An Evaluation of Clinical Treatment of Convergence Insufficiency For Children With Reading Difficulties

Wolfgang A Dusek; Barbara K Pierscionek; Julie F McClelland

Disclosures

BMC Ophthalmol. 2011;11(21) 

In This Article

Methods

Subjects

Initially 1001 subjects were referred from three educational institutes in Vienna, Austria diagnosed with difficulties in reading and writing that could not be attributed to a learning difficulty. All subjects had been assessed by an educational psychologist and had an IQ (intelligence quotient) over 70. Subjects with ocular pathology (e.g. cataract, glaucoma, strabismus) were excluded from the study (n = 11) and referred for ophthalmological investigation. The visual status of a subset of this population has previously been described in detail.[10] One hundred and thirty four subjects were diagnosed with CI.

CI was confirmed if a subject demonstrated all of the first three clinical signs below. CI was also identified if subjects demonstrated at least two of the first three clinical signs with at least one other additional sign (point 4 and/or 5);

  1. A near point of convergence (NPC) greater than 6 cm

  2. Exophoria at both near and distance which was at least 6 prism dioptres more at near than at distance.

  3. A low accommodative convergence to accommodation ratio (AC/A) (< 2:1)

  4. A binocular accommodative facility of less than 6 cycles per minute using (+2.00/−2.00 flipper lenses) and a monocular accommodative facility better than 10 cycles per minute

  5. Reduced vergence facility less than 6 cycles per minute (using base-out prism)

All subjects with CI and reading difficulties (n = 134) attended for a second assessment four weeks after the first visit. Table 1 details the age and gender distribution of the subjects and Figure 1 illustrates the refractive error profile of the group.

Figure 1.

Mean spherical equivalent refractive error of subjects with convergence insufficiency.

All subjects in the present study were attending mainstream schools. Ethical approval for the study was obtained from the University of Ulster Research Ethics Committee and the study adhered to the Tenets of the Declaration of Helsinki. Written informed consent was obtained from all parents of the subjects included in the study.

Procedure

Intervention Two different types of treatment for CI were employed: a computerised home visual therapy system (HTS) and reading glasses without additional refractive power but with 8Δ base-in.

Details of the two treatment options were explained to all subjects and their parents and subjects were free to choose either treatment option. This study was not a randomised controlled trial, however, inclusion of a subject in either treatment group had no dependency on degree of CI, refractive error, age, initial measures of reading speed, reading accuracy, binocular accommodative facility, amplitude of accommodation, near point of convergence, ocular posture, MEM retinoscopy or vergence facility. This was confirmed by statistical analysis (one way ANOVA (p > 0.05). Thirty-two subjects refused both types of treatment offered and agreed to return for a subsequent assessment four weeks later as a control group for the study. Sample sizes were based on available clinical data. The 8Δ base-in spectacle group included 51 subjects and the HTS groups also included 51 subjects.

The majority of subjects in the 8Δ base-in group did not have a significant distance refractive error and were issued with spectacles for near vision only. Five subjects (two myopic and three hyperopic), were issued with Franklin split bifocals with the 8Δ base-in incorporated into the near portion of the spectacles.

Subjects issued with the reading glasses (8Δ base-in) were advised to use the spectacles for all near vision tasks that were greater than five minutes duration.[18] Subjects given the HTS were given written and verbal information on installation of the programme and the protocol for use.

The HTS is a computerized visual therapy system which is used by the subject in his or her home environment at a distance of 40 cm. The programme uses images that the subject has to fuse in order to perceive three dimensional (stereoscopic) images. These stereoscopic images are resolved using red/blue spectacles. The HTS was developed by Dr. Jeffrey Cooper and Rodney K. Bortel, and is used widely in the United States for patients with asthenopic symptoms.[14,16,20]

A demonstration of the HTS was provided and subjects and parents were advised that they could contact the practitioner (WD) with any queries regarding the programme. Subjects were advised to perform 3–4 sessions per week, each session lasting approximately 15–20 minutes, similarly to that recommended by The Convergence Insufficiency Treatment Trial Group.[16] The parents were instructed to regularly supervise and ensure that their child was carrying out the procedure correctly. This was done using an instrument incorporated in the programme allowing the date, time and performance of the exercises to be reviewed. These reviews were also carried out on a weekly basis by the practitioner (WD).

A range of visual function tests were carried out pre and post treatment. The procedures for these tests have previously been described in detail.[10]

All 134 subjects were reassessed after four weeks and the tests were repeated in the same order using exactly the same testing conditions as previously. Subjects with clinically significant refractive errors (≥ +1.00D hyperopia, ≤ −0.50D myopia, ≤ −1.00DC astigmatism or ≥ 1.00D anisometropa), wore his or her habitual spectacles during testing at both visits. Prismatic reading spectacles were not worn during testing at either visit.

Reading Speed and Accuracy

Reading speed and accuracy were assessed using a standard Austrian test known as The Salzburg Reading Test. Age appropriate material suitable for each particular subject was selected and the test was conducted in a quiet room. The child was asked to start reading a prescribed section of text and the time taken to complete the task was measured with a stopwatch. In addition, the number of incorrect words read was noted and an error score calculated.[21]

Ocular Posture

A standard cover-uncover test and alternating cover test revealed the presence and direction of heterotropias and heterophorias at distance and near (5 m and 40 cm). The subject was asked to fixate an acuity appropriate Polatest target for three seconds before the eye was covered and uncovered. This was done for both eyes. A prism cover test was employed to assess the magnitude of the deviations present.[22]

Accommodation

Amplitude of accommodation was measured monocularly using the push-up method.[23] Binocular accommodative facility was assessed in cycles per minute using flipper lenses (+2.00/−2.00 D). This was repeated for one minute and the number of cycles noted.[24]

Accommodative response to a target at a specific distance was assessed using Monocular Estimation Method (MEM) retinoscopy. The distance refractive error was fully corrected and a near target attached to the retinoscope at a distance of 40 cm. The subject was encouraged to read the text aloud while the retinoscopic reflex was observed. If the retinal reflex indicated a hyperopic or myopic state, plus or minus lenses, respectively, were added in 0.25 steps until neutrality was achieved.[25]

Convergence

Near point of convergence (NPC) was assessed using a standard protocol. Subjects were asked to fixate on the light of a pen torch while it was moved towards the subject's face and to report the point at which diplopia was first observed. The clinician also objectively assessed the point at which the subject lost fixation, when one eye deviated. The points at which the subject and the observer noticed a loss of fixation were noted.[26,27]

Vergence facility was assessed in cycles per minute using a standard flip prism (3Δbase in/12Δbase out) that provides information about the condition and the speed of the vergence system.[28] Subjects were asked to fixate a small target on the Gulden stick at 40 cm and asked to try to keep the target single and clear. Prism (3Δ base-in) was introduced first and the subject was asked to report when it became single. When the target was single and clear the 12Δ base-out) was introduced. When the subject reported that the target was clear the prism was switched back to the 3Δ base in. This was repeated for one minute and the number of cycles was noted.[28]

The Accommodative Convergence System of the Eyes The AC/A ratio was assessed by measuring the near phoria at 40 cm using the alternating cover test and prism bar. This was then repeated using -2.00D lenses in front of the eyes while the subject maintained fixation on the target at 40 cm. The AC/A ratio was calculated as the difference between the measured phoria with and without the -2.00D lenses, divided by two.[29]

Statistical Analysis

All data were analysed for significance using SPSS 17.0 for Windows. All data were assessed for normality using the one sample Kolmogorov-Smirnov Test. Factorial analysis was used to evaluate between subject effects and within subject effects.

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