Children are not ‘small’ adults, yet often we see them fitted in frames designed for adults then ‘scaled down’ to size. Alicia Thompson, from the University of Aston in the United Kingdom, is undertaking a study to explore whether a sensible set of parameters and design features can be developed for spectacle frames, that mirrors the findings of a population study. The ultimate aim is to improve the fit of frames for all children.
There are various elements that form a child’s eye care pathway, all of which are deemed to be extremely important, and sometimes challenging to achieve. The final piece to the jigsaw, and equally important, is the fit of the spectacles. A good fit is pivotal in delivering the prescription or intervention as prescribed, in a comfortable, stable and desirable frame.
Consider the effect of a poor fitting pair of spectacles on the development of a child, not only in terms of visual development in those crucial early years, but also in terms of their education and social development. If the child is uncomfortable in their spectacles then it will be difficult for them to concentrate, or they may simply decide not to wear them. Similarly, if they cannot see clearly, then it is even harder to engage in a lesson or activity and ultimately, attention may wander.
All too often we see the evidence of poorly fitting spectacles (Figure 1). The majority involve frames designed by scaling down adult frame parameters. This results in the frame sliding down the nose until it finds the first area of lateral protrusion, leaving the child looking over the top rim. Additionally, because children inevitably spend the majority of their time looking upwards, the problem is compounded.
As a result, a child may be ‘wearing’ their spectacles but in effect, receiving no correction or intervention during that critical period. Even if the frame slips down the nose and the child still manages to look through the lenses, the increase in vertex distance (measured from the back vertex of the spectacle lens to the cornea) means the effective power received at the eye is no longer correct for higher powers. For myopic children, where bifocal or progressive lens dispensing is an option, the spectacles are rendered useless if the child is unable to reach the lower portion of the lens. A 10mm slippage of a frame on a -6.00 myopic child will only provide -5.66D correction.
Facial measurements for spectacle frame parameters can be time consuming to capture and are usually taken with a Fairbanks facial ruler (Figure 2).
This is not ideal for children as it consists of a long, swinging metal pointer and is incapable of taking certain measurements, which are negative in value for a young child.
For my study, I captured data using 3D photographic imaging technology (Figure 3), which is capable of capturing a 180 degree three-dimensional image in 1.5 milliseconds. This approach proved to be more suitable for children.
To date, I have captured over 1,300 images of children’s faces, ranging in ages from birth to 16 years, and including children from different ethnic backgrounds as well as children with Down’s Syndrome.
We know that young children have a much lower crest height1 in respect to the position of the adult bearing surface. This is the vertical relationship between the crest of the bridge and the lower lid. This impacts the vertical positioning of the frame on the child’s face and is found to be a negative value in most young children. Because of this, the bridge on a frame needs to be set lower than the Horizontal Centre Line (HCL) of the frame in order to position the pupils centrally (Figure 4).
We also know that:
- The bearing surface is generally much wider and flatter as well as lower on the face. The vertical angle (frontal) and angle of the splay of the nose are much flatter.
- The circle that fits the bearing surface at the bridge of the nose (apical radius) and the two width measurements below this point (distance between rims (DBR) measurements) are wider in younger children.
All of this means that frames with a narrow, high set bridge will have no contact with the child’s bridge and so invariably, will slide to find the first point of anchorage, usually at the nasal bulb. Bridges need to be designed with a wider splay or pads that are lower set and have more adjustability in order to site the bridge more appropriately.
Additionally, the front to bend, or side length measurements need to be of an appropriate length. It is, sadly, a common sight to see children with the drops of sides being so long that they are visible behind the lobes. Some sides can be physically shortened very successfully by cutting and re-tipping, but the ability to shorten (by a significant amount) is a design feature commonly overlooked.
CHILDREN WITH DOWN’S SYNDROME
Children with Down’s syndrome have a high prevalence of refractive correction,2 and this is often accompanied by reduced accommodation,3 hence the need to prescribe and dispense bifocals or progressive power lenses. Vertical positioning is extremely critical so that the child can achieve full use of both their distance and near correction.
Table 1 shows facial measurements for 99 children with Down’s syndrome (39 females and 60 males) age matched with typically developed children. Ages ranged from two months to 16.5 years (mean 7.41 years).
The results5 show that children with Down’s syndrome have a much lower crest height in comparison to typically developed children, concurring with earlier work1,4 in this field.
In terms of the frontal and splay angles in all children, the appearance at the bearing surface is predominantly quite flat (Figure 5) due to the immaturity of the nasal form.
For children with Down’s syndrome, a smaller apical radius was found in the majority of age groups. The distance between rims, indicating the width of the nose at two set points below the crest, was found to be wider in general in children with Down’s syndrome and not showing the usual narrowing with age as the nose emerges, lifting the crest and narrowing the angles. In terms of frame design, the variability shown in these measurements would indicate that an adjustable pad bridge or a strap bridge set low and wide would be the ideal to allow the contours of the developing bridge to be followed.
Head width, measured from earpoint to earpoint, was found to be larger in children with Down’s syndrome, and the front to bend measurement, which represents the side length of the frame, significantly shorter. Pupillary distance was smaller in the majority of children with Down’s syndrome, resulting in opposing fitting requirements. Ideally, the pupillary distance needs to match the horizontal centre distance (HCD) of the frame in order to align the pupil and optical centres, and avoid decentration. To achieve this for a relatively smaller pd, the HCD of the frame will be smaller, which means the temple and resulting head width will be too small. This will increase the tension on the sides of the head and force the frame front forwards down the nose. To solve this, the HCD needs to remain narrow but with a swept-back lug to facilitate the head width and allow for adjustment.
Summary of comparative data:
- Lower crest height
- Smaller apical radius
- Wider distance between rims
- Wider head width
- Shorter front to bend
- Narrower pupillary distance
Although earlier studies found no significant differences between facial measurements when considering the sex of the child, we found that the frontal and splay angles appear to be slightly larger in all females and the crest height lower. Additionally, the head width is generally narrower in females, indicating there should be parameter differences between male and female designs. We know that females tend to reach developmental maturity at an earlier age in comparison to males, but little is known about the particular facial areas relating to spectacle wear in terms of rate and time of growth.
To conclude, children with Down’s syndrome are not consistently smaller or larger in facial parameters than typicallydeveloped children. Therefore frames need to be designed specifically for these children with a significantly lower, wider splayed bridge, a narrow frontal angle, apical radius, and a larger temple and head width.
For children of different ethnicities, there are also different frame parameters required and this is why we need an improved range of frame designs in our practices with different parameters and a larger degree of adjustability.
FIT IS VITAL
Comfortable, stable and cosmetically acceptable frames should be available to all children. By guiding your young patients and their carers to the most appropriate frames, you can help to maximise their visual, academic and social development.
Alicia Thompson BSc (Hons) FBDO R (Hons) SLD SMC (Tech) is the director of professional examinations at the Association of British Dispensing Opticians (ABDO). With a special interest in paediatric dispensing she undertook a PhD with Aston University to research facial anthropometry for spectacle frame design.
- Kaye, J. Obstfeld, H. (1989) ‘Anthropometry for children’s spectacle frames’ Ophth. Physiol. Opt. vol. 9, pp. 293-298.
- Pueschel, S.M. (1987) ‘Health concerns in persons with Down’s syndrome’ New Perspectives in Down’s syndrome, Brookes:Baltimore, USA.
- Woodhouse, J.M., Meades, J.S., Leat, S.J., Saunders, K.J. (1993) ‘Reduced Accommodation in Children with Down Syndrome’ Invest. Ophth. Visual Sci. Vol.34, pp.2382-2387.
- Woodhouse, J.M. ,Hodge, S.J., Earlam, R.A. (1994) ‘Facial characteristics in children with Down’s syndrome and spectacle fitting’ Ophth. Physiol. Opt. vol.14, pp. 25-31.
- Thompson, A.J., Cubbidge, R.P. (2018) ‘Application of facial anthropometry to spectacle frame design in children with Down’s syndrome’ [Poster] Exhibited at World Down’s Syndrome Congress, Glasgow SECC, 25-27th July.
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