Keratic precipitates (KPs) are cellular deposits that appear on the inner surface of the cornea, the transparent front part of the eye. Think of them like fine sediment that settles at the bottom of a clear container, making the liquid cloudy or showing small particles. These deposits are not a disease in themselves, but rather a significant clinical sign. Their presence indicates that there is inflammation or another underlying issue within the eye, particularly in the anterior chamber, the fluid-filled space between the cornea and the iris.
The Cellular Makeup and Appearance of Keratic Precipitates
Keratic precipitates are primarily composed of inflammatory cells, such as lymphocytes, macrophages, and sometimes epithelioid cells, which have aggregated and adhered to the corneal endothelium. These cells originate from the inflamed aqueous humor. The appearance of KPs can vary widely, providing clues to the nature of the underlying inflammation.
One distinct type is “mutton-fat KPs,” which are large, yellowish-white, and have a greasy or waxy appearance, often resembling droplets of fat. These larger deposits are typically formed from macrophages and epithelioid cells. In contrast, “fine KPs” are smaller, dust-like particles that are often numerous and widely distributed across the corneal endothelium. “Stellate KPs” are characterized by their star-shaped appearance with fine, branching projections. Finally, “pigmented KPs” are older precipitates that have acquired melanin pigment from the iris, appearing darker and sometimes faded or irregular.
Underlying Medical Conditions
The presence of keratic precipitates signals inflammation within the eye, most commonly due to uveitis, an inflammation of the uvea, the middle layer of the eye. Uveitis can manifest in various forms, with anterior uveitis being the most frequent type leading to KP formation. In these cases, inflammatory cells and proteins leak into the aqueous humor, eventually settling on the corneal endothelium.
Viral infections are another common cause of KPs, particularly those caused by herpes simplex virus (HSV), varicella-zoster virus (VZV), and cytomegalovirus (CMV). These viruses can directly infect the eye, leading to an inflammatory response that generates KPs. Inflammation following eye surgery or trauma can similarly result in the formation of KPs. Certain corneal conditions, such as Fuchs’ endothelial dystrophy, can also be associated with KPs, although their appearance might be atypical in these cases.
Diagnosis and Clinical Evaluation
An eye doctor identifies and assesses keratic precipitates primarily through a slit-lamp examination. A slit lamp is a specialized microscope that illuminates the eye with a narrow, intense beam of light, allowing the ophthalmologist to view the cornea and other anterior structures with high magnification. This detailed view enables the doctor to detect even microscopic deposits on the inner corneal surface.
During the examination, the doctor observes the KPs’ size, shape, color, and distribution. A specific pattern known as Arlt’s triangle is particularly significant. This refers to a triangular accumulation of KPs, typically mutton-fat KPs, on the lower part of the cornea. This pattern occurs due to the combined effects of gravity and the natural convection currents of the aqueous humor within the anterior chamber, where warmer fluid rises and cooler fluid sinks. The appearance and specific distribution pattern of the KPs provide valuable clues, helping the doctor formulate a preliminary diagnosis regarding the underlying cause of the ocular inflammation.
Management and Treatment Approaches
The management of keratic precipitates focuses entirely on addressing the underlying medical condition that caused them, rather than treating the KPs directly. KPs are a symptom, and they typically resolve as the root cause of the inflammation or disease is brought under control. The specific treatment strategy depends on the diagnosed condition.
For uveitis, corticosteroid eye drops are commonly prescribed to reduce intraocular inflammation. In more severe or persistent cases, oral corticosteroids or other immunosuppressive medications might be used to suppress the immune response.
If a viral infection like herpes simplex or cytomegalovirus is identified as the cause, antiviral medications, often in combination with topical corticosteroids, are administered to target the virus and reduce inflammation. For conditions such as Fuchs’ endothelial dystrophy, treatment often involves monitoring the condition; however, if vision is significantly impaired due to corneal swelling, a corneal transplant may be considered to replace the damaged endothelial cells.