To compare the retinal nerve fiber layer (RNFL) and macular thickness in pediatric patients with congenital or developmental cataract after cataract surgery with age-matched controls using optical coherence tomography (OCT).
setting : Institutional. patient population : Forty-five children (90 eyes) in the age group 4–16 years: subjects with unilateral congenital or developmental cataract (n = 15) and bilateral cataract (n = 15), and age-matched controls with no ocular abnormality (n = 15). intervention : Phacoaspiration and intraocular lens implantation was done in children with cataract. main outcome measure : Retinal nerve fiber layer thickness (RNFLT) and central macular thickness (CMT) were measured using OCT in normal controls and 3 months postoperatively in children with unilateral and bilateral cataract.
Children with unilateral cataract had significantly thinner RNFL in affected eyes (85.46 ± 8.16 μm) compared with the fellow eye (93.93 ± 13.12 μm; P = .036). Average RNFLT in the operated eyes of unilateral cataract was significantly less (85.46 ± 8.16 μm) compared to the control group (94.6 ± 12.51 μm; P = .004). Average CMT in unilateral cataract (221 ± 42.05 μm) was significantly less compared to normal control (245 ± 15.87 μm; P = .004). Average RNFLT in bilateral cataract was similar in both eyes but significantly less compared to control group.
Children with unilateral cataract showed significant thinning of superior, nasal, and temporal RNFL compared to the fellow eyes as well as age-matched normal eyes on OCT. The central macular thickness was less in deprivational amblyopic eyes than in age-matched normal eyes, but there was no significant difference compared to the fellow nonamblyopic eyes. In bilateral cataract, there was significant thinning of RNFL in superior and nasal quadrants as compared to age-matched normal eyes.
Sensory or visual deprivation amblyopia develops because of hindrance of the passage of light secondary to a condition such as congenital cataract or severe congenital ptosis. Congenital cataract is an important cause of sensory deprivation amblyopia in children. It interferes in the development of the visual system during the period when the neuronal network between the retina and the cerebral cortex is developing, thereby affecting various levels of the visual pathway starting from retinal ganglion cell to retinal nerve fiber layer (RNFL), optic nerve, lateral geniculate nucleus (LGN), and visual cortex. Several animal studies have demonstrated that LGN and visual cortex are the structures that are mainly affected in deprivation amblyopia. It leads to shrinkage of cells in LGN that receive input from the amblyopic eye and a shift in the dominance pattern in the visual cortex. Visual acuity is usually worse in the affected eye because of lack of an appropriate stimulation. Unilateral deprivation produces completely different structural changes in LGN and striate cortex compared with those produced by bilateral deprivation.
There is no consensus on the changes that occur in the retina in eyes with amblyopia. It has been suggested that abnormalities in the retinal ganglion cells may be attributable to the effect of amblyopia on the process of postnatal reduction of ganglion cells. Several techniques such as red-free ophthalmoscopy, scanning laser polarimetry, and optical coherence tomography (OCT) can be used to evaluate RNFL and macular thickness. OCT is a noncontact, noninvasive, easily reproducible method. It allows objective measurement of the optic nerve head, RNFL, and macular thickness with a resolution of 5–10 μm. Spectral-domain OCT (SDOCT) is a further refinement of this technique, which allows imaging with a faster scan rate and at a higher resolution. Several studies have investigated involvement of the macula and optic nerve in anisometropic/hyperopic/strabismic amblyopia using OCT. Some authors found an increase in the RNFL and macular thickness; others did not observe any difference. Little information is available regarding structural changes in the retina in sensory deprivation amblyopia in children owing to congenital or developmental cataract. A recent study on pediatric patients by Kim and associates showed increase in nasal peripapillary RNFL thickness on SDOCT analysis of deprivational amblyopic eyes with unilateral congenital or developmental cataract compared with fellow nonamblyopic eyes and age-matched normal eyes.
This study represents children from age 4 years through 16 years where the critical period of visual deprivation has already been crossed, so our aim was to evaluate the changes on SDOCT of the optic nerve head and macula in operated eyes with bilateral cataract, unilateral congenital or developmental cataract, and control group with normal eyes.
In this case-control study, 45 children (90 eyes) in the age group 4–16 years, attending the pediatric ophthalmology clinic of the Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India were recruited. Children were assigned to 3 groups: children with unilateral congenital or developmental cataract, children with bilateral cataract (bilateral total/zonular), and age-matched children with no ocular abnormality. To begin with, our sample size was 60, with 20 patients in each group. Nine children were excluded owing to poor cooperation for OCT (4 children with unilateral cataract, 2 children with bilateral cataract, and 3 children from control group), 1 child was excluded because of postoperative glaucoma, and 1 patient with unilateral cataract was lost to follow-up 1 month after surgery. So to maintain uniformity among the 3 groups we reduced the final sample size to 45, with 15 children in each group. Institutional ethics committee approval (PGIMER, Chandigarh, India) was obtained prospectively before starting the study and a written informed consent was taken from guardians of all the patients enrolled. The study adhered to the tenets of the Declaration of Helsinki. The minimum follow-up for each child was 3 months.
The following were the exclusion criteria: (1) traumatic and complicated cataract, (2) preoperative or postoperative glaucoma, (3) other associated ocular disorders (ie, strabismus, nystagmus, microphthalmia, microcornea, coloboma, aniridia, persistent hyperplastic primary vitreous, optic nerve hypoplasia, or any other gross posterior segment abnormality), (4) any associated systemic abnormality, (5) inequality in the type and density of cataract in bilateral cases, (6) any surgical complication during cataract surgery, and (7) poor cooperation for OCT imaging.
Preoperative examination included assessment of best-corrected visual acuity (BCVA) using Snellen visual acuity chart (alphabet chart/Teller acuity chart or Lea charts), slit-lamp examination, measurement of intraocular pressure (IOP) using Goldmann applanation/noncontact tonometer/Perkins applanation tonometer, extraocular motility assessment, cycloplegic retinoscopy, and dilated fundus examination in eyes with relatively clear media. In children with denser varieties of cataract, the posterior segment was evaluated using B-scan ultrasound. Axial length was measured using A-scan ultrasound and keratometry using a handheld keratometer (Nidek Inc., Fremont, CA, USA) in patients wherever possible. The intraocular lens (IOL) power was calculated as per Dahan’s guidelines.
Surgery was performed by a single surgeon (J.R.) in all the children with unilateral and bilateral cataract under general anesthesia, strictly adhering to the principles of closed-chamber technique in both groups. A fornix-based conjunctival flap was made followed by 2 clear corneal side ports 160–180 degrees apart. Anterior capsulorrhexis, multiquadrant cortical cleaving hydrodissection, bimanual irrigation, and aspiration were performed for removal of lens matter. A scleral tunnel was made 1–1.5 mm from the limbus superiorly and the IOL was inserted into the capsular bag or fixated in the ciliary sulcus at the same sitting. In case of bilateral cataract the 2 eyes were operated at an interval of 4 weeks.
At 3 months postoperatively, BCVA, IOP measurement, and anterior segment examination were done. OCT images were obtained using HD-OCT (Cirrus; Carl Zeiss Meditec, Dublin, California, USA). We assumed that the postoperative inflammation as well as visual acuity became stabilized to a great extent by 3 months after surgery, so we preferred doing OCT at that time. All OCT measurements were performed following pupillary dilation with 2.5% phenylephrine hydrochloride and 1% tropicamide by an experienced ophthalmic technician. Internal fixation was used in all cases and centration of the scan was verified by direct observation of fundus structures on a video screen. Satisfactory quality of OCT scan was defined as (1) good centration on the optic disc and (2) signal strength ≥6 (10 = maximum). The scans were then reviewed for adequate delineation of retinal layers. The acquisition protocols for Cirrus HD-OCT included 5-line raster scan and macular cube 512 × 128 combo for all patients. For each eye, RNFL thickness was measured in 12 30-degree segments (represented by clock hours; the 1-o’clock value represents the segment between 0 and 30 degrees, with 0 degrees being superior) and displayed for 4 quadrants (superior, inferior, nasal, and temporal) in relation to the disc using 200 × 200 combo for all patients. Average RNFL thickness (RNFLT) was calculated. Children from the normal control group were examined for their OCT values of RNFLT and central macular thickness (CMT). In children with unilateral cataract, comparison of RNFLT and CMT was done with their fellow eye as well as with the control group.
In order to correct axial length–related ocular magnification, we applied the Littman formula (t = p×q×s), modified by Bennet and later by Leung and associates and Kang and associates, where t is the actual fundus dimension, p is the magnification factor for the camera of the imaging system, q is the magnification factor for the eye, and s is the measurement obtained using OCT. In case of Cirrus HD-OCT, p is 3.382, and the ocular magnification factor q of the eye can be determined with the formula q = 0.01306•(axial length − 1.82). The main outcome measures were RNFLT, CMT, and BCVA in the 3 groups.
The statistical analysis was carried out using SPSS software version 18.0 (SPSS Inc, Chicago, Illinois, USA). Snellen and Lea visual acuity was converted to logMAR scale for statistical analysis. Normality of data was checked by measures of skewness and Kolmogorov-Smirnov test. Paired Student t test or Wilcoxon signed rank test was used for the comparison between amblyopic and the fellow nonamblyopic eyes. Intergroup comparison was done using unpaired t test for normally distributed data and Mann-Whitney test for skewed data. For more than 2 groups, analysis of variance was applied. Since the bilateral cataract group and normal control group had more than 1 observation from each subject, degree of association/correlation was calculated using Pearson coefficient of correlation. All statistical tests were 2-sided tests with a significance level of P = .05.
The mean age of the pediatric patients was 8.0 ± 4.5 years (unilateral cataract), 9.2 ± 5.7 years (bilateral cataract), and 8.0 ± 3.4 years (control group). The axial lengths were similar among all 3 groups ( Table 1 ). The mean BCVA of the control group was 0.03 ± 0.07 logMAR (Snellen equivalent 20/21) with a perfect correlation between visual acuities of right and left eye. In pediatric patients with unilateral cataract, the mean preoperative BCVA in the eyes having cataract (1.36 ± 0.8 logMAR; Snellen equivalent 20/400) was significantly less than that of the fellow eye (0.09 ± 0.13 logMAR; Snellen equivalent 20/24) ( P = .001). The mean preoperative BCVA of all the cataractous eyes (n = 30) was 0.8 ± 0.6 logMAR (Snellen equivalent 20/125) in children with bilateral cataract. The BCVA of right (1.3 ± 0.6 logMAR; Snellen equivalent 20/400) and left eyes (1.4 ± 0.6 logMAR; Snellen equivalent 20/500) were almost similar ( P = .180). Postoperative BCVA was measured at completion of 3 months after cataract surgery. In children operated for unilateral cataract, mean postoperative BCVA of the operated eye (0.8 ± 0.4 logMAR; Snellen equivalent 20/125) was significantly less than that of the fellow eye (0.09 ± 0.13 logMAR; Snellen equivalent 20/24) ( P = .001). In children operated for bilateral cataract, mean postoperative BCVA of the operated eyes (n = 30) was 0.4 ± 0.16 logMAR (Snellen equivalent 20/50). There was again no significant difference in the postoperative BCVA of right (0.4 ± 0.17 logMAR; Snellen equivalent 20/50) and left eyes (0.4 ± 0.15 logMAR; Snellen equivalent 20/50). The postoperative BCVA of children with bilateral cataract was significantly more than that of unilateral cataract ( P < .001). The postoperative BCVAs of both these groups were significantly less than that of the control group ( P < .001) ( Table 2 ). There was a good correlation between visual acuities of right and left eye in children with bilateral cataract ( r = 0.718, P = .003).
|Unilateral Cataract (Affected Eyes) (N = 15)||Unilateral Cataract (Fellow Eyes) (N = 15)||Bilateral Cataract (N = 30)||Control Group (N = 30)||P Value|
|Age (y), ± SD||8 ± 4.5||9.2 ± 5.7||8 ± 3.4|
|Axial length (mm), ± SD||23.87 ± 1.56||23.20 ± 1.72||23.35 ± 1.60||23.88 ± 1.37||.078|
|Unilateral Cataract||Unilateral Cataract||Bilateral Cataract (N = 30 Eyes)||Control Group (N = 30)||P Value a||P Value b||P Value c||P Value d|
|Affected Eyes (N = 15)||Fellow Eyes (N = 15)|
|Preoperative BCVA ± SD (logMAR)||1.36 ± 0.8||0.09 ± 0.13||0.8 ± 0.6||0.03 ± 0.07||<.001||.001||.002||.001|
|Postoperative BCVA ± SD (logMAR)||0.8 ± 0.4||0.09 ± 0.13||0.4 ± 0.16||0.03 ± 0.07||.001||<.001||<.001||.001|
In the control group the RNFLT was 115.6 ± 16.47 μm in the superior quadrant, 119.2 ± 20.75 μm in the inferior quadrant, 72.2 ± 14.77 μm in the nasal quadrant, and 71.3 ± 13.47 μm in the temporal quadrant. Average peripapillary RNFLT was 94.6 ± 12.51 μm and central macular thickness was 245 ± 15.87 μm. The RNFLT in all the quadrants, average RNFLT ( r = 0.893, P < .001), and macular thickness ( r = 0.981, P < .001) were well correlated in both eyes.
In pediatric patients with unilateral cataract, the average peripapillary RNFLT in the operated eye (85.46 ± 8.2 μm) was significantly thinner when compared to that of the fellow eye (93.68 ± 3.7 μm; P = .04). The superior (103 ± 13.0 μm) and temporal (63 ± 6.53 μm) peripapillary RNFLT in the operated eye were also found to be significantly thinner as compared to superior (126 ± 22.0 μm; P = .017) and temporal (73 ± 15.2 μm; P = .018) RNFLT in the fellow eye. However, there was no statistically significant difference between the nasal (64 ± 6.87 μm) and inferior (114 ± 15.06 μm) peripapillary RNFLT of the operated when compared to nasal (71 ± 9.56 μm) and inferior (115 ± 15.30 μm) RNFLT of the fellow eye. The central macular thickness of the operatde eye was 226 ± 42.05 μm and that of the fellow eye was 235 ± 24.20 μm ( P = .233).
The RNFLT in the superior, nasal, and temporal quadrants, as well as average RNFLT in the operated eyes of unilateral cataract subjects, was significantly thinner when compared to normal eyes of the control group. Central macular thickness in eyes operated for unilateral cataract was also significantly less in comparison to that in the control group ( Table 3 ).