Graefes Arch Clin Exp Ophthalmol (2010) 248:1501–1505 DOI 10.1007/s00417-010-1418-6
PEDIATRICS
Do bifocals reduce accommodative amplitude in convergence excess esotropia? Michela Fresina & Costantino Schiavi & Emilio C. Campos
Received: 24 January 2010 / Revised: 10 May 2010 / Accepted: 14 May 2010 / Published online: 4 June 2010 # Springer-Verlag 2010
Abstract Background As therapy with bifocal lenses can generate a condition of acquired hypo-accommodation, we assessed the results of bifocal therapy in children with non-refractive accommodative esotropia in whom near point of accommodation (NPA) was measured before the prescription of the lenses and at the end of the study. Methods We examined 28 consecutive patients orthophoric for far, but with esotropia due to excess convergence for near (group 1), and 28 matched controls, orthophoric for far and near (group 2). The patients were prescribed bifocal lenses between the age of 5 and 8. The NPA was measured at time zero and after 4 years of follow-up in both groups. Results NPA values, measured at time 0, were lower than average (10 dioptres) in ten of the 28 patients in group 1, and increased over the 4 years of follow-up without exceeding 10 dioptres. Only one of the other 18 patients in group 1, with normal NPA, had a lower value at the end of the study, although the values were still above 10 dioptres. Conclusions In several patients, excessive convergence is secondary to the extra accommodative effort required due to the presence of a primitive NPA deficit. In these subjects, The study was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki. All persons gave their informed consent prior to their inclusion in the study. M. Fresina : C. Schiavi : E. C. Campos Ophthalmology Service, Department of Surgery and Anaesthesiology, University of Bologna, Bologna, Italy M. Fresina (*) Clinica Oculistica dell’Università, Via Palagi, 9, 40138 Bologna, Italy e-mail:
[email protected]
the prognosis can be made on the basis of NPA measurement, and treatment with bifocal lenses will always be required to compensate. Furthermore, the parents of these small patients should be informed, even before the prescription of bifocals, that prospective surgery of medial rectus muscles will not eliminate the need for bifocals. Keywords Bifocals . Near point of accommodation . Nonrefractive accommodative esotropia
Introduction Non-refractive accommodative esotropia is characterized by excessive convergence for near which is unrelated to the refractive error [1–3]. Convergence excess esotropia is caused by a high accommodative convergence and accommodation ratio (AC/A), usually 5 or above [1], in the presence of a normal near point of accommodation (NPA). Th near point of accommodation is that part of space conjugate to the retina during the visual process, when maximum accommodation is exerted, i.e., the closest point which the eye can focus on. There are considered to be two types of convergence excess esotropia. One is due to high AC/A ratio, and the other is due to excessive convergence in response to reduced NPA (hypo-accommodation). Patients with non-refractive accommodative esotropia are usually prescribed bifocal lenses, after cycloplegic refraction, with total correction in the far lens and an addition of a sphere of +3 dioptres [4] in the near lens. Since in these cases the maintenance of binocular vision is impeded by near deviation secondary to excess convergence caused by accommodative effort, bifocal lenses eliminate the need for near accommodation. Some ophthalmologists prescribe progressive lenses,
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which may appear more attractive, but in our opinion it is impossible to ensure that children use the lower part of the lens, with the higher correction for near. Others prescribe miotic eye drops, which are not free from side-effects [5–7]. After the age of 10, it is possible to wean off bifocal lenses, gradually decreasing the correction of the near lens until it is totally eliminated. Several ophthalmologists also prescribe exercises to promote dissociation between accommodation and convergence [8, 9]. If near esotropia persists, after several years of using bifocal lenses, a double recession of the medial rectus muscles can solve the problem, eliminating near deviation without generating strabismus for far [10–13]. Some studies, however, published by Breinin et al. [14] and subsequently von Noorden and Jenkins [15, 16], indicate that even therapy with bifocal lenses is not risk-free. Following the assumptions of prior studies, that examined the possibility that bifocal lenses might lead to a permanent accommodation deficit, overlapping presbyopia, von Noorden and Jenkins demonstrated the presence of a reduction in the NPA, as compared to normal values, in patients wearing bifocal lenses that persisted for a minimum of 1 year and a mean of 4 years. One of the limitations of this study is that there are no data concerning the near point of accommodation previous to the prescription of bifocal lenses. Therefore, it is not possible to establish whether the patients examined were dealing with early presbyopia caused by the use of the lenses or a pre-existing condition of hypo-accommodation, that is a form of hypo-accommodative esotropia, already described by Costenbader in two patients in 1958 [17, 18]. This condition is defined by excessive near convergence, secondary to the accommodative effort caused by a prior reduction in the NPA, which most frequently occurs in children with a low refractive error and an age of esotropia onset between 1 and 4 [19, 20]. In view of the lack of data in literature concerning the original NPA values in patients wearing bifocal lenses, prior to their prescription, and the possibility that although therapy with bifocal lenses protects binocular vision it may also generate acquired hypoaccommodation, we decided to investigate the relationship between excessive convergence esotropia and accommodation. Specifically, we decided to investigate whether, in esodeviations with excessive convergence, the accommodative deficit is the cause of strabismus or a consequence of its treatment.
Materials and methods Materials The research involved 28 patients in group 1 and 28 controls in group 2.
Graefes Arch Clin Exp Ophthalmol (2010) 248:1501–1505
Group 1 consisted of 28 consecutive patients (17 females and 11 males), orthophoric for far, but with esotropia for excessive convergence for near. These patients were prescribed bifocal lenses between the ages of 5 and 8 years (mean age 6.32±1.09 years). From a refractive point of view, the patients were emmetropic or mildly hypermetropic: two of the 28 patients did not need correction for far, (hypermetropia within 1 dioptre), 17 were slightly hypermetropic (hypermetropia between 1.25 and 2 dioptres), and six mildly hypermetropic (between 2.25 and 3 dioptres). Astigmatism did not exceed 1.25 dioptres. Group 2 consisted of 28 controls (20 females and eight males) orthophoric for far and near, between 5 and 8 years old (mean age 6.00±1.05). From a refractive point of view, the children were emmetropic or slightly– mildly hypermetropic: five did not need correction for far (hypermetropia within 1 dioptre), 20 had slight hypermetropia (between 1.25 and 2 dioptres), and three were mildly hypermetropic (between 2.25 and 3 dioptres), corrected with spectacles. Astigmatism did not exceed 1.25 dioptres. Methods Near point of accommodation was measured in the children from both groups, considering 10 dioptres as a normal value in children between 5 and 8. Measurement was performed for those who needed correction for refractive error, with total correction determined by retinoscopy after cycloplegia, obtained by means of topical cyclopentolate in three administrations. A phoropter (where optic correction, if required, was set) was used for measurement, with a stick holding a sliding illustrated card that also indicated the distance of the card from the phoropter in millimetres, and on the same stick, the equivalent in dioptres. Monocular measurement was performed in each subject, asking at what distance the illustration began to get fuzzy. The measurement was repeated 3 times, and no marked intra-patient variability was found, since the differences in the values were never more than 0.25 dioptres. The data reported represent the mean of these three measurements expressed in dioptres. Patients in group 1 were tested during the examination for bifocal lens prescription, before they began to wear them (time 0), and after 4 years of wearing them (time 1). Subjects in group 2 were measured during the recruitment examination and after 4 years. Near point of accommodation measurements have been made by the same two orthoptists, both at Time 0 and at Time1. They didn't know the children, norr which group they were in.
Graefes Arch Clin Exp Ophthalmol (2010) 248:1501–1505
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Total optical correction, as seen with retinoscopy after cycloplegia in all the subjects, did not exceed 3.50 dioptres of hypermetropia. Accommodative convergence and accommodation ratio (AC/A) was measured using the gradient method. Its range was between 6 and 11 (mean 9.04±1.60) in group 1 (cases), and between 2 and 4 (mean 3.00±0.86) in group 2 (controls).
Results Time 0 Group 1 The data collected show that the NPA values measured at time 0 were lower than average in ten of the 28 patients. Near point of accommodation mean value was 8.75, with 95% confidence interval from 7.99 to 9.51 and a standard deviation (SD) of 1.96.
Fig. 2 Bland–Altman plot representative of the distribution of the NPA values of controls at time 0 and after 4 years of follow-up (time 1). At time 1, only one patient is outside the 95% limits of agreement
Time 1 Group 1
Group 2 All subjects in group 2 at time 0 had NPA values equal to or greater than 10 dioptres. Near point of accommodation mean value was 10.96, with 95% confidence interval from 10.51 to 11.42 and a SD of 1.17. A simple t-test showed a statistical difference in NPA between groups 1 and 2 at T0 (p
