|Year : 2016 | Volume
| Issue : 2 | Page : 88-95
Sanitha Sathyan, NF Beena, Dhanyasree Nair, Angel M Varughese
Department of Ophthalmology, Little Flower Hospital and Research Centre, Angamaly, Kerala, India
|Date of Web Publication||20-Mar-2017|
Department of Ophthalmology, Little Flower Hospital and Research Centre, Angamaly, Kerala
Source of Support: None, Conflict of Interest: None
Convergence insufficiency is a common disorder of binocular vision in children and young adults. Common symptoms include eyestrain, headache, blurred vision, double vision, etc., Diagnosis of the condition involves a battery of tests for assessment of refraction, convergence, and accommodative functions. Management involves proper refractive correction, prism, and vision therapy. This review stresses on the systematic evaluation of this condition and the common treatment strategies employed.
Keywords: Convergence insufficiency, clinical features, management
|How to cite this article:|
Sathyan S, Beena N F, Nair D, Varughese AM. Convergence insufficiency. Kerala J Ophthalmol 2016;28:88-95
| Introduction|| |
Convergence insufficiency (CI) is a common dysfunction of binocular vision. Scheimann et al. defined CI as a condition characterized by exophoria greater at near than at distance, a receded near point of convergence (NPC), and reduced positive fusional vergence (PFV) at near and a low AC/A ratio. Various investigators have reported a prevalence of 4.2–6% for this condition.,,,
Common symptoms of CI include eyestrain, headache, blurred vision, double vision, difficulty in concentrating, moving prints, and loss of comprehension after short periods of reading or performing near activities. Thus, CI may affect academic performance and health-related quality of life.
Treatment modalities commonly prescribed for CI include home-based pencil push-ups, prisms and home-based/office-based vision therapy. The Convergence Insufficiency Treatment Trial (CITT) was the first multicentric randomized clinical trial conducted to evaluate the effectiveness of different forms of active therapy treatments for symptomatic CI in patients 9–17 years of age. As per the CITT, home-based pencil push-ups was found to be the most commonly prescribed treatment by both ophthalmologists and optometrists for symptomatic CI. However, office-based vision therapy was found to be more effective than home-based or placebo therapies. Both performance-related and eye-related symptoms improved after successful treatment.,
Clinical features of convergence insufficiency
Symptoms of CI are highly variable and are usually inversely related to the severity of CI. Most symptoms of CI are directly related to reading or other near tasks, and can be aggravated by stress, illness, or lack of sleep.
Headaches – occur after long periods of reading and are usually frontal or periocular due to tsustained effort to increase fusional convergence during near tasks.
Asthenopia – result from the increased convergence and/or accommodative effort needed to maintain convergence.
Difficulty with reading or near tasks – commonly described as intermittent blurring of words, moving prints, and difficulty with concentration/comprehension. Some patients tend to avoid the near tasks because of these symptoms.
Diplopia – in CI, the images are horizontally displaced. Many patients experience difficulty deciphering the double images and complain of blurred vision. Monocular closure may be attempted by some patients. Diplopia usually results from the related exodeviation at near seen with CI. Sometimes an underlying strabismic tendency (e.g., esophoria) can become “uncovered” when fusion is disrupted.
Less common symptoms include nausea, motion sickness, dizziness, panoramic headaches, and generalized fatigue. Convergence insufficiency symptom score is useful for grading based on symptoms [Table 1].
Signs of CI include:
- Exophoria greater at near than at distance
- Receded NPC
- Low AC/A ratio
- High CI Symptom Survey (CISS) score
- Reduced PFV
Direct measures of PFV
- Reduced smooth vergence
- Reduced step vergence
- Reduced vergence facility
Indirect measures of PFV
- Low negative relative accommodation (NRA)
- Difficulty in clearing plus lenses during binocular accommodative facility testing
- Low values in Monocular estimation method (MEM)
Patients with symptomatic CI often have an associated accommodative insufficiency. In such cases there is:
- Difficulty in clearing minus lenses during monocular and binocular accommodative facility testing
- Low positive relative accommodation (PRA)
- Low amplitude of accommodation
- Possible improvement in NPC testing with plus lenses.
- BCVA at distance and near
- Subjective refraction
- Cycloplegic refraction
Various authors have adopted different diagnostic criteria for convergence insufficiency [Table 2].
|Table 2: Diagnostic criteria for convergence insufficiency used by various authors|
Click here to view
Estimation of phoria
Most patients with CI exhibit exophoria at near and orthophoria or low exophoria at distance. Phoria measurement for near and distance is performed by:
- Cover test
- Von Graefe technique
- Modified Thorington technique
Cover test is performed with Gulden fixation stick at 40 cm for near phoria and 20/30 target in Snellen for distance phoria measurement; magnitude is determined by neutralization of prisms.
Von Graefe technique
Patient is given a 20/30 single letter target at distance with full correction. Six PD Risley prisms are placed base down in front of the right eye and 10–12 PD base before the left eye. Patient is asked to fix at the lower target (seen by the right eye) and move the upper target (seen by the left eye) by changing the prisms at a rate of 2 PD per se cond. The amount and direction of prism is recorded when the patient reports alignment.
Modified Thorington technique
Place the Maddox rod before the right eye of the patient wearing his full correction. Hold the Thorington card at 40 cm with a penlight behind the center hole of the card. Patient is asked to look at the center of the card and report the number through which the red line is passing and to which side. The Maddox rod is kept with striations held vertically for measuring horizontal deviations and horizontally for vertical deviations.
Estimation of near point of convergence
Receded NPC is the most consistent finding in CI, and is the most frequently used single diagnostic criterion. Methods employed for NPC determination include:
- RAF ruler
- With penlight and red-green glass
- Jump convergence
Patient is asked to maintain fixation at the target placed at 30–40 cm in the midline and the target is moved towards eyes until one of the eyes loses fixation and turns out (usually nondominant). The normal range for NPC is 8–10 cm. A distance closer than 5 cm is excessive, and an NPC farther away than 10 cm is remote.
NPC will be more receded in symptomatic patients compared to asymptomatic patients. In a recent study, Scheimann et al. observed that repetition of NPC estimation yields useful clinical information but has to be performed approximately 10 times. Another criterion is recovery point, which is the point at which an individual regains fusion after it has been lost during push-up convergence testing. Recovery point value significantly differing from break point value indicates more severe problem of convergence. Estimation of near point of convergence using RAF ruler is shown in [Figure 1].
With penlight and red/green glasses
Red glass is placed before the right eye and green glass is placed before the left eye. A pen torch is brought from a distance of 50 cm and moved towards the patient's nose. Patient is asked to report the point at which two separate color lights were seen (i.e. red and green) and that point is recorded as the break point. Then the penlight is moved away from the individual who is asked to report when two light become single. This is recorded as the recovery point.
It is tested by asking the patient to change fixation from a distant target to a near target positioned in the mid-line 15 cm from the patient's head. The position of the near target can be varied to determine the near point. The practitioner may observe either a smooth convergence of both eyes from distance to near or a variety of abnormal responses including a slow or hesitant movement; an overconvergence; versional movements followed by convergence; or no movement of either eye or movement of one eye only.
Deviation is measured by prism bar cover test as the patient fixates at 6 m distance and then again with fixation at 33 cm distance to a target that controls his accommodation (e.g., +3 PD accommodative effort).
AC/A ratio = IPD + (Δn −Δ0)/3
IPD = interpupillary distance in cm
Δn = Near deviation
Δ0 = Distance deviation
Esodeviations are given positive (+) and exodeviations negative (−) notations.
Normal value of AC/A ratio is between 3:1 and 5:1.,
Lens gradient method
The deviation is measured with the eyes in the primary position at a fixation distance of 33 cm with the patient fully corrected, and then the measurements are repeated after the addition of +3.00D and −3.00D lenses.
AC/A ratio = (Δ1− Δ0)/D
Δ1 = deviation with lens
Δ0 = original deviation
D = power of the lens
AC/A ratio can also be measured by:
- Fixation disparity method
- Haploscopic method
- Von Graefe technique
- Modified Thorington method
Positive fusional vergence
PFV is the amount of convergence available to overcome temporal disparity to maintain binocular fusion at near. To accomplish this measurement, the patient is instructed to keep a line of Snellen letters single and clear as base-out prisms are added in a slow and gradual manner. Diplopia will occur when fusion is no longer possible (break point). The amount of prism added to cause diplopia is the measurement of fusional convergence. The prism can then be reduced until fusion is re-established, which is the recovery point.
In CI, it is common to see low fusional convergence amplitudes, and thus, an inability to maintain near fixation. The recovery point at which fusion is re-established after being broken can also be an indicator of fusional potential. With low convergence amplitudes, the recovery point will be receded as well. Breakpoint and recovery point is found by changing prisms at a rate of 2 PD per se cond in phoropter (smooth vergence) or using prism bar (step vergence) by using an isolated 20/30 target set at 20 feet.
Gulden vergence facility prism (12 PD BO/3 PD BI combination) and Gulden fixation stick (20/30 target) are used and flipped until patient reports double, and the number of cycles the individuals can clear with BI and BO prisms for 60 seconds is determined.
Normal: 18 flips in 1 minute or 9 cycles per minute.
Negative relative accommodation and positive relative accommodation
Patient is asked to fixate at a near point card with vertical line of 20/30 letters. Add plus lenses in +0.25 D increments until patient reports first sustained blur or diplopia and this gives NRA. Now add minus lenses in −0.25 D increments until sustained blur or diplopia is reported, this gives PRA.
Monocular and binocular accommodative facility
It is the ability to quickly achieve clear vision while alternately viewing 20/30 print (Gulden fixation stick) at 40 cm through + 2 D and − 2 D lenses. Continue alternating sides of flipper lenses for 1 minute, calculating the cycles per minute achieved (1 cycle means one alteration of plus and minus lenses). In monocular accommodative facility determination, patient has to report when target is not clear; diplopia is not an issue.
Amplitude of accommodation – monocular
- Pull away method – slowly move away the Gulden fixation target from patient's eye at 1–2 cm/s until the patient can just report the letter on Gulden stick.
- Minus lens method – patient is asked to fixate on an illuminated near point card (reduced Snellen) at 40 cm. Add minus lenses until the patient reports first sustained blur. Addition of 2.50 D for working distance to amount of lens added gives amplitude.
Monocular estimation method
Patient is asked to read age appropriate MEM graded cards affixed to retinoscope held at the patient's habitual reading distance. Try to estimate amount of “with” or “against” motion for each meridian by making a sweep with retinoscope. A neutralizing trial lens can be interposed very briefly in front of one eye at a time to verify the estimation.
Random dot stereopsis test, TNO test, Worth four-dot test, etc., can be used.
Convergence insufficiency symptom survey score
The association of CI and symptoms in children has been investigated by the CITT Group who developed the CISS. The CISS is a questionnaire with 15 questions designed to quantify symptoms associated with reading and near work. Each question requires a verbal response of “never = 0, infrequently = 1, sometimes = 2, fairly often = 3, and always = 4.” The highest possible score is 60, and the lowest possible score is 0. Proforma for clinical evaluation of convergence problems is given [Table 3].
| Management|| |
Treatment modalities commonly prescribed include passive treatment with base-in prism reading glasses and active treatments such as home-based pencil push-ups, home-based/office-based vision techniques. Active therapies for the treatment of symptomatic CI typically involve purposeful, controlled manipulation of target blur, vergence demand, and/or target proximity, with the aim of normalizing the accommodative and vergence systems and their mutual interactions. Phases of vision therapy are given [Table 4].
Refractive error correction with lenses
Low degrees of myopia could be induced due to CI. Such cases require vision therapy is preferred and monitoring refractive error following vision therapy.
Sometimes significant hyperopia correction can lead to an increase in the amount of exophoria. It will result in increased demand on already inadequate PFV and may exacerbate patient's symptoms.
If a vertical deviation is present, vertical prisms are to be prescribed before vision therapy. BI prisms are given as relieving prisms for patients with CI. The amount of prism prescribed is based on the minimum amount necessary to meet Sheard's criterion:
Prism to be prescribed = 2/3 phoria – 1/3 compensating fusional vergence.
The amount of prism required is rounded up to the nearest half prism diopter and split equally between the two eyes. The patient is asked to wear these prism glasses for all reading and near tasks requiring more than 5 minutes. However previous study shows that the prescription of base-in prism reading glasses (based on Sheard's criterion) was no more effective than placebo reading glasses for the treatment of symptomatic CI in children.
Home-Based Pencil Push-ups
The pencil push-ups procedure uses a pencil with 20/60 size letters and a white index card placed in the background to provide a suppression check by using physiological diplopia awareness. The goal of the procedure is to move the pencil to within 2–3 cm from the brow just above the nose on each push up while trying to keep the target single and clear. Patients are instructed to perform the pencil push-ups procedure 15 minutes per day, 5 days per week, and to maintain home therapy log forms.,
Variable tranaglyphs come in pairs with one printed in red and other in green. Two slides are identical except for color and disparity. They are designed to create convergence or divergence demand by separating them horizontally and patient wearing red green glasses. Convergence demand is achieved by moving the green slide to the left and red slide to the right. A scale on the bottom of the tranaglyph target indicates the amount of prismatic demand at any given target separation.
The difference from tranaglyphs is that these are printed in a polaroid material and needs polaroid glasses. Compared to the tranaglyphs they are easier to use, however, are more expensive.
The targets are red and green printed on a clear background, and unlike variable there is only one slide per target. Each slide has a specific disparity and disparity cannot be altered. Demand is changed by having the patient switch fixation from one target to another on a particular slide or with the help of auxiliary lenses or prisms. All targets in this series present a fixed vergence demand and require an initial fusional vergence movement to obtain fusion.
Computerised orthoptics random dot stereopsis (CORDS) program
It is a basic binocular vision therapy program that can be used at the very early phase of vision therapy. Red/blue glasses are used and the technique is designed for use at 40 cm. The vergence demand is initially set at zero and can be set at a value that is easier for the patient. Targets used is a large square with a smaller random dot steropsis square located either on the top, bottom, right or left of the larger square. Patient is asked to move the joystick in the direction he sees the small square. Vegence demand is automatically increased 1 PD if the patient responds correctly and is reduced by 2PD if the response is incorrect. The computer automatically does scoring. Patient performing computer based convergence exercises is shown in [Figure 2].
Loose prism for fusional vergence therapy
Prisms can be used to increase or decrease the level of difficulty of the task by increasing or decreasing prismatic demand to supplement other fusional vergence therapy.
It consists of a ruler-like apparatus, two plastic slides – one with a single aperture (BO for divergence) and other with a double aperture (BI for convergence) – and 12 cards with varying disparities ranging from 2.5 PD to 30 PD. Cards are a combination of second degree (fusion) and third degree (stereopsis) targets. Each card contains antisuppression cues and accommodative controls. Each card also has a small set of eccentric circles that act as a third degree fusion target and when the patient fuses the inner circle comes closer with convergence and outer circle comes closer with divergence
Modified Remy separator
It consists of a septum and with auxiliary base out prisms. It is used while exercising with lifesaver cards, free space fusion cards or stereograms.
Eccentric circles/free space fusion cards
The cards present a third-degree fusion (steropsis) target and each card consists of antisuppression cues and accommodative controls. The right eye views the left card and the left eye views right card. When the right eye fixates left target, image of the right card is projected on to the nasal retina of the right eye. When patient converges to appropriate plane two middle images overlap and he/she perceives two images – one each to the right and left of the fused image. Eccentricity of inner circles provides stereopsis. The patient fuses by converging infront of the plane of accommodation or diverging beyond the plane of accommodation. Common fusional vergence procedures used for therapy are given in [Table 5].
| Voluntary Convergence Procedures|| |
It is used to create the awareness of convergence to normalize NPC in CI patients. It is a long white cord with three wooden beads of different colors. The first bead is attached 2 ft from the patient and others 1 ft away. When the patient looks at the closer bead (green), he/she can appreciate one green bead and two red beads with two strings crossing at the green bead and extending from each eye due to physiological diplopia. Similarly, when the patient fixates on red bead, he/she will report one red bead and two strings crossing at the red bead and two green beads.
Computerized vergence/accommodative therapy
Using this program, fusional vergence and accommodative therapy procedures including vergence base in, vergence base out, auto-slide vergence, and jump ductions vergence programs using random dot stereopsis targets can be performed. Much like a clinician would do at each follow-up visit, this computer program automatically modifies the therapy program after each session based on the patient's performance. This can be done using office-based or home-based modules.,
Prognosis and follow up
CI patients who seek treatment usually do so because of their symptoms interfering with day to day activities, and systematic evaluation and treatment results in marked reduction of symptoms. Primary outcome assessment should be made at the visit after 12 weeks of treatment. Protocol specified follow-up visits are conducted after 4–8 weeks after treatment period.
| Conclusion|| |
CI is one of the most common causes of ocular discomfort, and hence, it is of vast clinical significance. A systematic approach towards diagnosis and management can improve the symptoms associated with CI and can markedly improve the quality of life in these patients.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]