ABSTRACT

Congenital cataract is among the main causes of treatable vision loss in childhood. The first weeks and months of life are a critical time for the development of vision. Therefore, early cataract surgery and effective multifaceted treatment of the resulting aphakia in the early stages of life are of great value for the management of vision development. Among the treatment models, contact lenses (CL) have an important place in infancy and early childhood up to the age of 2 years. Although good visual gains were not considered very likely, especially in unilateral aphakia, important steps have been taken in the treatment of pediatric aphakia thanks to the surgical techniques developed over time and the increasing experience with optical correction systems, especially CLs. This review examines current developments in the types of CL used in pediatric aphakia, their application features, comparison with other optical systems, the features of amblyopia treatment in the presence of CL, and the results obtained with family compliance to CL wear and occlusion therapy in the light of existing studies.

Introduction

Congenital cataract (CC) is rare worldwide (2.2-13.6/10,000 births) but is one of the leading causes of vision loss in children.^1,2 It can be bilateral or unilateral and can be associated with systemic diseases or congenital abnormalities of the eye such as persistent fetal vasculature (PFV).³ Aphakia resulting from penetrating eye injuries, which are fairly common in the pediatric age group, often leads to treatment challenges because of the accompanying irregular astigmatism.^4,5,6

Cataract surgery should be performed as early as possible, as the presence of dense, vision-impairing cataract in the neonatal period and infancy causes amblyopia due to the lack of stimulation.⁷ On the other hand, especially in unilateral cataract, the high anisometropia that occurs after surgery carries the risk of amblyopia and secondary strabismus.^8,9 To promote visual development, it is important to provide appropriate optical correction as soon as possible following surgery, implement effective patching treatment, and perform regular follow-up for changes that occur in the growing eye, as well as potential complications.¹⁰

Glasses, contact lenses (CL), and intraocular lenses (IOL) are options that can be selected for the optical rehabilitation of aphakia in infancy. CLs are one of the most suitable treatment tools because they eliminate aniseikonia, can be used immediately after surgery, can be modified according to the changing refractive power of the eye of the growing child, are available in all dioptric powers, and are low-risk and highly effective.^11,12

Historically, a good visual gain was considered impossible 40-50 years ago, especially in unilateral CC.¹³ With increasing knowledge about the development of the optical system and developments in CL technology, it has been shown that visual acuity (VA) can be improved in unilateral infantile cataract through early surgery, successful CL fitting, and effective patching, without leading to permanent and deep amblyopia.^7,14

CL fitting and the management of vision development in pediatric aphakia is one of the most challenging and unique areas of study and includes many components. In this review, the types of CL used in pediatric aphakia, their characteristics, comparison with other optical systems, the features of patching treatment for amblyopia in the presence of CLs, and the results obtained with family adherence to CL wear and patching therapy are examined in the light of existing studies.

Conclusion

Aphakia is an important problem that can affect a child’s future, especially given the associated risk of deep amblyopia in the neonatal and infancy periods. Therefore, it is necessary to initiate treatment for vision development as soon as possible after cataract surgery. With their low risk and high efficacy, CLs have an important place in the treatment of aphakia in infants and young children up to 2 years of age. Although a wide range of lenses can be used in pediatric aphakia, SE lenses with high Dk/t values that enable continuous day and night wear are often preferred.³⁰ However, RGPCLs, SiH lenses, and more rarely hydrogel lenses are other important options that can also be used under the right conditions.^34,36,56 Despite this development and diversification in CL materials and technology, family adherence to CL use and occlusion therapy is the main factor affecting success.^79,80 With early diagnosis, early surgery, CL fitting as soon as possible after surgery, and full compliance with patching treatment, it is now possible to reach very high levels of vision.^7,14 However, there is still a lack of knowledge and experience related to the efficacy and safety of treatments being provided, and there is a need for more comprehensive scientific studies with long-term follow-up in which data can be standardized.

Non-contact Lenses Optical Options

Glasses are optical devices that are often preferred for visual rehabilitation in bilateral aphakia because they provide visual improvement comparable to other optical options and are easy to use and obtain.¹⁵ However, high-diopter (D) aphakic glasses are quite heavy and difficult to apply to the infant face. In addition, spectacle lenses have the effect of increasing the image size and narrowing the visual field, which can cause difficulties in children’s adaptation to the real world. In unilateral aphakia, they may not be a successful treatment option due to the anisometropia resulting from the high dioptric difference between the two eyes.^10,11

IOL implantation is a current treatment method with a growing area of use because of certain important advantages such as providing immediate optical correction and not requiring parent or child adherence. However, refractive predictability is low due to the rapid increase in axial length and changes in the corneal curvature that occur in the first two years of life. They may also increase the need for additional intraocular surgeries because of risks such as fibrin reaction, posterior capsule fibrosis, and VA opacification.^7,10 In recent years, comparing CLs with IOLs for the treatment of unilateral or bilateral infantile aphakia in terms of VA and complications has been one of the leading research topics.^7,15

A meta-analysis study by Chen et al.¹⁶ suggested that VA was better in eyes that underwent primary IOL implantation compared to those with CLs, while there was no increase in risk of complications. However, many previous studies on the subject (summarized in Table 1) demonstrated no difference in VA between high-compliance CL use and IOL implantation, while IOLs were associated with greater differences in change in axial length and astigmatism and higher prevalence of adverse events and risk of reoperation.^{18,19,20,22,23,28,29} The results of the studies indicated that CL wear is more advantageous in infancy, IOL implantation is safer after 2 years of age, and secondary IOL surgery at later ages will result in less refractive error.^{17,18,19,20,21,22,23,24,25,26,27,28,29}

Contact Lenses Options

Current CL options that can be used during infancy are rigid gas permeable contact lenses (RGPCLs), silicone elastomer (SE) lenses, and soft hydrogel and silicone hydrogel (SiH) lenses. High DK/t lenses that can be worn continuously (day and night) are needed for aphakic infants because of high hyperopia and the need for long sleep periods. While SE lenses are the first choice for this purpose, RGPCLs, SiH lenses, and less commonly hydrogel lenses are important options that can also be used in the right circumstances.³⁰

Rigid Gas Permeable Contact Lenses

As RGPCLs can be produced with the desired base curve (BC) and power, they have the advantage of being available in a wide range of parameters. In addition, being able to apply a lens with the needed dioptric power and the ability of rigid lenses to mask corneal astigmatism also offer the opportunity to achieve high visual quality.³¹ Furthermore, RGPCLs carry a lower risk of hypoxia and infection because they can be produced from a highly oxygen-permeable material (fluorosilicone acrylate), allow for adequate tear exchange, and have low water content.¹⁰ However, drawbacks that limit the preference for these lenses are discomfort caused by the rigid material, difficulty during wear, having to remove them every night, and the need for more experience and expertise to determine the appropriate lens.^10,12,30

The BC refers to the posterior surface slope of the CL, and a BC value 1.0-1.5 mm steeper than the flattest keratometry value is generally preferred.^30,31 Lens diameters vary from 7.8 to 9.5 mm and can be determined according to the diameter of the infant’s cornea. Lenses can be manufactured with a lenticular design to reduce edge thickness and thus increase lens comfort.^30,31 After inserting a trial lens, its position and movement on the ocular surface and the relationship of the lens to the cornea is checked by fluorescein staining (Figure 1). Many retrospective studies have investigated vision quality and risk of adverse events with corneal and intralimbal RGPCLs (Table 2). The results of these studies indicated that despite problems such as discomfort from the rigid material, application difficulties, and the requirement of daytime use, RGPCLs are safe and effective lenses that can be used successfully in all pediatric aphakia patients, including infants.^{32,33,34,35,36,37}

In addition, RGPCLs are especially used in trauma cases with irregular and high corneal astigmatism. With their good VA and ease of use, these lenses are reported to be successful options that can be preferred for pediatric traumatic aphakia.³⁸ Piggyback CL systems that utilize an RGPCL on top of a high oxygen permeability SiH CL can also be applied in eyes with irregular corneas and other cases where RGPCLs alone are not tolerated (Figure 2).³⁹ In addition, two separate studies conducted in recent years reported that mini-scleral and scleral lenses can also be used as safe and effective options in aphakic children.^40,41

Silicone Elastomer Lenses

SE lenses are among the most preferred CL options in pediatric aphakia. One of the main reasons for this is that SE lenses have very high oxygen permeability (Dk: 340, Dk/t: 58/0.61 mm) and low water content, and thus can remain on the eye without any problems for 15 days or even up to 1 month.³⁰ The fact that SE lenses do not need to be removed every day increases the safety and comfort of CL wear in infancy, a period in which CL insertion and removal difficulties may be encountered. Other superior features are that they provide high VA, are easy to insert and remove due to their lenticular design and minimal flexibility, and their material is resistant to bacterial colonization (Figures 3, 4).^30,42,43,44 On the other hand, SE is an extremely hydrophobic material, which may result in the formation of excessive lipid and mucus deposits on the lens surface. Special coating methods are used to improve its surface properties. However, gradual deterioration of these surface coatings and deposit accumulation can lead to lens wetting problems and visual disturbances (Figures 5, 6).^45,46 In addition, silicone is a waterproof material and the lens frequently adheres to the eye.⁴⁷ In addition to their surface issues, SE lenses usually need to be replaced every 3-6 months due to rapid refractive changes associated with infant development. As a result, the need to frequently replace these lenses increases the financial burden on families, and production and supply problems in recent years necessitated a search for different lens options.⁴²

Currently produced and available SE lenses are the Silsoft^® and Silsoft^® Super Plus (Bausch & Lomb Incorporated, Bridgewater, NJ, USA). Silsoft^® Super Plus lenses are often used in early infancy in parallel with the development of the child. These lenses come with BC options of 7.5, 7.7, and 7.9 mm, their diameter is 11.3 mm, and their power values range from +23.00 to +32.00 D in 3.00-D steps (+23.00, +26.00, +29.00, and +32.00). In addition, Silsoft^® aphakic lenses for use at older ages are available with 5 BC options (7.5, 7.7, 7.9, 8.1, and 8.3 mm), 2 diameters (11.3 and 12.5 mm), and power options ranging from +11.50 to +20.00 D in 0.50-D steps.^30,43

The efficacy and safety of SE lenses have been investigated in many studies, both as a first-line choice and in comparison to RGPCLs (Table 3).^{48,49,50,51,52} The common conclusion reached in these studies was that SE lenses can be used safely and effectively in the pediatric age group due to their ease of use, the advantages of extended wear, and the low rate of adverse events.^48,49,50 Additionally, the multicenter, prospective, randomized Infant Aphakia Treatment Study (IATS) examined the 1-year and 5-year results of unilateral aphakic children who underwent optical rehabilitation with SE lenses and RGPCLs. At the end of the 1-year period that was the first part of the study, it was reported that regardless of the lens type, successful VA results (+0.80 logarithm of the minimum angle of resolution [logMAR]) could be achieved with few adverse effects.⁵¹ According to 5-year follow-up data from the same study, VA better than 20/40 could be reached in 33% of those using RGPCLs and 20% of those using SE lenses, there was no significant difference in visual prognosis between the two lens types, and few adverse events were observed.⁵²

Soft Lenses: Hydrogel Lenses and SiH Lenses

Hydrogel lenses can be used in infancy and later childhood for pediatric aphakia. The low oxygen permeability of the hydrogel material may cause an increased risk of various complications such as corneal edema, neovascularization, endothelial polymegathism, and infective keratitis. Although lenses with high water retention can be used in aphakia to reduce the hypoxic complications of these lenses, oxygen permeability is reduced in high plus power lenses because of the thick central zone (i.e., the Dk/t ratio is still low). For this reason, daily insertion and removal is considered safe and effective.^53,54

In contrast, SiH lenses have high oxygen permeability and provide an important advantage in preventing corneal complications associated with hydrogel lenses. However, since the increased lens thickness required for high power also reduces Dk/t (i.e., oxygen transmission), SiH aphakic lenses are mostly used for daily use in infancy and early childhood. In addition, they offer low water content, ease of use, and the opportunity for frequent replacement.^55,56 Custom-made SiH lenses are also available now.⁵⁷ In our country, CLs produced from SiH material (Definitive 74: Filcon V3, water content: 74%, Dk [Fatt; mmHg]: 60) and replaced every 3-6 months can be used (Figure 7). As CL dioptric power decreases with age, children can be switched to SiH and hydrogel lenses, which are available within the production parameter ranges and can be applied in a daily use/monthly replacement regimen (Figure 8). There are also domestically produced aphakic CL options made of materials suitable for daily use (NL64: MMA-N-vinyl-pyrrolidone copolymer, water content: 67%, Dk/t: 36 @ -3.00 D).

The efficacy and safety of soft CLs have been investigated in various studies over the years. In their prospective 3-year follow-up study of 141 eyes of 83 infants, Amaya et al.⁵⁸ shared the results of daily use of hydrogel CLs with water content that was initially high and decreased with age. The authors reported that 85% of the patients continued CL use, but 46 eyes had significant complications such as bacterial conjunctivitis, hypoxic corneal ulcer, corneal edema, and pannus formation.

Chen et al.⁵⁹ retrospectively examined factors affecting VA in 5 infants with unilateral idiopathic CC and 10 infants with cataract secondary to PFV who received various daily use hydrogel CLs after cataract surgery. Successful VA outcomes (20/50 or better) were obtained in 50% of unilateral aphakic children over the age of 5 years. Surgical or ocular complications were found to negatively affect VA in the PFV group. The authors concluded that compliance with CL and patching was directly related to VA. In addition, they reported that the most common CL-related complications were corneal pannus (26.66%) and giant papillary conjunctivitis (20%), and 60% of the patients were switched to an RGPCL for this reason.

In their study examining 205 patients, 173 (84.4%) with RGPCLs and 32 (15.6%) with soft CLs, Subramanian⁶⁰ found that only half of the children successfully continued CL use, the highest VA achieved was 0.2 logMAR in a 4-year-old successful CL user, and visual success depended on correct CL selection and close follow-up.

The results of these studies conducted over approximately 30 years indicate that complications associated with daily use soft CLs have decreased over time, VA can reach fairly high levels, and correct CL selection and compliance with patching are directly related to visual success.^58,59,60

Contact Lenses Fitting and Patient Compliance

Dioptric power, BC, and diameter are important parameters in CL fitting, and among their determining factors, axial length, keratometric values, corneal diameter, and aphakic refractive error vary with age, especially in infancy (Table 4).^61,62 However, eye development differs in pediatric aphakia. Axial elongation may be affected by surgery, visual deprivation, optical defocus, or various potential pathologies associated with cataract (e.g., glaucoma, PFV).⁶³ Therefore, CL parameters should be determined by evaluating each child within the framework of these specific changes, as well as the natural developmental process of the eye.

Base curve and diameter selection: It may not always be possible to determine corneal keratometric values during infancy. Therefore, the BC value and diameter of the initial lens are often determined according to the infant’s age. When fitting Silsoft CLs, a 7.5 mm BC and 11.3 mm diameter are preferred as a rule because the infant cornea has a steep anterior surface slope and small diameter. As the corneal curvature will flatten by the age of 2 years, most children are switched to a 7.7 mm BC. However, in some children the cornea can maintain its steep slope and an SE lens with 7.5 BC can be used into later childhood. A steep fitting incompatible with the corneal anterior surface slope causes the lens to become immobile, while a flat fitting can lead to keratitis due to the central mechanical effect (Figure 9).^30,31,57

The basic principles of soft CL fitting are similar to those in adults. The BC should generally be 0.5 mm flatter than the corneal slope (which is ~6.9-7.1 mm at birth), which corresponds to about 7.4 mm. Moreover, the diameter of soft CLs should be 2.5-3.0 mm greater than the entire corneal diameter (i.e., 12.5 or 13.00 mm) to ensure lens stability and prevent dislocation. Again, these values are modified as the patient grows.⁵⁷

Determination of contact lenses power: Realistically, determining the dioptric power is more difficult than selecting the BC value. For this reason, the IATS working group protocol recommended that in cases where refractive error cannot be measured precisely, the initial lens power should usually be +32 D for Silsoft lenses and then modified as necessary as early as possible.⁶³ In their study with 50 patients who underwent cataract surgery at 2.4±1.7 months of age, Trivedi and Wilson⁶⁴ determined the mean refractive error was 29.6±4.4 D in the corneal plane and showed that lens replacement may be required in 22 of the 50 patients (44%) if a +32 D CL were used. Other researchers have reported that postoperative refraction examination may be difficult in infants and that estimating the CL power before surgery with the help of preoperative biometrics may reduce the need for lens change. On the other hand, the infant’s refractive error can change rapidly in the first year after birth, after which this rate of change gradually decreases. Therefore, it is important to verify CL dioptric power and compliance monthly for the first 18 months and then every 3 months for the next 3 years.^{53,54,55,56,57}

Contact lenses fitting and evaluation: While a CL can be inserted immediately after surgery, it is usually preferrable to have it applied at postoperative 1 week by an ophthalmologist in office conditions, after the infant is laid supine in the examination room, with head and arm movements minimized by the parents. The family is taught about CL insertion and removal in every detail and in practice. Fifteen minutes after CL insertion, lens movement and centration are evaluated, as well as fluorescein staining patterns for RGPCLs and SE lenses. SE lenses can be relatively easily applied to the small infant eye due to their thickness and design.⁶⁵ SiH lenses can also be applied more easily than hydrogel lenses due to their high modulus of rigidity.⁵⁷ The infant is examined at 1 day, 1 week, 1 month, and 3 months after fitting, after which follow-up can be recommended at least 4 times a year depending on the condition of the case. Corneal complications and pathologies such as glaucoma and retinal problems are evaluated. Surface problems specific to SE lenses can frequently occur. Due to these surface problems and dioptric changes parallel to eye growth, most patients may require lens replacement in 3-6 months.^30,65

Contact lenses wear time: SE lenses are fitted immediately or within the first week after surgery and can remain in the eye for up to 30 days unless there is a problem. However, most practitioners prefer that SE lenses are removed every 1 or 2 weeks and inserted the next morning after a night of rest.³⁰ Although parents initially have difficulty with the process of inserting and removing the lenses, they gradually gain experience and can often do it more easily while the infant is feeding or falling asleep. These lenses can be cleaned and disinfected with multi-purpose soft CL solutions. The recommended time for adequate disinfection is reported as 8 hours. In the early years, eye rubbing commonly results in ejection of a CL from the infant’s eye, and it may be found in their bed or among their toys.^30,52

Calculation of spectacle power over the contact lenses: Although measurements can be made with a pediatric autorefractometer, the retinoscope is primarily used in all circumstances. If over 1.5-2 years of age, spectacle correction over the CL for near vision (+2.0/+2.50 D) can be provided as monofocal, bifocal, or progressive according to the patient’s age.^50,53

Contact lenses compliance: As both the child’s reaction to CL wear and the parent’s adherence play a role in CL compliance, they can be evaluated together. All infants initially react to CL insertion, but with time their reactions to this process decrease, or contrariwise, they may reject lens use as they grow. The CL adherence of the family should be assessed according to their success in inserting and removing the lens and the continuity of wear.⁶⁶

Amblyopia Risk and Occlusion Therapy

The first weeks and months of life are a critical time for the development of amblyopia. An inadequate retinal image during this sensitive period hinders the formation of good visual perception in the occipital cortex and negatively impacts vision development.⁶⁷ However, if amblyogenic risk factors are reduced or eliminated in the early period, vision loss can be avoided thanks to the plasticity of the brain. Therefore, unilateral or bilateral cataracts detected in the neonatal period should be operated as soon as possible, refractive correction should be provided with the most appropriate CL and/or glasses immediately afterwards, and patching treatment for amblyopia should be initiated, especially in unilateral aphakia. In addition, attention should be paid to the risk of occlusion amblyopia that may occur in the other eye with excessive patching.⁶⁸ In bilateral cataract, the risk of amblyopia may be less and occlusion therapy may not be required if there is no strabismus. In acquired cataracts, the risk decreases but can continue until 5 years of age or later.^{69,70,71,72,73}

The duration of patching treatment is determined according to the patient’s age, unilateral or bilateral involvement, and their fixation and deviation status. This procedure is done using adhesive patches or patching tapes suitable for infants and children and requires complete occlusion of the well-sighted eye. The child is asked to play with near objects during the patching period, and as they grow they are asked to identify and track pictures and shapes in a book or digital environment while wearing near-glasses.^74,75

There are different patching regimens, such as patching methods tailored according to the VA of the fixating or treated eye, but none has been shown to be superior over the others.^76,77 Lambert et al.⁷⁸ from the IATS group started patching treatment 2 weeks after cataract surgery and defined the patching duration as 1 hour per day for each month of age for the first 8 months, then half of their waking hours each day or their entire waking time every other day.

Adherence to patching is one of the factors that has the greatest impact on vision development in unilateral aphakia.^79,80 To enable an objective evaluation, the information conveyed by parents in phone calls or written logs can be used as a primary source.^81,82 However, these practices require years of attention and dedication and are a significant source of tension and anxiety for children and families.⁸³ Several studies have shown that pediatric cataract significantly impairs the social and functional quality of life of the patient and their family.^84,85,86 As the stress experienced by families can have many important effects on children, from behavioral disorders to maladaptive parental approaches, it is important to evaluate this during the treatment of pediatric aphakia. Sources of stress and the factors influencing treatment adherence vary from the choice of treatment method to cost-related issues, and may change in severity as the child grows.^87,88

Contact Lenses Fitting and Follow-up in the Presence of Additional Pathologies

Persistent fetal vascular syndrome: The anatomic involvement in PFV is diverse and can be classified based on location as anterior, posterior, or combined.^89,90 Although it has been reported that visual gain is likely to be low in these cases, many studies have suggested that successful visual outcomes can be achieved in anterior PFV through early diagnosis, carefully planned surgical treatment, appropriate optical correction, and effective amblyopia treatment.^{91,92,93,94,95} Because PFV is often associated with microphthalmia, it may be difficult to obtain lenses with appropriate corneal BC, diameter, and dioptric power values. Such cases can be approached by first using glasses for optical correction and later switching to a CL when corneal parameters become suitable, or fitting can be attempted with different CL options.^30,35

Glaucoma: Glaucoma is a common pathology in pediatric aphakia, reported to occur at rates of approximately 12% in the 1-year results of the IATS study and 30% in the 5-year study, independent of the treatment modalities applied. This emphasizes the importance of close follow-up and treatment in aphakic children regardless of the optical correction used.^96,97,98 In infants who develop glaucoma, SE lenses may be advantageous because their use is suitable for medical treatment.⁵⁴ In cases of buphthalmos, it may be more appropriate to continue with glasses, considering that the corneal diameter and keratometric values will change and the refractive error will decrease to lower values.^99,100

Study Limitations

Apart from the IATS study, most previous studies have been retrospective and consisted of case series. Small patient samples and inadequate follow-up periods are limitations of these studies, as well as variability in many parameters that can affect vision, such as cataract type, surgical timing, timing of postoperative CL fitting, and family adherence to CL and patching treatment. Therefore, there is a need for long-term prospective studies that minimize these limitations to the evaluation of safety and efficacy and directly compare visual outcomes and quality of life with various CLs and amblyopia treatments in different patient groups.