PATIENTS

Patients with PPCs or posterior lenticonus (3-14 years of age) who needed cataract surgery at the Zhongshan Ophthalmic Center, Sun Yat-sen University in China were included. Patients who had relevant ocular disease other than pediatric cataracts or could not cooperate with to the examinations were excluded. The indication for surgery in all patients was significantly deteriorated visual function and amblyopia treatment failure (decline in best-corrected distance VA to 20/40 or worse). Amblyopia therapy included refractive correction, with or without patching. The patch was required for half of the waking time for children. The duration of eye patching was decreased according to the degrees of visual improvement after the operation. The treatment period was determined to be the duration until the peak best-corrected distance visual acuity (CDVA) was reached. The study adhered to the tenets of the Declaration of Helsinki. Written informed consent was obtained from the parent or guardian of each patient. The study protocol received ethical approval in each country with original approval granted by the Ethics Committee of Sun Yat-sen University-Zhongshan Ophthalmic Center Institutional Review Board. This study was registered at ClinicalTrials.gov (NCT05207007).

PREOPERATIVE EXAMINATION

Detailed ophthalmic examinations were performed preoperatively, including detailed history-taking, VA, eye position, slitlamp examination, autorefraction, and fundus examination. The axial length (AL) and keratometry parameters were measured with an IOL Master 700 (Carl Zeiss Meditec AG, Jena, Germany) in all patients. Moreover, the position and size of lens opacities were also measured preoperatively, and details are as follows.

The location of the cataracts was categorized as central, paracentral, or peripheral. If the cataract was located within 3 mm of the center of the lens but not centered over the visual axis, it was classified as paracentral. Cataracts >3 mm from the center of the lens were categorized as peripheral ( Figure 1 ).

Posterior polar cataract (PPC)—impairment of red reflex. The location of the cataracts was categorized as central, paracentral, or peripheral. Cataracts ≤3 mm of the center of the lens but not centered over the visual axis were classified as paracentral. Cataracts >3 mm from the center of the lens were categorized as peripheral.

The size of the lens lesion was measured by ImageJ (version 1.47; provided in the public domain by the National Institutes of Health, Bethesda, MD) on the slitlamp photograph, with the reference to corneal diameter. Briefly, horizontal corneal diameters were set to scale with the white-to-white corneal diameter measured by an IOL Master 700 (Carl Zeiss Meditec). The horizontal corneal diameter and area of the lens lesion were marked artificially by an experienced ophthalmologist, while the scale setting and area measuring were calculated automatically by ImageJ. The measurement for each image was repeated 3 times and the average size of the area was then calculated and recorded ( Figure 2 , A).

Slitlamp photographs of a representative case of posterior polar cataract before and after cataract surgery. A. The area of the lens lesion was measured using ImageJ software, with the reference to corneal diameter. B. A central continuous posterior capsulotomy was performed manually and the intraocular lens was implanted in the capsular bag.

VISUAL FUNCTION EVALUATION BEFORE AND AFTER SURGERY

Visual function examinations were performed preoperatively and ≥6 months postoperatively, including VA, stereopsis, monochromatic aberrations, and MTF for monochromatic light.

VA was measured using the Early Treatment Diabetic Retinopathy Study chart and was recorded as the logarithm of the minimal angle of resolution (logMAR). This study reports the CDVA. Stereoacuity was measured at 40 cm using the Randot stereotests (Stereo Optical Company, Chicago, IL) with the accompanying polarizing spectacles.

The monochromatic aberrations were measured by the iTrace Dynamic Laser Refraction system (Tracey Technologies, Corp, EyeSys Vision, Inc) which is a ray-tracing aberrometry instrument that sequentially projects 256 near-infrared laser beams (785 nm) into the eye to measure ocular aberrations after point-by-point data processing. After dark adaptation for 10 min in a dim room, the patients were measured with, or corrected for, a 4.0-mm pupil, a standard size that is often used to analyze ocular aberrations without using any mydriatic agents. A total of 3 repeated measurements were obtained and averaged for each participant. The corneal aberrations were calculated based on topography data, and the internal aberrations were calculated by subtracting the corneal aberrations from those of the entire eye measured by the raytracing aberrometer using the built-in program.

The optical quality was also studied by the MTF for monochromatic light. The MTF was measured with the Optical Quality Analysis System (OQAS, Visiometrics, S.L., Castelldefels, Spain), which was based on the double-pass technique that was developed to perform an objective evaluation of the optical quality of vision. The primary parameter was the MTF cutoff frequency (cycles per degree), which represents the highest spatial frequency at the lowest contrast (1% of contrast) when MTF reaches a value of 0.01.

SURGICAL TECHNIQUE

Cataract extraction combined with intraocular lens (IOL) implantation was performed by an experienced congenital cataract specialist (W.C.). All surgeries were performed under general anesthesia with tracheal intubation. After finishing a standard 2.2-mm scleral tunnel incision, an anterior continuous curvilinear capsulotomy was completed. The cortex and nucleus were then removed using an irrigation/aspiration device. Subsequently, a central continuous posterior capsulotomy was performed manually in combination with a limited anterior vitrectomy. Hydrophobic acrylic or polymethylmethacrylate IOLs were implanted. Figure 2 , B shows a representative postoperative case with the IOL implanted in the capsular bag.

The online calculators for Barrett Universal II formulas were used for IOL power calculations. For the children who underwent bilateral cataract surgery, the target postoperative refraction was based on the patient’s age and biometry. Hyperopia was prearranged as the target to compensate for a myopic shift to ultimately achieve mild myopia or emmetropia in adulthood. Specifically, the target refraction was +3.0 diopters (D) for children 3 to 4 years of age, +2.0 D for children 5 to 6 years of age, +1.0 D for children at 7 years of age, and 0 for children >8 years of age. However, for children with unilateral cataracts, the refractive status of the contralateral eye should be considered. When adjusting IOL power, a bilateral difference >3 D was avoided to prevent postoperative anisometropia.

DATA ANALYSIS

Chi squared tests, independent sample t tests, paired t tests, Fisher exact test, and nonparametric Mann-Whitney U tests were performed for comparative analyses. Multivariable analysis was carried out to assess which of the studied variables were associated with postoperative visual outcomes in children with posterior lens opacities. SPSS for Windows (version 19.0; SPSS Inc, Chicago, IL) was used for data analysis. P < .05 was considered as statistically significant.