Primary Care of Binocular Vision, Accommodative, and Eye Movement Disorders



Primary Care of Binocular Vision, Accommodative, and Eye Movement Disorders





A primary care optometrist is “a practitioner with ongoing responsibility for the total visual, ocular, and related care of a population of patients. Primary care optometry emphasizes the development and maintenance of a high level of knowledge and clinical ability over the entire area of eye/vision care and associated areas of eye-related health care.”1 What is expected in true primary vision care is an understanding of the entire breadth of eye care, whereby the provider recognizes what needs to be done for the patient and either provides or refers for the appropriate care.2 Thus, the primary care optometrist should be able to examine, diagnose, and treat most patients most of the time, and every patient who visits the primary care optometrist should expect a satisfactory outcome, even if it involves an appropriate referral.2

Applying this model to binocular vision, accommodative, and eye movement problems suggests that the primary care optometrist must be able to routinely examine and diagnose these problems, treating some of them, and making appropriate referrals when necessary for more detailed diagnosis and treatment. In our opinion, primary care optometry includes the diagnosis of routine binocular vision, accommodative, and eye movement disorders. Treatment of these problems using lenses, prism, occlusion, and home-based vision therapy also falls within the realm of primary care. Complex binocular vision, accommodative, and eye movement disorders and office-based vision therapy, however, are typically advanced-care treatment procedures requiring additional clinical training, office space, ability to train therapists, and equipment.

With the first and second editions of this book, our goal was to develop a text that would be valuable to both the optometrist wishing to practice advanced care of binocular vision, accommodative, and eye movement disorders (including office-based vision therapy) and the primary optometrist practicing with a more limited emphasis on these conditions (no office-based vision therapy available). We understand that many optometrists may find the diagnostic routine suggested in Chapter 1 to be too extensive for routine use in primary care practices. Further, most optometrists in primary care practice do not offer office-based vision therapy as a treatment approach. These doctors generally rely on the use of lenses, prism, home-based vision therapy, and in some cases referral to an optometric colleague with advanced experience in the area of vision therapy. This chapter is designed to stand alone as a reference for the primary care management of binocular vision, accommodation, and eye movement disorders. Table 4.1 summarizes the diagnosis and treatment techniques that we recommend for primary care practice.








Table 4.1 PRIMARY CARE HETEROPHORIA EXAMINATION AND TREATMENT











































































































































































































































































































Case history

High symptom scores on the CISS or VFS symptom questionnaires or complaints of eye strain, blurred vision, discomfort, double vision, loss of place, trouble sustaining, avoidance, and so forth, when symptoms are associated with visual tasks


Tonic vergence

Determine phoria magnitude and direction at distance with cover test or prism dissociation


AC/A ratio (calculated)

Determine whether AC/A ratio is high (more eso at near), normal (same distance and near), or low (more exo at near)


Calculated AC/A = IPD (cm) + NFD (m) (Hn – Hd)


Low AC/A Ratio (<3 Δ/D)

Normal AC/A Ratio (3-7 Δ/D)

High AC/A Ratio (>7 Δ/D)


Distance phoria

Eso

Normal

Exo

Eso

Normal

Exo

Eso

Normal

Exo


Near phoria

Ortho

Exo

More exo

Eso

Normal

Exo

More eso

Eso

Ortho

Vergence assessment

Base-out (distance)

y

y

X

y

y

X

y

y

X

Base-in (distance)

X

y

y

X

y

y

X

y

y

Supra and infra

Assess whether vertical phoria is seen on cover test OR whether symptoms exist (e.g., losing place when reading, getting on wrong line)

Base-out (near)

z

X

X

y

y

X

y

y

z

Base-in (near)

z

y

y

X

y

y

X

X

z

NPC (amplitude)

y

X

X

X

X

X

X

X

y

Facility

Near (12 BO/3 BI)

z

X

X

X

X

X

X

X

z

Associated phoria (lag)

Horizontal

z

y

y

z

y

y

z

y

y

Vertical

X

X

X

X

X

X

X

X

X

Comitance

y

y

y

y

y

y

y

y

y

Accommodation

Amplitude (push-up)

X

X

X

X

X

X

X

X

X

Facility (scaled)

X

X

X

X

X

X

X

X

X

Lag (MEM)

y

y

y

y

y

y

y

y

y

Sensory status

Stereopsis

y

y

y

y

y

y

y

y

y

Suppression

y

y

y

y

y

y

y

y

y


Treatment

Best correction

A

A

A

A

A

A

A

A

A

Added plus at near







+1.25

+1.25

+1.25




+1.25 near addition if abnormal findings on accommodative testing

Prism



Prescribe BO prism equal to one-third the distance phoria in esophoric patients

Horizontal

BO


BI (b)

BO


BI (b)

BO


BI (b)

Vertical



Prescribe vertical prism equal to associated phoria if symptoms exist (e.g., losing place when reading, getting on wrong line)

Home-based VT

b

A

A

b

A

A

b

b

Refer for office-based VT


Diagnosis: X, necessary diagnostic information; y, important at times; z, information that you may wish to gather.


Treatment: A or bold, necessary treatment; b, may be useful treatment.


AC/A, accommodative convergence to accommodation; BO, base-out; BI, base-in; CISS, Convergence Insufficiency Symptom Survey; eso, +; exo, -; Hd, distance phoria; Hn, near phoria; IPD, interpupillary distance (in centimeters); MEM, monocular estimation method; NFD, near fixation distance (in meters); NPC, near point convergence; VFS, Vision Function Scale; VT, vision therapy.






Diagnosis

Chapter 1 includes a comprehensive presentation of the case history and diagnostic testing required to manage binocular vision, accommodative, and eye movement disorders. Primary care optometrists may use Chapter 1 as a reference; however, this chapter presents a more streamlined evaluation. Using this approach will allow the primary care optometrist to expeditiously diagnose most of the problems most of the time, and to refer to a colleague for a more extensive evaluation and treatment when appropriate.



HISTORY AND SYMPTOMS

Use of a written symptom questionnaire, such as the Convergence Insufficiency Symptom Survey (CISS) or the Vision Quality Scale (VQS) can help establish the need for binocular vision and accommodative testing.
These questionnaires, illustrated in Figures 4.1 and 4.2, are standardized instruments that have been shown to be valid and reliable for measuring the type and frequency of symptoms for patients with convergence insufficiency and intermittent exotropia, respectively.3,4,5,6,7 Either can be used in clinical practice to efficiently determine whether a patient has symptoms related to binocular vision, accommodative, or eye movement disorders.






▪ Figure 4.1 Convergence Insufficiency Symptom Survey (CISS).






▪ Figure 4.2 Vision Quality Scale (VQS).







▪ Figure 4.2 (continued)


The CISS 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 greater than 16 on the CISS has been found to suggest significant symptoms5; for adults (18 and older), a symptom score greater than 21 on the CISS has been found to be significant.6

A generic tool for quality of vision assessment known as the Vision Function Scale (VFS) was developed by McKeon et al7 to measure the underlying construct of vision function of patients with intermittent exotropia; its domains were symptoms, physical functioning, and role functioning. The VFS has been modified (three questions dropped pertaining to the subject’s sex, age, and feeling of correctness of his or her answers) and relabeled as the VQS. Numerous applications of the VQS support its content validity. For example, the VQS discriminates between patients with and without asthenopia who have normal heterophoria, visual acuity, and ocular health. The patient chooses one of six possible answers (all of the time, most of the time, a good bit of the time, some of the time, a little of the time, none of the time). Each answer is scored from 0 to 6, with 6 representing the highest frequency of symptom occurrence (i.e., all of the time). The nine items are then converted to a percentage. A symptom score (percentage) of less than 71 on the VQS has been found to reliably suggest significant symptoms for patients older than 8 years.8

After symptoms and signs typically associated with binocular vision, accommodative, and eye movement disorders are identified in the case history (or through a standardized questionnaire), evaluation of binocular vision involves several distinct steps. The testing protocol we suggest requires minimal equipment and setup time, with most of the equipment readily available in most primary care practices. Our suggested minimum database (Table 4.1) for a primary care examination (after determination of the refractive error) includes the cover test at distance and near, determination of the calculated accommodative convergence to accommodation (AC/A) ratio, the near point of convergence, vergence facility, and testing of accommodation (amplitude and binocular facility testing). The setup and administration of these procedures is described in detail in this chapter.


Diagnostic Evaluation


DETERMINATION OF REFRACTIVE ERROR

Accurate measures of alignment and accommodation are facilitated by performance of a full-plus refraction with a binocular balance. Such an examination is often aided by an initial objective determination of the refractive error, which can be accomplished with static retinoscopy, autorefraction, or even starting with the patient’s previous refractive correction. To perform a modified full-plus binocular refraction, we recommend the following procedure:



  • 1. Use a 20/30 line (or an acuity line two lines above threshold).


  • 2. With the left eye occluded, add plus (0.25 diopters [D] at a time) to the objective findings until the right eye is barely able to read the 20/30 threshold line. If too much plus is used, the next step will be difficult, so you may want to back off slightly (add -0.25 D, at most).


  • 3. Perform Jackson cross-cylinder (JCC) testing (adding plus in the earlier step allows the patient to make more accurate JCC responses).


  • 4. Repeat for the left eye, with the right eye occluded.


  • 5. Add prism (3 Δ up before the right eye; 3 Δ down before the left eye) and +0.75 D to each eye.


  • 6. Perform a dissociated balance by adding plus to the clearer target until both eyes are reported to be equally blurred.


  • 7. Remove the dissociating prism and slowly add minus until the patient can just read 20/20. Do not arbitrarily add some amount of minus.


  • 8. Place the vectographic slide in the projector with analyzers in the phoropter. Place “I” target with letters on each side in the patient’s view and ask if both sides are equally clear. If not, add +0.25 D to the clearer side. This is a binocular balance but not a true binocular refraction (in which the JCC would be performed under these conditions as well).


  • 9. Perform stereopsis testing.


  • 10. Return to the standard slide and check visual acuity. If the patient cannot see 20/15, check whether -0.25 more OU improves the acuity. It is virtually never necessary to add more than -0.50 OU total. Do not arbitrarily add some amount of minus.

The maximum-plus refraction technique breaks down when acuity is very unequal (e.g., amblyopia). In these instances, where often no refractive technique works well, use retinoscopy to determine balance after attempting to achieve maximum plus on the “good” eye (make the retinoscopic reflexes appear equal for the two eyes).



Assessment of Nonstrabismic Binocular Vision Disorders


GENERAL CONSIDERATIONS

Primary care evaluation of binocular vision involves several distinct steps. The first phase of testing is measurement of the magnitude and direction of the phoria at distance and near, along with determining the calculated AC/A ratio. In a primary care practice, the most convenient procedure to accomplish phoria measurement is cover testing.


ASSESSMENT OF SIZE AND DIRECTION OF THE PHORIA


Cover Test (in the Absence of Strabismus)

1. Purpose The cover test is an objective method of evaluating the presence, direction, and magnitude of the phoria.

2. Important issues

(a) Controlling accommodation The most important aspect of the cover test procedure or any other test of binocular alignment is control of accommodation; underaccommodation will result in an overestimation of the degree of exophoria or an underestimation of the esophoria. Overaccommodation will yield the opposite results. Two techniques can be used to maximize control of accommodation during the cover test procedure. The examiner can use multiple fixation targets to maintain attention and accommodation on the task. This can easily be accomplished using Gulden fixation sticks that have 20/30 targets on both sides of the stick (see Fig. 1.2). Periodically, the fixation stick is turned around to change targets. The patient is asked to identify the target during the cover test. These refinements to the basic procedure tend to increase attention on the task.

Another useful procedure is to move the target from the left to the right very slightly (1 to 3 cm), between movements of the cover paddle. The examiner looks for a small pursuit movement in the uncovered eye. If a pursuit movement occurs when the target is moved from the left to the right, it suggests that the patient is attending to the target. Attention on the target tends to encourage accommodation.

(b) Objectivity Because the cover test is an objective technique, it is one of the most valuable methods for assessing the motor characteristics of binocularity. It becomes particularly valuable when working with children.

3. Expected values Although the expected finding for the cover test has not been specifically studied, the expected distance phoria (tonic vergence) is 1 exophoria, with a standard deviation of ±1 Δ. The mean expected near phoria is 3 exophoria, with a standard deviation of ±3 Δ.


Calculated AC/A Ratio

1. Purpose To determine the change in convergence that occurs when the patient looks from distance to near.

2. Important issues

(a) Significance in diagnosis and treatment The AC/A finding is a key characteristic in the final determination of the diagnosis and is also one of the most important findings used to determine the appropriate management sequence for any given condition. For example, esophoria at near associated with a high AC/A ratio generally responds well to plus lenses. If the same degree of esophoria is associated with a normal or low AC/A ratio, the recommended treatment approach would include prism correction or vision therapy or both.

(b) Calculated AC/A ratio The calculated AC/A ratio is determined using the following formula:

AC/A = IPD (cm) + NFD (m) (Hn – Hf)

where

IPD = interpupillary distance in centimeters

NFD = near fixation distance in meters

Hn = near phoria (eso is plus and exo is minus)

Hf = far phoria (eso is plus and exo is minus)

Example: IPD = 60 mm, the patient is 2 exophoric at distance and 10 exophoric at near (40 cm).

AC/A = 6 + 0.4 (-10 + 2) = 6 + 0.4 (-8) = 6 + (-3.2) = 2.8


When using this formula, remember to use the correct signs for esophoria and exophoria. A rule of thumb is that a high AC/A ratio will result in findings of more eso or less exo at near, and a low AC/A ratio will lead to findings of less eso or more exo at near.

(c) Controlling accommodation A source of measurement error in the AC/A evaluation is failure to control accommodation. Emphasize, in the instructional set, that clarity of the target is essential because variation in accommodative response from one measurement to another can adversely affect results.

3. Expected values The expected calculated AC/A ratio is 6:1, with a standard deviation of ±2.


Vergence Assessment

Gall et al8 found that the use of 3 Δ base-in/12 Δ base-out for vergence facility testing can differentiate symptomatic from nonsymptomatic patients. We recommend vergence facility testing on all primary care patients. In this view, vergence range measures only need to be performed on selected patients and in selected directions—for example, it is useful to assess convergence amplitudes on patients with distance exophoria but not as useful to determine the divergence ability of these same patients (Table 4.1).


Vergence Range Testing

Detailed vergence range measurement can often be deferred in a busy primary care practice.


Vergence Facility Testing

Notwithstanding the possibility of deferring testing of fusional vergence ranges, some vergence assessment is important. Use of 3 Δ base-in/12 Δ base-out for vergence facility testing can differentiate symptomatic from nonsymptomatic patients.



  • 1. Purpose Vergence facility testing is designed to assess the dynamics of the fusional vergence system and the ability to respond over a period of time.


  • 2. Important issues



    • (a) Strength of prism to use and target to use Gall et al8 performed a systematic study of vergence facility and found that the magnitude of choice is 3 Δ base-in/12 Δ base-out. This combination of prism yielded the highest significance for separating symptomatic from nonsymptomatic subjects as well as producing repeatable results (R = 0.85) when used for near vergence facility testing. In another study, Gall et al9 compared the use of three different vertically oriented targets for vergence facility testing and found that vergence facility is nearly independent of the target and that a simple vertical column of 20/30 letters is an appropriate target.


Near Point of Convergence

The third vergence area that should be evaluated is convergence amplitude. Generally referred to as the near point of convergence, this test is particularly important in the diagnosis of one of the most common binocular vision disorders—convergence insufficiency. Important issues include the type of target or targets to be used and performance over time.10,11



  • 1. Purpose The purpose of the near point of convergence is to assess convergence amplitude. A remote near point of convergence was found to be the most frequently used criterion by optometrists for diagnosing convergence insufficiency.12


  • 2. Important issues



    • (a) Target to be used and number of times to perform the test We recommend repeating the near point of convergence twice—first using an accommodative target and then using a transilluminator or penlight with red/green glasses.


ANCILLARY VERGENCE TESTING


Fixation Disparity

Fixation disparity testing represents a more recent method of assessing binocular vision and provides additional information that should be included in primary care assessment when deciding on a prism prescription for vertical heterophoria. The primary advantage of fixation disparity testing is that it is performed under binocular or associated conditions, in contrast to other tests that are performed under dissociated conditions.



Fixation Disparity Assessment



  • 1. Purpose In contrast to cover testing, which is done under conditions in which one eye is covered and fusion is prevented, fixation disparity testing is designed to evaluate binocular vision under associated conditions.


  • 2. Important issues



    • (a) Fixation disparity testing is performed under binocular conditions The main deficiency of the typical phoria measurement is that the evaluation occurs under dissociated conditions. Although some clinicians suggest the routine use of fixation disparity testing, we have found that in the majority of cases, phoria/vergence testing is sufficient to reach a tentative diagnosis and management plan. In situations in which the diagnosis is unclear or a vertical or base-out prism prescription is being considered, fixation disparity testing is an important addition to the examination procedure.


    • (b) Determination of prism correction Fixation disparity is currently considered the method of choice for determining the amount of prism to prescribe for vertical heterophoria.


Assessment of Accommodative Disorders


GENERAL CONSIDERATIONS

The traditional evaluation of accommodative function (Table 4.2) involves measurement of the amplitude of accommodation using the Donder push-up method. It is also important to test accommodative response and facility as well as amplitude.13,14,15,16,17,18,19 An important concept is that an individual may experience asthenopic symptoms and have an accommodative disorder even when the accommodative amplitude is normal.16,18 Wick and Hall20 studied the relationship among the three areas of accommodation (amplitude, facility, and response) that are usually tested. They screened 200 children and, after eliminating those who had strabismus or significant uncorrected refractive error, found that only 4% had deficits in all three of the accommodative functions. Their results suggest that it is impossible to predict the results of one test based on the results of another.

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Apr 13, 2020 | Posted by in OPHTHALMOLOGY | Comments Off on Primary Care of Binocular Vision, Accommodative, and Eye Movement Disorders

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