Alison Y. Firth

Visual side effects from transdermal scopolamine (Hyoscine)

Transdermal scopolamine may be used to reduce drooling in children with disabilities. Side‐effects include dilated pupils and a reduction in the near point of accommodation (the closest point at which clear vision is possible). Two male children with epilepsy, one with spinal dysraphism (aged 7y 6mo) and one with cerebral palsy (aged 5y 8mo), who have undergone treatment for drooling with transdermal scopolamine are described. Near visual acuity was reduced, and both children showed dilated pupils with reduced or no response to light. These responses became normal on cessation of the scopolamine patch. As the effect of this drug may be cumulative, and many patients are unable to communicate difficulties, clinicians need to be aware of these possible side‐effects.

Orthoptic status before and immediately after heroin detoxification

Aim: To determine whether changes in orthoptic status take place during withdrawal from heroin and/or methadone. Method: A prospective study of patients, using a repeated measures design, attending a 5 day naltrexone compressed opiate detoxification programme. Results: 83 patients were seen before detoxification (mean age 27.1 (SD 4.6) years) and 69 after detoxification. The horizontal angle of deviation became less exo/more eso at distance (p<0.001) but no significant change was found at near (p = 0.069). Stereoacuity, visual acuity, and convergence were found to be reduced in the immediate post-detoxification period. Prism fusion range, refractive error, subjective accommodation, and objective accommodation at 33 cm did not reduce but a small decrease was found in objective accommodation at 20 cm. Conclusions: The eso trend found in these patients may be responsible for the development of acute concomitant esotropia in some patients undergoing heroin detoxification. However, the mechanism for this trend does not appear to be caused by divergence insufficiency or sixth nerve palsy.

Heroin withdrawal as a possible cause of acute concomitant esotropia in adults

Purpose To report the possible effects of heroin withdrawal on binocular vision.Methods A case series of patients is presented in whom esotropia developed on cessation of heroin use.Results In each case the esotropia was concomitant and prismatic correction restored binocular single vision. Intermittent spontaneous control occurred in one patient, the deviation resolved in one and one patient was lost to follow-up.Conclusions Heroin withdrawal should be considered as a cause of acute concomitant esotropia. However, an accurate history of other medication is needed to ensure that this is not the cause of decompensation.

Is the Cardiff Acuity Test effective in detecting refractive errors in children

Purpose. Refractive error is a common cause of reduced visual acuity in young children. This reduced vision should be detected as soon as possible to avoid development of squinting and educational disadvantage. The Bailey-Lovie Chart (BLC) is based on the logarithm of the minimal angle of resolution (logarithm of the minimum angle of resolution [logMAR]) and is widely accepted as the clinical standard for visual acuity testing. However, most young children are unable to perform this test because of its symbolic level. The Cardiff Acuity Test (CAT) overcomes these symbolic demands and is the test of choice for young children in most U.K. orthoptic departments. The purpose of this study is to determine how effective the CAT is in detecting reduced visual acuity caused by refractive error in young children. Methods. Visual acuity of the right eye was tested without spectacles in 68 children (mean age, 74 ± 14.6 months) with known bilateral symmetric refractive error (40 male) using the CAT and the BLC. Subjects were randomized to receive CAT or BLC first in a single assessment using a crossover design. Subjects scoring 0.2 logMAR or better were classified as having passed the test. Results. The CAT correctly identified reduced vision caused by uncorrected refractive error in 25% (17) of the children compared with a detection rate of 97% (66) for the BLC using the specified pass criteria. Further analysis with an adjusted cut point for the CAT (0.0 logMAR), as used to identify abnormal vision in clinical practice, identified a detection rate of 56% (38 of the children). Conclusions. This study casts doubt on the current clinical practice used in orthoptic clinics by suggesting that assessment of visual acuity with the CAT alone will underdiagnose reduced acuity caused by refractive errors.

The response AC/A ratio: differences between inducing and relaxing accommodation at different distances of fixation.

Purpose: To determine if there is a difference between the response AC/A ratios when measured using the gradient method at near and distance fixation with plus and minus lenses respectively in young adults with normal binocular single vision. Methods: A repeated measures design was used. The accommodative response of the right eye was measured objectively using the Shin-Nippon SRW-5000 autorefractor (Grand Seiko Company, Fukuyama, Japan) (open view) at 33 cm with and without plus lenses (2DS or 3DS) and at 3.8 m with and without minus lenses (2DS or 3DS) dependent on the participants’ ability to obtain subjectively “clear” vision. The angle of deviation was measured using the alternate prism cover test at 33cm and 3.8m fixing with the right eye with the participant sat at the autorefractor. LogMAR 0.0 (6/6) was used for fixation. Response AC/A ratios were calculated. Results: Twenty-five participants were examined; mean and standard deviation of their ages were 21.2 ± 4.04 years. The mean and standard deviation of the near response AC/A ratios was 4.73 ± 2.34/1 and at distance was 3.05 ± 1.71/1. Pearson’s Product Moment Correlation Coefficient showed no correlation between the 2 sets of data. Paired t-test showed that there was a statistically significant difference between the near and distance response AC/A ratios (t = 3.30, p = 0.003). The difference was found to be greater in participants who were non-orthoptic students. Conclusion: The response AC/A ratio was found to be slightly higher at 33 cm with plus lenses than at 3.8 m with minus lenses. No reason was identified for this difference but adaptation and perceptual effects could be further explored.

Comparison of the visual effects of Fresnel prisms in normal and amblyopic eyes

PURPOSE To assess the effects of Fresnel prisms on visual acuity and peak contrast sensitivity in the amblyopic and sound eyes of participants with amblyopia and to determine whether these functions were affected by Fresnel prisms to a different degree than those of controls. METHODS The LogMAR visual acuity and peak contrast sensitivity of 10 unilateral amblyopic participants (mean age, 22.6 years) and 9 controls (mean age, 26.2 years) were tested with Fresnel prisms of powers 5(Delta), 10(Delta), 15(Delta), 20(Delta), and 25(Delta) and without a Fresnel prism. RESULTS A statistically significant reduction in visual acuity with increasing prism power was found for all 3 groups, with the visual acuity of the amblyopic eyes being the least affected by the prisms. No statistically significant differences were found between the control and the sound eyes. No statistically significant differences in the effects of the prisms on peak contrast sensitivity could be detected between the 3 groups. Fresnel prisms were found to have a smaller effect on those amblyopic eyes with a poorer baseline visual acuity, indicating that these eyes may tolerate strong prisms without substantially impairing their visual acuity. CONCLUSIONS Fresnel prisms have a lesser effect on the visual acuity of amblyopic eyes than on controls. In contrast, results for peak contrast sensitivity were very similar for each of the groups tested, and no significant differences were evident between the amblyopic, sound, and control eyes.

Adie syndrome: evidence for refractive error and accommodative asymmetry as the cause of amblyopia

PURPOSE To report objective changes in accommodation in a child with Adie syndrome. METHODS A child aged 2 years 10 months when initially examined was found to have good visual acuity in both eyes, a low degree of hypermetropia (isometropic), and Adie pupil presumed to be caused by chicken pox that had occurred 2 months earlier. Amblyopia developed but responded well to treatment, which involved correction of the refractive error and occlusion therapy. Objective changes in the refraction of the eye were measured on the Canon R1 autorefractor at 3.8 m and 33 cm. RESULT The degree of accommodation in the affected eye when both eyes were open was markedly reduced. CONCLUSION The presence of isometropic hypermetropia, which remains uncorrected when Adie syndrome is present, can lead to the development of amblyopia in a child.

Botulinum toxin for the treatment of acute-onset concomitant esotropia in Chiari I malformation

Acute-onset esotropia (ET) is a rare presentation of Chiari I malformation. The ET may resolve following neurosurgical decompression, although this is not usually immediate.1 Where neurosurgery is not undertaken, Kowal et al 2 suggest prismatic correction or strabismus surgery. The latter may result in temporary correction of the strabismus, as the strabismus can recur and resolves only following decompression.3 Botulinum toxin (BT) has been reported as successful in one case where the ET did not resolve following neurosurgery.4 Despite BT being a common treatment for acute acquired concomitant ET,5 no previous case has been reported in which BT …

Non-linearity of the response accommodative convergence to accommodation ratio.

Abstract Purpose: Previous studies have reported variation in stimulus accommodative convergence to accommodation (AC/A) ratio across differing accommodative stimuli. Response AC/A ratio was assessed across 4 accommodative demands to determine if these differences could be due to accommodative inaccuracies to stimuli. Methods: Twenty-three student participants aged 18 to 26 years (mean age 20.3 ± 1.7 years) successfully completed all testing conditions. The modified Thorington technique was used at 4 m to measure heterophoria. The Shin Nippon SRW 5000 infrared autorefractor was used to determine accommodative change to −1.50, −3.00, −4.50, and −6.00D lens stimuli. Results: Significant differences were found in response AC/A ratio between different minus lens stimulated accommodative demands (p < 0.001). Mean AC/A ratio values were 3.11 ± 1.29 with the −1.50D lens stimulus; 4.03 ± 2.11 with −3.00D; 4.14 ± 1.40 with −4.50D; and 4.48 ± 1.56 with −6.00D. No differences in linearity were noted between myopes and non-myopic participants, but myopes tended to have higher response AC/A ratios than non-myopes, mean 4.88 ± 1.89 for myopes vs 3.61 ± 1.47 for non-myopes (p = 0.045). Conclusions: Response AC/A ratio did not display linearity across 4 minus lens accommodative stimuli, but tended to increase with accommodative demand. Significant variability in response AC/A ratio was found, both within individuals to different accommodative demands, and between individuals across the data set.

Binocular Visual Acuity in Intermittent Exotropia: Role of Accommodative Convergence

Ahn and associates presented their findings regarding the level of accommodation, monocularly and binocularly, in patients with intermittent exotropia.1 They noted that “binocular interaction of visual acuity is associated with accommodative response,” with which we agree. However, they assume that this is the result of accommodative convergence. In the person trying to maintain binocular single vision during forced convergence, Semmlow and Heerema demonstrated that the blur was the result of convergence accommodation, not accommodative convergence, because on removal of the stimulus, the vergence after response was in the convergence direction.2 This was the result of accommodation actively being brought back into play (otherwise divergence would be expected as accommodation relaxed). Hasebe and associates found that in intermittent exotropes and decompensating exophorias, a larger lag of accommodation occurred in the monocular state compared with the binocular state, and patients with lower as well as higher accommodative convergence-to-accommodation (AC/A) ratios had been shown to respond to minus lens therapy3 (for review see Firth4). If the mechanism was accommodative convergence, only those with high AC/A would be expected to respond. These findings led Firth to argue that the increase in accommodation in patients with intermittent exotropia, when binocular, was the result of convergence accommodation. 4 In a closed-loop condition, convergence accommodation normally is inhibited; however, as the limit for this is reached, the patient either has to accept blur or has to become manifest. Minus lens therapy may be used to allow convergence accommodation to occur and give clear vision. Indeed, this was demonstrated (Firth AY, Davis H. Convergence accommodation in a distance exotrope. Paper presented at the British Isles Paediatric Ophthalmology and Strabismus Association Conference. September 23–25, 2009; Glasgow, United Kingdom) in a patient with reduced CBA of 6/18 resulting from an increase of accommodation of approximately 2 diopters in the binocular state compared with the monocular state. The patient’s AC/A ratio was low, and dissociated measurement of the deviation showed no observable difference when viewing through −3.00-diopter lenses. Recently, Horwood and Riddell found that disparity driven accommodative response gain and accommodative response at 33 cm are higher in controlling intermittent exotropes than in matched non-strabismic controls.5 The participants showed higher convergence accommodation to convergence ratios and responded mainly to the disparity in visual targets to drive responses, as did controls. They suggest that the increased vergence necessary to control the exodeviation brings along over accommodation, which explains the blur and loss of stereopsis found by Ahn and associates.1 Also, they found no evidence that any of the exotropes used blur cues to drive their responses any more than did the controls, and their response AC/A ratios were no higher. In simple terms, the need to converge drives accommodation, rather than accommodation being used to drive convergence. Considerable inter-individual variability in the strength of the association between convergence and accommodation account for this not being a universal finding. Although various reports in the literature, as included by Ahn and associates, refer to the mechanism for controlling an intermittent exotropia as being accommodative convergence, our findings challenge this premis.1 We contest that the mechanism behind the change in accommodation is driven by vergence.