Management of paediatric cataract

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Introduction-

Paediatric cataract can be congenital or acquired. Congenital cataract is one of the treatable causes of blindness in children[1]. Acquired cataract could be due to trauma, inflammation or other pediatric ocular diseases. Management of cataract in a child is different from adults because of the anatomically younger ocular tissues, continuous ocular growth and other associated structural anamolies. Management can be challenging for a surgeon intra-operatively as well as post-operatively because of potential immediate and long term complications and the necessary long term follow ups for adequate management of associated amblyopia.

Pre-operative workup-

Visual assessment-

Age appropriate visual acuity test to assess the visual function helps in knowing the effect of opacification on visual development and amblyopia.

• In preverbal children- assessment of ability to fixate and follow light or objects, response to OKN drum rotation, preferential looking test such as teller’s acuity card and patterned VEP, resistance to occlusion of either eye .

• In verbal children- using optotypes charts such as Allen pictures, LEA symbols

Evaluation of strabismus and nystagmus-

Strabismus is found as common association in congenital cataract with a wide range of 26% to 78.9% noted especially in bilateral congenital cataract[2]. Similarly, nystagmus is also commonly associated in nearly 24.2 % in congenital cataract[3]. Presence of either of them gives a clue about visual significance of cataract and warrants surgery, ideally prior to onset of nystagmus in bilateral cases .

Anterior and posterior segment examination-

A full exam must be done in detail before surgery for both congenital and acquired cataract.

• In case of infants, examination with hand held slit-lamp is useful

• Examination under general anesthesia (EUA) to do a detailed anterior segment examination.

• Measurement of corneal diameter

• Intraocular pressure

• Dilated fundus examination to look for persistant fetal vasculature ( PFV /PHPV) or any other posterior abnormality.

• Ultrasound with B-scan for posterior segment if fundus is not visible. US helps to rule out persistant fetal vasculature, retinal detachment, retinoblastoma or fundal coloboma[2].

• Measurement of axial length, ACD using A-scan and Keratometry (details as described below).

Biometry and IOL power calculation-

Due to the continuous growth of the eyes after surgery and the difficulty in obtaining parameters required for IOL calculation in younger children, IOL power calculations are a challenging task in paediatric age group. Accurate measurement of all the parameters for IOL calculation can often only be obtained when a child is sedated or anaesthesized with general anaesthesia. Full sedation during an EUA allows for a thorough exam, including gonioscopy, corneal diameter measurement, retinoscopy, etc.

Biometric parameters:

• Axial length(AL)- Axial length at birth is 17–17.5 mm approximately[4]. It increases rapidly in the first 6 months (0.46 mm/month), then has a relatively slower (infantile phase) growth (0.15 mm/month) till 18 months, followed by a slow (juvenile phase) growth (0.10 mm/month)[5]. It can be estimated with both immersion A‑scan and indentation A‑scan.

• Keratometry - Keratometry values are obtained using auto keratometer. Keratometry also steeply reduces in the first 6 months (−0.40 D/ month), −0.14 D/month in the next 6 months, and − 0.08 D/month in the second year, reaching the adult range at about 3 years of age[6].

Optical biometer- can be used to calculate AL and keratometry in older children.

• IOL power calculation- The IOL power depends on various factors which include the age of presentation, morphology of cataract, visual acuity at presentation, time of development of cataract (congenital/developmental), biometry at presentation, unilateral or bilateral cataract, and refractive status of the fellow eye. IOL can be implanted in eyes with AL >17 mm and corneal diameter >10 mm[7]. As the eyes grow, a myopic shift is expected. To compensate for this change, a goal for the immediate post operative period of moderate hyperopia is desired.

Methods commonly used to undercorrect the IOL power-

a. According to Dahan and Drusedau[8] undercorrection of 20% in children <2 years and 10% in children between 2 and 8 years

b. Prost[9] suggested 20% undercorrection between 1 and 2 years of age, 15% undercorrection between 2 and 4 years, and 10% between 4 and 8 years of age.

c. Enyedi[10] suggested postoperative target refraction to be used for IOL power calculation according to age (age + postoperative refraction = 7)


Intraoperative aphakic refraction or aberrometry can also be used to calculate the IOL power[11]. IOL calculating formulae – SRK/T and Holladay 2 have shown to have least predictive errors[12].


Laboratory investigation-

Apart from routine blood check up for anaesthetic and operative purpose other tests are specific and chosen according to history and morphology of cataract. A thorough history of prenatal period with history of fever, rashes in mother helps to get a clue about intrauterine infectious causes and advising adequate investigations accordingly. Other important history to elicit which will further help in diagnosis are consumption of any drugs or alcohol, history of trauma during delivery, preterm delivery (retinopathy of prematurity), failure to thrive, and vomiting (galactosemia). Various laboratory tests in bilateral cataract includes-

• CBC

• Blood sugars

• TORCH titers

• Venereal Disease Research Laboratory (VDRL) test

• BUN

• Red cell galactokinase

• Serum Calcium and phosphorus

• Urine analysis for reducing substances and amino acids

• Newer tests- Advances in DNA sequencing technologies, so-called Next Generation Sequencing (NGS) not done commonly but is seen as a future testing to improve the diagnosis of congenital cataract especially for genetically heterogeneous conditions[13].

A unilateral cataract doesn’t require extensive work up as most of them are isolated, non hereditary with no systemic and genetic abnormality.


General systemic evaluation-

This is done by a paediatrician to rule out any systemic associations of cataract which is not only important for bilateral but also unilateral cataract[14][15].


Treatment options-

Non surgical treatment-

Non- surgical treatment-

Indication- for visually insignificant cataract as follows-

• Cataract < 3mm

• Peripheral or paracentral cataract not obscuring the visual axis or vision

• Blue- dot cataract which is not afftecting the vision

• Presence of good red glow in distant direct ophthalmoscope

• Absence of strabismus or nystagmus

• Observation with careful regular monitoring to look for any change or progression in cataract and/ or development of amblyopia. In either of case, the treatment has to be converted into surgical.

• Dilating drops- can be used to increase the pupil size and making child use the part of clear zone. But strong cycloplegic drops should be avoided as they can cause loss of accommodation and can lead to amblyopia by themselves.

• Occlusion of other eye is useful in case of unilateral cataract, for few hours to prevent amblyopia until surgery is completed.


Surgical treatment-

Indication of surgery-

• Any cataract that is visually significant: >3mm central opacity, centrally obscuring posterior pole , with strabismus or nystagmus

Timing of surgery-

• Unilateral cataract should be operated as early as possible at 4- 6 weeks of age. Operating a child before 4 weeks increases the risk for complication of general anaesthesia and increase risk of aphakic glaucoma and if operated later after 6 weeks can lead to amblyopia.

• Bilateral cataract should be operated by 6-8 weeks of age- each eye one week apart. If the child is systemically a high risk case for general anaesthesia, both eyes can be simultaneously operated by an experienced surgeon with completely different set of instruments for other eye.

Anaesthesia-

The choice of anaesthesia depends upon age and systemic condition of patient. Risk and benefits of general anaeshthesia has to be considered. Infants less than 1 month have immature organ systems and thermoregulation system and are at greater risk for post-operative apnea[16]. For older children, of more than 10 years age, who can understand and cooperate for local anaesthesia, peribulbar block with or without sedation can be used.

Surgical steps and consideration-

The important difference between children and adults eye is that they have lower corneal and sclera rigidity, very elastic anterior capsule, soft lens, and well‑formed vitreous. These factors play a role intraoperatively and warrant slight modifications in various steps of cataract surgery as described below-

• Incision – superior incision is preferred as it is covered by lid and protected by Bell’s phenomenon in case of any trauma as children are more prone for trauma. Either scleral or corneal incision can be made, as the difference in post-operative astigmatism is insignificant[17]. A paracentesis should also be made to aid in cataract extraction and cortical removal. In case of infants less than 7 months who are left aphakic, lens aspiration can be done from paracenteses only.

• Anterior capsule management- A good and optimal anterior capsulotomy is important to determine further steps including IOL placement in bag. An ideal anterior capsulotomy should be a continuous curvilinear capsulorrhexis which is round, regular and is of adequate size of around 5.5-6mm. Capsule of paediatric age is very elastic and hence it is challenging to make a continuous curvilinear capsulorrhexis. Trypan blue(0.06%) is used to stain the anterior capsule for good visualization. Trypan also reduces the elasticity of capsule which aids in making a continuous capsulotomy[18]. Anterior capsulorhexis is completed with the help of a cystitome or bent needles, utratas, intravitreal 23G forceps or Intraocular capslorrhexis forceps. Other methods of performing anterior capsulotomy in paediatric population are vitrectorhexis with low aspiration and high cut rate in vitrectomy cutter, especially useful if IOL placement is not planned. The disadvantage of vitrectorhexis is that the irregular edges created by this method can lead to unanticipated tear of capsule. Radio-frequency diathermy and Fugo plasma blade have been also advocated for anterior capsulorhexis but have same disadvantages as vitrectorhexis. Femtosecond laser can be employed for both anterior and posterior capsulotomy with good precision and decreased corneal endothelial damage. However, its not cost-effective and may have micro- irregular edges. Studies[19] that analyzed pediatric anterior capsulotomy techniques in the porcine model and found that manual capsulorhexis produced the most extensible capsulotomy with the most regular and stable edge. Precision pulse capsulotomy has also been shown to create well-centered and strong capsulotomies in a pediatric age-group.

Rhexis with Utrata.jpeg
Image showing capsulorhexis made with intra-ocular forcep

• Hydrodissection – should be minimal, gentle and in all quadrants. Inadvertent excessive hydrodissection in patients with pre-existing PCR can lead to drop of lens matter in vitreous cavity

• Lens aspiration- the lens in paediatric cataract is generally not hard. After adequate hydrodissection, a gentle lens aspiration can be done using automated lensectomy technique or manually with a simcoe cannula or irrigation-aspiratopn cannula from limbal route. Some prefer pars plana route to perform the same especially when IOL implantation is not planned.

• Posterior capsulotomy- it is performed in children less than 6 years of age to prevent post op visual axis opacification(VAO)[20].It can also be also be performed in children older than 6 years (with mental retardation or with nystagmus) who may not cooperate for laser capsulotomy on a slit lamp later. Techniques to perform posterior capsulotomy are similar to anterior capsulotomy including capsulorhexis using forceps, vitrectorhexis, radio-frequency Endodiathermy and Femtosecond laser assisted capsulotomy . The size of posterior capsulotomy is made 1-2mm smaller than anterior capsulotomy.

• Anterior vitrectomy- It is done when there is break in anterior vitreous face due to posterior capsulotomy or to breaks the scaffold for proliferating LECs(lens epithelial cells) and metaplastic pigment cells, thus preventing VAO formation. Additionally, in younger children, post-operative inflammation causes a fibrous reactionary membrane over an intact anterior vitreous face, leading to VAO. A thorough anterior vitrectomy is often done in children of less than 6 years old following posterior capsulotomy. Vitrectomy can be performed through anterior route or pars plana route depending on surgeon’s preference.

• Lens implantation- IOL implanatation is the primary mode of visual rehabilitation in children more than 1 year of age[21]. In younger children, especially in infants it is almost impossible to predict the adequate IOL power because of their fast growing eyes and change in all parameters. In a multicenter, randomized clinical trial done by The Infant Aphakic Treatment study[22], it was found that compared to infants with no IOL after cataract removal, patients treated with primary IOL implantation prior to 7 months of age had more adverse events and required more additional intraocular surgeries over the first five years following surgery for unilateral congenital cataract, with most occurring during the first postoperative year. IOL placement in the bag is most preferred site, though IOL can be placed in ciliary sulcus when posterior capsular support is inadequate. Infants who are left aphakic are planned for secondary IOL later and till that time visually rehabilitated with glasses or contact lens.

• Preferred IOL material- Acrylic hydrophobic foldable IOLs have unique benefits in children due to increased biocompatibility[23]. There is less chance of postoperative inflammation and posterior capsular opacification in this kind of IOL[24]. Due to its foldable ability it can be used with small incisions. PMMA (polymethylmethacrylate) lens also have good biocompatibility but due to its rigid nature, it can’t be used with small incisions. In terms of safety profiles, studies[25] have shown that primary implantation of PMMA in paediatric cataract surgery is comparable to soft acrylic IOLs. Due to their low expense PMMA lenses are economical and are very useful in developing countries. PMMA lens are also useful for in-sulcus implantation or for optic capture[26] with haptic in sulcus when thin capsule rim cannot support the optic of lens.

• Closure of wound- After completion of surgery and thorough washing of viscoelastic from anterior chamber, the wounds are sutured using 10-0 nylon owing to the fragility of the eyes. Some people advocate usage of absorbabale 10-0 vicryl suture also as there won’t be need to take up the patient in sedation or anesthesia to remove the sutures



Complications-

Classified as early ana late as follows[22][27]

Early complications-

a. Wound leakage

b. Iris or vitreous incarceration in wound

c. lOL capture

d. Post-operative inflammation

e. Post operative raised IOP

f. Vitreous haemorrhage

g. Retinal haemorrage due to low IOP

h. Retinal detachment

i. Post operative endophthalmitis

Late complications-

a. Secondary glaucoma- due to postoperative inflammation or structural and anatomical destruction as a result of surgery. The incidence of secondary glaucoma is found to be higher in aphakic patients, history of surgery within the first month of life, children with family history of aphakic glaucoma, persistent fetal vasculature syndrome, and nuclear cataract. The risk of developing glaucoma is life-long, hence, regular monitoring of IOP should be done.

b. Visual axis opacification(VAO)- if not detected and managed can cause amblyopia. Apart from posterior capsulotomy and anterior vitrectomy, some surgeon prefers optic capture[28] in the posterior capsulotomy also known as posterior optic button hole to prevent LEC migration and VAO. In case of VAO has occurred, immediate treatment with Nd:YAG laser capsulotomy under general anesthesia or surgical membranectomy should be performed.

c. Retinal detachment- Its rare but there is life long risk of RD in these patients especially with PFV and hence should be followed regularly for complete dilated fundus examination.


Post operative treatment-

• Post operative inflammation is more in paediatric cataract surgery due to immature blood aqueous barrier. Hence Patients are prescribed topical steroids (prednisolone acetate 1% six times/day) and cycloplegics (preferably homatropine 2%) postoperatively along with antibiotics. The steroids are tapered over a period of 6-8 weeks. Patient is followed up frequently upto 1 month and every 3 monthly thereafter.

• Visual rehabilitation – in form of glasses, contact lenses to correct post operative refractive error should be started as early as possible. Treatment of amblyopia with occlusion therapy should also be implemented early.


Conclusion-

Paediatric cataract surgery is challenging but has evolved tremendously with various techniques. After thorough pre operative work- up, the standard treatment in paediatric cataract which require surgery is lens aspiration with anterior vitrectomy and primary or secondary IOL implantation. But the management doesn’t end with surgery and every child requires proper visual rehabilitation with correction of post operative refractive error, treatment of amblyopia with patching. And the follow ups are life-long, so as to monitor for any late complications and treating them adequately.

References –

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