Purpose
To evaluate central corneal thickness (CCT) in children with congenital/developmental cataracts before and after cataract removal, to correlate CCT with corneal diameters before cataract surgery in this same group, and to evaluate CCT over time in a separate group of children who were already aphakic or pseudophakic at study entry.
Design
Longitudinal study.
Methods
Children with cataract (Group 1, with pre-cataract-removal CCT) and aphakia/pseudophakia (Group 2, presenting after cataract removal) were included. CCT measurements were performed using ultrasound pachymetry. Normal fellow eyes of unilaterally affected cases served as controls. In bilateral cases, right eyes were used for analyses.
Results
Group 1 comprised 66 children. Before cataract surgery, unilateral cases (n = 31) showed similar CCT and strong association between the affected and fellow eyes (552.0 ± 32.9 μm vs 550.9 ± 40.4 μm, respectively; r 2 = 0.71, P = .0001). After cataract surgery, affected eyes (n = 13) showed mean CCT increase of 29.7 ± 43.1 μm ( P = .03) while fellow eyes remained unchanged. Similarly, before cataract surgery, bilateral cases (n = 35) showed similar CCT between the right and left eyes. After cataract surgery, mean CCT increase was 27.4 ± 39.4 μm for first operated eyes of bilateral cases (n = 17, P = .01). Group 2 comprised 50 aphakic/pseudophakic children lacking pre-cataract-removal CCT. CCT was higher in eyes with glaucoma vs those without, at both first and last measurements (ΔCCT 58.9 ± 27.0 μm at first examination, P = .034, and 56.4 ± 27.1 μm at last examination, P = .043, respectively). There was no statistically significant CCT change over the study interval (median 28 months) for either Group 2 eyes with or those without glaucoma.
Conclusions
CCT in children with cataracts increases after cataract surgery while the fellow eye remains stable. This increase seems to occur early after surgery, likely remaining stable thereafter, though glaucoma can accentuate the increase.
The effects of central corneal thickness (CCT) on applanation intraocular pressure (IOP) measurement are well documented. Although the relationship between CCT and measured IOP is not linear, IOP tends to be overestimated in eyes with thick corneas and underestimated in those with thin corneas. In the Ocular Hypertension Treatment Study, CCT was found to be an important predictive factor for development of primary open-angle glaucoma. In addition, the Early Manifest Glaucoma Trial found that lower CCT was a significant risk factor for glaucoma progression in patients with a higher baseline IOP. Hence, CCT is now routinely measured in adults with suspected or known glaucoma.
Despite increasing information in the adult literature about CCT and glaucoma risk, less is known about CCT in the pediatric population and how it should be used clinically to assess children at risk for or with established glaucoma. In normal children, mean CCT correlates closely with that in adults, with values of between 549 ± 46 μm and 555 ± 37 μm reported in healthy children. As in adults, mean CCT has been demonstrated to be slightly lower in normal eyes of black vs white children. CCT abnormalities have been reported in pediatric patients with congenital glaucoma, Down syndrome, Marfan syndrome, aniridia, and osteogenesis imperfecta. In addition, CCT has been reported to be higher in aphakic and pseudophakic eyes of children, compared with normal eyes ; this higher CCT was more pronounced in those eyes with glaucoma. The origin and evolution of higher CCT in eyes of children after cataract removal, and especially those with glaucoma, remain speculative. Previous studies have suggested that higher CCT in aphakic pediatric eyes is an acquired phenomenon, but longitudinal studies are lacking. Children who have undergone cataract surgery are at high risk of developing secondary glaucoma, and the study of CCT changes in this particular group may assist in our understanding and management of this unique group of patients.
The primary purpose of our study was to evaluate changes in CCT in a group of children with congenital/developmental cataracts who were followed after cataract removal. Secondary objectives were to correlate CCT with horizontal corneal diameters before cataract surgery in the same group, and to study CCT changes over time in a separate group of children who were already aphakic or pseudophakic at time of entry into the study.
Methods
THIS IS AN ONGOING, LONGITUDINAL STUDY.
Subjects
Children seeking treatment at the Pediatric Ophthalmology Service of Duke Eye Center from February 1, 2004 through March 31, 2010 were recruited to participate in the study. Group 1 included those subjects with unilateral and bilateral congenital or developmental cataracts entering the study prior to cataract surgery; Group 2 included those with aphakia or pseudophakia who entered the study after cataract surgery. Excluded were children diagnosed with conditions known to have abnormalities of CCT (eg, Down syndrome, Marfan syndrome, aniridia), as well as those with corneal scarring or opacity. Informed consent was obtained in all cases.
Data Collection
Data collected included age, gender, race, ocular diagnosis, IOP, and length of follow-up in all subjects. Goldmann applanation tonometry was always preferred; Tono-pen applanation (Tono-Pen XL; Medtronic Ophthalmics, Jacksonville, Florida, USA) was used when it was not possible to obtain IOP with the former method.
Standard measurements of CCT were performed in all eyes using a DGH ultrasound pachymeter (the Pachette or the Pachmate; DGH Technology Inc, Exton, Pennsylvania, USA) as described in a previously reported study. Briefly, after topical proparacaine was instilled for corneal anesthesia, the tip of the probe was touched to the center of the cornea perpendicularly. In the former case, 5 sequential readings were taken and averaged; in the latter case, the Pachmate automatically averaged 25 separate measurements. CCT measurements were taken before and after cataract surgery in Group 1 and serially (from the first to last visit) in Group 2. Normal fellow eyes of children with unilateral cataracts and unilateral aphakia or pseudophakia served as controls.
For Group 1 subjects, pre-cataract-removal assessments performed under anesthesia included clinical description of cataract morphology in affected eyes of unilateral cases and both eyes of bilateral cases and horizontal corneal diameter (HCD) measurement using calipers for all eyes. Eyes with a horizontal corneal diameter of ≤10.0 mm were considered to have microcornea. CCT and HCD measurements were taken by a single surgeon (S.F.F.) except some CCT measurements, which were taken by the fellow (Z.L.) postoperatively.
For Group 2 subjects (without pre-cataract-removal CCT), we further subdivided the subjects into those with glaucoma and those without. Glaucoma was defined as cup-to-disc ratio >0.4 or asymmetry >0.2 with clinical suspicion of glaucoma (including elevated IOP). We did not include visual field loss as a requirement for diagnosis of glaucoma since most of our subjects were too young for reliable visual field testing. The number of topical glaucoma medications used at the time of each visit was recorded for eyes with glaucoma.
For both groups, the number of surgeries performed from time of first to final CCT measurement was recorded. Strabismus surgeries did not contribute toward the number of surgeries. All cataract surgeries were performed by a single surgeon (S.F.F.).
Statistical Methods
The fellow eyes of children with unilateral cataracts served as controls. Where analyzing subjects with bilateral cataracts, right eyes were used for data collection and analysis. CCT values (in μm) were reported as mean ± standard deviation, unless otherwise stated. Group means were compared using an unpaired t test, while a paired t test was applied to compare 2 eyes of a single subject or when comparing preoperative vs postoperative changes in the same eye of a patient; P values < .05 (2-tailed) were considered significant. Linear regression was used to analyze the relationship of CCT values between affected and fellow eyes of children with unilateral cataracts and right and left eyes of those with bilateral cataracts or aphakia/pseudophakia. SPSS Statistics version 18 (SPSS Inc, Chicago, Illinois, USA) was used to analyze data.
Results
Group 1: Unilateral and Bilateral Congenital or Developmental Cataracts (With Preoperative and Postoperative Central Corneal Thickness Data)
Demographics
There were 66 subjects with pre-cataract-surgery data. Mean age was 39.5 months (range 0.3–133). The gender ratio was 37 male to 29 female. Study subjects included 41 white subjects, 20 black, and 5 children with mixed or unreported race. Thirty-one subjects had unilateral cataracts, while 35 had bilateral cataracts. Mean age at cataract removal was not statistically different between cases with unilateral vs bilateral cataracts (32.5 ± 39.2 months vs 45.7 ± 46.3 months, respectively, P = .21). Thirty-seven subjects had post-cataract-surgery CCT data. The mean age of children whose eye(s) were left aphakic (n = 20) was much younger than that of children whose eye(s) had primary intraocular lens implantation (n = 17): 2.6 ± 2.7 months vs 55.4 ± 41.3 months respectively, P = .0001.
The mean baseline IOP (before cataract removal) was 15.1 ± 4.2 mm Hg. In 65 subjects, data on cataract morphology were available and recorded for the affected eye of unilateral cataract cases and the right eye of bilateral cases. Twenty-eight percent (18/65) were dense cataracts, 26% (17/65) were posterior subcapsular/posterior lenticonus, and 17% (11/65) were lamellar cataracts. Of note, persistent fetal vasculature comprised 14% (9/65) of all cases. Nuclear and cortical cataracts contributed 4 cases each (6%) and anterior polar contributed 2 (3%).
In children with unilateral cataracts, the mean HCD of the affected eyes (recorded preoperatively in 28 cases) was significantly smaller than that of the corresponding fellow eyes (mean difference 0.3 mm, P = .003, Table 1 ). Persistent fetal vasculature comprised 23.3% (7/30, data unavailable for 1 case) of the unilateral cases. Among the 15 subjects younger than 1 year of age at cataract removal, the mean HCD of the affected eye was similarly significantly smaller than that of the fellow eyes (10.5 ± 0.7 mm vs 11.0 ± 0.7 mm respectively, P = .001).
| Mean HCD ± SD (mm) | Mean Δ ± SD (mm) | P Value | |
|---|---|---|---|
| Unilateral AFFECTED eye (n = 28) | 11.1 ± 1.0 | 0.30 ± 0.4 | .003 |
| Unilateral FELLOW eye (n = 28) | 11.4 ± 0.9 | ||
| Bilateral RIGHT eye (n = 33) | 10.7 ± 1.4 | 0.04 ± 0.2 | .39 |
| Bilateral LEFT eye (n = 33) | 10.7 ± 1.3 |
In children with bilateral cataracts, the mean HCD of the right and left eyes were similar ( Table 1 ). When comparing the affected eye of unilateral cases and the right eye of bilateral cases, the smaller corneal diameter of the bilateral vs unilateral eyes with cataracts was not statistically significant (10.7 ± 1.4 mm vs 11.1 ± 1.0 mm, P = .16).
Considering all eyes with cataracts (n = 66 eyes of 66 children), those 17 eyes with microcornea (HCD ≤10.0 mm) had a higher mean CCT than the 49 eyes with HCD >10 mm (585.4 ± 54.5 μm vs 559.1 ± 40.3 μm, respectively; mean difference 26.3 ± 11.4 μm, P = .025). The racial and age composition of those eyes with microcornea vs those with larger corneas were similar (data not shown).
Central Corneal Thickness Measurements Before and After Cataract Removal
In children with unilateral cataracts (n = 31), CCT of affected vs fellow eyes was similar before cataract removal, (mean CCT 552.0 ± 32.9 μm vs 550.9 ± 40.4 μm, respectively, P = .78), with strong association between the CCT of the affected and fellow eyes using linear regression ( Figure 1 ). In children with bilateral cataracts (n = 35), the mean CCT of right eyes vs left eyes was similar (578.2 ± 45.6 μm vs 580.2 ± 47.4 μm, respectively, P = .56), again with a strong association between right and left eyes ( Figure 2 ).
Comparing mean CCT in bilateral cases (n = 35 for all right eyes) vs mean CCT in affected eyes of unilateral cataracts (n = 31) before cataract removal, mean CCT was higher in the bilateral than in the unilateral cases (578.2 ± 45.6 μm vs 552.0 ± 32.9 μm, respectively, P = .01). The racial distribution in the unilateral group (white 19/31 [61%], black 9/31 [29%], other 3/31 [10%]) was similar to that in the bilateral group (white 22/35 [63%], black 12/35 [34%], other 2/35 [3%]).
Central corneal thickness increased after cataract surgery, compared to preoperative values, in both unilateral (mean CCT increase 29.7 ± 43.1 μm, P = .03, Figure 3 ) as well as in bilateral cataract cases (mean CCT increase 27.4 ± 39.4 μm for first eyes, P = .01, Table 2 ). By contrast, unaffected fellow eyes of unilateral cataract cases did not show an increase in CCT over the same relatively short time interval (median 6.5 months after cataract removal, Figure 3 ). For this analysis, we excluded eyes that developed glaucoma during the interval between pre- and post-cataract CCT measurements. Not all subjects with pre-cataract-surgery CCT had post-cataract-removal CCT information available. Hence, 16 of the 31 cases with unilateral cataracts had post-cataract-removal CCT data; 3 eyes were excluded because of development of glaucoma, leaving 13 eyes for analysis. Similarly, 21 subjects with bilateral cataracts (30 eyes, as data were not always available for both eyes) had post-cataract-removal CCT data; 5 eyes were excluded because of development of glaucoma, leaving 25 eyes for analysis.
| Mean CCT ± SD (μm) | Δ CCT (postop − preop) (μm) | P Value | Median Follow-up (Months) | |
|---|---|---|---|---|
| Preoperative 1st eye (n = 17) | 572.8 ± 42.6 | 27.4 ± 39.4 | .011 | 5.4 |
| Postoperative 1st eye (n = 17) | 600.2 ± 55.1 | |||
| Preoperative 2nd eye (n = 8) | 585.5 ± 45.5 | 16.0 ± 18.6 | .046 | 9.0 |
| Postoperative 2nd eye (n = 8) | 601.5 ± 36.0 |
a Ten of the 17 “first eyes” had more than 3 months of follow-up (range 0.5 to 26.8); 5 of the 8 “second eyes” had more than 3 months of follow-up (range 0.9 to 60.5).
Although numbers were small, separate analysis considered CCT change after cataract surgery in children with unilateral cataract, dividing eyes left aphakic (n = 9) vs those that received primary intraocular lens implantation after surgery (n = 4), exclusive of the eyes that developed glaucoma. Mean CCT increase following cataract removal was 39.5 μm in eyes left aphakic vs 7.5 μm in eyes that became primarily pseudophakic ( P = .23). Fellow eyes of each group remained stable over the same time interval (mean CCT change +0.75 μm vs −4.1 μm for fellow eyes of aphakic vs pseudophakic eyes, respectively, P = .72).
Glaucoma developed in 8 eyes (3 of 16 unilateral affected eyes, 5 of 30 bilateral eyes) of 7 children in Group 1, with onset after cataract removal but before the final CCT measurement. Six cases were left aphakic, with the remaining 2 pseudophakic. The median age at surgery was 1.3 months (range 0.3–8.6 months). Mean horizontal corneal diameter in these eyes was 9.8 mm. Pre-cataract-removal CCT for these 8 eyes was 575.3 ± 32.4 μm and final CCT was 653.2 ± 90.1 μm (mean increase 78.0 ± 88.2 μm, P = .041), with median follow-up of 7.2 months (mean 13.6 months). These eyes were on mean 1.5 glaucoma medications and had an average of 1 intraocular surgery. Although the absolute increase in CCT for these 8 eyes was larger than that recorded in the 30 total eyes without glaucoma (both unilateral and bilateral cataract cases, 1 eye from each child), this difference in CCT increase was not statistically significant ( P = .2).
Group 2: Aphakic and Pseudophakic Children (With Post-Cataract-Removal Central Corneal Thickness Data Only)
Demographics
There were 50 subjects with a mean age of 84.6 months (range 3.5-178); 27 were male. Study subjects included 35 white subjects, 11 black, and 4 children with mixed or unreported race. Of the 50 included eyes, 38 were aphakic, while 12 were pseudophakic. The majority (39/50, 78%) had glaucoma. Mean age of those with and without glaucoma was similar (87.4 vs 74.7 months, respectively, P = .4). Mean IOP at first CCT measurement was higher in the eyes with glaucoma than in those without glaucoma (23.9 ± 6.0 mm Hg vs 17.5 ± 2.6 mm Hg, respectively, P = .001). The median follow-up time from first to most recently measured CCT was 28.4 months (range 0.7–89.9).
In the Group 2 cases with glaucoma (n = 39 eyes of 39 children), the average number of glaucoma medications used per visit was 2.1 (range 1–4). Twenty-three eyes (59%) did not have intraocular surgery between the first and last CCT measurements, while 13 (33%) underwent 1 surgery (9 eyes underwent glaucoma-related surgery, and the remaining 4 had non-glaucoma-related intraocular surgery). The remaining 3 eyes (8%) each required 2, 3, and 4 surgeries, respectively.
In the Group 2 cases without glaucoma (n = 11 eyes of 11 children), 8 eyes (73%) did not undergo any subsequent surgeries, while 2 (18%) underwent 1 intraocular surgery, and the remaining 1 child (eye) required 2 intraocular surgeries.
Baseline and Change in Central Corneal Thickness Over Time in Group 2 Eyes
Comparing CCT between the Group 2 eyes with and without glaucoma, CCT was higher in eyes with glaucoma at both the first and last measurements (CCT difference 58.9 ± 27.0 μm at first examination, P = .034, and 56.4 ± 27.1 μm at last examination, P = .043, respectively) ( Figure 4 ). By contrast, there was not a statistically significant change in CCT between the initial and final measurements for either the eyes with glaucoma or those without glaucoma ( Figure 4 ).
