Visual Perception

Of visual perception

There are many assumptions made about a student’s performance on visual perception tests. After all, these tests give norm’ed results which can be helpful in goal making and identifying a potential cause for an academic problem.

But do the results actually reflect visual perpetual skill?

Many factors can hamper the reliability and validity of visual perceptual testing.

  • Visual acuity-is this patient in best correct visual acuity? Have they had an eye exam and been prescribed the appropriate glasses? Do the glasses fit well to allow for the intended benefit?
  • Binocular vision skills?-Poor binocular vision skills can result in double vision and blurred vision up close which can affect the results of visual perceptual testing?

These two factors, when not corrected, make for a “garbage in-garbage out” situation and taint the results of the testing, increasing the likelihood for invalid results in the patient.

Imagine putting a glove on a patient then asking that patient to identify coins that they are holding in the gloved hand. They would have a difficult time doing this, not because of an inability to process the feel of the coin, but because the stimuli to be interpreted is muted. It becomes difficult to process to the correct conclusion when the initial stimulus is faulty.

Behavior and cognition matter too

With best corrected acuity and good binocular visual skills, other factors, such as attention can play a role in visual perceptual testing. Common visual perceptual tests can take as long at 45 minutes of monotonous testing making even the most attentive children bored and possibly affecting results.

Most visual perceptual tests are designed so the child with a visual perceptual problem misses three consecutive items in a section, then advance forward to the next section. The pattern is irregular (child misses one item then 3 correct then misses two items, then one correct) perhaps attention is playing a role in the test results.

Visual Percetual Testing

In my clinic, I do not test visual perception until after binocular vision issues have been corrected and the patient is in best corrected visual acuity.

With these things in place, you will find visual perception intervention much more effective and testing will be more valid and reliable.

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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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Hemispatial Neglect or Field cut?

Field cut vs. Neglect following Stroke

Patients frequently present with a reduced awareness of their affected side following a stroke or brain injury.  This decreased awareness can be a visual field cut or a hemi-spatial neglect or both. Here are some ways to tell just why your patient cannot find half of the world.

Anatomy of field cut vs. neglect

A stroke with neurological neglect is generally associated with middle cerebral artery strokes. These are the most common strokes. The temporal/parietal lobes tend to be affected in these strokes with hemiplegia also occurring.

Generally, a true field cut is associated with a posterior cerebral artery stroke with the occipital lobe being affected. This is stroke is less common. The patient may not have any other symptoms from the stroke.

Functional differences between field cut and neglect

There are many difference functional in patients that have neglect vs field cut.

Patients with a field cuts:

  • show awareness of the field cut, they will tell you “I can see on my right side”
  • They begin compensations quickly
  • Show organized search patterns during cancellations tasks. This mean left to right, top to bottom pattern

Patients with neglect present differently

  • They may not be aware of the field loss and may not be aware of any of the stroke related deficits. This lack of insight to their condition is a big hurdle to treatment
  • They do not compensate well. This is probably related to the lack of insight.
  • Problems with attention in general. Perseveration (unable to shift attention) and distractibility are common.
  • Patient with neglect have difficulty with crossing midline. The eyes may not track across midline to affected side.  Slow saccades to affected side.
  • Poor search patterns on cancellation tests.  These patients randomly search for targets. It is important to watch how a patient completes cancellation assessments as a patient with a field cut and neglect will have similar looking cancellation tests when completed.
  • These patients tend to be oriented (posture and head position) away from the affected side.

Treatment differences of field cut vs neglect

Early resolution of neglect is vital to improving functional status following stroke.  Here are some of my favorite activities for treating neglect:

Field cuts tend to be a bit easier and are discussed here.

Neglect and filed cuts are common consequences to stroke and confusion about just what the patient is experiencing can make treatment difficult. I hope the helps!!!

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Assessment and treatment of Saccade Problems

Saccades – The Quick Movement of the Eyes

Saccades are quick short movements of the eyes. The cavemen used them to quickly assess the environment and see where a threat (or dinner) might be. We use them now for reading, in a series of quick movements and fixation. We also use saccades to update changes in our environment, so they are influenced by peripheral awareness.  They help build a spatial map of the environment. The movements are involuntary and triggered by changes in the spatial environment.

One can look for inaccurate saccades associated with TBI, concussions and strokes. Inaccurate saccades are also associated with most binocular vision problems, like convergence insufficiency.

Measuring the Saccade Problem

Saccades testing can show a therapist overshooting or undershooting, but objective measurement helps set goals.  We use the Developmental Eye Movement test. The DEM provides good objective data concerning eye movement accuracy.

The Developmental Eye Movement test (DEM), is a standardized assessment of saccade accuracy. It is standardized for 5-13 year olds. An adult version is currently being developed and tested, but testing indicates values for a 13 year old are generally valid for an adult. 

The DEM has 4 parts, all involve the timed reading of a list of numbers. The first part is sample of horizontal numbers used to insure the patient can see the text adequately. In the next section, two vertical columns of numbers are read and timed with errors noted.  There are two vertical tests with the times added.

There is the final horizontal test which present horizontal lines of unevenly spaced numbers, which the subject reads while being timed with omissions and substitutions noted.

Times are compared to norms based on age or grade percentiles, They are then used to derive a ratio of horizontal to vertical times that help to identify the cause of the errors, either automatically (subjects ability to call out numbers) versus ocular motor difficulty.

The test is quick and correlates well to reading problems.

The DEM is not perfect as the person must be verbal and recognize numbers. Frequently the task of reading out loud produces a lot anxiety for children that have problems with the task also. Observation of behaviors during the DEM and the reading can also give some insight.

The tester should note…

  • does the child hold the material very close to his face ?
  • …or far?
  • does he squint or rub his eyes during the assessment?
  • does he use his finger to follow the letters?
  • does he move his head during testing? This is very telling as using head movement rather than eye movement slows fluency and saccade accuracy.
  • are there long pauses at the beginning of a new as the child attempts to find the correct line
  • does accuracy of words get worse as the reading continues or does the child use context to fabricate the end of the sentence?
  • Does he turn his head to the left or right?

Following reading, I ask some specific questions if the child had difficulty to help identify what the child is seeing. These questions sound crazy, but make perfect sense to child with saccade or near vision problems.

  • do the words move when try to read them?
  • do you see double?
  • do they blurry then clear then blurry?
  • do they appear to float?

Sometimes the children have a hard time describing just what they see. Parents are often very surprised at the responses to the questions. The child did not know that everyone does not see that way.

Treatment

The treatment for saccade problems, like all ocular motor problems, assumes the child is in best corrected visual acuity.

I also use a sheet or graph paper with random dots for the children to draw small , vertical lines through.

The Hart Chart Decoding activity is also a good task.  This task has a grid of letters on one sheet and themed (there’s SpongeBob and Sports, and others)secret messages on another. Each letter in the massage corresponds to a column/row combination that the child counts to find the letter. Initially the child is allowed to use his finger to help count the rows and columns, but as they get better at the task, the finger is no longer allowed.

EyeCanLearn.com   is an amazing website with vision games and printable with saccade activities.

Having a child read the first letter of words in a paragraph can improve saccade accuracy as well simple vertical strips of letters that can be more further apart. The therapist can add a metronome to these tasks to help increase the pace.  Add balance to these task to increase the challenge of the brain and visual system.

Saccade strips are two strips of paper with vertical letters. The patient reads the letters left to right and top to bottom. Start with the strips close together then separate them as the the patient gets quicker. Remember to keep the head still, even if the therapist has to help!

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Assessing visual fields

Assessing visual field in the OD office

Heres is how visual fields are assessed in the optometry office.

humphery

This is Humphery visual field tester. The test is generally done monocularly first. The patient places their face on the chin rest and clicks a switch when they see a light in the field. The device monitors fixation during the test and lets the tester know if the patient “cheated” by moving their eyes. Binocular testing may be done separately if needed. During this, the patient is allowed to move their eyes.

The results are very precise with even small peripheral reductions in field picked up. But there are some limitations. The patient must be able to respond in a timely manner by clicking a button, so motor response time and even posture can affect the ability to perform testing on this device.

Confrontation Field Testing

Visual field testing by confrontation is a way to perform visual field testing in clinic without the computerized tester.

In the test, the therapist sits in front of the patient presenting fingers in each field with patient reporting the number of fingers up. This is done for each eye.

It is important to present stimulus in all four quadrants of the visual field. Results of this can be correlated with other visual cancellation tests.

There is also campimetry which uses a specialized disk with different fixation points.

photo (15)

With the campimetry device shown above, the patient fixates on numbers on the disk and reports if they can see the middle spot.

There is also a web-based Damato Multifixation Campimeter test for visual fields that is  free.

Types of visual field cuts

Homonymous hemianopia is the most common visual field loss following a neurological event. This is lose of half of the visual field in each eye . These can affect right or left visual field (generally contralateral to the affected side of the brain, left brain right field cut). These tend to be associated with tempro-parieital lobe or occipital lobe damage. Left side field cuts tend to have a neglect aspect associated with them. The patient may not even be aware of the left sided vision loss making treatment of the field cut more difficult. Right sided field cuts tend to be more occipital lobe related with the patient showing improved awareness of the loss and improved recovery. Here is what it would like using a Goldman 30-2 test. This test looks at each eye separately and requires fixation.  The similar patterns in each eye tells us this a visual pathway problem, not and orbit problems.

visualfields-page-003 visualfields-page-002

 

Here is what it looks like on the Easterman Binocular Test. This test uses both eyes, allows for eye movements and is a more functional look at patient useful visual field.

visualfields-page-001

Quadrantanopia is loss of vision in a quadrant of the visual filed (upper right, lower right, upper left, lower left). It can also be homonymous (in both eyes) and may be described a superior right homonymous quadrantanopia.

quad

This is what that might look like.  They might also be bitemporal ( in the lateral fields of both eyes) or binasal (in the medial fields of both eyes)

A central scotoma is is loss of the central visual field and is associated with age-related macular degeneration.

visualfields-page-005 visualfields-page-004

 

 

Visual field treatment

Their are two common strategies behind improving functional status for patients with a field cut. We tend to use a combination of both at the optometry office.

The most common technique is to improve scanning strategies by having the patient perform scanning tasks into the area of the field cut. This can be done with any number of devices such as a Dynavision or a Sanet Vision Integrator. Both of these devices, and others, present random targets in a field with the patients ability to find these targets being timed. With either of these, patient practice scanning strategies which improves their awareness of the field and improves their time locating targets in the missing field.

In optometry, we have other tools available. We can use field expansion systems such as the Peli-lens or Gottlieb Field awareness system. Both of these involve the application of small pieces of prism to the lens of the patients glasses. These small strips move visual stimuli into the patient’s existing field “reminding” them to look to the affect side.  They cue the patient to scan into the missing field, something like a warning system.

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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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