Article Text
PDF
Abstract
Aims To compare astigmatism with clear corneal incision versus scleral tunnel incision following paediatric cataract surgery with primary intraocular lens implantation.
Methods Retrospective, comparative case series of 218 eyes of 138 children <12 years of age undergoing cataract extraction with intraocular lens implantation. The study cohorts were grouped into two categories based on incision location: group 1 comprising 108 eyes from 65 children with scleral incision; group 2 comprising 110 eyes from 73 children with clear corneal incision. Cycloplegic refraction was performed at 1, 3 and 6 months postoperatively.
Results The mean age in group 1 was 61±39 months and in group 2, 51±41 months. The mean postoperative astigmatism in group 1 was 1.28±0.97 D, 1.42±1.00 D and 1.38±0.98 D at 1, 3 and 6 months respectively. The change in astigmatism between 1 and 6 months was non-significant (p=0.26). The mean astigmatism in group 2 was 1.34±1.20 D, 1.13±0.88 D and 1.03±0.89 D at 1, 3 and 6 months respectively. Astigmatism in group 2 decreased significantly with time (p<0.001). The amount of astigmatism was comparable between the two groups at 1 month postsurgery (p=0.90), while it was significantly lower in the corneal incision group at 3 (p=0.03) and 6 months (p=0.01).
Conclusions Postoperative astigmatism after paediatric cataract surgery by clear corneal incision was lower compared with scleral incision. However, the difference was small and clinically insignificant.
- Paediatric cataract surgery
- astigmatism
- Intra ocular lens
- clear corneal incision,scleral tunnel
- Lens and zonules
Statistics from Altmetric.com
- Paediatric cataract surgery
- astigmatism
- Intra ocular lens
- clear corneal incision,scleral tunnel
- Lens and zonules
Introduction
Cataract surgery is the most commonly performed paediatric intraocular surgery worldwide. With the advent of modern microsurgical instruments and high-molecular-weight viscoelastic agents, complications have been rapidly decreasing. The intraocular lens (IOL) implantation is gradually gaining wider acceptance, and there is a shift towards cataract surgery with minimal astigmatism.1 2
Magnitude of astigmatism is well documented after adult cataract surgery. Several factors influence the amount of astigmatism such as the site of incision, length of incision, tightness of suture, amount of cautery applied and use of postoperative steroids.3 4 Astigmatism has been seen to change slightly after adult cataract surgery.5
Postoperative astigmatism is important for children because it may affect the clarity of vision and subsequently may contribute to amblyopia.6 Recent reports suggest that the amount of astigmatism after cataract extraction in children undergoes a spontaneous decline.7–10 The literature comparing scleral and corneal incisions in paediatric cataract surgery is very sparse. Astigmatism outcome after scleral tunnel incision and clear corneal incision were found to be statistically comparable after 5 months of follow-up.11 Non removal of sutures may be associated with many complications like suture degradation, suture track vascularization, loose sutures and suture-related infections.11 Unattended sutures might have affected the final astigmatism. Removal of the sutures is an effective procedure for modulating the astigmatism as has been well documented in adults.12 13
The aim of the present study was to compare the amount of astigmatism with clear corneal incision and scleral incision with IOL implantation in children aged between 6 months and 12 years of age.
Methods
This was a retrospective study of 218 eyes of 138 children, between 6 months and 12 years of age, who had undergone cataract extraction with primary IOL implantation at our institute between January 2006 and December 2007 using a clear corneal or scleral tunnel incision. The study protocol was approved by the Ethics committee of L V Prasad Eye Institute.
The exclusion criteria were history of ocular trauma, evidence of any ocular or systemic abnormality and follow-up less than 6 months.
Intraocular lens power calculations
Keratometry was carried out preoperatively for all the children. In those who were uncooperative preoperatively, the keratometry was carried out by using a handheld autokeratometer (Nidek KM 500, Sight Reach Surgical, Kensington, USA), whereas for cooperative children, it was carried out using a manual keratometer (Bausch & Lomb Keratometer).
The biometer allowed step-by-step processing to collect and analyse 10 readings for axial-length measurements using the contact technique in A-Scan (Manual and Auto modes) (Alcon UltraScan, Alcon Laboratories, Forth Worth, Texas, USA). Based on the axial length, we used a standard recommended formula for IOL selection, that is, SRK II, SRK T. We implanted an IOL power according to an age-appropriate undercorrection.
All surgeries were performed by experienced paediatric ophthalmologists, and all children underwent lens aspiration with IOL implantation. The following steps were common to both the groups. Two paracentesis incisions were made at 10 and 2 o'clock. Anterior capsulorrhexis was started with a 26 G bent needle and completed with paediatric rhexis forceps after injecting high-molecular-weight viscoelastic (Healon GV OVD, Santa Ana-based AMO, Illinois, USA) into the anterior chamber. Lens matter was removed with automated bimanual irrigation and aspiration. Also, enhanced meticulous capsular bag cleaning was carried out. Primary posterior capsulotomy and anterior vitrectomy were carried out in children less than 7 years of age or according to the surgeon's discretion before or after the implantation of the IOL through the limbal approach.
Scleral tunnel group (group 1)
One hundred and eight eyes of 65 children were included in group 1. An appropriate-sized fornix-based conjunctival flap was reflected, and haemostasis was achieved by judiciously applying wet-field cautery. The scleral tunnel construction in all cases was superiorly located. A 3.2 mm partial thickness scleral groove was made 2.5 mm from the posterior limbal line using a surgical Bard parker blade no 15. A tunnel was constructed using a 2.2 mm, bevel-up crescent blade (Alcon blade). The tunnel dissection was carried out 1 mm into the clear cornea. Anterior chamber entry was carried out using a 3.2 mm bevel-up keratome (Alcon blade).
Clear corneal group (group 2)
One hundred and ten eyes of 73 children underwent clear corneal wound construction. The clear corneal partial thickness groove was made 1 mm inside the superior limbus. A tunnel was constructed using a 2.2 mm bevel-up crescent, and the anterior chamber entry was carried out using a 3.2 mm keratome.
All patients were implanted with single-piece, acrylic, foldable IOLs with an optic size of 6.0 mm and 13.0 mm overall diameter. The IOL was intended to be implanted in the capsular bag in all cases, but in a few cases it was implanted in the sulcus. All three incisions (paracentesis and main port) were sutured with a 10-0 monofilament nylon nonabsorbable suture (Aurolab, Madurai, India). A single radial suture was applied to all the ports.
Postoperatively, patients were prescribed topical ofloxacin 0.3% eye drops four times a day for a week, homatropine 2% eye-drops twice a day for 2 weeks and prednisolone acetate 1% eight times a day, gradually tapered over 6–8 weeks. Children who did not cooperate were seen on the first postoperative day with a torch-light examination, while a slit-lamp examination was carried out for all the cooperative children. Examination under anaesthesia was carried out at 1 month, 3 months and 6 months. In all patients, all sutures were removed at 1 month postoperatively.
Retinoscopy was carried out at each of the follow-up visits by an experienced optometrist. Glasses were prescribed at 4 weeks from the date of surgery. The surgical interval between the two eyes in cases of bilateral cataract was 1–4 weeks (1 week in the majority of the cases exception being medically unfit children for general anaesthesia). Amblyopia therapy was initiated in appropriate cases wherever necessary, immediately after the glasses prescription.
Statistical analysis
Linear mixed effect models were fitted to assess the effect of incision location on the astigmatism at 1, 3 and 6 months postsurgery. Separate models were also fitted to assess the effects of other predictor variables, namely age, gender, axial length, IOL power, IOL position (bag or sulcus) and primary posterior capsulotomy on the postoperative astigmatism. A linear mixed-effect model is a linear model which quantifies the relationship between a continuous dependent variable and one or more predictor variables, specifically used with clustered, longitudinal or repeated measures data.14 It can include fixed- and random-effect parameters, accounting for the correlation among random-effect parameters. While the fixed-effect parameters describe the relationship between the predictors and the dependent variable for the entire population, random-effect parameters describe the relationship specifically for the clusters within the population. All the predictor variables mentioned above were treated as fixed-effect parameters, and the child was treated as a random-effect parameter in the mixed models. Statistical analyses were performed using commercial software (Stata ver. 10.0). A p value of <0.05 was considered statistically significant.
Results
Group 1 included 108 eyes of 65 children, and group 2 included 110 eyes of 73 children. The mean age of children in group 1 (61±39 months) was comparable with that in group 2 (51±41 months, table 1). Other baseline variables such as sex, axial length, IOL power and IOL position (bag/sulcus) were also comparable between the two groups (table 1).
Demographic and characteristic features of children in sclera and corneal incision groups.
Table 2 shows the astigmatism in groups 1 and 2 at 1, 3 and 6 months postsurgery. Although there was a slight increase in the amount of astigmatism in group 1 with time (figure 1), it was not statistically significant (p=0.26). In group 2, the amount of astigmatism decreased significantly with time (p<0.001, figure 1). Table 2 also shows that the difference in astigmatism between group 1 and group 2 was comparable at 1 month postsurgery (p=0.90), while it was significantly lower with clear corneal incision at 3 (p=0.03) and 6 months (p=0.01).
Amount of astigmatism (in dioptres) in the two groups at 1, 3 and 6 months postsurgery
The change in the magnitude of astigmatism over 6 months between the two incision groups.
Table 3 shows the effect of other predictor variables on the magnitude of astigmatism at 6 months postsurgery. Except for the site of incision (p=0.009), none of the other factors had a significant influence on the postoperative astigmatism at 6 months.
Linear mixed model evaluating the factors associated with increase in astigmatism 6 months postcongenital cataract surgery
With-the-rule astigmatism was the most common form of astigmatism in both groups (58 and 56 eyes in group 1 and 2 respectively). Oblique and against-the-rule astigmatism was noted in 20 eyes each in group 1, and noted in 16 and 15 eyes respectively in group 2. There were no cases of any suture-related complications in our study group.
Discussion
The size, architecture and location of the incision together influence surgically induced astigmatism. The incision is more than a port of access to the anterior chamber; it represents an important step of the operation, affecting ocular integrity and corneal stability.15 The rationale behind the present study was the lack of sufficient information for the amount of astigmatism after cataract surgery in children with different types of incisions. Postoperative astigmatism is of special significance in children, as it affects the visual clarity and subsequent effect on amblyopia.5 Previous reports document regression in the amount of astigmatism after cataract surgery in children. Brown et al reported regression of mean cylindrical correction. The first retinoscopy performed 1 to 15 days after surgery was 6.71±1.63 D reduced to 1.93±1.48 D after 31–45 days postoperatively. The study was conducted in 10 eyes of nine children. They implanted the IOL through 6.25 mm scleral incision.7 Spierer et al performed cataract surgery with IOL implantation through 3.2 mm scleral incision in 11 eyes in children aged between 2 months and 12 years. They observed regression of astigmatism from 5.8±3.6 D (range 3.0–14.0 D) at 1 week to reach a mean value of 2.1±1.3 D (range 1–4.0 D) 5 months after surgery. The change in the difference between the mean values at 1 week and at 5 months was statistically significant (p<0.005).9
There have been reports of regression with the use of clear corneal incision as well. Lam et al studied 31 eyes of 22 children who underwent cataract extraction with IOL implantation through 3.2 mm clear corneal incision. They reported mean postoperative refractive astigmatism the first day after surgery 2.35±1.37 D, which decreased to 1.48±0.98 D by postoperative months 2–4.10 Spierer et al also noticed a statistically significant decline in the magnitude of astigmatism between 1 week and the third postoperative month.16
However, Bradfield et al reported minimal postoperative astigmatism after cataract surgery in children, which remained stable after surgery with 3.0 mm clear corneal incision.17
There has been only a single report by Spierer et al comparing the magnitude of astigmatism between scleral incision and clear corneal incision. They retrospectively compared the amount of astigmatism with the two incision types and reported spontaneous regression of astigmatism with both incision types up to 5 months of follow-up.11
In our study, we compared 108 eyes undergoing scleral incision with 110 eyes with clear corneal incision. Ours is the largest study group comparing astigmatism in paediatric cataract surgery. Previous studies reported that the sutures were not removed in any of the patients.7–11 16 18 We removed sutures for all the children at 1 month to prevent the suture-related complications if the sutures are allowed to remain in place.9–11 17
We noticed a statistically significant decrease in the magnitude of astigmatism with clear corneal incision from 1.31±1.23 D at 1 month to 1.03±0.89 D at 6 months of follow-up. This finding was consistent with the previous reports of regression during the postoperative follow-up period. However, we observed an increase in the magnitude of astigmatism with scleral incision during the follow-up period. However, the amount of astigmatic change was clinically insignificant, and the observed difference decreased within the interobserver variation.
Possible explanations for the regression for the magnitude of astigmatism were provided by Spierer et al11:
The ocular tissues in children exhibit a high degree of elasticity. In adults, wound compression caused by the sutures does not change over time, whereas in children, because of the elasticity of the cornea and sclera, the tissue tension may spread evenly to neighbouring areas, reducing the amount of astigmatism.
Growth of the globe continues in children under constant centrifugal intraocular pressure and results in a more spherical growth of the eye, thereby diminishing the amount of astigmatism.
Although there was a difference in the amount of astigmatism with the two incisions with clear corneal incision appearing superior to scleral tunnel incision, this variation in the magnitude of astigmatism is well within the interobserver variability of the estimate of the astigmatic error of 0.25–0.50 D.19 20
The most common form of astigmatism noted in our series was with-the-rule astigmatism as observed by Spierer et al.9 Bradfield et al in their study reported that children aged <36 months have less astigmatism than older children.17 Bar-Sela et al observed younger patients to have a higher postoperative astigmatism.18 There was no consensus in the previous series regarding the age association with the magnitude of astigmatism.
In our series, we noticed that the magnitude of astigmatism does not vary with age. We also studied the effect of many other parameters such as sex, IOL position, axial length, etc, so as to be sure that there were no other confounding factors in the results. The site of incision was the only factor that was statistically significant.
Since this was a retrospective study, there are several limitations. Preoperative refractive astigmatism could not be measured in all patients owing to the density of the cataracts. As we performed retinoscopy on these children to look for the magnitude of the astigmatism, which includes both cornea and lenticular components, postoperative keratometry would have been a useful method to compare postoperative values to preoperative values to gain an insight into the surgical induced astigmatism. However, this was not done in our study. Also, multiple surgeons operated on these cases, so a surgeon-dependent variable is another factor to be taken into account. However, all surgeons were experienced paediatric ophthalmologists. Retinoscopy performed by multiple optometrists was another significant limiting factor.
In conclusion, clear corneal incision seems to be comparable with the scleral tunnel approach. Because the amount of astigmatism may be higher in the early postoperative period, it requires a close follow-up after surgery. Regular refractions are needed in children expecting a frequent change in the magnitude of astigmatism. A further prospective study enrolling children operated on by a single surgeon is warranted.
References
Footnotes
Funding This study was funded by the Hyderabad Eye Research Foundation, India.
Competing interests None.
Patient consent Obtained.
Ethics approval Ethics approval was provided by the Ethics Committee of L V Prasad Eye Institute.
Provenance and peer review Not commissioned; externally peer reviewed.