Fig. 15.1
An infant wearing aphakic spectacles
In cases of unilateral aphakia, spectacles are not an option due to aniseikonia and prismatic imbalance between the eyes [17]. In these cases correction with a contact lens provides optimal management of the anisometropia. In certain circumstances, however, spectacles can be prescribed if the parents are struggling with contact lens handling, with the spectacles only to be worn whilst undergoing occlusion therapy.
15.3 Pseudophakia
As previously described the use of IOLs in the management of congenital cataract has now become more common. Pseudophakic eyes are deliberately left hypermetropic to allow for axial elongation with the corresponding myopic shift. The desired refractive result for infants undergoing surgery under the age of 10 weeks should be 8–9 dioptres of hypermetropia, reducing to 4 dioptres at 12 months of age and 2 dioptres by 24 months. The final refractive status, following cessation of axial elongation, is aimed at emmetropia or low myopia [14]. The recent IATS group under corrected the IOL power by 8 dioptres for those infants operated between 4 and 6 weeks, and by 6 dioptres for infants aged 7 weeks but less than 7 months [10]. The residual refractive error can then be corrected with either spectacles, or in cases of unilateral pseudophakia, a contact lens in the early months, gradually reducing the lens power until the eye reaches an emmetropic state and refractive correction is no longer required or spectacles can be prescribed.
A retrospective case review was carried out at Manchester Royal Eye Hospital [22] of infants 6 months and younger fitted with contact lenses following IOL implantation in 23 eyes of 17 infants, with six infants having bilateral IOLs. About one-half of eyes operated on achieved a best sphere residual refraction of +8.00 to +9.00 dioptres, 35 % had a best sphere of +7.00 dioptres and the remainder had a best sphere greater than +9.00DS but not exceeding +11.50DS. The median refractive error was +9.00DS. At age 1 year the median refractive error was +3.00DS with a range of plano to +8.00DS, resulting in a myopic shift of the median refractive error of −6.00D.
By 2 years of age, 25 % of eyes had a best sphere refractive error of plano to −3.00DS, 45 % of eyes had a refractive error of +0.25DS to +3.00DS, and 20 % of eyes were +3.25DS to +4.50DS. The remaining two eyes had no recorded refractive error, however these eyes also demonstrated ‘no interest’ when assessing visual acuity with one of these eyes diagnosed with anterior segment dysgenesis and the other with persistent fetal vasculature. Both cases had multiple systemic health issues. All the infants were fitted with contact lenses to correct the residual refractive error, by 1 year of age 48 % of eyes were still corrected with a contact lens with the other 52 % discontinuing lens wear as the refractive error had reduced to a level that did not require correction (plano to −2.00DS) or could be corrected with spectacles (plano to +5.00DS). There were no infants still wearing a contact lens by the age of two.
15.4 Examination Techniques and Contact Lens Fitting
15.4.1 Case History
A detailed history is very important in the fitting of contact lenses to these patients. If the baby was born prematurely then they will most likely have steeper corneal curvatures [8] and smaller overall corneal diameters [16]. Many of these infants often have systemic co-morbidity with the parents having to deal with multiple hospital appointments, and making contact lens wear less successful. It is also very important to know whether or not the parents have had experience with handling and maintaining contact lenses for themselves, and whether or not they themselves have any visual impairment making contact lens handling more difficult. The IATS examined the impact of parental stress associated with caring for an infant who had undergone IOL treatment compared to contact lens correction for unilateral aphakia. They expected the main issues to be associated with lens insertion and removal, however found that there was no statistical difference to stress levels between the two treatment groups [5].
15.4.2 Anterior-Segment Examination
As with the adult patient, examination of the anterior segment is an important aspect of contact lens fitting and aftercare. A very simple method to determine the presence of corneal staining or ulceration is to use an ultraviolet lamp with fluorescein to determine the location and extent of the lesion. In babies, a major slit lamp can be used with the ‘flying baby’ technique and in infants and young children a hand-held slit lamp can be used to examine the anterior segment in more detail. Older children, from 3 or 4 years of age, can usually sit at a slit lamp, kneeling on a chair and grasping the headrest support bars.
15.4.3 Keratometry
A hand-held automated keratometer can be used to determine the corneal radius of curvature in young infants and children too young to sit at a conventional keratometer (Fig. 15.2).
Fig. 15.2
Hand held keratometry
15.4.4 Refraction
Determination of the refractive error or a contact lens over-refraction is performed with retinoscopy using hand-held lenses or a paediatric trial frame in an older child. The use of a cycloplegic drug is recommended in those children with normal accommodative function in the fellow eye. It is also useful to dilate the pupil in aphakes and pseudophakes where there is a small or displaced pupil or where significant media opacity is apparent, e.g., posterior capsular thickening.
Since infants in the early stages of visual development require a focal length of around 30–50 cm to see a face, the power of the selected contact lens is usually 2–3 D greater than the ocular refraction. This over-correction should be reduced at 18 months to 2 years when the toddler becomes more mobile and aware of distant objects. A reading correction or bifocals can be prescribed from around 3–4 years of age when the child starts preschool education.
15.4.5 Biometry
Prior to cataract surgery, the axial length of the eye can be measured with ultrasound and the corneal radius of curvature by keratometry. These measurements can be used to determine the power of the contact lens required post-operatively by using an IOL calculation formula, e.g., Holladay, which can determine the ocular power at the corneal plane postoperatively. This is particularly useful as it allows more or less correct specifications to be ordered, which alleviates the need for many lenses to be used at the initial fitting and allows for fewer lenses to be kept in stock.
15.4.6 Measurement of Corneal Diameter
This is usually done at the time of surgery whilst the infant is under general anaesthesia so that an accurate measurement can be taken. This measurement aids the optometrist in selecting the appropriate contact lens total diameter.
15.5 Contact Lens Selection
Contact lens technology and lens availability has changed dramatically over the past 10–15 years, providing many more choices in terms of lens selection in the care of aphakic and pseudophakic infants. Contact lens types include soft lenses, both hydrogel and silicone hydrogel lenses, rigid lenses and silicone elastomer lenses.
15.5.1 Hydrogel Soft Lenses
High water content hydrogel lenses were traditionally the most frequently used lens types in paediatric contact lens fitting as they are easy to fit, comfortable to wear, can be manufactured in a wide range of parameters to fit any size and shape of eye and are readily available. Parents tend to be less apprehensive about inserting and removing a hydrogel lens and daily wear should always be actively encouraged to reduce the risk of infection as oxygen transmission is reduced through high-powered lenses used to correct aphakia [1]. However, as babies and young children sleep during the daytime, the lenses can remain in the eye during these periods.
Soft hydrogel lenses do, however have some disadvantages including dehydration caused by dry eyes due to the relatively low blink rate of infants. They do not correct any corneal astigmatism. Insertion may be difficult particularly in infants where there is excessive lid squeezing or a small palpebral aperture causing frequent lens loss and damage. There may be a degree of corneal hypoxia due to the combination of the low oxygen permeability of the lens material and the increased central thickness. Long term corneal hypoxia can lead to corneal vascularization, stromal oedema and chronic endothelial dysfunction [4].
Lenses are usually fitted according to age or based on keratometry readings and corneal diameter. Table 15.1 shows appropriate contact lens parameter selection for each age.
Table 15.1
Hydrogel lens specifications based on age for an aphakic eye of normal size
Age (months) | BOZR (mm) | TD (mm) | Power (D) |
|---|---|---|---|
1 | 7.00 | 12.00 | +35.00 |
2 | 7.20 | 12.50 | +32.00 |
3 | 7.50 | 13.00 | +30.00 |
6 | 7.80 | 13.50 | +25.00 |
12 | 8.10 | 13.50 | +20.00 |
BOZR back zone optic radius, TD total diameter
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