CLINICAL ASSESSMENT OF CORNEAL DISEASE: SYMPTOMS & SIGNS
Thorough clinical assessment is crucial in corneal disease as diagnosis is feasible in most cases on the basis of history and clinical examination. A history of trauma or contact lens wear can often be elicited, with foreign bodies and abrasions being the two most common acute corneal abnormalities. Identifying any past or family history of corneal disease can be critical. Herpes simplex infection and corneal erosion are often recurrent, but since recurrent erosion is extremely painful and herpetic keratitis is not, they can be differentiated by the history. Use of topical medications, including nonprescription preparations, should be elicited. Topical corticosteroids predispose to bacterial, fungal, and viral disease, especially herpes simplex keratitis. Many medications and preservatives can cause contact dermatitis or corneal toxicity. Toxicity is an important cause of corneal and conjunctival disease. The keys to examination of the cornea are adequate illumination and magnification, making the slitlamp essential. Examining the reflection as light is moved carefully over the entire cornea identifies rough areas indicative of epithelial defects. Fluorescein staining highlights superficial epithelial lesions that might otherwise not be apparent. Examination, particularly after trauma, is facilitated by instillation of a local anesthetic. Further methods of imaging in corneal disease are listed in Table 6–1.
Table 6–1.Methods of Corneal Imaging ||Download (.pdf) Table 6–1. Methods of Corneal Imaging
|Method ||Description ||Applications |
|Corneal topography (see Chapter 2) || |
Computer analysis of keratoscopy images to produce three-dimensional corneal profile displayed as refractive power, elevation, and thickness maps.
Wavefront aberrometry to analyze the quality of the optical image may be incorporated.
|Diagnosis and monitoring of corneal ectasia |
|Specular microscopy ||High-magnification image of corneal endothelium. ||Diagnosis of endothelial disorders; quantification of endothelial cell density |
|Anterior segment optical coherence tomography (OCT) ||Cross-sectional image of cornea and anterior chamber. ||Measure depth of corneal scars; assessment of position of endothelial grafts |
|Confocal microscopy ||Imaging of cellular structure of the cornea and corneal nerves. ||Diagnosis of Acanthamoeba and filamentary fungal keratitis |
Microbial keratitis is a major cause of visual loss throughout the world. Prevention, early diagnosis, and prompt management are essential to avoid long-term visual impairment. Table 6–2 outlines the most common risk factors for microbial keratitis. Examination of corneal scrapings, using Gram and Giemsa stains, may allow identification of the organism, particularly bacteria. Cultures for bacteria, fungi, Acanthamoeba, or viruses should be undertaken at presentation if indicated clinically or later if there is lack of response to treatment. Polymerase chain reaction (PCR) provides rapid identification of herpes viruses, Acanthamoeba, and fungi. Appropriate therapy is instituted as soon as the necessary specimens have been obtained. It is important that laboratory results are interpreted in conjunction with the clinical picture.
Table 6–2.Main Risk Factors for Microbial Keratitis