In order to gain as much information as possible there is an efficient order in which parts of the EUA should be planned and carried out. Where possible, we recommend pharmacologic dilation of the pupil for the EUA after IOP is measured and the anterior segment is examined - in those cases where surgery is not contemplated. In cases where only one surgery is possible it is better to dilate the child in the office / outpatient department preoperatively so as to maintain a small pupil for possible surgery. It is helpful at each step to establish a routine in which the right eye is examined before the left eye and then the findings recorded in that order. This will help avoid confusion and error later when records are consulted. If the disease is unilateral, one should still examine in every case the normal, unaffected, eye as well for comparison. Also, remember that children who require ongoing EUAs, must also have periodic awake examinations to test vision, pupillary reactions (afferent pupillary defects), strabismus, and to monitor amblyopia treatment.
EUA and handheld slit lamp
Step 1: Cornea and Anterior Segment
An operating microscope or hand-held slit lamp are essential pieces of equipment to examine for:
Cornea edema that is noted to be slowly disappearing may suggest that the intraocular pressure (IOP) was elevated moments before, and anesthesia may be lowering it. There may be epithelial edema alone or there may be stromal edema as well. When the stroma is cloudy, the hazy media may not be corrected by removal of the epithelium.. There may also be localized and often linear edema, due to a new Haab’s striae. Also consider: glaucoma, Hurler syndrome, or CHED (congenital hereditary endothelial dystrophy). Other causes for corneal opacity are: keratitis (herpes, rubella), Peters’ anomaly, storage diseases, congenital corneal dystrophy, and forceps-related birth trauma.
|Horizontal diameter (white to white) may be increased when the onset of glaucoma is before 3 years of age. This measurement can be done with calipers or with a ruler held close to the eye.
Measuring horizontal diameter “white to white”
An enlarged cornea may be found in congenital megalocornea. This condition is always bilateral and present in boys (x-linked recessive). It is often associated with iris transillumination defects, pigment dispersion on the lens, angle structures, and cornea. The enlarged anterior segment in megalocornea is not associated with an enlarged antero-posterior globe length evident on ultrasound or refraction. The eye pressures are normal.
|Corneal & iris structure. These include breaks in Descemet’s membrane [Haab’s striae]. Other findings should be noted including: peripheral opacification and pannus in aniridia in older children, posterior embryotoxon in Axenfeld-Rieger, and Lisch nodules in neurofibromatosis (NF). (Note: Lisch nodules are very rare in infants with NF and very rare in eyes with glaucoma secondary to NF; look for them in the fellow eye). In neurofibromatosis, an ectropion uvea is frequently present as well as an hypoplastic iris. It is also an important sign of the iris ectropion syndrome, a condition frequently complicated by childhood glaucoma. Although the anterior chamber cells of uveitis are very hard to see without a standard awake slit lamp examination, keratitic precipitates (KP) can be seen on the corneal endothelium and synechiae may be seen also. If available, pachymetry will help to interpret the relative values of IOP. The iris is often thin and hypoplastic in Axenfeld-Rieger's abnormality and associated with irregular pupils but this may not appear until a number of months post-natally.
Step 2: Intraocular Pressure (IOP)
In order to minimize changes to the cornea from tonometer trauma IOP measurements are done carefully. In the case of scarring of the cornea, an attempt to determine the IOP is best done using the clearest and most normal appearing part of the cornea. Any tonometer (Schiotz or applanation) may be used by the same type should be used for every examination as slight variations may be introduced otherwise. If no tonometer is available, or the cornea is unsuitable for IOP measurement (from scarring, band keratopathy, etc.), use finger tension to estimate IOP. Some surgeons advocate early IOP determination before corneal examination so as to decrease the effect of anesthesia-induced reduction of the IOP.
Sources of artifact in determining IOP include:
Falsely low IOP: Halothane and related inhalation agents, corneal epithelial edema, if using Perkins – too much fluorescein on the eye surface causing large mires, hyperventilation with low end tidal CO2, poor systemic hydration, thin corneas.
Falsely high IOP: patient not fully asleep, pressure from mask, pressure from speculum, ketamine, intubation (up to 5 minutes after intubation), malfunctioning Tonopen (try replacing batteries), hypoventilation with high end tidal CO2, small thickened cornea
Step 3: Posterior Segment
Detailed examination and documentation of the optic nerve head (ONH) and surrounding retina should be made for purposes of diagnosis and for future comparison. Examination with a 20D lens and indirect ophthalmoscope may not give enough detail to draw an accurate depiction of the ONH. An exact image of the ONH can be obtained using a portable camera with good quality output. On the other hand, direct ophthalmoscopy will provide details of the neuroretinal rim width, size of optic nerve head, and blood vessel pattern which, when drawn accurately, are excellent for follow-up. The remainder of the retina is also examined for associated pathology – mainly tumors, abnormal tissue, or malformations.
Another useful technique is to apply a smooth-domed direct gonioscopy lens to the cornea in conjunction with a direct ophthalmoscope that is used to view the fundus through the goniolens and an undilated pupil. This magnifies the optic nerve head by about 10-15% and allows extended examination without drying the cornea.
Step 4: Gonioscopy
A direct (Koeppe-style) goniolens with a hand-held slit lamp or tilting operating microscope or an indirect gonioscope (Goldmann, Sussman, or Zeiss) with the operating microscope can all be used equally well. The newborn or infantile angle is immature and different from the adult angle. There is often a high insertion of the iris in newborns with glaucoma. Increased opacification of the angle tissues is characteristic of infantile primary congenital glaucomas. Signs of neovascularization from tumors or cicatricial ROP may be recognized. This is also an opportunity to assess the angle for future or previous angle surgery, or for trauma. In the case of a central corneal opacity, gonioscopy may be the only way in which the anterior segment can be seen.
Step 5: Supplemental Examination
An ultrasound examination determines the axial length and, where media opacities prevent a good view of the posterior or anterior segments provides some useful information. It is also beneficial for those children who have crowded orbits (mainly Asians) and are being considered for tube implant surgery. The implant plates can be difficult to insert in a crowded orbit so planning with ultrasound results may be helpful before performing this type of surgery. Similar to monitoring corneal diameter, monitoring the axial length of young children’s eyes provides examiners with an objective measure of IOP control over time. If one eye is noted to be increasing in axial length at a significantly greater rate compared to the other eye, or from established guidelines for normal growth; it can be assumed that the IOP of the elongating eye is too high. This can also be ascertained indirectly by refraction, as evidenced by increasing myopia or decreasing hyperopia.
If pachymetry is available it should be done as the last stage of the EUA to avoid corneal distortion.
Step 6: Diagnostic Paradigm
With information gained during the EUA, a great deal of information is available, but what “weight” should be given to each of the findings and to them as a whole in trying to arrive at a working diagnosis? What is most important for assessing the child’s condition and planning treatment? We know IOP is affected by many variables (see above). From this, we can assume that while IOP determination is important, it is not the best single criterion for diagnosing glaucoma without other more reliable parameters. Making a diagnosis of glaucoma is like fitting together the pieces of a puzzle. To do the job right, all of the parts must fit. For example, it is not uncommon for a newborn infant with glaucoma to have a low applanation IOP. The status of the cornea (size, edema, appearance of [new] Haab’s striae) and the ONH are more reliable for determining the initial diagnosis and the continuing status of the eye. Detailed drawings or pictures done at each EUA of the optic nerve and Haab’s striae, for example, are useful for assessing changes in the condition. Imitators of glaucoma must be ruled out. Remember congenital megalocornea (usually X-linked recessive with iris transillumination and no Descemet’s breaks); birth trauma from forceps (these may cause breaks in Descemet’s membrane that are vertical and straight unlike the scalloped multidirectional Haab’s striae), coloboma of the optic nerve, optic pits, and other conditions can be confusing when attempting to arrive at a final diagnosis of glaucoma.
In short, the emphasis should be on ONH and cornea findings as objective signs of disease or its progression. IOP is important but is not as objective. IOP is important if it is extremely high and no extraocular reason is found for it. It must be remembered that once surgery is done on a child the child is automatically labeled as “glaucoma”, thus the responsibility is on the first surgeon to properly assess and diagnose the disease, determine its etiology, and to document its initial findings.
Step 7: EUA Summary
At the end of the EUA, and using the paradigm described above, a diagnosis of glaucoma should be possible or at least suggested in appropriate cases and a baseline for treatment and future follow-up established. The criteria for diagnosis in primary infantile and other pediatric glaucomas may include typical changes in the cornea, gonioscopic abnormalities, and optic nerve head cupping along with elevation of the IOP. Other findings include increased axial length, increasing myopia, photophobia, and family history. The examiner’s experience and awareness of all of the possibilities will help with the assessment of these patients. In those cases where associated pathology is found, appropriate steps should be taken to deal with the primary problem, but the glaucoma may have to be treated even in the face of such disease. After these seven steps have been completed, one can then proceed with surgical intervention or with medical treatment.