Low AC/A Conditions: Convergence Insufficiency and Divergence Insufficiency
This chapter discusses the characteristics, diagnosis, and management of nonstrabismic binocular disorders associated with a low accommodative convergence to accommodation (AC/A) ratio. Although there are some significant differences among these conditions, they are grouped together based on the classification system described in Chapter 2. The unifying characteristic of the conditions described in this chapter is the low AC/A ratio. This similarity is important because it is the basis for the development of the management plan. Specifically, the AC/A ratio is the major factor that determines the sequence of management decisions in patients with heterophoria (Chapter 3). Consequently, certain general treatment strategies are shared by all binocular conditions associated with a low AC/A ratio. However, there are also important differences among these conditions. After a review of general principles that apply to all low AC/A disorders, each condition is described separately to highlight the differences in characteristics, diagnosis, and management.
The specific conditions discussed in this chapter are divergence insufficiency and various forms of convergence insufficiency (CI).
Overview of General Management Principles for Heterophoria Associated with Low AC/A Ratio
Table 9.1 lists the various sequential management issues presented in Chapter 3. The specific sequence in which these factors should be considered is primarily dependent on the AC/A ratio. Thus, the magnitude of the AC/A ratio (low, normal, or high) establishes the treatment sequence. The direction of the phoria (exophoria, esophoria, or hyperphoria) determines certain particulars of treatment, such as whether prism base-out, base-in, up, or down should be prescribed or whether convergence or divergence should be stressed in the initial phases of vision therapy. For binocular vision disorders associated with a low AC/A ratio, the specific management sequences we suggest are listed in Tables 9.2 and 9.3.
A comparison of Tables 9.1, 9.2, 9.3 reveals some similarities, but also several important differences in approach. The major difference that distinguishes low AC/A problems from conditions associated with high and normal AC/A ratios is the relative ineffectiveness of lenses in effecting a change in the size of the heterophoria. An example of this is Case 9.1.
Case 9.1
A 21-year-old man presents with a complaint of intermittent diplopia that is more bothersome when he looks at a distance. The problem has been present for several years. The refraction is +0.50 D OD and OS, the distance phoria is 10 esophoria, and the near phoria is ortho. The calculated AC/A ratio in this case is 2:1.
Prescribing for the ametropia in this case would have virtually no effect on the distance esophoria, reducing it from 10 esophoria to 9 esophoria. Of course, added plus lenses at distance for divergence insufficiency cannot even be considered because it would cause distance vision blur.
Table 9.1 SEQUENTIAL CONSIDERATIONS IN THE MANAGEMENT OF NONSTRABISMIC BINOCULAR ANOMALIES | ||||||||||
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Table 9.2 SEQUENTIAL CONSIDERATIONS IN THE MANAGEMENT OF CONVERGENCE INSUFFICIENCY | ||||||||||
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Table 9.3 SEQUENTIAL CONSIDERATIONS IN THE MANAGEMENT OF DIVERGENCE INSUFFICIENCY | ||||||||
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Another example of the lack of effectiveness of lenses in low AC/A cases is illustrated in Case 9.2.
Case 9.2
A 14-year-old girl presents with complaints of eyestrain, blurred vision, and watery eyes after 10 minutes of reading. The near point of convergence is 20 cm with orthophoria at distance and 10 exophoria at near. The subjective is −2.00 D OD and OS. The AC/A ratio is 2:1 (interpupillary distance [IPD] = 60 mm).
Correction of ametropia or use of added lenses in this case would again have little effect on the magnitude of the deviation.
Therefore, the consideration of the use of added lenses is moved close to the bottom of the list in Tables 9.2 and 9.3. However, optical correction of ametropia still remains the first issue that a clinician should consider. As stated in Chapter 3, the first consideration for all patients with accommodative and nonstrabismic binocular anomalies is optical correction of ametropia. In low AC/A cases, although lenses have little effect on the size of the deviation, the presence of an uncorrected refractive error may create an imbalance between the two eyes. This imbalance may lead to sensory fusion disturbances, or create decreased fusional ability because of blurred retinal images.
As a general rule, when CI is associated with more than 0.5 D of anisometropia, a refractive correction should be prescribed. If CI is associated with myopia, management is not as simple. If a mild degree of myopia is present, the myopia may be secondary to the CI. A cycloplegic refraction may help in the determination of whether an accommodative spasm is present. In such a case, the myopia may be secondary to the underlying binocular vision problem and should not be treated with a minus lens prescription. Rather, vision
therapy should be prescribed and the refractive error monitored. This issue is covered in more detail later in this chapter. With moderate to high degrees of myopia, a prescription is indicated. Moderate degrees of astigmatism, particularly against-the-rule and oblique astigmatism, can contribute to discomfort during near work; 0.5 D or more of oblique or against-the-rule astigmatism and 1 D or more of with-the-rule astigmatism should be corrected.
therapy should be prescribed and the refractive error monitored. This issue is covered in more detail later in this chapter. With moderate to high degrees of myopia, a prescription is indicated. Moderate degrees of astigmatism, particularly against-the-rule and oblique astigmatism, can contribute to discomfort during near work; 0.5 D or more of oblique or against-the-rule astigmatism and 1 D or more of with-the-rule astigmatism should be corrected.
With divergence insufficiency, the presence of hyperopia or anisometropia is significant. Although it is important to prescribe for ametropia in these cases, there is no need to have the patient wear the glasses for 4 to 6 weeks before prescribing other treatment because the effect on the size of the deviation is minimal.
When considering the final prescription for these patients, it is important to first determine whether a vertical deviation is present. London and Wick1 have demonstrated that prescribing for even small amounts of vertical deviations can have a very positive effect on the horizontal deviation. We suggest prescribing for vertical deviations as small as 0.5 Δ and basing the prescription on fixation disparity assessment (Chapter 15).
A key difference between the sequential management of CI and divergence insufficiency is the differential effectiveness of horizontal prism for these two conditions. The use of prism is one of the early considerations for divergence insufficiency. Base-out prism prescriptions have been reported to be the most effective treatment strategy2,3,4 for divergence insufficiency. For CI, however, prescribing base-in prism has a relatively low position in the sequential considerations for children,5 although base-in prism may be more useful with the presbyopic population.6 In a randomized clinical trial,5 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. Nearly half of the children assigned to each of the two treatment groups reported a statistically significant decrease in symptoms, although neither group achieved a decrease in symptoms to a level considered clinically asymptomatic. In another study,6 29 symptomatic CI subjects aged 45 to 68 years were assigned two pairs of progressive addition glasses in a randomized sequence, one with base-in prism and one with the same lens prescription but no prism (placebo). Subjects wore each pair of glasses for 3 weeks. The authors reported that the progressive addition glasses with base-in prism were found to be effective in alleviating symptoms of presbyopes with symptomatic CI.
Vision therapy is the primary treatment option for CI,7,8,9,10,11,12,13 whereas it has much less value in divergence insufficiency. Vision therapy is particularly challenging with divergence insufficiency because improvement of fusional divergence at distance is one of the more difficult goals to accomplish.
Although amblyopia is uncommon in nonstrabismic binocular vision anomalies, it will occur if the phoria is associated with a significant degree of anisometropia. In such cases, one of the early considerations should be treatment of amblyopia using occlusion and vision therapy. The use of occlusion and specific vision therapy procedures for the treatment of the amblyopia and any associated suppression always needs to be considered immediately after prescribing for the anisometropia and considering prism to compensate for a vertical phoria. In cases of CI or divergence insufficiency associated with anisometropia, we recommend part-time occlusion. Several (2 to 3) hours of occlusion using an opaque patch, along with active amblyopia therapy, are usually sufficient to resolve the amblyopia. Complete details about the evaluation and management of anisometropic amblyopia are provided in Chapter 17.
In almost all cases, however, amblyopia will not be present in either convergence or divergence insufficiency. Thus, after consideration of ametropia and prism, vision therapy is the next treatment issue. Vision therapy has been shown to be so effective for CI that it should always be presented as the treatment of choice for this condition.
The final sequential management consideration listed in Tables 9.2 and 9.3 is surgery. In Chapter 3, we discussed how infrequently such a recommendation would be necessary for CI. In addition, even if the nonsurgical approaches are ineffective, the research about the effectiveness of surgery for CI is equivocal.14,15,16,17,18,19 There are no quality randomized clinical trials of the effectiveness of surgical treatment of CI. In addition, the choice of outcome measures used in recent studies18,19 is problematic. For example, in a study by Farid,19 the outcome measures were the change in angle of deviation at distance and near, and the near-distance disparity. These are questionable outcome measures because they not include a measure of symptoms, the near point of convergence, or positive fusional vergence (PFV) which define CI. In addition, none of the surgical studies have included either a masked examiner or a control group. Given the weaknesses in the literature regarding the effectiveness of surgical treatment of CI, along with the potential for postsurgical diplopia,19 and the proven effectiveness of office-based vision therapy, surgical treatment should be a last resort. For divergence insufficiency, surgery is also unlikely to be necessary. Generally, a combination of nonsurgical approaches will be effective. However, when the magnitude of the distance deviation is large and all nonsurgical approaches have been unsuccessful in relieving the patient’s symptoms, surgery may occasionally be helpful.
PROGNOSIS FOR TREATING BINOCULAR VISION DISORDERS ASSOCIATED WITH LOW AC/A RATIOS
Using the management approach suggested earlier, the prognosis for treating CI is excellent. Vision therapy is the primary treatment option for CI, and numerous studies have demonstrated its efficacy, with success rates between 73% and 95%.7,8,11,12,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38 Virtually all recognized textbooks recommend vision therapy/orthoptics as the preferred treatment approach for CI.39,40,41,42,43,44 Vision therapy has also been shown to be effective for all age levels.7,8,12,20,34,35,36,37,38 Vision therapy should be effective in virtually all cases, as long as good motivation and compliance are present.
For divergence insufficiency,45 prism is the primary treatment modality, although the use of lenses, added lenses, and vision therapy may be helpful. Depending on the magnitude of the esodeviation at distance, surgery may be required.46,47,48 Because prism is so important in the management of divergence insufficiency, the magnitude of the deviation is particularly critical. Most patients can be successfully treated if the degree of esophoria at distance is 15 Δ or less. As the distance deviation increases, the prognosis for complete relief of symptoms decreases. Although divergence insufficiency has the poorest prognosis for any of the nonstrabismic binocular vision anomalies described in this text, it is important to realize that even for this condition, the prognosis is good.
SUMMARY OF KEY POINTS IN TREATING PHORIA PATIENTS ASSOCIATED WITH LOW AC/A RATIOS
The important issue in the sequential management of low AC/A binocular vision problems is the de-emphasis of added lenses. Because of the low AC/A ratio, added lenses have minimal effect on the angle of deviation. For these problems, horizontal prism and vision therapy are the principal treatment alternatives. Horizontal prism is most effective for divergence insufficiency, and vision therapy is best for CI.
Convergence Insufficiency
BACKGROUND INFORMATION
Definition and Prevalence
CI is a condition in which there is an exophoria at near, orthophoria or low exophoria at distance, a receded near point of convergence, reduced PFV, and a low AC/A ratio. Of the various nonstrabismic binocular vision problems, CI is the most common and has received the most attention. The prevalence of CI has been reported to be about 3% to 5% of the population.49,50,51,52,53 Scheiman et al49 and Rouse et al50,51 studied the frequency of CI in schoolchildren in both clinical and school settings. These authors have been careful to clearly define CI. Scheiman et al49 defined CI as a condition with a receded near point of convergence, along with at least three additional low findings from the following categories: direct or indirect measures of PFV, exophoria greater at near than at distance, or a low AC/A ratio. They found a prevalence of 5.3% in a population of 1,650 children (6 to 18 years old). Rouse et al50,51 used the term definite CI to describe a patient with exophoria at near that is 4 Δ or greater in magnitude than the far phoria, a receded near point of convergence, and insufficient PFV. Using this specific definition, they found a frequency of 6% in children (8 to 12 years old) in a clinic setting50 and 4.2% in children (9 to 12 years old) in a school screening setting.45 Porcar and Martinez-Palomera54 did a similar study in a university setting. They defined CI as exophoria at near greater than 6 Δ, a low AC/A ratio, reduced PFV at near, and a receded near point of convergence. They found a prevalence of 7.7% in a population of 65 university students. More recently, a number of studies have investigated the prevalence of CI in different populations such as American Indians (6.2%),55 Iranian children and adults (5.5%),56 Indian children (16.5%),57 South African high school students (4.3%),58 and South Korean children (10.3%).59
CHARACTERISTICS
Symptoms
Most symptoms are associated with reading or other close work. Common complaints include eyestrain and headaches after short periods of reading, blurred vision, diplopia, sleepiness, difficulty concentrating, loss of comprehension over time, a pulling sensation, and movement of the print12 (Table 9.4). Some patients with CI are asymptomatic. Cooper and Duckman60,61 suggested that this absence of symptoms may be due to suppression, avoidance of near visual tasks, a high pain threshold, or occlusion of one eye when reading. Clinicians should always inquire about avoidance of reading or other near tasks if a patient with CI reports an absence of
other symptoms. Avoidance is as important a reason for recommending therapy as any of the other symptoms associated with CI.
other symptoms. Avoidance is as important a reason for recommending therapy as any of the other symptoms associated with CI.
Table 9.4 SYMPTOMS AND SIGNS OF CONVERGENCE INSUFFICIENCY | ||||||||||||||||||||||||||
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Although symptoms in CI are commonly reported in the literature, until recently there had been no standardized symptom survey for documenting the type and frequency of symptoms in this population. Borsting et al62 gathered validity-related evidence on child and parent versions of a CI symptom survey (Fig. 3.1). This questionnaire, the Convergence Insufficiency Symptom Survey (CISS), is the first standardized instrument that has been shown to be valid and reliable for measuring the type and frequency of symptoms before and after treatment for patients with CI.63,64,65,66 It can be used in clinical practice to compare symptoms before and after optometric intervention for patients with CI and other binocular vision and accommodative disorders.
The CISS allows a two-factor analysis of symptoms: first, whether the symptom is present, and second, how frequently it occurs. The questionnaire consists of 15 items. The patient chooses one of five possible answers (never, infrequently, sometimes, fairly often, always). Each answer is scored from 0 to 4, with 4 representing the highest frequency of symptom occurrence (i.e., always). The 15 items are summed to obtain the CISS score, with the lowest possible score being 0 (totally asymptomatic) and the highest possible score being 60 (most symptomatic). For children aged 9 to 17 years, a symptom score of 16 or higher on the CISS has been found to differentiate those with symptomatic CI from those with normal binocular vision. For adults (18 and older), a symptom score of 21 or higher on the CISS has been found to be significant. Research using this survey has demonstrated that a score of less than 16 for children and less than 21 for adults or a change in 10 or more points is clinically significant.
Since the publication of validation studies of the CISS and the Convergence Insufficiency Treatment Trial (CITT) study, several studies have raised questions about the suitability of the CISS as an outcome measure of
CI symptoms. One study67 administered the original CISS emphasizing reading or a modified CISS replacing “reading” with their favorite near activity. Subjects were children with normal binocular vision. Their data suggest that a large percentage of the CISS score are actually created by the academic nature of the activity being surveyed, rather than any impairment in the visual system. Given that the CISS score can vary with the type of near activity, it follows that subjects may interpret the questions in different ways. It may be that the increasing use of electronic devices in the past 20 years has impacted the validity of the CISS. Another study68 cautioned clinicians about the use of the CISS because “The questions are very general and other problems can lead to positive answers.” Previous studies have suggested a poor relationship between signs and symptoms as measured by the CISS.69,70,71 In addition, a large placebo effect with placebo and prism glasses was found previously with the CISS.5 Most recently, the results of a large randomized clinical trial showed a significant change in the CISS in the placebo control group that was equivalent to the change in the CISS score in the active vision therapy group. In contrast to prior clinical trials, the subjective assessment of symptom severity as measured by the CISS did not correspond with the objective improvements in convergence function. Thus, the CISS, in its present form, may no longer adequately quantify the change in symptoms attributable to the change in visual function in 9- to 14-year-old children with CI. Given the large disparity in this study between changes in clinical measures and subjective measures, it may be necessary to reconsider the use of the CISS in its current form as an outcome measure.
CI symptoms. One study67 administered the original CISS emphasizing reading or a modified CISS replacing “reading” with their favorite near activity. Subjects were children with normal binocular vision. Their data suggest that a large percentage of the CISS score are actually created by the academic nature of the activity being surveyed, rather than any impairment in the visual system. Given that the CISS score can vary with the type of near activity, it follows that subjects may interpret the questions in different ways. It may be that the increasing use of electronic devices in the past 20 years has impacted the validity of the CISS. Another study68 cautioned clinicians about the use of the CISS because “The questions are very general and other problems can lead to positive answers.” Previous studies have suggested a poor relationship between signs and symptoms as measured by the CISS.69,70,71 In addition, a large placebo effect with placebo and prism glasses was found previously with the CISS.5 Most recently, the results of a large randomized clinical trial showed a significant change in the CISS in the placebo control group that was equivalent to the change in the CISS score in the active vision therapy group. In contrast to prior clinical trials, the subjective assessment of symptom severity as measured by the CISS did not correspond with the objective improvements in convergence function. Thus, the CISS, in its present form, may no longer adequately quantify the change in symptoms attributable to the change in visual function in 9- to 14-year-old children with CI. Given the large disparity in this study between changes in clinical measures and subjective measures, it may be necessary to reconsider the use of the CISS in its current form as an outcome measure.
Another symptom questionnaire that could be used is the College of Optometrists in Vision Development Quality of Life Outcomes Assessment (COVD-QOL) described in Chapter 3.72,73,74,75,76 Several authors have reported on the use of the COVD-QOL short form to evaluate symptoms before and after vision therapy75,77,78 and found the assessment to be a valuable clinical tool. Unlike the CISS, its use has not been evaluated in the context of a large, multicenter randomized clinical trial.
Signs
See Table 9.4 for signs associated with CI.
Refractive Error
A clear trend has not been identified in the literature in regard to refractive error in CI.
Near Point of Convergence
A remote near point of convergence is considered the most consistent finding in CI.79 A survey conducted by Rouse, Hyman, and the Convergence Insufficiency and Reading Study group79 determined that a receded near point of convergence was used in making the diagnosis of CI by about 94% of the optometrists surveyed; 35% of the doctors indicated that one criterion was sufficient to diagnose CI, and the most frequently used single diagnostic criterion was the near point of convergence.
Normative values for the near point of convergence in schoolchildren and young adults have been reported. Hayes et al80 studied 297 schoolchildren in kindergarten, third, and sixth grades using a standardized protocol. They recommended using a cutoff value of 6 to 10 cm for children. Maples and Hoenes81 reported a similar value in children, with a cutoff value of 5 cm. Scheiman et al82 studied 175 young adults and suggested a cutoff value of 5 to 7 cm.
The near point of convergence test is traditionally performed by slowly moving a target toward the eyes until the patient reports diplopia or the examiner notices a break in fusion. Several modifications to this traditional approach have been suggested in the literature to make the test more sensitive. Wick83 and Mohindra and Molinari84 recommended that the near point of convergence test be repeated four to five times. Davis85 claimed that asymptomatic patients manifest little change in the near point with repeated testing, whereas symptomatic patients have significantly less convergence with repeated testing. This recommendation is designed to improve the diagnostic sensitivity of the break of the near point of convergence test. Scheiman et al82 confirmed the value of repeating the near point of convergence test. They found a recession of the near point of convergence after repetition in both normal subjects and CI patients. In the subjects with normal binocular vision, however, the amount of recession was small—less than 1 cm. In the CI group, the amount of recession was 1.5 cm after 5 repetitions and about 4 cm after 10 repetitions. These findings suggest that repetition of the near point of convergence may yield useful clinical information, but the test would have to be performed about 10 times. Maples and Hoenes81 also investigated the changes in the near point of convergence after repetition and found that the near point of convergence break and recovery do not change appreciably with multiple repetitions of the test.
Another criterion utilized for assessment of convergence ability is the recovery point, or the point at which an individual regains fusion after it has been lost during the push-up convergence testing. Capobianco86 reported that a recovery point greatly different from the break indicates greater convergence problems. She also
suggested that if one assesses the near point of convergence with a penlight, and then a penlight and red glass are held before the patient’s right eye, the test becomes more sensitive. Several authors83,84,87,88 have suggested that this procedure be part of the standard assessment of convergence amplitude. Scheiman et al82 found that in normal subjects, there was no significant difference in the near point of convergence when measured with an accommodative target, a penlight, or a penlight with red/green glasses. Subjects with CI, however, did show greater recession of both the break and recovery with the penlight and red/green glasses compared with the accommodative target. The mean break with an accommodative target was 9.3 cm; with a penlight and red/green glasses, the mean break was 14.8 cm. The recovery finding with the accommodative target was 12.2 cm, and with a penlight and red/green glasses it was 17.6 cm. For both the break and the recovery, therefore, there was a difference of about 5.5 cm between the accommodative target and the penlight and red/green glasses. Statistically significant differences were not found for an accommodative target compared with a penlight or a penlight compared with a penlight and red/green glasses. The use of a penlight and red/green glasses therefore does seem to have some additional diagnostic value in distinguishing CI patients from normal subjects.
suggested that if one assesses the near point of convergence with a penlight, and then a penlight and red glass are held before the patient’s right eye, the test becomes more sensitive. Several authors83,84,87,88 have suggested that this procedure be part of the standard assessment of convergence amplitude. Scheiman et al82 found that in normal subjects, there was no significant difference in the near point of convergence when measured with an accommodative target, a penlight, or a penlight with red/green glasses. Subjects with CI, however, did show greater recession of both the break and recovery with the penlight and red/green glasses compared with the accommodative target. The mean break with an accommodative target was 9.3 cm; with a penlight and red/green glasses, the mean break was 14.8 cm. The recovery finding with the accommodative target was 12.2 cm, and with a penlight and red/green glasses it was 17.6 cm. For both the break and the recovery, therefore, there was a difference of about 5.5 cm between the accommodative target and the penlight and red/green glasses. Statistically significant differences were not found for an accommodative target compared with a penlight or a penlight compared with a penlight and red/green glasses. The use of a penlight and red/green glasses therefore does seem to have some additional diagnostic value in distinguishing CI patients from normal subjects.
Finally, Pickwell and Stephens89 described another method of assessing convergence ability, which they termed jump convergence. In this procedure, the subject first fixates a target at 6 cm and then changes fixation to a target at 15 cm. Pickwell and Hampshire90 reported that this jump convergence test appears to have more clinical significance and is a more sensitive way of determining the presence of convergence problems than the near point of convergence.
Characteristics of the Deviation
Patients with CI generally have greater exophoria at near, decreased PFV, and a receded near point of convergence.
Some authors have suggested that a 10 Δ difference from one distance to another is a useful guideline. This suggestion, however, has no firm research basis and should be used only as a guideline. Rather than depend on this guideline, we find it more useful to think about the difference one would expect based on the presence of a low AC/A ratio. Because an AC/A ratio of less than 3:1 is considered low, as little as an 8 Δ difference between distance and near would be sufficient to fit the diagnosis of CI.
Clinicians should also use their judgment and rely on other characteristics in addition to the magnitude of the angle at distance and near to reach a diagnosis. For instance, the near deviation may be an intermittent or constant strabismus versus a phoria at distance. This finding, along with a receded near point of convergence, would lead to a diagnosis of CI even if the difference in magnitude was less than 8 Δ. Thus, a comparison of the proportion of time the deviation is present, as well as the magnitude at distance and near, is an important part of the diagnostic process.
AC/A Ratio
A low AC/A ratio (<3:1) is generally considered to be present in CI. This is well accepted, based on the calculated AC/A, and is an important factor when treatment is considered.
ANALYSIS OF BINOCULAR AND ACCOMMODATIVE DATA
All direct tests of PFV will tend to be low in CI (Table 9.4). This includes step, smooth vergences, and jump vergences. In addition, tests that indirectly assess PFV (Table 9.4) will be low as well. Tests performed binocularly with plus lenses evaluate the patient’s ability to relax accommodation and control binocular alignment using PFV. Two examples are the negative relative accommodation (NRA) and binocular accommodative facility (BAF) tests. A low finding with either of these tests may be due to an inability to relax accommodation or due to reduced PFV. The differential diagnosis is based on assessment of accommodation under monocular conditions. An easy and helpful technique is to simply cover one eye after the patient reports blur on the NRA test. If the blur continues, the problem is accommodative (accommodative excess). If the patient’s vision clears, the problem is associated with binocular vision (PFV). Normal monocular accommodative ability on other tests suggests reduced PFV.
Another important indirect test is monocular estimation method (MEM) retinoscopy. It is not unusual to find an abnormal result on this test in CI. An MEM finding of less plus than expected suggests that the patient is using accommodative convergence to supplement inadequate PFV to maintain binocular vision.
In some instances, a secondary accommodative excess is present along with the CI. In such cases, in addition to the signs described earlier, the patient will perform poorly on monocular accommodative facility (MAF) with plus lenses. Covering one eye after the NRA test, as described previously, is useful in this differential diagnosis. When an accommodative excess is present along with a CI, the accommodative problem is thought to be secondary to excessive use of accommodative convergence to supplement the inadequate PFV. This continual use of excessive accommodative effort may lead to a spasm of accommodation. In such cases, the patient may also
report blurred distance vision. At first, this distance blur is transient. If the condition persists untreated, the distance blur may become permanent as myopia develops.
report blurred distance vision. At first, this distance blur is transient. If the condition persists untreated, the distance blur may become permanent as myopia develops.
DIFFERENTIAL DIAGNOSIS
CI is considered to be a benign condition with no serious consequences other than the visual symptoms listed in Table 9.4. It is relatively easy to differentiate from other binocular vision disorders associated with exophoria, such as basic exophoria (equal deviation at distance and at near) and divergence excess (greater exophoria at distance).
Richman and Cron91 described a condition called pseudo-CI that can be confused with CI. Pseudo-CI is a condition in which the primary problem is accommodative insufficiency. The amplitude of accommodation and all other tests assessing the ability to stimulate accommodation are reduced. It is believed that this condition is basically an accommodative insufficiency with a secondary CI. The patient tends to accommodate as little as possible for any given demand. As a result, accommodative convergence is reduced, placing a greater demand on PFV. If a patient is already moderately exophoric with borderline PFV, this additional demand can simulate a CI. Case 9.3 is an example of pseudo-CI.
Case 9.3
Joseph is a 13-year-old who is complaining of eyestrain and blurred vision after 10 minutes of reading. He is healthy and is not taking any medication. He has been a patient in your practice for several years, and his most recent examination was 2 years ago. At that time, he had no complaints. The findings from the previous and current examinations are listed next:
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If this were the first time you examined this patient, the findings could easily be confused with true CI. The key findings for the differential diagnosis are the amplitude of accommodation and other tests that probe the ability to stimulate accommodation. In true CI, these findings are normal. If an accommodative anomaly exists, it tends to be an accommodative excess. Thus, if the accommodative amplitude is reduced, along with other probes of the ability to stimulate accommodation, pseudo-CI is the probable diagnosis. Because the patient accommodates as little as possible to identify the stimulus, the amount of near point exophoria increases and the measured PFV decreases. Clinically, repetition of the near point of convergence with +0.75 or +1.00 lenses may actually improve performance in cases of pseudo-CI. With the low plus lenses, the patient may accommodate more accurately, leading to improvement in the near point of convergence.
CI can also be associated with serious underlying conditions. A condition called convergence paralysis is a supranuclear gaze disorder that must be ruled out. Patients with this condition can fully adduct their eyes during conjugate gaze movements, and the deviation is comitant. Convergence paralysis can occur secondary to ischemic infarction, demyelination, and flu or other viral infection.92 When secondary to flu, it can be transient
or permanent. If convergence paralysis exists in isolation of accommodative or pupillary involvement or other evidence of central nervous system disease, it may be difficult to differentiate from a functional CI. The primary differential is the history. A recent onset of diplopia and asthenopia is suspicious. The history of a patient with CI is generally associated with long-standing chronic complaints.
or permanent. If convergence paralysis exists in isolation of accommodative or pupillary involvement or other evidence of central nervous system disease, it may be difficult to differentiate from a functional CI. The primary differential is the history. A recent onset of diplopia and asthenopia is suspicious. The history of a patient with CI is generally associated with long-standing chronic complaints.
Table 9.5 DIFFERENTIAL DIAGNOSIS OF CONVERGENCE INSUFFICIENCY | ||||||||
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A receded near point of convergence has also been reported secondary to Parkinson disease, Parinaud syndrome, and medial rectus weakness in multiple sclerosis and myasthenia gravis. One must therefore be cognizant of the differential diagnosis of CI and first rule out the more serious disorders that can cause CI. Table 9.5 lists the various conditions that must be considered in the differential diagnosis of CI.
Summary
A serious underlying etiology must be ruled out in all cases of CI. This differential diagnosis depends very much on the nature of the patient’s symptoms. Typically, CI presents with long-standing chronic complaints and a negative health history. The history is also negative for any medication known to affect accommodation. The primary functional disorder that must be differentiated from true CI is pseudo-CI, which has an accommodative etiology. When managing a case of CI that is thought to have a functional basis, if symptoms and findings do not improve as expected, it is wise to reconsider the etiology of the condition.
Convergence paresis associated with serious underlying disease has an acute onset, and medical problems or neurologic symptoms are usually present.
TREATMENT
We recommend the management sequence listed in Table 9.2.
Lenses
In all cases of binocular, ocular motor, and accommodative dysfunction, the first management consideration is correction of any significant refractive error. With CI, it is important to prescribe glasses if a significant degree of myopia is present. When a low degree of myopia is present, it is possible that the myopia is secondary to the CI. The presence of accommodative excess would support such a conclusion. In such cases, we recommend not prescribing glasses for low degrees of myopia. Rather, vision therapy to remediate both the CI and the accommodative excess should be prescribed. As therapy progresses, the refractive error should be monitored. If a change in the myopia does not occur, glasses can be prescribed at the completion of therapy.
The prevalence of hyperopia in CI does not appear to be any greater than in the general population. If hyperopia is present, however, it does create a management problem. Even though the AC/A ratio is low, if there is a significant degree of hyperopia, correction of the refractive error will lead to an increase in the amount of exophoria. This will create a greater demand on the already inadequate PFV and may exacerbate the patient’s symptoms. In some cases, a borderline problem might become clinically significant or an exophoria at near may decompensate into an intermittent exotropia. Case 9.4 is an example of the effect of correction of hyperopia on a borderline CI.
Case 9.4
Robert, a 41-year-old accountant, presents with complaints of eyestrain, blurred vision, burning, and frontal headaches. These problems begin every afternoon during the workweek and have been occurring for the last 6 months. He has never worn glasses before. Testing reveals +2.50 OD and OS, orthophoria at distance, and 8 exophoria at near without correction. With correction, he is 6 exophoric at distance and about 15 exophoric at near.
Base-out ranges at near (without the correction): 8/16/8
Base-out ranges at near (with the correction): 4/10/4
Near point of convergence (without correction): 3 to 6 in.
Near point of convergence (with correction): 6 to 10 in.
In such cases, we must decide whether the patient’s symptoms are secondary to the uncorrected refractive error, the CI, or both. Case 9.4 illustrates that the patient is uncomfortable when reading and needs a correction for the hyperopia. However, with this correction, the findings suggest a CI. Several treatment alternatives could be recommended for this patient:
Prescribe the full prescription and instruct the patient to wear the glasses full-time and return for a reevaluation after 4 to 6 weeks. If symptoms persist, vision therapy could then be recommended.
Prescribe a partial prescription and instruct the patient to wear the glasses full-time and return for a reevaluation after 4 to 6 weeks. If symptoms persist, vision therapy could then be recommended.
Prescribe the full prescription and instruct the patient to wear the glasses full-time and simultaneously begin vision therapy.
Prescribe a partial prescription and simultaneously begin vision therapy. After vision therapy is complete, consider changing the prescription and increasing the amount of plus.
The best approach will depend upon the specifics of the situation and the clinician’s management philosophy. In Case 9.4 we suggest that a partial prescription (+1.50 OD and OS) along with vision therapy would lead to the most rapid resolution of the patient’s symptoms. Once the patient’s PFV and near point of convergence improve, additional plus could be prescribed.
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