What is Convergence Insufficiency?
Convergence insufficiency (CI) is a condition affecting the coordination of the eyes, making it hard to focus on nearby objects because the eyes tend to drift apart. Typical symptoms of CI include issues like eye strain, double vision, headaches, blurry vision, printed words appearing to move while reading, and trouble understanding what you’re reading. Other symptoms you might notice after a brief spell of reading or after focusing on something up close for a long time include feeling sleepy and having trouble concentrating.
What Causes Convergence Insufficiency?
Vergence eye movements refer to how your eyes move together in response to something you see. This can involve your eyes either moving towards each other (convergence) or away from each other (divergence). When someone has what’s known as convergence insufficiency, their eyes don’t team up properly in near vision tasks. This issue is thought to be a result of imbalance in the factors that drive these eye movements.
There are four factors that influence these movements, often referred to as Maddox components of vergence: tonic vergence, proximal vergence, fusional vergence, and accommodative vergence.
Tonic vergence is like your eyes’ default setting when they aren’t focusing on anything. The natural position of your eyes determined by tonic vergence may not align with the target your eyes are trying to fixate on, leading to a condition known as phoria. A phoria is like a misalignment in your eye’s aim, only noticeable when one eye is closed.
Next, proximal vergence is how your eyes react to perceived distance or depth. This results in large shifts in your gaze and leads to most of the changes in your eye’s focus. As your eye’s focus settles after these big shifts, fusional vergence takes over to maintain the aim with small adjustments. Fusional vergence uses feedback from the difference in images seen by each eye to fine-tune this alignment.
Lastly, accommodative convergence describes how your eyes’ physical reaction to near vision tasks is linked to the changes your eyes undergo to keep things clear.
In the case of convergence insufficiency, treatment is focused on improving tonic and proximal vergence through specific therapies. These involve exercises to make these components better at their job. On the other hand, the fusional and accommodative vergence components are considered untrainable.
Risk Factors and Frequency for Convergence Insufficiency
Convergence insufficiency, or the inability to maintain proper eye alignment when looking at nearby objects, affects a variable percentage of school-age children, estimated at 2% to 13%, but is cited most commonly around 5%. This condition is found in about 1 out of every 6 people older than 19. There’s not enough research available to compare these rates effectively. The reason for the shortage of information on convergence insufficiency in people with presbyopia, or age-related difficulty in seeing close objects, can be attributed to how presbyopia impacts the ability of the eyes to converge, and a natural tendency of people turning more exophoric (a tendency for eyes to drift outward) with time. As of now, there doesn’t seem to be a direct connection between gender and convergence insufficiency, but a family predisposition has not yet been thoroughly studied.
Signs and Symptoms of Convergence Insufficiency
Convergence Insufficiency (CI) is a condition that can be definitively diagnosed by considering several factors during a physical examination. These factors are:
- Exophoria, a condition where the axis of vision veers off to the side, that is more pronounced when looking at close objects compared to far objects. This deviation should be at least by 4 prism diopters.
- The Near Point of Convergence (NPC), the point at which eyes can no longer maintain binocular vision while following an object moving towards the person, should be 6 cm or more.
- A lack of Positive Fusional Vergence (PFV), which is the ability to maintain binocular vision as an object moves closer. If there’s not enough PFV to meet Sheard’s Criterion, it could indicate CI. Sheard’s Criterion states that the reserve fusion (the ability to maintain single vision) must be twice the demand.
- Patient symptoms should match those in the Convergence Insufficiency Symptom Survey (CISS) test.
Exophoria refers to the alignment of the eyes where they naturally, at rest, deviate outward, while esophoria is the alignment where eyes deviate inward. The alternating cover test is used to determine this alignment.
The Near Point of Convergence (NPC) measures the ability of the eyes to maintain single vision as they follow an object moving in towards the person’s nose. This can be measured using different targets like an accommodative target, a penlight, and a penlight with red/green glasses.
Positive Fusional Vergence (PFV) is a measure of how much the eyes can converge without double vision setting in. It is measured in prism diopters and represents how much the eyes can turn inward to maintain single vision. Differences in measurement methods might result in slightly different results, but they are typically consistent within 6 prism diopters.
The Convergence Insufficiency Symptom Survey (CISS) consists of 15 questions relating to symptoms of CI. Answers are selected from 5 possibilities, ranging from “never” to “always” and are given scores from 0 to 4. The total score can help determine whether a patient likely has CI, especially if the symptoms relate to close-up tasks like reading.
Testing for Convergence Insufficiency
To diagnose convergence insufficiency, a standard eye exam that tests binocular vision, or the ability to focus both eyes on an object, is performed. The precise diagnosis is confirmed by using a ‘cover test’ to measure a person’s ‘phoria’, which is the tendency of one eye to drift when the other eye is covered. Also checked are the ‘Near Point of Convergence’ (NPC) – the closest point that a person can maintain clear, binocular vision, and ‘Positive Fusional Vergence’ (PFV) – the ability to keep the eyes properly aligned. These tests can be performed in open space or behind an instrument called a ‘phoropter’.
Treatment Options for Convergence Insufficiency
Office-based vergence therapy (OBVT) is often the first choice for treating children with symptomatic Convergence Insufficiency (CI). CI is a condition that makes it difficult to keep both eyes working together when focusing on a close object. OBVT, combined with practices at home, has been shown to be more effective at reducing symptoms and improving clinical signs compared to other treatments, such as pencil push-up exercises at home, computer-based exercises, prism glasses, or even surgery. Approximately 75% of patients have been observed to benefit from OBVT, making it the only treatment found to be more effective than a placebo, or a treatment designed to have no effect.
Typically, OBVT involves a weekly office visit that lasts about an hour where patients work with a trained therapist on various exercises. These can include exercises using Brock strings, barrel cards, vectograms (a type of tool used in vision therapy), and eccentric circles free-space fusion cards, which all aim to train the eyes to work better together. After each visit, the patient is given instructions for exercises to do at home. These exercises usually take about 15 minutes a day, five days a week. Through these measures, OBVT has shown a significant improvement in reducing CI symptoms, enhancing the close point of convergence (NPC – the point at which eyes can no longer focus together), improving stereo acuity (depth perception), and expanding positive fusional vergence (PFV – the ability of the eyes to turn inward together).
While OBVT may not directly treat learning disabilities, it has been suggested that by relieving symptoms of CI, it could reduce obstacles to better academic performance. This is because CI can make tasks like reading difficult, so managing this condition could improve a child’s comfort and ability to focus in school.
What else can Convergence Insufficiency be?
When trying to diagnose certain eye conditions, doctors often need to rule out several possibilities. These include:
- Exotropia (XT): This is when one or both eyes turn outward, away from the nose. Doctors identify this condition by performing a test where one eye is covered while the other one is observed. If the uncovered eye moves inward, this suggests Exotropia.
- Basic Exophoria: This condition causes your eyes to drift outward when you’re not focusing on something. It’s diagnosed when both the near and far vision are drifting outward to the same extent.
- Acquired Exotropia: It mostly happens in adults, unlike XT which is often present at birth or early childhood.
- Diplopia: This is a condition where a person sees two images of a single object. It is commonly known as double vision.
- Dorsal Midbrain Syndrome: This is a neurological disorder that affects eye movement and pupil size.
- Internuclear Ophthalmoplegia: It hinders the movement of your eyes towards each other (like when you’re looking at your nose), or moving up or down.
- Myasthenia Gravis: This is an autoimmune disease that causes weakness in the skeletal muscles which control movement.
- Oculomotor Nerve Palsy: It’s a condition that results in eye muscle weakness causing droopy eyelids or problems with eye movements.
- Thyroid Eye Disease: This condition, which often occurs in people with thyroid problems, can cause the eyes to protrude or cause double vision.
To correctly diagnose the condition, doctors would conduct a variety of tests based on these possible diagnoses.
What to expect with Convergence Insufficiency
Patients diagnosed with convergence insufficiency (CI) generally have a good outlook. Research reveals that after 12 weeks of in-office and at-home treatment, about 73% of patients showed improvement in CI symptoms and the ability to bring the eyes together. Even after halting the treatment for a year, most patients remained symptom-free.
However, the prognosis can be affected by the availability of offices offering these therapy services and the cost of treatment. It’s worth noting that if CI occurs after a concussion or other trauma, recovery might take longer.
Possible Complications When Diagnosed with Convergence Insufficiency
While not receiving a diagnosis or treatment for convergence insufficiency (CI) doesn’t pose a major health risk, it’s important to note that the symptoms associated with this condition will continue if left untreated.
Preventing Convergence Insufficiency
It’s important for patients to understand how effective vision therapy can be and what results they can expect. However, one thing to keep in mind when considering this treatment is that most insurance companies do not cover vision therapy costs, which could mean patients have to pay for it themselves. Therefore, patients need to be aware of the potential costs when deciding on their treatment options.
