Generally speaking, evaluations for CLs are conducted 3 months after surgery if there are no ocular contraindications. But it should be noted that refraction should be avoided when the pediatric patients appear unwell. Guidance should be patiently provided to parents on manipulation and caring of CLs, so as to help the child accept the wearing of the CLs as soon as possible.

Choosing appropriate powers of CL is particularly important for aphakic correction in children, and CLs of improper power can cause amblyopia. Infants and young children generally require better near vision, while distance vision becomes more important as they grow. Cycloplegic refraction for each aphakic child should be performed plus over- or under-correction. The dosage of over- or under-correction is controversial. The authors prescribe under-correction of 1.50–3.50D for infants (<1 year) and under-correction of 0.50–1.50D for toddlers (1–4 years).

The following issues need to be considered prior to the decision whether or not to wear CLs:

Commonly used CLs include RGP and soft CLs. With good heat conduction, a desirable moisturizing performance, and high oxygen permeability, RGP lenses are especially suitable for children with higher degrees of astigmatism and irregular corneal surface. Their disadvantages lie in weak elasticity, easy warping, lack of comfort, and a longer period of adaptation.

Soft CLs are flexible, with a desirable elasticity, and they cover the entire cornea; in addition, they have the advantages of being comfortable to wear and require only a short period of adaptation. These are compared with RGP lenses, whose disadvantages are that they are liable to surface deposition and have a short duration of service. Currently the most widely used material in soft CLs is hydroxyethyl methacrylate (HEMA). Plastic polymeric materials (also termed hydrogel) that are soft and hydrophilic are added to this type of lens. As a result, they contain 30–80 % water, which guarantees comfortable wearing. In the last 10 years, the materials used in the manufacture of soft CLs are no longer confined to conventional hydrogel. Instead, various monomers, mostly siloxane-polydimethylsiloxane (PDMS, also called silicone hydrogel), are added to increase oxygen permeability.

For young children, CLs with high oxygen permeability and design for overnight wear should be chosen to reduce frequency of application and removal and thus reduce the opportunity for ocular surface injury. This type of lens allows for continuous use up to 30 days, which is convenient for infants and young children, as well as for parents in handling and care. They also cause less foreign body sensation due to their special hydrophilic treatment. The frequency of replacement of these lenses is typically once or twice a year. Additionally, RGP lenses with added UV filter may reduce ocular damage induced by UV irradiation. It is suggested that a backup set of lenses should be available since RGP lenses are frequently lost when crying and rubbing the eyes. In the early period of wear by older children, RGP lenses should be examined once a month, while those of infants under 1 year should be checked once a week, so as to identify any reaction of ocular tissues and to observe the appearance and condition of the CLs.

Modern design CLs with high oxygen permeability have improved safety for long-term wearing. However, CLs are more demanding on a child’s ocular surface and cooperation, as well as their parents’ understanding and education levels. Therefore, in offering the choice of whether or not to wear CLs, we should consider not only their indications but also practical situations of both the children and their parents.

With a high prevalence worldwide (2–5 %), amblyopia is the first disorder causing monocular visual impairment in children [1, 2]. Amblyopia severely impairs both monocular and binocular visual functions. A study on monocular amblyopia has found that trauma, inflammation, and visual field damage are more likely to occur in the fellow eye [3]. The diagnostic criteria for amblyopia vary in different countries. The classical concept of amblyopia is, a developmental disorder of visual function caused by abnormal visual perception including form deprivation or binocular interaction during visual development [4]. American Academy of Ophthalmology (AAO) has proposed an accurate definition of amblyopia encompassing visual acuity criteria and diagnostic criteria (Table 26.1).

Amblyopia is typically caused by strabismus, anisometropia, refractive errors, and form deprivation (congenital cataract and ptosis). These anomalies may lead to disrupted development of visual function if they occur during visual development [6].

Visual development may be divided into the critical period, the sensitive period, and the plastic period [7]. In the critical period, the development of visual perceptual functions reaches the same level as that in adults. In the sensitive period, visual disturbance can give rise to functional disorders of vision. While in the plastic period, visual function can be restored after developmental disorders have occurred. Actually, there are no clearly defined time limits for the three periods, and sensitivity to visual stimuli gradually decreases from the critical period toward the plastic period. There are great differences in visual functions among different species, populations, and individuals. Currently there is huge disagreement over the respective duration of these periods. It is generally acknowledged that the critical period occurs at about 5 years to 6 years, the sensitive period at 8 years, and the plastic period at 11–12 years. Previous studies have shown that normal visual perception could no longer be established once beyond the plastic period. However, studies from the authors and other investigators all reveal that there is still certain restoration capacity for impaired visual functions, even in children beyond the plastic period. Therefore, further research is required to confirm whether there is a certain time limit for the plastic period or it has a lifelong duration. But it can be deduced from the three periods of visual development that the sooner amblyopia treatment starts, the better the visual outcomes are. Additionally, treatment should start in a period of greater plasticity, so that visual function can be recovered to a greater degree.