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A Practical Approach to and Long-Term Results of Fitting Silicone Contact Lenses in Aphakic Children after Congenital Cataract

de Brabander, J. Optom., M.Sc.; Kok, J. H.C. M.D., Ph.D.; Nuijts, R. M.M.A M.D., Ph.D.; Wenniger-Prick, L. J.J.M. M.D., Ph.D.

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Purpose. This prospective study investigated characteristics of fit and performance of silicone contact lenses under conditions of permanent wear in cases of aphakia after congenital cataract.

Methods. Seventeen aphakic children (8 eyes unilateral, 18 eyes bilateral) were fitted with silicone contact lenses on an empirical basis without the use of keratometry. The lenses were worn on a permanent basis, with a routine replacement every 3 months. The follow up was 6 years, with evaluation lens parameters, fitting characteristics, lens condition, replacement rate, wearing time, complications, and visual acuity.

Results. The back optical zone radius (BOZR) remained stable at 7.50 mm, up to the age of 1.5 years old. At the age of 4 years, almost all eyes needed a BOZR of 7.90 mm. Mean ± SD contact lens power was +25.47 diopter (D) ± 4.0 (range +32.00 D – +20.00 D) at 3 months of age, and +17.94 D ± 3.8 (range +29.00 D – +15.00 D) at 3 years of age.This represents an average decrease of 0.23 D per month. The power decrease in unilateral cases was significantly lower (P < 0.01) than in bilateral aphakia. Snellen visual acuity at 4 years of age was 0.1 to 0.3 (20/200–20/60) in 15 eyes, 0.3 to 0.5 (20/60–20/40) in 10 eyes and greater than 0.5 (>20/40) in 1 eye. Lens usage over a total period of 90 wearing years was 5.6 lenses/eye/year, including the regular exchange every 3 months. No serious complications occurred. A positive correlation (r = 0.89) was found between age and deposit buildup. With the need for permanent wear reduced, therefore, 73% of the eyes were refitted with high-water content soft lenses or high gas-permeable (HGP) lenses, when the patients ranged in age from 4 to 6 years old.

Conclusions. The procedure for fitting silicone lenses in aphakic children is feasible in an easy and logical way without keratometry. Permanent wear with a low complication rate is possible up to the age of 3, with a lens usage (including a 3-month regular exchange) of 5.6 lenses/eye/year. From the age of 3, deposit formation is the determining factor for refitting with high-water content soft or HGP lenses.

From the Eye Research Institute Maastricht, Department of Ophthalmology, University of Maastricht, Maastricht (J.deB., R.M.M.A.N.); the Medical Center Jan van Goyen (J.H.C.K.); and the Department of Ophthalmology, Academic Medical Center at the University of Amsterdam (L.J.J.M.W-P.), Amsterdam, The Netherlands.

Accepted July 18, 2001.

Address correspondence and reprint requests to Dr. John de Brabander, Eye Research Institute Maastricht, AZM, Dept. of Ophthalmology, PO Box 5800 6202 AZ Maastricht The Netherlands. E-mail: john.de.brabander@planet.nl.

Congenital cataract is one of the leading causes of form deprivation amblyopia in children. 1,2 Surgical correction is essential at an early age to prevent amblyopia, strabismus, or poor fusion and should be followed by immediate and permanent optical correction of the resulting aphakia. Preferably, treatment should start within the critical period of the visual system, 17 weeks after birth. 3–6

Spectacles have the disadvantage of distorted peripheral images, constriction of the visual field, and problems of low compliance. Intraocular lenses and epikeratophakia are difficult to use because of the subsequent growth of the infant eye, resulting in changes of necessary refractive power. Furthermore, the long-term effects of intraocular lenses in infant eyes are not known. Early contact lens fitting seems to be the most practical solution for correction of infant aphakia. 7,8

Fitting contact lenses in infant aphakia involves several characteristic problems. Measuring the eye parameters of such young children is not easy, and assessment of the fit on the eye with a routine slit lamp examination is practically impossible. Usually, keratometry and evaluation of the lens fit need to be done under sedation or general anesthesia, in the operating room. 9 The necessary, high plus refractive power leads to lenses with remarkable center thickness. To avoid decentration (especially low riding) or lens loss, the lens diameter must often be taken as large as the cornea, and a relatively steep fit is indicated. The insertion and removal of the lenses on a daily-wear basis may be a stressful event for both parents and child. Because the young aphakic eye must be corrected during all sporadic waking hours, 10 extended wear is a key demand for successful treatment, at least up to an age of 3 to 4 years old.

For these reasons, the use of rigid contact lenses has not been successful. The high risk of lens loss and the chance of lens binding on the cornea are further complications. High-water content soft contact lenses, although comfortable to wear and easy to fit, show a high rate of complications due mainly to reduced oxygen transmission in the high-plus thick lens modality. 9 Therefore, contact lenses made of silicone elastomer with high oxygen permeability have the potential to meet the high demands in the correction of young aphakic children.

Silicone contact lenses have had a long and troublesome history of development. 11–14 Since the experiments of Becker, in 1956, the material, lens design, production, and reproducibility improved, but only slowly. In September 1984, the Silsoft (Bausch & Lomb, Rochester, NY) lens, manufactured from a silicone elastomer, was the first lens that reached U.S. Food and Drug Administration (FDA) approval as a 30-day extended-wear lens for aphakia. 13 The basic material is hydrophobic, and, therefore, a surface treatment (with the formation of hydroxyl groups on the lens surface) is required. This process gives the lens a low contact angle without making it hydrophilic. 15 This means that there is no dehydration in low humidity, and the more stable lens usually gives a better visual acuity than hydroxyethyl methacrylate (HEMA) lenses. 16 The material is soft but stable enough to assure good optical quality and high resistance to tearing; and it has a good thermal conductivity. 15–17

The most important feature of silicone elastomer is its high oxygen permeability. Equivalent oxygen percentage (EOP) is a measure of the amount of oxygen that is available to the cornea. The baseline of the EOP scale is 21% oxygen available from air, without contact lens wear. For safe, permanent wear (including closed-eye conditions), a minimal EOP value of 18% has been indicated. Hill 18 showed that Silsoft lenses have an average EOP of 18.7% and 18.4% in lenses that had been worn more than 12 hours per day during an 8 to 10 month period. Barr 15 demonstrated a graph from the work of Fizgerald that yields approximately the same EOP value results but also shows that the EOP value is independent of lens thickness.

Oxygen transmissibility of a contact lens can also be given as the Dk/L value. The oxygen permeability of the material is Dk, and L is the lens thickness. The Dk value of Silsoft lenses is stated by the manufacturer as 340 × 10−11 cm2 mL O2/sec mL mm Hg. Glasser and Weissman 19 found a value of only 50, whereas Weissman, Fatt, and Pham 20 reported a value of 190 using a single-chamber polarographic technique. The high standard deviation (SD = 79) found in the latter study led the authors to suggest that better methods should be developed to evaluate oxygen performance of high-Dk materials. According to the same study, lens thickness does correlate with oxygen transmissibility, but, even with a very thick lens, oxygen transmissibility is high enough to meet the demand for permanent wear (Dk/L = 90).

The aim of this long-term prospective study was to investigate the performance of Silsoft contact lenses under permanent wear conditions in children with aphakia after congenital cataract.

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SUBJECTS AND METHODS

An important patient-intake criterion in this study was an early diagnosis to ensure that the cataract was congenital. 21 All patients in this study underwent surgery at the Academic Medical Center, University of Amsterdam, The Netherlands. Normal standards were followed to establish a multidisciplinary diagnosis, prognosis, pre- and postoperative care, and informed consent.

All aphakic eyes were fitted with Silsoft contact lenses (Table I) as soon as possible after surgery. The fitting of the lenses was performed without sedation in the consulting room, and the fitting procedure did not involve keratometry. In all cases, a lens with a BOZR of 7.50 mm and a total diameter (TD) of 11.3 mm was inserted as first choice. Using a penlight, a magnifying lens (+10 D), and an ophthalmoscope or hand-held slitlamp, the motility and centering of the lens were evaluated 30 minutes after insertion. If the lens moved too much or decentered, the TD was increased to 12.5 mm. In cases of insufficient motility, a lens with a flatter BOZR was used and evaluated again. Lens power was calculated from retinoscopy. An addition of +4 D (counted from birth) was given to assure optimal focussing at short distance. This addition was decreased by 1 D each year.

Table 1

Table 1

Parents were directed to routinely check the eyes of their child. They were instructed to look for a clear reflex of the front surface because this indicates the wettability of the lens. If dull areas were present, parents were to apply a saline solution containing no preservative. Parents were also directed to routinely insert one drop of saline (no preservatives) when the child awakened. Parents were taught how to remove, clean, and insert the lens and were advised that cleaning should only be done in case re-wetting failed. As long as the surface was wet and the eye remained clear, the lenses were worn permanently. If the eyes became red or there was any doubt about the lens or eye condition, the parents were instructed to consult the clinic immediately.

Follow-up visits were scheduled at 1 night, 1 week, 1 month, and every 3 months thereafter. During follow-up visits, an ophthalmologic examination was performed that included assessment of movement, centration, and condition of the lens. The refractive power of the lens was checked using retinoscopy with and without the lens in situ. Lenses were routinely exchanged every 3 months. To make sure no wearing time was lost due to delay in ordering of lenses, spare lenses were stocked in the clinic for all children.

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RESULTS

Seventeen children completed this study. Eight (2 male, 6 female) patients suffered from unilateral congenital cataract, and nine (4 male, 5 female) patients suffered from bilateral congenital cataract (Table 2). A total of 26 eyes were treated. The confirmed etiology of the congenital cataract was hereditary (3 cases), associated with Down syndrome (3 cases), associated with rubella infection and microphthalmos (2 cases), and associated with encephalopathy (1 case). Typically, in the remaining 8 cases (47%), the etiology was idiopathic. In 3 eyes, persistent hyperplastic primary vitreous (PHPV) was present. Surgical technique consisted of lensectomy with anterior vitrectomy in all eyes.

Table 2

Table 2

The time period between birth and the start of contact lens wear averaged 20.3 weeks and ranged from 8.6 to 41 weeks. This wide spread in time period could already be found in the time interval between birth and diagnosis, averaging 11.2 weeks and ranging from 1 to 22 weeks. Surgery was performed at an average of 6.7 weeks after the diagnosis (range 1–26 weeks). Contact lens wear was started at an average of 2.4 weeks (range 1 day–9.5 weeks) after surgery.

Snellen visual acuity at the age of 4 years is listed per eye and per type of aphakia in Table 3. The typical discrepancy between visual acuity in bilateral and unilateral cases can be seen. Visual acuity in bilateral cases was significantly better (chi squared P < 0.05) than that of the treated eye in unilateral aphakia.

Table 3

Table 3

Few complications occurred until patients reached the age of 3 years (cumulative wearing time 72 years). In 4 eyes (2 patients), a bacterial conjunctivitis caused by Haemophilus influenzae occurred. Both cases resolved without sequelae. In one case an acute red eye was associated with lens binding, and a flatter lens solved the problem. In 4 eyes, decentration of the lens was better corrected using a 12.5-mm lens compared to a 11.3-mm lens with steeper base curve.

Lens power at 3 months of age showed a large range (+26 – +32 D) that was equal for both unilateral and bilateral aphakia. In Figure 1, the distribution of mean ± SD of lens power, from 3 to 36 months old, is given for bilateral and unilateral aphakia. The mean ± SD contact lens power at 3 months of age for the total group (+28.40 D ± 2.76), the bilateral group (+28.00 D ± 3.10), and the unilateral group (+29.00 D ± 2.45) were not statistically different (P > 0.01). With increasing age, the power spread in bilateral cases generally channels into a lower range of +15 to +18 D (mean +16.44, ± 1.24) at 3 years of age. This is not so much the case in the group of unilateral aphakia, with a range of +16 to +29 D (mean + 19.63, ± 5.01). The effect on the SD is entirely due to the two cases of unilateral aphakia with the etiology of Rubella-associated microphthalmos. Excluding these two cases from the analysis in the unilateral group reveals a power range of +26 to +29 D (mean 27.50 D, ± 2.68) at 3 months of age and +16 to +18 D (mean +17 D, ± 1.1) at 3 years of age. The latter figures are not statistically different (P > 0.1) from the bilateral group.

FIG. 1

FIG. 1

The average change in power per month of age for the total group, the bilateral group, and the unilateral group were 0.32 D, 0.35 D, and 0.28 D, respectively. If the two cases of Rubella associated with microphthalmos are excluded from the unilateral group, the change in power per month of age is 0.31 D. The individual cases of Rubella showed power changes of 0.18 D and 0 D per month of age.

BOZR changes follow a remarkable line (Table 4). Until the age of 1.5 years, almost all eyes needed a BOZR of 7.50 mm. Within the next 2 years, significant changes are made to a BOZR of 7.70 and 7.90 mm.

Table 4

Table 4

At around the age of 3 years, deposit formation increased rapidly and patients were refitted with hydrophilic or HGP lenses under daily wear conditions (see Table 4). A further analysis of the age relation for the total of 60 extra replacements for deposits revealed a significant positive correlation with age (r = 0.89 at P < 0.05).

Table 5 shows the number of lenses needed up to the age of 4 years (cumulative wearing time 90 years) and the reasons for lens replacements. Although the standard procedure included replacement of lenses every 3 months, this turned out to be lower than planned (3.2 lenses/eye/year) because routine replacements were combined with lenses replaced for other, specific reasons. Extra lens replacements per eye per year were made, in order of importance, because of deposits (0.7), power (0.7), BOZR (0.4), lens loss (0.4), defects (0.2) and diameter (0.04). The total average number of lenses used per eye/year was 5.6. A dramatic spread in lens usage per child was found. Some children needed only the routine 4 lenses per eye/year, whereas others used many more lenses; results showed that replacement also was often needed for the same reason per child.

Table 5

Table 5

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DISCUSSION

Generally, the results on the fitting procedure with Silsoft contact lenses in aphakia after congenital cataract are in accordance with data found by Lightman and Marshall. 22 It was also found that, up to 6 months of age, a BOZR of 7.50 mm and a diameter of 11.3 mm are good starting points for successful fitting without keratometry. In some cases, increasing the diameter was a better method for preventing lens decentration than fitting with a steeper BOZR. In our study, the crucial period in which patients needed changes in BOZR also started around the age of 18 months. The shift in BOZR to 7.70 and 7.90 mm takes place between 1.5 and 4 years of age. At age 4 years, 77% of the eyes were wearing a base curve 7.90 mm.

Comparing the average powers needed at 6, 12, 24, and 36 months to those of Lightman and Marshall, 22 our study used, on average, lenses of lower power (1.8 D); however, the rate of power change in our study (0.32 D per month) is practically the same as they reported (0.35 D per month).

The two cases of microphthalmia showed a different pattern in both BOZR and power change, but there were also differences between the cases. In one case, both BOZR and power remained constant up to the age of 6 years, which would indicate no dimensional development of the eye. The other case showed a change of BOZR from 7.50 mm to 7.70 mm at an age of 2 years and a change in power from +32.00 to +26.00 from 3 to 36 months of age, indicating a change in the usual direction but less than normal.

Results of visual acuity data in unilateral cases turned out lower than in bilateral cases. Because there was no selection concerning visual acuity prognoses in this study, this result is not surprising. This study shows that, although successful permanent optical correction is feasible in infant aphakia, it is not the only answer to visual development; this is in accordance with conclusions by Moore. 23 The question remains whether it is worth the risk of surgery and the necessary intensive treatment in case of unilateral congenital cataract if visual acuity remains low. Opinions in the literature are diverse on this issue. Some studies are negative, 24 others show the possibility of stimulating visual acuity but with variable results 25,26 or as possible only for a select group of patients. 27 Although binocularity remains a problem, there are also reports of relatively good results. 28–30 With the advancements in surgical techniques, the risk of operating on infant eyes is greatly reduced, and as shown in our study, permanent optical correction is possible. The remaining issue, particularly in unilateral cases, seems to be the development of optimal orthoptic treatment schemes 23 to reduce the unequal competition between the eyes. 31

Some studies report difficulties in removing deposit formation, 28,32 but these studies are not specific on the age of onset. Because of the higher risk of deposits associated with permanent wear, Lightman and Marshall 22 recommended daily wear. In this study, deposit formation was found to become disturbing around the age of 3 years. Prior to that age, deposit formation was not a significant problem in permanent wear when combined with a routine wetting procedure. However, strict follow-ups, replacement of the lenses whenever needed, intensive instruction to the parents and parental cooperation, together with a clinical setting that provides for emergencies on a 24-hour basis are essential requirements for providing optimal care in this patient group. Also, a lens usage of 5.6 lenses per eye per year seems to be necessary to successfully correct aphakic children after congenital cataract, with silicone contact lenses. It seems that, from the age of 4 years, silicone lenses are no longer compatible with tear composition and should, in most cases, be replaced by daily-wear high-water content soft lenses, or, at a later age, replaced with HGP lenses.

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Acknowledgments

With this publication we honor our dearest friend and the initiator of this study, Dr. Jan H.C. Kok who died at a much too early age on November 21, 1998. We would also like to thank V.S. Gangaram Panday, M.D. for his help in processing the data.

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REFERENCES

1. Lloyd IC, Goss-Sampson M. et al. Neonatal cataract: Aetiology, pathogenesis and management. Eye 1992; 6: 184–96.
2. Sorsby A, Incidence and causes of blindness in England and Wales, 1963–68. H.M.S.O. 1972.
3. Hubel DH, Wiesel TN. Receptive fields of single neurons in the cat’s striate cortex. J Physiol (Lond) 1962; 148: 574–91.
4. Noorden GK von. Management of congenital cataracts. Trans Acad Ophthalmol Otol 1970; 74: 352–59.
5. Awaye S, Miyake S. Form deprivation amblyopia: Further observations. Graefe’s Arch Ophth 1988; 226: 132–36.
6. Cheng KP, Hiles DA, et al. Visual results after early surgical treatment of unilateral congenital cataracts. Ophthalmology Jun 1991; 98: 6.
7. Dutton J, Slamovits T, (ed.). Visual rehabilitation of aphakic children. Surv of Ophthalmology 1990; 34;5: 365–84.
8. Hales RH. Unilateral pediatric aphakia: Current treatments and choices. Contact Lens Forum 1986; Nov: 34–5.
9. Matsumoto ER, Murphree AL. The use of silicon elastomer lenses in aphakic pediatric patients. Internat Eye Care 1986; 2;4: 214–7.
10. Schmidt P. Clinical implications in aphakic pediatric patients. Int Eye Care 1986; 2; 4: 217.
11. Baily NJ. Soft silicon lenses: the beginning. Contact Lens Spectrum 1987: March: 17–22.
12. Fitzgerald JK. The silicon lens that works. Contact Lens Forum 1981; June: 43–50.
13. Blackhurst RT. New flexible silicone contact lens: A thirteen month clinical experience. Contact And Intraocular Lens Medical J 1980; 6; 3: 252–7.
14. Baily NJ. Bausch & Lomb pitches in for Dr. Simon. Contact Lens Spectrum 1987; April: 53–60.
15. Barr JT. Silicon lenses are elastic and permeable. Rev of Optometry 1981; April: 59–60.
16. Hill JF, Anderson FL, Johnson TK, Rigel LE, Seelye RR. Eighteen-month clinical experience with extended wear silicon contact lenses on 400 patients. Am J Optom Physiol Optics 1983; 60; 7: 578–81.
17. Woodward EG. Therapeutic silicon rubber lenses. J British Contact Lens AssJan 1984; 7; 1: 39–40.
18. Hill RM. The elastomer outlook. Contact Lens Forum 1980; Dec: 39–41.
19. Glasser DB, Weissman BA. Mean oxygen permeability of four flexible contact lens materials. CLAO J 1983; 9: 29–31.
20. Weissman BA, Fatt I, Pham C. Polarographic oxygen permeability measurement of silicon elastomer contact lens material. J Am Optom Assoc 1992; 63: 187–90.
21. Moore BD. Pediatric cataracts–diagnosis and treatment. Optom Vis Sci 1994; 71: 168–73.
22. Lightman JM, Marshall D Jr. Clinical evaluation of back optic radius and power determination by age in pediatric aphakia due to congenital cataract fitted with a silicone elaster contact lens [published erratum appears in Optom Vis Sci 1996 May;73(5):352]. Optom Vis Sci 1996; 73: 22–7.
23. Moore BD. Pediatric aphakic contact lens wear: Rates of successful wear. J Pediatr Ophthalmol Strabismus 1993; 30: 253–8.
24. Ryan SJ, Maumenee AE. Unilateral congenital cataracts and their management. Ophthalmic Surg 1977; 8: 35–9.
25. Enoch JM, Rabinowicz IM. Early surgery and visual correction of an infant born with unilateral eye lens opacity. Doc Ophthalmol 1976; 41: 371–82.
26. Cheng KP, Hiles DA, Biglan AW, Pettapiece MC. Visual results after early surgical treatment of unilateral congenital cataracts. Ophthalmology 1991; 98: 903–10.
27. Scott WE, Drummond GT, Keech RV, Karr DJ. Management and visual acuity results of monocular congenital cataracts and persistent hyperplastic primary vitreous. Aust N Z J Ophthalmol 1989; 17: 143–52.
28. Moore B. The fitting of contact lenses in aphakic infants. J Am Optom Assoc 1985; 56: 182–3.
29. Beller R, Hoyt CS, Marg E, Odom JV. Good visual function after neonatal surgery for congenital monocular cataracts. Am J Ophthalmol 1981; 91: 559–65.
30. Pratt Johnson JA, Tillson G. Visual results after removal of congenital cataracts before the age of 1 year. Can J Ophthalmol 1981; 16: 19–21.
31. Birch EE, Stager D, Leffler J, Weakley D. Early treatment of congenital unilateral cataract minimizes unequal competition. Invest Ophthalmol Vis Sci 1998; 39: 1560–66.
32. Rogers GL. Extended wear silicone contact lenses in children with cataracts. Ophthalmology 1980; 87: 867–70.
Keywords:

Congenital cataract; Infant aphakia; Contact lenses; Permanent wear; silicone elastomer

© 2002 The Contact Lens Association of Ophthalmologists, Inc.