment

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