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  • Clinical Evaluation of Pediatric Glaucoma Patients

    Glaucoma
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    A thorough, accurate clinical evaluation is essential for diagnosis, classification and treatment of pediatric glaucoma, which may be primary or secondary. Primary congenital glaucoma (PCG) occurs in about 1 in 10,000 births, representing 50 to 70 percent of congenital glaucoma cases and 22 percent of all pediatric glaucomas. Examination of a pediatric patient can be challenging, especially for certain glaucoma-specific exam elements or when the patient is uncooperative or unwilling. This article discusses the most important exam elements for glaucoma diagnosis and management.

    Tonometry: Intraocular Pressure 

    Intraocular pressure (IOP) is the key exam element in the diagnosis, classification and treatment of pediatric glaucoma. Optimal IOP measurements are obtained in the office because IOP is usually lowered by most anesthetic agents and sedatives.1,2 Normal IOP in infants ranges from 10 to 15 mmHg under anesthesia.2 If an exam under anesthesia (EUA) is needed, IOP should be measured as soon as possible after anesthesia is induced.2 In contrast, other medications, such as ketamine and succinylcholine, may raise IOP.1,2 Since crying and screaming also elevate IOP, measurements should ideally be taken in the office when the baby is not crying or is distracted. Although chloral hydrate does not appear to affect IOP in either normal or glaucomatous eyes,1,3 this is not a convenient method for repeat office exams.

    A variety of methods can be used for office IOP measurement. Parents can be told not to feed the baby for two hours prior to the appointment, at which time the patient is fed. While the baby is drinking from a bottle, IOP can often easily be measured. In children who are older but still under four to five years of age, the portable Perkins applanation tonometer (Haag-Streit USA, Inc.) is a dynamic method that allows the examiner to know the child's IOP between cries or when not squeezing. A lid speculum is not recommended because it often upsets both parents and patients. Plus, by manually holding the eyelids open, the examiner can assess when the patient is not squeezing and when IOP measurement is most accurate. Slit-lamp Goldmann applanation tonometry is still the gold standard; so when the patient is a few years old and certainly by age four or five, attempts should be made to check the IOP at the slit lamp. Other authors have also used the Tono-Pen XL (Medtronic Solan) for infants and young children.1,4,5

    Central Corneal Thickness

    Since the importance of central corneal thickness (CCT) measurement was emphasized by the Ocular Hypertension Treatment Study (OHTS) in 2001, CCT measurement has become an integral part of the glaucoma exam.6 Thicker central corneas are associated with artifactually higher IOP readings. CCT measurements can be obtained with a portable device, such as the Pachmate DGH55 (DGH Technology, Inc.).

    In adults, mean normal CCT has been reported as 537 μm (with a range from 427 to 620 μm).7 In normal children, CCT does not vary significantly with age (Table 1). Although CCT appears to be similar in normal children and those with PCG, thicker CCT has been noted in various disease states, such as aphakic glaucoma, Sturge-Weber syndrome, aniridia and microcornea (Table 2).

    Information extracted from Hussein MA, Paysse EA, Bell NP, et al. Corneal thickness in children. Am J Ophthalmol. 2004;138(5):744-748.

    Table 1. Normal central corneal thickness (CCT) values by age.

     

    Information was extracted from Lopes JE, Wilson RR, Alvim HS, et al. Central corneal thickness in pediatric glaucoma. J Pediatr Ophthalmol Strabismus. 2007;44(2):112-117.

    Table 2. Central corneal thickness (CCT) values in eyes with pediatric glaucoma or related conditions.

    Corneal Exam

    Normal horizontal corneal diameter is 9.5 to 10.5 mm in full-term newborns and smaller in premature newborns.1 A buphthalmic eye with corneal diameter larger than 12 mm in the first year of life may be an indication of elevated IOP.1,2 High IOP may also be associated with corneal edema and tears in Descemet's membrane (Haab's striae).1,2 Both of these corneal changes can be detected using a slit lamp and often account for symptoms of epiphora, photophobia and blepharospasm.

    Gonioscopy

    Gonioscopy findings are a critical component in pediatric glaucoma diagnosis, treatment decisions and prognostic determinations. During an EUA, one can use a Koeppe lens with either a portable slit lamp or a hand-held binocular microscope and Barkan illuminator. Other options include using the operating microscope with either a Goldmann lens or operating direct gonioscopy lens.

    Angle evidence of PCG may be difficult to discern since normal angle findings in infants are different from adults.8 Nevertheless, significant angle findings in PCG include an open angle, a high flat iris insertion, absent angle recess, peripheral iris hypoplasia, peripheral iris pigment epithelium tenting, thickened uveal trabecular meshwork, scalloped iris root and prominent major arterial circle vascular loops.1,2

    Ophthalmoscopy: Optic Nerve Head Evaluation

    Aside from office evaluation, an EUA affords the best evaluation of the optic nerve head (ONH). In a preoperative EUA in which the pupil is ideally not dilated prior to angle surgery, direct ophthalmoscopy of the ONH can be performed through a Koeppe lens. If the pupil can be dilated, photographic documentation of the ONH can be made with a portable fundus camera, such as Nidek's NM-200D hand-held nonmydriatic fundus camera or Clarity Medical Systems' RetCam 3.

    Glaucomatous cupping in childhood is characterized by preferential loss of neuroretinal rim tissue in both the superior and inferior poles and enlargement of the scleral canal.1,2 Scleral canal enlargement is unique to pediatric glaucoma and may cause cupping without significant neural tissue loss.1,2 These changes also explain the apparent reversal of cupping that can occurs when IOP decreases.

    Indirect Indicators of Uncontrolled IOP: Increasing Axial Length and Myopia                                   

    Uncontrolled elevated IOP may result in buphthalmos, which can be reflected by increasing myopia and axial length greater than expected for normal eye growth. Thus refraction and ultrasonography may provide indirect signs of high IOP.1,2

    Prevention of Amblyopia

    Amblyopia is the leading cause of visual acuity of worse than 20/40 in pediatric glaucoma patients.9 Refractive errors need to be treated as early as possible in order to prevent amblyopia from myopia (e.g., due to increasing axial length and buphthalmos) and astigmatism (e.g., due to Haab's striae).

    Conclusions

    In summary, IOP measurement, CCT evaluation, corneal examination, gonioscopy, ophthalmoscopy and refraction are essential for the accurate diagnosis and treatment of pediatric glaucoma. If an ophthalmologist is not comfortable with these exam elements, referral to a pediatric glaucoma specialist may be warranted.

    References

    1. Congenital glaucoma. In:Allingham RR, Damji KF, Freedman S, Moroi SE, Shafranov G, eds: Shields' Textbook of Glaucoma. Philadelphia, Pa: Lippincott Williams & Wilkins; 2005:235-251.
    2. Childhood Glaucoma. In: Cioffi GA, Durcan FJ, Girkin CA, et al, eds. Basic and Clinical Science Course Section 10 Glaucoma. San Francisco, Calif: American Academy of Ophthalmology; 2008:155-165.
    3. Jaafar MS, Kazi GA. Effect of oral chloral hydrate sedation on the intraocular pressure measurement. J Pediatr Ophthalmol Strabismus. 1993;30(6):372-376.
    4. Bordon AF, Katsumi O, Hirose T. Tonometry in pediatric patients: a comparative study among Tono-pen, Perkins, and Schiötz tonometers. J Pediatr Ophthalmol Strabismus. 1995;32(6):373-377.
    5. Lasseck J, Jehle T, Feltgen N, Lagrèze WA. Comparison of intraocular tonometry using three different non-invasive tonometers in children. Graefes Arch Clin Exp Ophthalmol. 2008;246(10):1463-1466.
    6. Brandt JD, Beiser JA, Kass MA, Gordon MO. Central corneal thickness in the Ocular Hypertension Treatment Study (OHTS). Ophthalmology. 2001;108(10):1779-1788.
    7. Wolfs RC, Klaver CC, Vingerling JR, Grobbee DE, Hofman A, de Jong PT. Distribution of central corneal thickness and its association with intraocular pressure: The Rotterdam Study. Am J Ophthalmol. 1997;123(6):767-772.
    8. Freedman SF, Walton DS. Approach to infants and children with glaucoma. In: Epstein DL, Allingham RR, Schuman JS, eds: Chandler and Grant's Glaucoma. Baltimore, Md.: Williams & Wilkins; 1997:586-597.
    9. Biglan AW. Glaucoma in children: are we making progress? J AAPOS. 2006;10(1):7-21.