Legally Blind

“Pt is legally blind”

What does it mean when a patient is legally blind? Technically, to be legally blind, ones visual acuity in best correction is less than 20/200. Here is a great simulator to help one imagine what that would look like. But functionally, how does does being “legally blind” affect the patient?

We need more information

A patient can be legally blind for several reasons. Cataracts, macular degeneration, and diabetic retinopathy all leave a patient with reduced visual acuity but leave the patient with very different residual vision and different functional problems as a result of this condition.

A patient with macular degeneration will have reduced vision in the central field affecting reading and the ability to see faces like the below picture.

can-macular800

Glaucoma will result in reduced peripheral vision that could affect balance and peripheral awareness.

Vision-With-Glaucoma-2

With retinopathy, the areas of reduced vision may be more random and will have different affects depending on just where these damaged areas are.

retinopathy

How bad is it?

Is the patients vision truly 20/200 or is it worse. Visual acuities can be 20/400/ or even 20/1000. A patient that was 20/400 and now is improved to 20/200, will find their vision to be much improved and very happy about that. A patient may have an acuity described as “nlp” or no light perception. In this case, the patient would see nothing but blackness.

Is the described acuity with glasses in place? A specialized low vision refraction from a low vision optometrist could get the patient improved visual acuity optimizing their residual vision.

Ask the Right Questions

Why does this patient have low vision? How bad is there acuity? Are they wearing the best possible glasses for their diagnosis? With this information, we will be better able to assess the functional implications of this patients reduced vision and come up with the most effective strategies to keep them independent and safe.

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“Can eye movement problems be related to torticollis?”

Ocular Torticollis

Torticollis can be caused by several things. Delays or problems in the integral development of muscle tone, the vestibular system and propreioception can all be causes.  Eye alignment, nystagmus and acuity problems can also affect head position.  When vision is the primary cause for torticollis, it is referred to as ocular torticollis.  One study found 20% of torticollis related to ocular problems. (1)

Eye alignment

Head tilts and head turns are common signs of eye alignment problems. Deviations between eyes in the horizontal plane (hyper- or hypo- tropia) can cause head tilts in the brains attempt to see a single, fused image. Head turns (rotation) to right or left can be caused by strabismus (eso- or exo- tropia). Again, the brain turns the head in attempt to not see double. Other more complex movement patterns can also cause head position and posture problems.

Nystagmus

Nystagmus is an involuntary movement of the eyes. This is generally associated with a neurological problem. They can be congenital or acquired. Many times, patients with a nystagmus will turn their head to find the point at which the nystagmus stops. This point, called the “null point” allows for improved vision for the patient.

Acuity problems

Astigmatism, a condition in which the eyeball is not perfecting round but more football shaped, can also cause visual acuity problems that might facilitate a head tilt in order to improve vision.

Eye Exam

Every child should have their first eye exam at 6 months (per AOA recommendations). A through eye exam that includes a binocular vision exam would find eye alignment problems most likely to cause ocular torticollis.  If treating a patient with torticollis of unknown cause, a binocular vision exam could be helpful in identify the problem. Frequently, prisms and lens can be prescribed that can help reduce the torticollis.

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Worth 4 Dot

Worth 4 Dot

The worth 4 dot is simple tool for assessing suppression and fusion. The results oworth4dotf the quick assessment can give us clues to the function of the eyes. The worth 4 dot (W4D) test is is made up of a pair of red-green glasses and light with 4 dots, 2 green, one red and one white.

The patient puts on the glasses and the light in placed near (40cm or less) and asked how many lights they see.  It is then moved to distance (1 M) and asked once again how many lights are seen.

W4D Responses

There are 4 appropriate responses. Other responses should be considered a failure of the patient to understand the instructions.

  1. 4 lights, near and/or far indicate using both eyes. I will ask if the lights are moving or not to see if the fusion is steady.
  2. 3 lights or two lights- three light indicates suppression of one eye. Which eye depends on the red green arrange of the particular test one is using. They may suppress at near or far or both, so an answer of 3 close and 2 far would be appropriate.
  3. 5 lights- a response of 5 lights indicates the patient is having double vision at the range. It may be near or far or both.

The W4D is usually the first test I do as it gives me early clues what to look for as I begin looking at eye movements. This test can also indicate how a patient may do on stereopsis testing as suppression of of an eye could me reduced stereopsis.

Getting a Worth 4 Dot

Worth 4 dot is available from Bernell.com. There are several version but the idea is the same for all.

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Vision Resources for Occupational Therapist

Vision Rehab Resources for Occupational Therapists

It has been my pleasure to share information with OT students, PTs, SLPs and anyone else that will listen. It is my belief that information should be free and accessible to all. It is very exciting working in a unique OT area where there is so much to share.

Where can an occupational therapist learn more about vision rehab??

My first course was Mary Warren’s Vision Processing Impairment . This teaches the basics of eye movement assessment, visual field treatment and puts it in a nice functional context. It was a great course that got me much more aware of the visual problems neurological patients face and how to fix them.

If Mary Warren is the OT reaching towards optometry, Mitchell Scheiman is the optometrist reaching out to OTs. His courses and books are specifically teaching OD skills to OTs. I refer to this book frequently and it needs to be on more OT’s shelves.

Dr Scheiman also teaches a two day course for therapists that discusses the mechanics of vision the first day and interventions on the second. He is also on the faculty of Salus University’s post professional OTD program in Vision Rehabilitation.

There is also the course that I teach for PESI Education on assessment and treatment of binocular vision disorders.

Vision Rehab articles that are important for OT’s

Here are some of my favorite journal articles.

The Convergence Insufficiency Trial is important. It proves that that in-office treatment of convergence insufficiency works.

A systematic review of what works for treating visual field defects.   

The website of the Neuro Optometric Rehab Association is a great resource for information on treating the visual problems of stroke TBI and concussion.

For the EI therapists, here is a nice piece on the development of the visual system in infants.

The Journal of Behavioral Optometry and Optometry and Visual Performance are located at the Optometry Extension Program Foundation website. Complete article are available. There is a great bookstore too!

Vision Rehab and Occupational Therapy websites

Eyecanlearn.com has great activities.

Hartchartdecoding has a fun saccade activity.

Michigan Tracking is a tracking/Saccades task.

Learning Works for Kids is a great website that has search engine to find apps that address specific skills a for specific ages .

LittleBearSees.org offers great information about cortical visual impairment for therapists and parents alike.

Who cares about eyes anyway?

As one discovers more about vision it becomes obvious that as OTs we must be evaluating vision better. Eye movement accuracy affects balance, academic performance and overall development and it can be improved.

Visual processing, balance, gross motor development and reading cannot be successfully treated while a child has poor eye movements! It is like testing for sensation while a patient has gloves on.

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Balance and Vision

 

Two Visual Pathways

The focal, central or Parvocelluar visual system is called the “What” vision system. It is responsible for object identification. It allows us to focus on a specific object in the visual field. This information is interpreted in the occipital lobe.

The ambient/peripheral or Magnocellular visual system is the “Where” system responsible for spatial information, balance, coordination and peripheral awareness. This information is shared with the occipital lobe, in addition to links to the cerebellum and balance areas of the brain. Functional MRI shows this information actually reaching 99% of the cortex. Using ambient vision, we can automatically change our posture and gait to walk uphill or protect ourselves from falling over as someone bumps into us.

Functionally, these two systems allow use to look at the road ahead of us (focal vision) and be aware of the car to our left(ambient). It also allows us look at the TV but be aware of where the door in the room is. It allows us to be focused on a word in reading, but still make accurate saccades to the next word.

Notice what happens to the people attempting to walk through the tunnel.

Notice how the people in the tunnel are leaning to one side. The tunnel walls have confused their ambient vision system and affected the gait and balance.

A tool for rehabilitation…

Frequently this system can become faulty following a neurological event. In a condition called Post Trauma Vision Syndrome”, patients become over-centrally focused. This is seen clinically as decreased balance, decreased reading accuracy and poor spatial awareness a midline shift or toe/heel walking.  The patients also report becoming “over-stimulated” by visual information.   A visual field done a patient with this condition might look like this

peripheral loss

This is one eye, but the other may look the same. Notice the reduced periphery that might not show up in typical in-clinic screening of visual fields.  This visual field test is called a Goldman 30-2 and is done on each eye.  It  should be a standard part of the assessment of all of the post-TBI/CVA patients.

Improving Ambient Visual Function

To improve function of the ambient system, binasal occlusion may be added to a patients glasses with or without mild base in prisms.  How does this help?

A person that is over-centrally focused has a difficult time seeing the entire word. They tend to see letters rather than the whole word which greatly reduces reading fluency and comprehension. Saccades also become less accurate due to the decreased awareness of the line of text  making the person lose their place frequently.

This can also improve posture and gait. As the brain becomes more aware of the ambient visual system, it is better able to correctly adjust gait and posture. Remember the tunnel?

Optometrists that offer this type of service are involved in neuro-optometry. The organization is called the Neuro-Optometric Rehabilitation Association. This is a multi-disciplinary organization that was started by ODs who wanted to understand brain injury better and exchange information with other providers of care in the  TBI community like OTs and PTs. There is a provider list on their website to help you find a NORA optometrist in your area.

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How do we see up close?

The Near Vision System

“I can’t see the board” is a common reason children come for their first eye exam. But problems seeing close are more closely related to academic success then distance vision problems. With more computer use, and frequent changes from looking at the board to a notebook, school can be a workout for the near vision focusing system.

Watering eyes, rubbing eyes, and headaches are early signs of discomfort with near vision. These soon lead to difficulty reading and falling grades. The child may also show avoidance behaviors when trying to do school work as it is physically painful to see up close. But worst of all, the child may not say anything at all, as they do not know that their vision is not working right. Typical school vision screenings may miss the problem also.

The near vision system is a balance of several processes…

So what are the mechanisms involved in near vision focusing??

There are 3 processes involved in near vision focusing. Optometrists call it the near vision triad.

1) Pupil constriction- as an object moves closer, the pupils constrict to improve focusing of incoming light to the fovea. The fovea is an area on the retina with the highest density of light receptors. This area gives us our most acute vision.

2) Accommodative Convergence– as an object moves closer, the eyes move nasally to keep the object on the fovea. Both eyes should smoothly convergence together as the target moves closer.

3) Accommodation– lens of the eye focuses- In humans under 40 years old, the lens of the eye changes focus as objects move closer. This is much like a camera lens. As children, the lens is very flexible allowing for a large focusing range. After 40, the lens tends to become less flexible, so we end up wearing bifocals.

Here is a great example of it all working together:

As something moves toward us, the brain adjusts with the right amount of accommodation and convergence, in addition to the pupil constriction. The amount of both convergence and accommodation can be calculated by the the optometrist to come up with the AC/A ratio. This number gives the optometrist clues to the efficiency of the system.

What does it look like when it does not work right??

 

In some children, both of the lenses tend to over focus making them work very hard to maintain focus of near vision objects. The optometrist can assess this and improve it with glasses also. The child with accommodation problems will be rubbing his eyes during close work. He might complain of headaches when reading. He may show poor comprehension and poor reading skills. Or he may not show any of these signs. He may have a short reading span, or have a difficult time hold still, perhaps mis-identified as ADD.

Without enough convergence, the muscles that focus the lens tire as they work to keep near things in focus. They cause similar problems as poor accommodation and frequently a child will has both. This multi-process system is very flexible in children. Therefore, some children have problems coordinating the system. The condition is called convergence insufficiency and is a common vision problem in children. There will be a separate discussion of CI later.

This is easy to screen using the Near Point Convergence test .  

Only the optometrist can identify these problems, but as therapists, teachers and parents, we need to be aware of the signs of near focusing problems. The Convergence Insufficiency Symptom Survey  is a well researched tool that is very effective in identifying patients with possible CI.

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Assessing Eye Movements

Assessing Eye Movements

As therapists, we should assess EOM or extra ocular movements, the optometry term for eye range of motion. Looking at these movements can give information about brain and cranial nerve function as well as help identify limitations on functional tasks like reading .

Eye movements use similar names as other movements with inferior being downward, superior being upward, lateral movements described as duction with adduction  moving toward the nose (nasal)and abduction away from the nose (temporal). Optometry also has vergence, which is the movement of both eyes toward the nose (convergence) or away from the nose (divergence). Smooth convergence and divergence is important in the near focusing system.

With the patient seated and focused on a point about 40 cm away, the eyes should be still. This is called fixation.  A small rhythmic movement, called nystagmus, is a sign of a central nervous system problem. It is often associated central nervous system problems like Multiple Sclerosis.  It is a frequent early sign of the disorder. It is also closely linked to the vestibular system and the patient might report dizziness. When congenital, the brain adjusts to movements as in the video below.

Congenital Nystagmus

9 points of primary gaze are assessed having the patient follow a point to left/right/up/down/up left/low left/upright/low right. The eyes should move together through all of these points.

9points of gaze_normal_540

Assessing Cardinal Gaze

Each of these movements is control by cranial nerves and failure of an orbit to move in a direction could be a sign of cranial nerve problem or a muscle problem. This occurs frequently as a result of brain injury or trauma to the eye or orbit. This can also be congenital. This eye turn is referred to as a strabismus.  Strabismus causes diplopia or double vision. They can be improved with prism by an optometrist or possible surgery to shorten or lengthen the muscle by an ophthalmologist.

To assess convergence use the near point convergence test. In this assessment, a target held about 1 meter from the patient’s nose and slowly brought toward the nose. The patient is instructed to tell the tester when they see two of the targets. The target should get to within 6cm to be considered “normal”. The test should be done 5 times with the final result be the distance at which the child saw double on this final trial. Reduced convergence is not uncommon following brain injury and stroke and is linked to reading difficulty in children. Reduced convergence makes near vision tasks more difficult as the brain has work harder to see clear. This is called convergence insufficiency. The condition even has its own  website.  This has also become more common in adults we put demands on our near vision system with increased use of smart phones.

Near Point Convergence test

In tracking, the patient follows a target in a circular pattern, both clockwise and counter-clockwise making 2 revolutions each direction. Tester notes the number of fixation loses, the smoothness of the movements and the ability of the eyes to move together.

Eye Pursuits or Tracking

Saccades are very quick eye movements of very short duration. It is a series of fixations and saccades that allows one to read efficiently. Inaccurate saccades are frequently associated with poor reading skills. Optometry can improve saccade accuracy and improve reading .  Saccades testing has the patient fixate from one point to another with the tester noting adjustments following the fixation and if the eyes move together. We can perform the Developmental Test of Eye Movement  or the King-Devick for objective testing of eye movement.  Saccade accuracy can be an indicator for possible concussion as well.

Saccade testing

Abnormal EOM tests should be referred to optometry for complete assessment. They are often related to central nervous system problems, cranial nerve palsy’s or cerebellar problems. They are common in stroke and brain injury survivors and cause decreased reading ability, balance and depth perception.  Patients frequently suffer with eye movement problems for years following a stroke or brain injury, but with the right tools, they can be improved improving a patient’s functional ability.

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