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Bilateral congenital cataract is the most common cause of treatable blindness in children, particularly in developing countries.¹ A recent report indicated that infants with bilateral congenital cataract who underwent early surgery (performed within one month of age) and received appropriate optical rehabilitation could obtain visual acuity of better than 0.4 and could even achieve stereopsis.² However, because of relatively late detection and diagnosis, unavailability of facilities for infant anesthesia, and poor compliance with long-term follow-up, the visual prognosis for infants with congenital cataract in developing countries is different compared with that in industrialized countries.³ To our knowledge, the results of long-term follow-up of dense bilateral congenital cataract in China have not been well documented. The purpose of this study was to evaluate the long-term visual function results of dense bilateral congenital cataract at a major tertiary referral center for ophthalmology in southern part of China.

Patients
We retroactively reviewed the medical records of patients treated surgically for dense bilateral congenital cataract between January 1992 and December 2000 at Zhongshan Ophthalmic Center of Sun Yat-sen University, China. Inclusion criteria were as follows: (1) opacities that were dense and large enough to obscure the fundus view through an undilated pupil were defined as dense cataract; (2) absence of other obvious ocular and systemic malformations; (3) without severe surgical complications, such as retinal detachment; (4) follow-up of not less than 5 years. Forty-seven patients met the inclusion criteria for our study. We attempted to contact these patients by telephone, and we were able to contact and enroll 38 patients in the study. These patients had been followed for 60−167 months with a mean follow-up period of 107.6 months. The mean age at the last follow-up was (9.3±2.7) years (range 5.5 to 15 years). Twenty-nine of the patients (76.3%) were male. Informed consent was obtained from all patients in the study, in accordance with the rules of the Hospital Ethics Committee.

Retrospective investigation
Preoperative examination included ocular motility and eye position, anterior segment microscopy, fundus examination with dilated pupil, and intraocular pressure measurement. Morphologic characteristics of the cataract, keratometric measurements, and axial length were recorded. The posterior segment was examined with B-scan ultrasound.

The surgery included two procedures: cataract extraction and secondary intraocular lens (IOL) implantation. General anesthesia was used in all patients. Both eyes were operated on simultaneously. The surgical technique of cataract extraction consisted of a superior limbal incision, anterior capsulorhexis, hydrodissection, irrigation/aspiration of the nucleus and cortex, and posterior capsulorhexis together with anterior vitrectomy in some cases. After surgery, patients were fitted with aphakic glasses as soon as possible.

All patients received IOL implants after 2 years of age. Intraocular lens power was calculated with the SRK II formula. Slight hypermetropia was targeted in accordance with age and expected axial length.⁴ Before 1997, PMMA IOLs, including 722C, 811C and 822C (Pharmacia, Sweden) were used. More recently, three-piece acrylic foldable IOLs (MA60BM, Alcon, USA and AR40e, AMO, USA) were implanted. All IOLs were placed in the sulcus.

The children were examined at 1 day after surgery, once a week for 1 month, then every 1−3 months during the first year and every 3−6 months after the first year in the postoperative follow-up period. Clinical examination included all procedures performed pre-operatively, as well as best corrected visual acuity (BCVA) measurement.

Patients' records included age at onset and diagnosis, family history, and events during pregnancy (for example, intrauterine infection, drug exposure, or ionizing radiation), delivery, and the neonatal period were investigated.

Current follow-up study
All the patients enrolled in our study each received a full ophthalmological examination, including all the procedures done at the pre- and post-operative examinations. In addition, we evaluated stereoscopic vision, using Synoptophore (MT-364, TAKAGI SEIKO, Japan). Eye deviation was evaluated with cover-uncover test at 6 m and 33 cm and measured in prism diopters (Δ) in primary position. An ocular deviation of 10^Δ or more was defined as strabismus.

Statistical analysis
Spearman rank-order correlation was calculated for correlation analysis between age at cataract extraction and BCVA of the better eye. Student's t test of paired data was used for the evaluation of BCVA between post- and pre-treatment of amblyopia. Statistical analysis was performed with SPSS version 10.0 (SPSS Inc., USA). A P value < 0.05 was considered statistically significant.

Age at cataract detection varied from 1 month to 7 months (mean age (3.5±1.9) months). There was a positive family history in 9 cases (23.7%), intrauterine infection in 2 cases (5.3%), perinatal disorders in 18 cases (47.4%), and unrecognized cause in 11 cases (28.9%).

In all cases, cataract extraction was performed when the patients were between 3 months and 12 months of age, with a mean age of (5.6 ± 2.7) months. Secondary IOL implantation was performed between 2.4 and 15 years (mean age (4.2 ± 4.7) years).

At the last follow-up, the mean BCVA was 0.25 (range 0.05 to 0.4) in the better eye, and 0.16 (range hand movement to 0.4) in the fellow eye. Stereoscopic vision was absent in all patients, and only 3 children had simultaneous perception. In addition, preoperative and postoperative nystagmus was detected in all cases, and strabismus was detected in 35 cases (esotropia in 25 cases, exotropia in 10 cases) (Table). A high correlation was found between timing of surgery and final BCVA of the better eye (r=−0.55, P=0.00), with earlier cataract extraction being associated with better visual outcome (Fig.).

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Table. Long-term visual function results of patients with dense bilateral congenital cataract

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Fig. Correlation between age at cataract extraction and BCVA of the better eye (Spearman rank-order correlation, r=−0.55, P=0.00), with earlier cataract extraction being associated with better visual outcome. BCVA: best corrected visual acuity.

Twenty-two of 38 patients (57.9%) underwent amblyopia treatment. Age at amblyopia treatment in 22 children varied from 3 years to 7.8 years (mean age (4.8±1.9) months) and the duration of treatment varied from 1 month to 57 months (mean (29.2±22.3) months). The mean BCVA of post-treatment of amblyopia was 0.27±0.14 (range of 0.05 to 0.4), significantly higher than that of pre-treatment (mean 0.12±0.09, range of 0.01 to 0.3) (t=5.65, P=0.00).

Four frequent surgical complications included posterior capsular opacification in 66 eyes (86.8%), pupil distortion in 40 eyes (52.6%), anterior synechiae in 3 eyes (3.9%), and aphakic glaucoma in 2 eyes (2.6%). The posterior capsular opacifications were managed successfully with Nd:YAG laser or secondary manual capsulotomy. The aphakic glaucoma, which was caused by pupillary block, was controlled by peripheral iridectomy with Nd:YAG laser.

Dense congenital cataracts often cause severe visual impairment because of form deprivation during the sensitive period of visual development. In the present study, all patients had cataract extraction at 3 months of age or later. The visual results of the better eyes averaged 0.4 or worse. None of the patients developed stereopsis. All patients had preoperative and postoperative nystagmus, and most had strabismus. Higher age at cataract extraction was associated with a worse BCVA in the better-seeing eye.

These results, similar to those found in previous studies,^2,5,6 suggest that the timing of congenital cataract surgery is the most important factor for visual prognosis, with earlier cataract extraction having a better visual outcome. Studies have shown that focused images on the immature retina in infancy during the critical period, which extends from 4 weeks to 4 months, are essential for adequate visual development.^7-9 The most critical period of motor fusion development is probably the first 2 to 4 months of life.^10-12 To prevent interruption of visual maturation, continuous clarity and optical correction of the visual axis must be maintained, as nystagmus resulting from sensory deprivation presents within 2 to 3 months.¹³ Nystagmus is a clinical indicator of impending dense amblyopia and a compromised visual prognosis.⁶ Early cataract extraction with accurate optical correction during the critical period is recommended to avoid irreversible impairment of visual development.

On the other hand, the advantages of early surgical intervention must be weighed against a higher rate of complications, especially glaucoma, the most serious threat. Lundvall and Kugelberg² observed that glaucoma was more common in eyes that underwent cataract surgery during the first 4 weeks of life than in those that had surgery later. Vishwanath and coworkers¹⁴ reported that the 5-year risk of glaucoma in at least one eye was 50% in children undergoing bilateral lensectomies within the first month of life compared with 14.9% in children whose surgery was performed later. In our current study, no surgeries were performed before the age of 3 months, only 2 eyes (2.6%) developed pupillary block glaucoma. Moreover, the safety of general anesthesia during infancy has been shown to be higher in preterm infants less than 44 post-conception weeks of age.^15,16 For these reasons, Lambert¹⁷ has proposed that the most favourable time for infants with dense congenital cataract to undergo surgery is 4–6 weeks of age. More recently, Lambert et al¹⁸ concluded that good visual outcomes could be achieved beyond the first 5 to 8 weeks of life, but the incidence of poor visual outcomes increased if surgery was delayed beyond 10 weeks of age.

However, a large difference exists between developed and developing countries with regard to age of congenital cataract detection and diagnosis. In southern part of China, cataract was usually detected after 1 month of age instead of in the first week of birth, as in industrialized countries. Confinement after childbirth (usually lasting 100 days) and lack of knowledge about congenital cataract are the most important reasons for the delayed detection and diagnosis. These reasons, combined with the absence of general anesthesia and the different timing of surgery according to the judgments of different surgeons, result in that most of patients with dense bilateral congenital cataract treated surgically after 3 months of age.

Our findings combined with previously reported results indicate that dense bilateral congenital cataract cannot be successfully treated after the age of 3 months. We emphasize earlier surgery and adequate optical correction in the sensitive period of visual development for infants presenting with dense bilateral congenital cataract. It is difficult in China to screen for congenital cataract in all newborns, but it is imperative to screen neonates with positive family history or risk-associated events during pregnancy, delivery, and the neonatal period. All parents of newborns should be taught to recognize a white reflex of the eye and to seek treatment if it is detected. In addition, our data also showed that BCVA was improved by amblyopia treatment. And the importance of compliance with long-term follow-up should be emphasized.

In summary, nystagmus developed predominantly in children with dense bilateral congenital cataract when extraction was performed 3 or more months after birth. To achieve better visual acuity, surgery should be performed earlier. Amblyopia treatment based on adequate optical rehabilitation contributed to better visual acuity.

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