5.15.5 Interpretation

Children and adults should be able to converge to within about 7.5 cm and recovery should return within 10.5 cm (Rouse et al. 1999). An NPC larger than these figures suggests possible convergence insufficiency and should be investigated further. This investigation should include jump convergence (section 5.16), distance and near heterophoria (sections 5.7–5.10), near fusional reserves (section 5.12) and near fixation disparity (section 5.13). Given the high prevalence of accommodative insufficiency in children with convergence insufficiency (Rouse et al. 1999), tests of accommodation (sections 5.17–5.19) should also be conducted in these patients. The effect of any new refractive error or refractive change on these measurements should be assessed.

Instead of a failure of one eye to converge it is possible that diplopia will be reported and/or that both eyes are seen to no longer view the target because of over-convergence by one eye. This is rarely encountered but when is does arise it suggests that the patient may have an abnormally high AC/A ratio (section 5.11). This should be recorded and additional investigations should be carried out.

5.15.6 Most common errors

1.Measuring the subjective NPC only. This can lead to an incorrect finding of a remote NPC in older patients who can confuse blurring of the target with doubling and therefore report ‘doubling’ at their near point of accommodation, which is typically much further away than the NPC.

2.Carrying out the test once only; the test should be carried out at least twice to gain an impression of test repeatability.

3.Moving the target too rapidly or unsteadily.

4.Moving the target too slowly causing the patient, especially children, to lose interest.

5.Not encouraging the patient enough to keep the target single (particularly children).

6.Testing the eyes in upward or primary gaze instead of slightly downward gaze.

7.Carrying out the test in patients who have a heterotropia. Such patients will suppress the image in the deviating eye and may therefore never experience doubling of the target.

5.16 JUMP CONVERGENCE

The test involves assessing the quality of convergence as fixation jumps from a distant or middistant target to a near target. There are two versions of this test but the principle and procedures to be followed are identical in the two cases. In one case, the ability of the patient to quickly switch fixation between a distant (6 m/20 feet) and a near (e.g. 20 cm) target is assessed. In the other version, jump convergence is assessed between two relatively near targets (e.g. one at 60 cm, and the other at 20 cm).

5.16.1 Convergence ability

See section 5.15.1.

5.16.2 Advantages and disadvantages

Tests of jump convergence are not normally included in the diagnosis of convergence insufficiency, perhaps because it provides qualitative rather than quantitative data. However, the test has its advocates and the task carried out by the patient in the jump convergence test has the advantage that it more closely reflects typical near viewing situations where fixation is continually switching between near targets; it is seldom in the real world that we would encounter a target that moves slowly and predictably towards us along the midline as with the NPC task. Early research suggested poor jump convergence was more prevalent than a remote NPC and was more closely associated with symptoms (Pickwell & Hampshire 1981). The test is relatively easy to perform and can be used as an additional assessment in patients who show signs of convergence insufficiency, and in patients with symptoms that could suggest convergence problems who show a normal NPC. However, the test is limited by the qualitative nature of the results and is less well known than the NPC. Furthermore, it has not been subjected to the same research evaluation as the test of NPC.

5.16.3 Procedure

1.Seat the patient comfortably with their head erect and eyes in slightly downward gaze. The patient should wear their refractive correction for distance viewing. Sit directly in front of the patient so that both eyes can be viewed simultaneously, but so that distance fixation is not obscured.

2.Keep the room lights on. If necessary, position additional lighting to illuminate the patient’s eyes and/or the target, thus avoiding shadows.

3.Indicate clearly to the patient both a distant single letter of a size one line larger than the patient’s VA of the poorer eye (e.g. if the patient’s VAs are 6/4 and 6/9, use a 6/12 letter as a target) and near (fixation rule) target. Position the near target about 20 cm in front of the patient. In another version of the test, the patient may be asked to switch fixation between a target at, say, 60 cm and another at, say, 20 cm.

4.Ask the patient to alternate fixation from the near target to the more distant target and back again.

5.Observe the eyes as they converge and diverge in order to gain an impression of the speed and accuracy in switching between the two target locations.

5.16.4 Recording

Record whether the jump convergence is smooth and fast or whether there are any jerky movements or an inability of one eye to converge adequately to the target. For example:

Jump convergence: smooth & fast;

Jump convergence: jerky, RE slower to converge.

5.16.5 Interpretation

Fast, smooth jump convergence should be observed to 10–15 cm. Poor, jerky jump convergence suggests

possible convergence insufficiency and should be investigated further. As previously stated, the investigation for possible convergence insufficiency should include distance and near heterophoria (sections 5.7–5.10), near fusional reserves (section 5.12) and near fixation disparity (section 5.13) and the patient’s accommodation (sections 5.17–5.19) should be fully assessed. The effect of any new refractive error or refractive change on these measurements should be determined. The near pupillary reflex should also be investigated.

5.17 PUSH-UP/PUSH-DOWN AMPLITUDE OF ACCOMMODATION

The amplitude of accommodation is the maximum amount of accommodation or focusing ability that the patient can exert in response to a near target. The near target is moved closer to the patient’s eyes until it first blurs (the push-up amplitude) and then moved away from the eyes until it becomes clear (the push-down amplitude). An average of these two threshold values provides an indication of the amplitude of accommodation.

5.17.1 Amplitude of accommodation

Accommodation or focusing allows targets to be made clear over a large range of distances. The amplitude of accommodation measures the full range of accommodation: from the far point, where accommodation is fully relaxed, to the near point, with maximum accommodation exerted. If the far point is at infinity (as in the case of emmetropes and those wearing optimal refractive correction for distance vision), then measurement of the near point allows the amplitude of accommodation to be determined with ease. The amplitude is calculated simply by taking the inverse of the near point of accommodation, which is expressed in metres. For example, if the near point was 10 cm, the amplitude of accommodation is 1/0.10 10 D. The amplitude of accommodation gradually falls with age, and causes patients over the age of about 45 years to have difficulty with near work and require reading glasses. Measurement of the amplitude of accommodation can help to identify the appropriate reading add

required to alleviate the patient’s near visual problems (section 4.22.3). The amplitude of accommodation becomes zero at age 55–60 (Charman 1989). If you obtain a measure for amplitude of accommodation in patients over 60 years of age, you are measuring their depth of focus and not accommodative amplitude.

5.17.2 Advantages and disadvantages

The push-up/push-down test is quick and easy to perform and assessment of the near point of clear vision relates to the typical symptom reported by early presbyopes. A combination of the push-up and push-down measurements is preferred as it provides a useful compromise between the slight overestimate of the push-up technique and the slight underestimate of the push-down technique (Rosenfield 1997). The most commonly used alternative involves using increasing amounts of minus spherical lens power until distance vision blurs (‘Sheard’s technique’). This method typically provides lower estimates of amplitude of accommodation than those provided by the push-up method (Kragha 1986) and it can only be satisfactorily measured using a phoropter. In addition, the minus lens method provides a less clinically relevant measure than the push-up technique, which provides a direct measurement of the near point of clear vision (Atchison et al. 1994).

5.17.3 Procedure

1.Explain the test to the patient: ‘I am going to measure the focusing power of your eyes.’

2.The test is usually performed with the patient wearing their optimal distance correction, but can be performed with the patient’s spectacles as a screening test. If the test is to be performed on early presbyopes

they should wear a partial addition

( 1.00 for 45–55 years) to ensure they can see the stimulus at the end of the near-point rule. The clinician should sit directly in front of the patient to allow a simultaneous, unobstructed view of the two eyes. In young children with very high amplitudes, slight linear differences of the near point produce

large dioptric differences, and it is useful to add a 3.00 D lens to place the near point further from the spectacle plane. This also ensures that depth-of-focus errors are minimised (Atchison et al. 1994).

3.Direct additional lighting over the patient’s shoulder to illuminate the reading card without shadows.

4.The test is usually performed monocularly (right and left) followed by a binocular measure of accommodation amplitude. The procedure is common for all viewing conditions. For monocular measures occlude one eye.

5.Indicate to the patient to view the smallest size text they can see on the near chart when positioned at about 40 cm (often N5, 0.4M, 20/20). The angular size of the text will increase as it is moved closer to the patient.

6.Move the target slowly towards the patient. Instruct the patient: ‘Please look at this print. I am going to move it closer to you and I want you to tell me when it first becomes blurred.’ Keep moving the target until the patient notices that the letters begin to blur.

7.At this first noticeable blur, ask the patient to try and clear the print. If they can, continue to move the print closer to the eye until the first sustained blur is reached and measure the distance to the spectacle plane.

8.From a point very slightly ( 0.50 D) beyond the first blur position, gradually move the target away from the patient and ask them to indicate when it first becomes clear. Measure the distance to the spectacle plane.

9.The amplitude of accommodation can be determined by taking the dioptric average of these two values (push-up amplitude and push-down amplitude).

10.Add the effect of any additional lenses to the measured dioptric near point to obtain the true amplitude. For example, if a 1.00 DS lens was added and the measured amplitude was 4.50 D, the actual amplitude of accommodation is 3.50 D as the additional lens provided 1.00 D. If a 3.00 DS lens was added and the scale indicates

an amplitude of 7.50 D, the true amplitude is 10.50 D.

11.Repeat for the left eye.

12.Repeat binocularly.

13.If the measured amplitude differs significantly from known age-matched normal values, repeat the test to ensure that the abnormal finding is not an artefact of the procedure. In young adults, differences of less than 1.50 D between recorded and age-matched values, or between recordings on two separate occasions, are not usually clinically significant (Rosenfield & Cohen 1996).

5.17.4 Recording

Record the number of dioptres of accommodation for each eye. Examples:

Amps (push-up/push-down) RE 8.50 D, LE 8.50 D, BE 10.00 D

Amps (push-up) OD 4.00 D, OS 4.00 D, OU 5.00 D.

5.17.5 Interpretation

Push-up values for the amplitude of accommodation may be artificially raised due to the effect of depth of focus. As the print is brought closer to the patient, its angular size increases and, as a result, more and more defocus can exist before the patient becomes aware of it. This can be overcome by using increasingly smaller print as the near card is brought closer to the eyes (Atchison et al. 1994). It can also be limited by adding a 3.00 D lens in front of a younger patient’s eyes, so that the measured near point is moved further away from the eyes. By combining the push-up finding with the push-down result (which tends to slightly underestimate the amplitude), this problem is minimised.

Normal values of monocular spectacle accommodation are shown in Table 5.5. If the measured amplitude is significantly ( 1.50 D; Rosenfield & Cohen 1996) lower than the age-matched normal values, the patient may have accommodative insufficiency. Binocular values of the amplitude of accommodation are usually a little higher (1–2 D) than the monocular values as the convergence response

Table 5.5 Monocular expected accommodation levels as a function of age.

Duane–Hoffstetter formula for probable amplitude of accommodation:

Maximum amplitude 25.0 0.40 age. Average amplitude 18.5 0.30 age. Minimum amplitude 15.0 0.25 age.

helps to induce additional accommodation (convergence accommodation). If amplitude of accommodation is reduced to a level below 5.00 D in a patient aged over 40 years wearing optimal distance correction but who has difficulty reading, the patient is presbyopic.

Anomalies of accommodation may be associated with a wide variety of conditions including various systemic and ocular medication (probably the most common cause), trauma, inflammatory disease, metabolic disorders such as diabetes and other systemic diseases (Rosenfield 1997). Reduced amplitudes of accommodation have also been reported in children with Down’s syndrome (Woodhouse et al. 1993) and cerebral palsy (Leat 1996). Wick & Hall (1987) found that a battery of tests (amplitude, lead/lag of accommodation, accommodative facility and a cycloplegic refraction) was required to detect accommodative dysfunction, and that just because a patient had an adequate amplitude of accommodation, this did not mean that accommodative function was normal.

5.17.6 Most common errors

1.Not stressing to the patient to report the first signs of blur; it should be stressed that this is not the same as the point at which they can no longer read the text.

2.Not investigating whether, at the first reported blur, the patient can ‘bring the print back into focus’.

3.Carrying out the test without optimal distance correction in place. This will have the effect of overestimating the amplitude in myopes and underestimating the accommodative amplitude in hyperopic individuals.

4.Moving the card too slowly and from too far away will tire the patient and can result in an artificially low score.

5.18 NOTT AND MEM DYNAMIC

RETINOSCOPY

Nott and Monocular Estimation Method (MEM) dynamic retinoscopy provide an objective assessment of accomodative error to a near target.

5.18.1 Accommodative lag or lead

Accommodative lag and lead indicate whether a patient’s accommodation level to a target is slightly less (lag) or slightly more (lead) than expected. This can be measured objectively using various dynamic retinoscopy techniques or subjectively using relative accommodation measurements or the binocular crossed-cylinder method. The latter two subjective measurements are more often used in the assessment of accommodation to help determine the tentative reading addition and are discussed elsewhere (section 4.22).

5.18.2 Advantages and disadvantages

Dynamic retinoscopy offers a quick, repeatable and valid means for establishing the accuracy of the patient’s accommodation system (McLelland & Saunders 2003) and requires minimal extra equipment. Both dynamic retinoscopy tests provide results that are less variable than the crossed-cylinder or near duochrome techniques (Rosenfield et al. 1996). As with most clinical techniques, practice is required in order to develop proficiency in carrying out the tests, especially in relation to the short time in which to make retinoscopy judgements. One study has

suggested that the Nott technique provides more accurate estimates of the accommodative response (Rosenfield et al. 1996) as it does not require the introduction of supplementary lenses.

5.18.3 Nott dynamic retinoscopy procedure

1.The patient should wear their optimal distance refractive correction in the trial frame, or their existing spectacles if lens powers are not significantly different from the optimal refraction result. The phoropter should not be used for this test because of the risk of inducing proximal accommodation.

2.Explain the test to the patient: ‘I am going to check the focusing ability of your eyes using this torch that will shine a light into your eye.’

3.The test should be carried out in conditions that approximate, in so far as possible, normal reading conditions and the card to be viewed by the patient needs to be located close to the patient’s typical reading distance (e.g. 40 cm). The card should contain letters (or pictures for young children) in a position that permits you to perform retinoscopy close to the patient’s visual axis. A near chart with a central aperture works well. The letters should be one line bigger than the binocular near visual acuity (typically N6, 0.5M, 20/30).

4.Dim or turn off the room lights but use additional lighting to illuminate the near chart.

5.Ask the patient to focus on the letters.

6.Perform retinoscopy on the right eye from 50 cm (typically 10 cm behind the near point card) along the horizontal meridian (with the streak vertical). Perform retinoscopy as quickly as possible as the retinoscope light will interfere with binocularity.

7.If neutrality is not observed at 50 cm, change the working distance (further away if ‘with’ movements are seen at 50 cm, and closer if ‘against’ movements are seen) until the neutral point is seen. Note the distance of your retinoscope when the neutral point is obtained.

8.Repeat the procedure on the left eye.

5.18.4 MEM dynamic retinoscopy procedure

1.Attach a MEM card or hold a fixation stick to the front of your retinoscope. The card should contain letters or pictures around a central aperture, through which retinoscopy is performed.

2.Dim or turn off the room lights and use additional lighting to illuminate the near chart.

3.Ask the patient to focus on the letters. To maintain appropriate fixation and accommodation you may need to ask children to read some of the letters out aloud or to name details in the picture.

4.Perform retinoscopy on the right eye from the patient’s typical working distance (usually around 40 cm) along the horizontal meridian (with the streak vertical). Retinoscopy should be performed in the usual manner, but the lenses should only be placed in front of the patient’s eyes for the least amount of time possible. This is to maintain binocularity, which is interrupted by the retinoscope’s light. Try to ensure that the accommodative system does not change in response to any added lenses. To ensure the latter does not occur, you need to place the plus lens in front of the eye for 0.50 seconds or less.

5.Record the dioptric power of the lens that provides neutrality.

6.Repeat the procedure on the left eye.

5.18.5 Recording

For the Nott technique, record the dioptric difference between the near chart and the position of the retinoscope when neutrality is observed. If the neutrality point is behind the near chart position, then there is a lag of accommodation. If the neutrality point is in front of the near chart position, then there is accommodative lead. For example, if the near chart is at 40 cm and neutrality is observed at 57 cm, then the accommodative lag is 2.50 D

1.75 D 0.75 D. It is useful to learn corresponding distances and dioptric values, such as 80 cm (1.25 D), 67 cm (1.50 D), 57 cm (1.75 D), 50 cm (2.00 D), 44 cm (2.25 D) and 40 cm (2.50 D).

For the MEM technique, record the dioptric value of the lens that produces neutrality. Positive lenses indicate a lag of accommodation and negative lenses indicate a lead of accommodation.

5.18.6 Interpretation

Typically, the accommodative response to a target is slightly less than the accommodative stimulus. For example, a target positioned at 40 cm provides an accommodative stimulus of 2.50 D, but the normal accommodative response is slightly less, at about 2.00 D. The target remains clear due to depth of focus. Accommodative lags of 1.00 D or greater could be due to uncorrected (or insufficiently corrected) presbyopia and/or hyperopia, or it can indicate a lack of accommodative amplitude or reduced accommodative facility in a pre-presbyopic patient. The lack of an accommodative lag or an accommodative lead can indicate latent hyperopia, pseudomyopia or accommodative spasm. It is claimed that the MEM technique provides lags which are on average twice those found using the Nott method (Cacho et al. 1999) but most studies find results that are similar (reviewed in Rosenfield 1997).

5.19 2.00 DS FLIPPERS

of 2.00 D spheres, are used to assess a patient’s ability to rapidly change accommodation without changing vergence.

5.19.1 Accommodative facility

Accommodative facility is the ability of a patient to rapidly change accommodation. A reduced accommodative facility has been shown to be related to symptoms experienced in near viewing and it may exist even when other accommodative measures, such as the amplitude of accommodation (section 5.17), are at normal levels (Wick & Hall 1987).

5.19.2 Advantages and disadvantages

The test can be performed rapidly with minimal additional equipment. Measures of accommodative facility may be useful in diagnosing binocular vision problems in symptomatic patients whose phorias and visual acuities are normal (Gall & Wick 2003). It appears to have diagnostic value in that a reduced facility correlates with near symptoms and facility increases as symptoms are alleviated through treatment. Indeed, flippers can be part of the treatment. There is little justification for the use of the 2.00 DS flippers other than that they are the power traditionally used. Indeed, it may be that what is required is a range of flipper powers that relate to the patient’s amplitude of accommodation (Wick et al. 2002). For example, for a young patient with an amplitude of 12.00 D, the 2.00 DS represent only a 33% range of the amplitude, whereas they represent a 67% range of the amplitude in an older patient with an amplitude of 6.00 D. Yothers et al. (2002) suggest using an amplitude-scaled test for adults, which uses a test distance that requires 45% of the amplitude of accommodation to be exerted and a lens flipper range that is 30% of the amplitude. For example, a patient with 7.00 D of accommodation would indicate the use of an approximate working distance of 32 cm (1/3.15, i.e. 45% of 7.00) and a flipper range of 2.10 (30% of 7.00) giving a flipper power of 1.00 D.

5.19.3 Procedure

Many authors recommend measuring the binocular accommodative facility with a suppression check (typically using Polaroid glasses with the Bernell No. 9 vectogram). For appropriate comparison, the monocular measurements should be made with the same set-up except that one eye is now fully occluded. Alternatively, accommodative facility can be measured using standard near charts with binocular facility only measured if other tests indicate that the patient does not suppress at near. In this case, the ‘clinical pass’ values (section 5.19.5), which were obtained using the Polaroid system, cannot be used for comparison. Some authors just test binocularly first and only measure monocular facility if the binocular results are reduced. If the binocular facility is reduced, but monocular facility values

are within normal limits, then this suggests a binocular dysfunction not associated with accommodative facility.

1.If testing monocularly, occlude one eye. Keep the room lights on and if necessary, use localised lighting so that the patient’s eyes can be easily seen without shadows.

2.Explain the measurement to the patient: ‘I am now going to test how quickly your focusing muscles can work.’

3.Ask the patient to hold a near chart at the normal reading distance (40 cm is often used as standard). Ask them to look at a letter one line bigger than their binocular near visual acuity. This would typically be about N6 (0.4M, 20/30).

4.Explain the test to the patient: ‘I want you to keep looking at the word/letter … I am going to place a lens in front of your eye that may make the word appear blurred. I want you to focus and make the print clear again as soon as you can. As soon as it becomes clear, say ‘clear’. I will then flip another lens in front of the eye that may make the word appear blurred again. As before, I want you to refocus quickly and make the word clear again, and then say ‘clear’. We will repeat this for 60 seconds.’ Demonstrate the procedure to the patient so that they understand what is required of them before the test is started.

5.Start your watch as soon as you place the2.00 D lens in the lens flippers (twirls) in front of the patient’s right eye and ask them to tell you as soon as they get it clear by saying ‘clear’.

6.As soon as the patient reports that the word is clear, quickly flip the lens flippers to the –2.00 lens and ask the patient to inform you as soon as the letters become clear again.

7.Count the number of times the patient utters ‘clear’ in 60 seconds. One cycle consists of clearing both the plus and the minus lenses.

8.Repeat for the left eye.

9.Repeat the test binocularly if the patient does not suppress at near. Some practitioners use a polaroid bar reader placed over the near chart