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Emmetropisation in normal and strabismic children and the associated changes of anisometropia
R M Ingram1, L E Gill, T W Lambert
1Department of Ophthalmology, Kettering General Hospital, Northants, England, UK. robertmingram@lineone.net
Insights
Emmetropisation, the natural development of normal vision, was deficient in at least 80% of children with strabismus. This visual development issue occurred regardless of their initial refractive error, leading to increased anisometropia (unequal vision between eyes).
Area of Science:
- Ophthalmology
- Pediatric Ophthalmology
- Vision Science
Background:
- Strabismus is a common condition in children, often associated with refractive errors.
- The process of emmetropisation, or the development of normal visual acuity, is crucial in early childhood.
- Understanding emmetropisation failure in strabismic children is key to early intervention and management.
Purpose of the Study:
- To determine if emmetropisation fails in children with strabismus, irrespective of their initial refractive error.
- To assess simultaneous changes in anisometropia (difference in refractive error between eyes) in these children.
- To investigate the incidence of hypermetropia increase preceding esotropia onset.
Main Methods:
- Cycloplegic retinoscopy was performed on 2920 infants at 5-7 months and again at 42 months.
- Refractive changes in 210 children with strabismus were compared to 2710 controls.
- Statistical analysis was used to compare refractive changes and anisometropia development between groups.
Main Results:
- Emmetropisation was deficient in both eyes of at least 80% of strabismic children, regardless of infancy refraction.
- Anisometropia increased in 53% of children with strabismus, compared to 6% in controls.
- Hypermetropia decrease was less pronounced in strabismic children, and refractive errors persisted outside the normal range more frequently.
Conclusions:
- Emmetropisation is significantly impaired in a majority of children with strabismus.
- Strabismus is associated with a higher incidence of developing anisometropia.
- The findings do not strongly support the theory that increasing hypermetropia directly causes esotropia through accommodation-convergence mechanisms.
Abstract:
The purpose of this study was to measure whether emmetropisation failed in children who had strabismus irrespective of their refraction in infancy, and to record simultaneous changes in anisometropia. We also report how often hypermetropia increased before these children presented with esotropia. A total of 2920 infants had a cycloplegic retinoscopy at age 5-7 months and again at 42 months or when defective vision was identified. Changes of refraction in 210 children with strabismus are compared with the remaining 2710 who did not. When the spherical equivalent of the fixing eyes was > +2.75 D in infancy, hypermetropia decreased less in both eyes of those who had microtropia (p <.001) and heterotropia (p <.001) than in normal children. When it was < +2.75 D, the spherical and/or cylindrical refraction more often remained outside the 'normal' range in both eyes of those who had microtropia and heterotropia (p <.05). Emmetropisation was deficient in both eyes of at least 80% of these strabismic children irrespective of their refraction in infancy. Furthermore, in the strabismic children, the mean change of refraction was less (p <.05) in their fellow eyes than in their fixing eyes, the difference between the two eyes being on average three times greater than that in those who had normal vision. Thus, anisometropia increased in 53% of those who had strabismus but remained within normal limits (< ca. 0.75 D spherical equivalent) in 94 % of those who did not. 'Abnormal' anisometropia in infancy did not, per se, permanently affect vision because 72% of all those who had it did not have strabismus. Finally, the spherical hypermetropia of fixing eyes increased in only 35% of the children with esotropia - similar to the incidence in those who had a microtropia (p =.36). This does not obviously support the concept that increasing hypermetropia causes accommodation to increase before convergence.