Binocular Vision and Eye Movement Disorders in Older Adults

Abstract

Purpose.: To determine the prevalence of binocular vision (BV) and eye movement disorders in a clinic population of older adults.

Methods.: Retrospective clinic data were abstracted from files of 500 older patients seen at the University of Waterloo Optometry Clinic over a 1-year period. Stratified sampling gave equal numbers of patients in the 60 to 69, 70 to 79, and 80+ age groups. Data included age, general and ocular history and symptoms, use of antidepressants, a habit of smoking, refraction, visual acuity, BV and eye movement status for the most recent full oculo-visual assessment, and an assessment 10 years prior. The prevalence of any BV or eye movement abnormal test (AT) result, defined as a test result outside the normal range, was determined. This included strabismus (any) or phoria; incomitancy; poor pursuits; and remote near point of convergence (NPC). The prevalence of significant BV disorders (diagnostic entities, i.e., a clinical condition that may need treatment and may have functional implications) was also determined.

Results.: The prevalence of any BV or eye movement AT was 41%, 44%, and 51% in the 60 to 69, 70 to 79, and 80+ age groups, respectively. These figures were lower for 10 years earlier: 31%, 36%, and 40% for ages 50 to 59, 60 to 69, and 70+, respectively. The prevalence of any BV or eye movement disorder was 27%, 30%, and 38% for the three age groups and 17%, 19%, and 24% for 10 years prior. Age and use of antidepressants most commonly predicted BV or eye movement AT or disorder.

Conclusions.: BV disorders are common among older adults.

Introduction

There has been little attention paid to age-related changes in binocularity or to the prevalence of binocular vision (BV) disorders in older adults. ¹ The definition of what is included as a BV disorder differs between studies, making them hard to compare. Despite this, it appears that the overall prevalence of BV disorders in prepresbyopic clinic populations is quite high, ranging from 10% ² when only near esophoria or convergence insufficiency were included, to 21.8% ³ when any one of the following conditions were included: convergence insufficiency, basic eso- or exophoria, divergence excess, divergence insufficiency, convergence excess, or reduced fusional vergence ranges. Porcar and Martinez-Palomera ⁴ found a total of 15.3% who exhibited either convergence insufficiency, convergence excess, basic eso- or exophoria, or fusional vergence dysfunction in a population of university students. These studies excluded people with strabismus and the figures quoted here exclude accommodative disorders. The prevalence of strabismus has been found to be between 2.7% and 5.5% in schoolchildren ^5–11 and is similar in the adult population. ^12–14 Therefore, this percentage should be added to the prevalence of nonstrabismic BV disorders quoted above. There are, as far as we are aware, no studies of the overall prevalence of BV disorders specific to older adults. 

There are, however, a few studies regarding specific binocular changes in older adults. Yekta et al. ¹⁵ found increased near exophoria in adults aged up to 65 years and Palomo Álvarez et al. ¹ found no change in distance phoria in adults aged up to 70 years. Pickwell ¹⁶ reported an increase in prevalence of high near associated exophoria between the ages of 40 to 59 and 60+ years. There have been reports of decreased prism adaptation with age ^17,18 and Palomo Álvarez et al. ¹ showed significant decreases in positive and negative distance fusional recovery points with increasing age. Older adult patients may be more prone to a breakdown of BV, which could result in poorer stereopsis, asthenopic symptoms, and possibly diplopia. There are several reports of decreased stereopsis with age, with especially large changes for some individuals aged over 60 years. ^19,20 Haegerstrom-Portnoy ²¹ has shown that stereoacuity deteriorates with age more than high contrast visual acuity, becoming 10× poorer in adults aged 90 to 95 years compared with those aged 60 years. Deficits in stereoacuity may be due to sensory losses (monocular or binocular decreases of visual acuity [VA]), but may also be caused by a breakdown of BV due to changes in heterophoria or the onset of strabismus. Of patients aged over 60 years receiving strabismus surgery, the majority had strabismus secondary to disease processes (neuroparalytic, mechanical restriction, or as a result of sensory loss) ²² and 26% of the total had a vertical component. Mechanical restriction included strabismus secondary to thyroid disease, retinal detachment surgery, orbital floor fracture, and multiple surgical procedures on the sinuses. The most common reasons for strabismus surgery were diplopia and asthenopia. Magramm and Schlossman ²² concluded, based on patients having treatment, that the pattern of strabismus is different in older adults compared with younger patients. 

There are frequent reports that poor stereopsis is one of the visual risk factors associated with falls and hip fractures in older adults. ^23–28 Other aspects of vision that are associated with the frequency of falls are poor visual acuity, reduced contrast sensitivity, and visual field loss (see Lord et al. for a review ²⁹ ). Not all studies, however, have found a significant association between falls and these measures of visual function. ³⁰ Reduced stereopsis has also been shown to be associated with postural instability (increased sway on a foam surface that disrupts proprioreception). ³¹ Thus, maintaining good stereoacuity may help to reduce the incidence of falls and improve general visual function and quality of life for older people. Good BV is a prerequisite for maintaining good stereopsis. ^32,33  

Our hypothesis is that there are changes in binocular function with advancing age. Our goals are to determine the prevalence of BV and eye movement disorders in an older clinic population and compare it with the prevalence in the same population 10 years earlier. We also investigated factors that may be associated with poorer BV and eye movement function. 

Methods

This is a retrospective study of clinical information from the files of 500 patients, aged 60 years and older, who were seen for a full eye examination in the Primary Care Clinic at the School of Optometry and Vision Science, University of Waterloo, between January 22, 2008, and June 29, 2009. The files of patients who had attended the clinic for at least 9 years were randomly selected based on their clinic file number. Data were retrieved from the most recent full oculo-visual assessment, and an assessment 9 to 11 years prior, and entered into the database. Files were selected until there was a stratified sample with respect to age for the most recent eye examination. This allowed an equal number of patients aged 60 to 69, 70 to 79, and 80+ years to be included for analysis. Patients in their 80s and 90s were grouped together due to the relatively low proportion of clinic patients aged 90+ years. Additionally, the study did include three patients aged 59 years (59, 59.6, and 59.9 years). 

Data Extraction

The data extracted included the patient's sex and age; entering symptoms (with a separate note taken of the presence of diplopia); existing ocular and systemic diagnoses; a habit of smoking; use of antidepressants (as it was thought that they might have an effect on BV ^34,35 ); the presence of any strabismus; presence and amount of vertical and horizontal distance and near phoria as measured by the alternating cover test, and by Maddox rod, if undertaken; near point of convergence (NPC); ocular motility; pursuits; incomitancy (based on either Maddox rod or the alternating cover test performed in the different positions of gaze or observations during broad H motility testing); and best corrected visual acuity. In the situation when there was a discrepancy between the cover test and the Maddox rod results, the Maddox rod result was used. Data from the following tests were also included for those patients for whom they were measured; fusion with the Worth 4 Dot, stereopsis, and fusional reserves. The patient file has prompted data entry boxes for all these tests. The testing procedures for the individual tests are taught and undertaken according to descriptions in Hrynchak et al. ³⁶ The standard tests used in the clinic are listed in Table 1. As it is a teaching clinic, occasionally there were cases in which the supervising optometrist adjusted a student's assessment. In such situations, the corrected values provided by the optometrist were used in the database. The case history section of the patient file has checklist prompts for symptoms such as diplopia, previous eye surgery or injury, current smoking, medications, medical care, and last medical examination. The same research assistant, who acted as transcriber, entered the data for both clinic visits. She was not masked regarding the results of the previous visit, but did not compare back or confirm data between visits. Any queries were dealt with by one of two optometrists who were investigators in the study. 

Table 1. 

 

Criteria for AT Results and Disorders

	Criteria for AT Result	Criteria for Disorder
Strabismus (unilateral cover test)	Any	Any
Distance or near vertical phoria (alternating cover test using prism bars or MR with room lights dimmed using a variable prism)	>2 pd by CT or >1 pd by MR in the primary position51	As for AT
Distance exophoria (as for vertical phoria)	>4 pd exophoria (by CT or MR) in the primary position52,53	As for AT PLUS abnormal +ve fusional reserves or symptoms of diplopia or suppression (i.e., a distance phoria with evidence of decompensation)
Near exophoria (alternating cover test using prism bars)	>8 pd exophoria (by CT or MR)52,53	As for AT PLUS NPC >10 cm or symptoms of diplopia or decreased stereopsis or suppression (i.e., a near phoria with evidence of decompensation)
Esophoria (alternating cover test using prism bars)	Any	Any
NPC	>10 cm	See near exophoria
Incomitancy (as for vertical phoria but in the horizontal and vertical positions of gaze, motility testing undertaken with the broad H)	>1 pd vertical change or >5 pd horizontal change between any direction of gaze (by CT or MR) or any incomitancy in motility testing	As for AT
Anomaly of pursuits (observation with target moved in horizontal and vertical directions)	Any	Any
Suppression (performed in the dark, and if abnormal results, repeated in the light)	Any suppression or unfused response on W4D	See distance and near exophoria
Stereoacuity (Randot or Titmus circles at 40 cm)	>60 s	See near exophoria

 The standard test used in the clinic is briefly described in parentheses. CT, cover test; MR, Maddox rod; W4D, Worth-4-Dot.

This study was approved by the University of Waterloo's Office of Research Ethics and followed the tenets of the Declaration of Helsinki. Patients at the University of Waterloo Optometry Clinic were made aware that data may be used from their files for research purposes and that it would be anonymous and kept confidential. Patients could opt out of this implied consent agreement. 

Definitions of Terms

Several criteria were adopted in order to assess binocular function. A single test result outside of the normal range was defined as an abnormal test (AT). The criteria used to define ATs are listed in Table 1. The total percentage of people who had one or more ATs of BV or eye movements was determined (prevalence of ATs). The prevalence of each individual type of AT was also calculated, with the exception of poor stereopsis and abnormal Worth-4-Dot responses. The prevalence was not calculated for stereopsis and Worth-4-Dot as these tests were not undertaken routinely on patients. Since a single AT may not result in the experience of a disability (i.e., a difficulty in interacting with the environment ³⁷ ), we also defined BV disorders in the following way: a clinical condition that may need treatment and may have functional implications (see Table 1 for definitions of specific disorders). The percentage of people who had one or more of these BV or eye movement disorders was determined. 

A comorbidity score was determined by counting the number of comorbidities that were reported by the patient and listed in the case history section of the file for that patient encounter using the categories shown in Table 2. If a patient reported more than one condition in a category (e.g., more than one type of cancer), it was counted only once. This is an approach that has been shown to give a good estimate of the severity of comorbidity. ^38,39 Similarly, a score for the number of already diagnosed ocular health conditions was determined from the case history and the categories used for this are also shown in Table 2. VAs were measured using Snellen notation and converted into log of the minimum angle of resolution (logMAR). Participants were separated according to whether they had a visual acuity impairment (defined as a VA worse than 6/7.5 ⁴⁰ or logMAR 0.1 in the better eye) or low vision (defined as a VA worse than 6/12 ^40,41 or logMAR 0.3 in the better eye). VA was also considered for analysis in terms of the logMAR VA for the right eye, left eye, the eye with poorer VA, and the eye with better VA. 

Table 2. 

 

Conditions Counted Toward the Comorbidity Score and the Ocular Disease Score

Comorbidities Counted for the Comorbidity Score	Ocular Diseases Counted Toward the Ocular Disease Score
Hypertension	Glaucoma
Heart disease and cardiovascular disorders	Diabetic retinopathy or macular edema
Cancer (not including skin cancer)	Cataract or other media opacity
Respiratory disorders	Age-related maculopathy
Depression	Previous retinal detachment
Thyroid disorders	Epiretinal membrane
Cerebrovascular disorders (stroke)	Retinal vein or artery (or branch) occlusion
Arthritis (osteo and rheumatoid)	Other retinal conditions (e.g., retinoschisis, macular hole)
Diabetes
Other (e.g., dementia, seizures, Parkinson's disease)

Statistical Analysis

To consider the change in prevalence longitudinally, the 95% confidence intervals of the prevalence were calculated by the Wald method and were considered significantly different if the confidence intervals for each percentage did not overlap. Cross-sectional association with age was considered with univariate logistic regression. The prevalence of the following independent variables were first considered in a logistic univariate analysis: age, sex, better and worse eye corrected VA, presence of visual impairment, presence of low vision, comorbidity score, ocular disease score, smoking, and use of antidepressants. All univariate and multivariate analyses were undertaken on the data collected in the same time period (i.e., not between the current and past datasets). The dependent variables were the presence of either BV or eye movement AT, disorder in the current data or 10 years prior. For each of these dependent variables, a multivariate analysis was undertaken using forward stepwise logistic regression, with alpha to enter equaling 0.05 and alpha to remove equaling 0.15. The independent variables that were included were those that reached significance (P < 0.05) or were moderately close to significance (P < 0.15) in the univariate analysis. Univariate analysis was also used to determine any association with age for each of the individual past and current ATs and disorders (e.g., presence of strabismus or large distance exophoria). Data were analyzed in a spreadsheet application (Microsoft Excel; Microsoft Corp., Redmond, WA) for the descriptive statistics and a statistics software package (Systat; Systat Software, Inc., Chicago, IL) for the regressions. For significance, a value of P < 0.05 was used. 

Results

The total percentage of females was 56.8%. Figures 1A to 1I show plots of the prevalence of the individual BV and eye movement ATs and Figure 2 shows the prevalence of disorders that were classified differently than ATs (decompensated distance and near exophoria). Figure 3 and Table 3 show the final prevalence of any AT or disorder according to age for the current and past visits. When equivalent age groups were compared between the past and present data, no significant differences were found for either AT or disorder (Fisher exact test, P > 0.05). Longitudinal analysis of the change of prevalence across the 10-year period (comparing the same patients currently and 10 years prior) was undertaken to determine changes with age. The Fisher exact test showed that there were no significant differences in the ATs (except when comparing the group aged 70–79 years with the group aged 80+ years), but there were significantly more disorders with increasing age (Table 3). 

Figure 1. 

 

Prevalence of BV and eye movement abnormal test results. Past data were from the same patients but approximately 10 years prior to the current data. (A) Strabismus. (B) Distance or near vertical phoria. (C) Distance phoria >4pd. (D) Near exophoria >8pd. (E) NPC >10cms. (F) Distance esophoria. (G) Near esophoria. (H) Incomitancy. (I) Anomaly of pursuits. NPC, near point of convergence.

Figure 2. 

 

Prevalence of BV disorders that were classified differently from the AT results shown in Figure 1. (A) Decompensated distance exophoria. (B) Decompensated near exophoria. Decompensated distance exophoria was defined as >4 pd exophoria in the primary position PLUS abnormal +ve fusional reserves or symptoms of diplopia or suppression. Decompensated near exophoria was defined as >8 pd exophoria PLUS NPC >10 cms or symptoms of diplopia or decreased stereopsis or suppression. pd, prism diopter.

Figure 3. 

 

Final prevalence of any AT result or any disorder. (A) Any abnormal test result. (B) Any disorder.

Table 3. 

 

Prevalence (%) of BV and Eye Movement AT Results and Disorders According to Age

	AT Results				Disorders
Years	50–59	60–69	70–79	80+	50–59	60–69	70–79	80+
Past assessment	30.9	35.5	39.8	–	17.3	19.3	23.5	–
Current assessment	–	40.5	43.5	51.2	–	26.8	29.8	38.4
Fisher exact test (comparing the same age, but different groups)		P = 0.432	P = 0.505			P = 0.155	P = 0.214
Fisher exact test (comparing the same group past and current)		P = 0.088	P = 0.181	P = 0.046		P = 0.048	P = 0.043	P = 0.004

The results of the univariate logistic regression analysis are shown in Table 4. Only those parameters that were significant or close to significant at the P < 0.05 level, are shown. It can be seen that the use of antidepressants and age were most commonly associated with BV and eye movement AT or disorder. AT in the past data was significantly associated with age and antidepressants, but the association with antidepressants was significantly stronger than that with age (as judged by the nonoverlapping confidence intervals of the odds ratios). Current AT was best predicted by the number of comorbidities or antidepressants, and these were not significantly different in their association (as judged by the overlapping confidence intervals of the odds ratios). Disorder in the past data was best predicted by antidepressants or worse eye VA, but these were not significantly different in their association. Current disorder was significantly associated only with age. Age was significantly associated with past BV or eye movement AT (P = 0.028, Fig. 1A, Table 4) and with current disorder (P = 0.035, Fig. 1B, Table 4), but this association did not reach significance for current AT or past disorder. 

Table 4. 

 

Results of Univariate Analysis for Any AT Result and Any Disorder for Past and Current Data

	Odds Ratio (Lower–Upper CI)
Past AT result
Age	1.02 (1.00–1.05)	0.028*
Number of comorbidities	1.23 (0.99–1.52)	0.066
Antidepressants	3.16 (1.13–8.86)	0.028*
Worse eye VA	2.24 (0.81–6.22)	0.121
Better eye VA	5.22 (0.80–34.1)	0.085
Current AT result
Age	1.02 (0.997–1.04)	0.098
Number of comorbidities	1.23 (1.05–1.44)	0.010*
Antidepressants	5.78 (1.16–4.21)	0.016*
Worse eye VA	2.27 (0.88–5.84)	0.090
Past disorder
Age	1.02 (1.00–1.05)	0.083
Antidepressants	4.26 (1.56–11.7)	0.005*
Worse eye VA	3.28 (1.08–9.97)	0.037*
Current disorder
Age	1.02 (1.00–1.05)	0.035*
Number of comorbidities	1.16 (0.99–1.37)	0.075
Worse eye VA	2.20 (0.84–5.79)	0.109
Better eye VA	2.95 (0.74–12.0)	0.131

 Data show those whose probabilities were P < 0.15. Those that are significant at the P = 0.05 level are indicated with *. CI, confidence interval.

It is notable that the prevalence of a large near exophoria (Fig. 1D) is significantly higher than the prevalence of such a phoria that shows signs of decompensation (Fig. 2B). Thus, based on our criteria, the majority of people with a large near exophoria do appear to be able to compensate for it. Although not shown, it is also worth noting that 51 patients (10.2%) reported diplopia at their most recent examination and 33 patients (6.6%) in the past examination. 

Univariate (cross-sectional) analysis showed that the only individual ATs that were significantly associated with age were anomalies of pursuits (Fig. 1I); distance esophoria (Fig. 1F); and exophoria (Fig. 1C) for the current data and anomalies of pursuits and distance exophoria for the past data (P < 0.05). Table 5 shows the combined prevalence for all age groups for any AT or disorder and for the various measures of AT and disorder that were consistently measured at both visits. This longitudinal analysis shows that there was no change in the prevalence of abnormal distance phoria over the 10-year period, whereas there were significant increases in the prevalence of vertical phoria; near exophoria; remote NPC (Fig. 1E); and anomalies of pursuits (Table 5). These would appear to contribute to the increasing prevalence of any BV and eye movement AT and disorder (also shown in Table 5). 

Table 5. 

 

Combined Prevalence for All Age Groups for AT Results and Disorders

	Prevalence, Past	Prevalence, Current	P, Fisher Exact Test
Any BV and EM abnormal test result	35.4	45.0	0.003*
Any BV and EM disorder	20.0	31.6	<0.001*
Strabismus	5.8	6.4	>0.05
Vertical phoria	3.6	14.4	<0.001*
Distance exophoria	2.2	2.4	>0.05
Near exophoria	7.4	12.0	0.018*
NPC >10	6.8	13.8	<0.001*
Distance esophoria	4.4	5.0	>0.05
Near esophoria	3.8	3.4	>0.05
Incomitancy	4.4	3.6	>0.05
Anomaly of pursuits	3.4	7.4	0.005*
Decompensating distance exophoria	0.4	1.0	>0.05
Decompensating near exophoria	1.2	1.6	>0.05

 EM, eye movement; NPC, near point of convergence.

*  Indicates a significant difference in prevalence at the P = 0.05 level.

The results of the multivariate regression analysis are shown in Table 6. Age and use of antidepressants were the factors that most frequently came into the models, with number of comorbidities explaining current AT and worse eye VA explaining some of the variation in past disorder. 

Table 6. 

 

Models From Forward Multivariate Logistic Regression for Any AT Result or Disorder

	Coefficient		P for Model
Past AT result
Antidepressants	1.17	0.027	0.007
Age	0.02	0.027
Current AT result
Number of comorbidities	0.21	0.010	0.010
Past disorder
Antidepressants	1.45	0.005	0.003
Worse eye VA	1.20	0.037
Current disorder
Age	0.02	0.035	0.034

Discussion

The overall prevalence of BV and eye movement ATs and disorders are high in the older population, ranging from 31% to 51% for any AT and from 17% to 38% for any disorder. As far as the authors are aware, this is the first study giving the prevalence of a range of BV disorders in older adults and an additional strength is the longitudinal component of the data. It is impossible to compare this study precisely with other studies of the prevalence of BV disorders, as different definitions have been used, different conditions included, and different age groups sampled. However, the previously reported prevalence of BV disorders is quite high even in younger adult populations ranging from 15% to 26.7%, if 5% is added for strabismus. ^2–10,12,13 Thus, it appears that in clinic populations, BV disorders have a high prevalence in adults of all ages. The present study found an additional 3% to 5% prevalence of incomitancy (see Fig. 1H) and a 1% to 2% prevalence of anomalies of pursuits (Fig. 1I). 

In the present study, there was an association of BV and eye movement ATs and disorders with age, although it was not always the best predictor. The use of antidepressants, comorbidities, and VA in the worse eye were better predictors than age in some cases (current AT and past disorder; Tables 4, 5). The link with antidepressants is interesting and relevant as the use of antidepressants is common and increasing in the older population. ⁴² There are occasional references to associations between use of antidepressants and specific BV disorders in the literature. Gilmartin ³⁴ mentions that the use of tricyclic and related antidepressants may be associated with decompensation of an existing hyperphoria, very occasionally resulting in diplopia. Aminoff ³⁵ reports that certain drugs, including tricyclic antidepressants and antianxiety drugs (benzodiazepines), may be associated with diplopia due to a breakdown of heterophoria or more rarely due to extraocular muscle palsy, gaze palsy, or internuclear ophthalmoplegia. To our knowledge, this is the first study which links the prevalence of general BV and eye movement disorders to the use of antidepressants. Similarly, although the association between specific diseases (such as, thyroid disease, diabetes, and cerebral vascular accident) and incomitancy and strabismus is known, we are not aware of any other studies that specifically link the prevalence of general BV disorders with a comorbidity score. 

The prevalence of strabismus once a person reaches school age is quite consistent between studies at approximately 5% ^5–10,12,13 ; and we have found a similar result (Fig. 1A). In the present study, strabismus did not increase significantly with age. The increase of near exophoria with age is in agreement with the few previous studies that consider the change of exophoria for presbyopes (for prepresbyopes and early presbyopia, there is the additional factor of decreasing accommodation). Yekta et al. ¹⁵ reported an increase of near exophoria, associated phoria, and fixation disparity with age from 10 to 65 years, and that the rate of change appears to be constant over the prepresbyopic and presbyopic years. Hrynchak et al. ⁴³ found a continued increase of the prevalence of near exophoria and exotropia well after the onset of absolute presbyopia. Thus, the present study and that of Hrynchak et al. ⁴³ differ regarding changes in the prevalence of strabismus at near. This may be because the present study counted distance and/or near strabismus together (which may tend to mask the changes that occur specifically at near), whereas Hrynchak et al. ⁴³ considered only strabismus at near. However, the two studies are in agreement regarding the trend of increasing prevalence of exodeviation at near and some of these exodeviations may be expected to breakdown from a phoria to a strabismus. Yekta et al. ¹⁵ point out that the increase in near exophoria happens gradually over the prepresbyopic and presbyopic years (i.e., it does not seem to be related to the provision or increase of a reading addition). Our results confirm this as all the patients in the current study were presbyopic, requiring a reading addition. 

Although some longitudinal studies of distance phoria in younger populations show changes with age, ^44,45 those that have included older populations show no significant change ¹ (Irving EL, IOVS 2012;53:ARVO E-Abstract 1785). Pickwell, ¹⁶ in a cross-sectional study, found no age trends for prevalence of distance associated phoria. Our longitudinal analysis is in agreement that there is no significant change of the prevalence of either distance eso- or exophoria with age. 

The increasing prevalence of ATs and disorders with age seems to be influenced by an increasing prevalence of vertical phoria, near exophoria, decreased NPC, and anomalies of pursuits. Although we did not find a significant change in the prevalence of strabismus or incomitancy, the large change in the prevalence of vertical phorias (3.6%–14.4% over 10 years, Fig. 1B) might lead to strabismus. Magramm and Schlossman ²² reported that 26% of patients aged over 60 years receiving strabismus surgery had a vertical component to their strabismus and the majority had strabismus secondary to disease processes (neuroparalytic, restrictive or as a result of sensory loss) . 

BV problems are common in the older adults, and may result in reduced stereopsis, which has functional consequences, ⁴⁶ including being a known risk factor for falls in older adults. ²⁹ However, the management of BV disorders may not be receiving the attention that it deserves. Magramm and Schlossman ²² reported that on average, patients aged over 60 years experienced symptoms (most commonly diplopia and asthenopia) for a duration of 8 years prior to obtaining surgery for strabismus. Some of these BV disorders may be treatable, either with surgery, prismatic correction, or vision therapy that may be successful in older adults. ^47,48 Wick ⁴⁹ reported that vision training for convergence insufficiency reduces symptoms in presbyopic patients and Cohen and Soden ⁵⁰ report on a cohort of adults aged over 60 years whose symptoms associated with convergence insufficiency decreased and whose near point of convergence measurements improved with in-office and home-based visual therapy. However, there are no randomized clinical trials of the effectiveness of vision therapy for binocular disorders in older adults, which may be an area for future study. 

Acknowledgments

We thank Linda Lillakas for editing the text and for creating the figure files. 

Supported by Vision Services Plan and the Canadian Optometric Education Trust Fund. 

Disclosure: S.J. Leat, None; L.L.-L. Chan, None; P.-D. Maharaj, None; P.K. Hrynchak, None; A. Mittelstaedt, None; C.M. Machan, None; E.L. Irving, None