Convergence insufficiency (CI) is a leading cause of uncomfortable vision. Also known as under-convergence, it can result in eyestrain, double vision or headaches. Some people with convergence insufficiency have no symptoms because they have learned to adapt - they may move in close to their work and tilt their head to the side, they may cover one eye when reading, some move further away from their work, and others adapt by staring out the window (avoidance),
Convergence insufficiency in a fairly common binocular (eye-teaming) visual disorder where the eyes do not work easily together as a co-ordinated team with near tasks. Instead of converging, the eyes tend to move out. To prevent double or blurred vision, the person has to exert excessive effort, which can lead to a number of frustrating symptoms that interfere with the ability to read, comprehend and work comfortably at near.
Convergence insufficiency can be the result of not having developed this skill, or a decrease in function due to the skill not being adequate for the required work load.
Signs and symptoms of CI:
- Blurred near vision
- Double vision
- Reduced concentration
- Short attention span when reading
- Reduced comprehension
- Squinting, rubbing, closing or covering one eye
- Sleepiness during near activities
- Words appear to move, jump, swim or float
Treatment of Convergence Insufficiency
The CITT scientific study showed that children responded quickly to in-office Vision Therapy with homework (15 min a day, 5 days a week). 75% achieved either full correction of their vision or saw marked improvements within 12 weeks.
Stress-relieving lenses and / or prism lenses can be prescribed to decrease some of the symptoms of convergence insufficiency.
Convergence Excess (or over-convergence) occurs when the eyes posture is closer in than required for near vision tasks (esophoria at near). For example when reading we would ideally aim and focus the eyes together on the words on the page, in cases of convergence excess the eyes meet to aim at a point closer in than the page. Often individuals can be noted to work closer to the page when this occurs.
This excess of vergence may be associated with an Accommodative Insufficiency. The eyes battle to focus accurately, so in an attempt to compensate for this, the eyes over-converge. This leads to a mismatch between vergence and focus, thus affecting binocular vision accuracy.
Convergence excess can also be associated with nearpoint stress.
With convergence excess, headaches, dizziness and / or nausea can result when doing near work for a while. This can lead to an inability to concentrate and even irritability.
Although some children with convergence excess may tire with near visual tasks and may even avoid them, there are others that are excellent and avid readers.
Management of convergence excess requires either therapeutic spectacle prescription lenses (plus-powered stress-reducing lenses) and / or Vision Therapy, to enhance the focus efficiency, thus reducing the need to pull the eyes closer in.
Usually over time prescriptions and wearing time can be reduced.
Without effective management, myopia (shortsightedness) can often result in later years, such as in high school.
Eye movements are required for locating an object in space, following an object in space, (like a ball), and for tasks such as reading.
Deficiencies in ocular motilities have been associated with learning difficulties.
When reading, there are two types of eye movements that are important, pursuits (tracking) and saccades.
Pursuits: ability to follow a moving target or lines of print smoothly and accurately.
Saccades: ability to make rapid accurate movements of the eyes from one target / word to another, and from the end of one line to the next.
To obtain the maximum amount of information in the shortest time with the least effort, our eyes must be able to smoothly follow a moving object, make continuous adjustments in the positions of our eyes, and shift our focus quickly and accurately from one object to another.
For efficient reading, tracking needs to be smooth and accurate with only eye and no head movements.
Inadequate eye movement control may lead to loss of place when reading or copying from the board, skipping or repeating words or lines, the need to follow printed words with one’s finger, and difficulty in sports involving eye tracking.
Accommodation (Focusing) Difficulties
The continued use of vision at near distances requires effort. A significant portion of this effort is due to maintaining an adequate focus at the near distance. A child needs to learn control of their focusing system so that they use the proper amount in order to carry out desk work tasks without fatigue.
Accommodation is the ability to focus clearly on near objects or words. Those with difficulties may:
This causes reduced ability to focus clearly for near work and sustain that focus for an extended period of time, as is required in reading. Near work is very tiring and it may be noticed that it is easier to read or work at the beginning of the day than the end of a day, or at the beginning of a book than the end of a book.
Over-accommodation – Accommodative Excess:
More focusing is exerted than is necessary and this can become exhausting. People with accommodative excess often notice that after periods of near work they may battle to see in the distance.
Have inflexible accommodation - Accommodative Inflexibilty or Infacility:
The inability to make rapid and accurate changes in focus from near to far and vice versa, as is required for copying tasks (especially from the board). Copying tasks may therefore be slower or have more errors.
Inadequate focusing ability can lead, to requiring excessive time to complete assignments, blurring of print, fatigue, headaches and eye-aches, daydreaming, avoiding close work and poor comprehension.
Visual Efficiency and Reading
Children (& adults) are expected to spend many hours a day engaged in near visual tasks. This requires comfortable vision and the ability to sustain that focus for adequate periods of time. On top of this are the voluntary near visual tasks on tablets, phones and computers.
To be able to read easily, our eyes and brain need to:
- fixate on the words
- focus and make them clear
- co-ordinate the eyes to
- work together as a team
- track accurately across a page.
Lastly we need to be able to interpret or comprehend what we have read.
When we are efficient at reading we manage all of the above with ease, but many children have not yet built these skills required for sustained near work, or the skills may 'break' down due to eye stress.
Visual efficiency problems can interfere with higher level visual processing in the brain, as well as reduce reading speed, fluency and comprehension.
The longer a child with visual efficiency problems reads, the harder it gets, often resulting in difficulty sustaining attention in the classroom and during homework.
Signs of Visual Efficiency Problems
holds book or paper too close
frequently rubs eyes during reading or homework
loses place or rereads lines when reading
omits or substitutes words
uses finger to read
homework is slow
reading comprehension decreases with time
slow reading speed
tilts or turns head
closes or covers one eye
squints or blinks during reading
red or watery eyes after reading
crossed or drifting eye
clumsy, poor depth perception
Symptoms of Visual Efficiency Problems
headaches, worse later in the day
eyestrain, sore eyes
tired, burning or itchy eyes during reading
words move or run together when reading
blurry vision when reading or copying
A vision assessment by a Behavioural Optometrist is recommended to address these difficulties with lenses, prism and / or vision therapy.
Amblyopia is the medical term used when the vision in one of the eyes is reduced. This is not a problem with the eye but a difficulty with binocular vision - the two eyes working as a team. The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye (suppressing the vision in the amblyopic eye).
This condition is also sometimes called a lazy eye.
You can also get binocular amblyopia where the brain suppresses the vision in both eyes, usually due to a high refractive error (prescription) in both eyes.
Amblyopia is fairly common:
- It accounts for more vision loss in the under 45 year old population than ALL other ocular problems combined
- It occurs in about 2 to 4% of people
Amblyopia is treatable:
- With glasses or contact lenses and vision therapy, we can often prevent or reverse the impairment
- The goal of treatment is to maximize clear vision and maximize binocularity (the ability of the two eyes to work together as a team)
Amblyopia often goes undetected until a child has an eye test or eye screening.