Corneal Diseases in Children: Imaging



Fig. 2.1
A 1-week-old boy presented with a cloudy left cornea (a), noted at birth. On exam, the left cornea was opacified, the intraocular pressure was 9 in the right eye and 10 in the left eye, and the vision was blink to light in both eyes. At age 10 months, an exam under anesthesia with ultrasound biomicrocopy was performed to determine the extent of the pathology. The ultrasound biomicroscopy showed a thickened cornea, extensive iridocorneal adhesions without any lenticular corneal adhesions and an atrophic ciliary body consistent with Peter’s anomaly (b). The decision was made not to proceed with corneal surgery



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Fig. 2.2
A 4-year-old boy presented with a diffuse dome shaped lesion, covering part of the left cornea (a). A UBM was performed, which revealed a diffuse dome-shaped elevation of the corneal/scleral interface measuring approximately 0.97 mm. There appeared to be a demarcation line identified but the lesion did appear to extend into the corneal interface (b). The lesion was removed and the pathology report came back as “conjunctiva lining dense connective tissue with hair follicles, adipose tissue, and nerves, consistent with a dermoid”


Options available: Slit lamp cameras can be used with cooperative children who are able to sit at the slit lamp and focus at a specific location. Children as young as 3 years of age, who are cooperative, can often position at the slit lamp, as long as the chair and headrest are adjusted properly.

A video capture technique, which will tolerate a degree of motion greater than is acceptable for standard flash-based slit lamp imaging systems, can be useful in children who are unable to maintain focus (Mireskandari et al. 2011). The video capture technique can also be used to image dynamic phenomenon such as Seidel tests, phacodonesis, and subtle eye movement anomalies.

Children who are photophobic and unable to tolerate the minimum light requirement associated with slit lamp photography can sometimes be imaged using simple digital single-lens reflex cameras with medium telephoto macro lenses with a ring flash setting to minimize shadows (Mireskandari et al. 2011).

An increasing number of adaptors are now available for various smartphones, most specifically the iPhone® and these can be used to obtain ophthalmic images. Some of these adapters are specifically designed for use in conjunction with the slit lamp, the indirect ophthalmoscope, or the direct ophthalmoscope, but others allow the smartphone itself to be used as the primary device, often with a relatively low level of light (Myung et al. 2014). These are especially useful in children since many children feel more comfortable with a smartphone than with traditional ophthalmic imaging systems.

When used to image the anterior segment, fundus cameras lead to images with peripheral distortion, so their usefulness is limited in this setting. However, in patients with posterior segment pathology, the convenience of imaging both the anterior segment and the posterior segment with a single device may be worth sacrificing some peripheral details.



Microscopy


When to use: Confocal and specular microscopy can be used both to establish an initial diagnosis and to monitor patients over time. This high-resolution imaging modality is indicated when there is need for detailed imaging of a specific cell type, most commonly the endothelial cells. Specular microscopy can be used to assess endothelial cell counts both pre- and postoperatively.

This is especially useful in cases of congenital hereditary endothelial dystrophy (CHED). Patients with CHED have traditionally been treated with penetrating keratoplasty (PKP) for replacement of damaged endothelium, a technique associated with multiple long-term complications, including need for suture removal (often under anesthesia in children), risk of neovascularization, rejection, and loss of structural integrity of the cornea. However, Descemet’s stripping endothelial keratoplasty (DSEK) is becoming an accepted treatment for CHED and may lead to lower complications, relative to PKP, in pediatric cases (Busin et al. 2011). As DSEK becomes more commonly performed in children, long term studies comparing the complication rates and endothelial cell loss between these two techniques will be critical to help determine the best surgical choice for these patients. Specular microscopy is critical to follow the endothelial cell count and morphology in these patients pre and post operatively.

Confocal microscopy provides extremely high-resolution imaging of specific regions of the cornea and is a useful tool in management of complex corneal infections, especially fungal and acanthamoeba infections. Though the gold standard for diagnosis of corneal ulcers, especially fungal and acanthamoeba, remains microbial culture, there is debate over the ideal culture medium for specific microorganisms (Boggild et al. 2009). Additionally, not all ophthalmic offices are equipped with onsite microbiology laboratories, so turn around time for these cultures can be significant. Therefore, in centers where confocal testing is available, it can provide a useful adjunct to microbial cultures. It can also be used to follow patients over time, and is especially useful when the infection is located in the deeper layers of the cornea (which often occurs with both fungal and acanthamoeba infections) (Oldenburg et al. 2011; Keay et al. 2011).

Confocal microscopy can also be used to assess morphological changes in the epithelium and stroma following corneal cross-linking in patients with keratoconus (Mazzotta et al. 2001). As corneal cross-linking becomes more widely performed, this will become increasingly relevant. Also, as this treatment modality is relatively new, data regarding the long term (greater than 10 years) effects on the morphology as well as the topography of the cornea will be critical to access the safety as well as the efficacy of the treatment.

Options available: Though only available in large, primarily academic centers, the confocal microscope allows the clinician to examine and image individual cells in all layers of the cornea. The specular microscope, is more readily available and allows for a similar level of high-resolution imaging, but is limited to the endothelium. Endothelial cell counts can be followed using specular microscopy in children who are able to maintain position in camera chinrest and who are able to focus. Though the confocal microscope is able to image a wider range of cell types and cell layers, it is much more challenging to use in children. The scan times are significantly longer for confocal microscopy versus specular microscopy and many models require the use of a coupling gel, which further limits tolerability in children.


Anterior Segment Optical Coherence Tomography (OCT) Ultrasound Biomicroscopy (UBM) and Posterior Segment Ultrasound


When to use: Both anterior segment OCT and UBM are useful for imaging the structures of the anterior segment, including all layers of the cornea, the iris, and the morphology of the angle. Therefore, they are useful in imaging patients with both congenital and acquired anomalies of the anterior segment, including tumors (Fig. 2.2b), Peter’s anomaly (Fig. 2.1b), ICE syndrome, congenital glaucoma, and following ocular trauma (Cauduro et al. 2012). Both anterior segment OCT and UBM can be useful in the pre and postoperative management of patients (Nesi et al. 2012). Vengayil et al. reported the use of OCT to enable visualization of a retained host Descemet membrane following PKP for CHED, before and after surgical removal (2008).

Though the structures imaged by the UBM and anterior segment OCT are similar, there are some differences between the two modalities. The primary difference is that OCT requires a relatively clear cornea and media, since it relies on light for imaging. This precludes its use in patients with opaque corneas. Since ultrasound relies on sound waves, this imaging modality is especially useful when corneal opacities limit the view to the anterior and posterior segments. In complex diagnostic cases with co-existing anterior segment dysgenesis, the UBM can be used to assess the need for additional procedures and surgical approach prior to corneal transplantation, including cataract extraction, intraocular lens implantation, iris reconstruction, and glaucoma procedures. UBM is also helpful in planning tumor excision. For anterior segment tumors, the UBM offers overall better anatomic resolution, especially of posterior tumor margins. The anterior segment OCT, however, demonstrates better resolution of anterior tumor margins (Bianciotto et al. 2011).

The contact B-scan is used to scan the posterior segment of the globe to identify pathology. Examples of this would be vitreous debris or various types of choroidal lesions, excavation of the optic nerve head, and orbital pathology. In pediatric patients, B-scan often visualizes the superior ophthalmic vein within the intraconal space.

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Dec 19, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Corneal Diseases in Children: Imaging
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