Studies Of Central Corneal Thickness In Aphakic And Pseudophakic Patients Following Congenital Cataract Surgery

IntroductionGlaucoma continues to be one of the most common complications of successful congenital cataract surgery.The reported prevalence of postoperative glaucoma varies between 5%and 32%.¹²The overall incidence does not appear to decrease despite the development of microsurgical technologies,we can control well about the pars plana lensectomy,but the incidence of glaucoma did not decrease.The onset of glaucoma may be acute or insidious and notoriously refractory to treatment.Angle closure glaucoma may occur in the early postoperative period;but the most common type of glaucoma to develop after congenital cataract surgery is open angle glaucoma.Several risk factors have been identified and both chemical and mechanical theories have been proposed for its pathogenesis.Unlike children with congenital glaucoma,those with paediatric glaucoma following congenital cataract surgery are usually asymptomatic despite high intraocular pressure.They may require regular evaluation under anaesthesia,whenever there are any suspicious findings.Unlike congenital glaucoma, the first line of treatment for glaucoma in aphakia/pseudophakia may be medical. Because the difficulty to perform in chidren we need to study the pathophysiology and risk factors to effectively prevent the happening of the glaucoma and prevent its development.Transient or permanent intraocular pressure(IOP) elevation occurs in aphakic and pseudophakic eyes as a result of several mechanisms.Hence,the use of the term "aphakic glaucoma" is generally discouraged because it implies that the state of aphakia as such is the only cause of glaucoma.This group of glaucomas may be described as "glaucomas associated with aphakia and pseudophakia" or "the glaucomas in aphakia and pseudophakia," which conveys the notion that multiple mechanisms contribute to the development of elevated IOP after congenital cataract surgery. So,the diagnosis of glaucoma in aphakic children is a challenging problem because of difficulties in measuring intraocular pressure(IOP) and in conducting gonioscopy,fundus examination,and visual field tests³.As IOP is the key parameter for diagnosing glaucoma,any variable that can affect the measurement of IOP could lead to an incorrect diagnosis of glaucoma.Central corneal thickness(CCT) influences IOP masurements using Goldmann applanation tonometry.When the CCT is low,the true IOP may be underestimated,and the converse is true when the CCT is high⁴.Overestimation or underestimation of IOP in patients with glaucoma can have a significant impact on their treatment and overall prognosis.CCT has been studied extensively in patients with primary open angle glaucoma,ocular hypertension, normotensive glaucoma and congenital glaucoma^5-8.By contrast,there is little information on CCT in aphakic glaucoma following congenital cataract surgery.This study compared CCT measurements of aphakic and pseudophakic patients after such surgery with those of age matched normal subjects.MethodsThis study included 45 eyes of 45 aphakic and pseudophakic patients following congenital cataract surgery.46 healthy,age and sex matched volunteers were recruited for comparison with the patients.After a complete eye examination,corneal thickness and intraocular pressure were measured.ResultsIn the study group,35 eyes were aphakic,and the remaining 10 eyes were pseudophakic.The median CCT was 556.0μm(range 490-640μm) in the control group and 626μm(range 523-870μm) in the study group(p＜0.05).There was a significant difference in CCT between aphakic and pseudophakic eyes in which an intraocular lens (IOL) had been implanted at the time of congenital cataract surgery(p=0.011).The same difference was not observed between aphakic and pseudophakic eyes in which an IOL had been implanted secondarily(p=0.835).The median age of the patients at the time of lensectomy was 36 months(range 1 week to 120 months).There was a negative correlation between the age at lensectomy and CCT(r=-0.485,p=0.001).ConclusionAphakic and pseudophakic patients have significantly thicker corneas than age matched comrols.This difference can have an important effect on interpreting intraocular pressures in these patients.It is also important to assess the effects of early surgery for congenital cataracts,as well as those of primary and secondary IOL implantation,on CCT.