Keratic precipitates (KPs) are deposits of inflammatory cells that have migrated from the uvea, the eye’s middle layer. These clusters settle on the inner surface of the cornea, the transparent front dome of the eye. The presence of KPs is a direct sign that an active inflammatory process, known as uveitis, is taking place within the eye.
Defining Keratic Precipitates
Keratic precipitates are cellular deposits that adhere to the corneal endothelium, the single layer of cells lining the back surface of the cornea. These deposits are primarily composed of various white blood cells, including lymphocytes and macrophages.
Fine, small, or dust-like KPs are typically associated with non-granulomatous inflammation, where the cellular response is less intense. Mutton-fat KPs are a distinct type that is large, greasy, and yellowish-white in color, resembling droplets of fat. Mutton-fat KPs contain large numbers of macrophages and epithelioid cells, indicating a granulomatous type of inflammation. Due to gravity, these deposits often settle and accumulate in a triangular pattern on the inferior cornea, sometimes termed Arlt’s triangle.
Underlying Causes of Formation
The formation of KPs is not a disease itself but a consequence of inflammation, most frequently due to anterior uveitis, which affects the iris and ciliary body. These inflammatory cells circulate in the aqueous humor, the fluid filling the front part of the eye, before adhering to the cornea. The underlying causes of uveitis are broadly categorized into non-infectious autoimmune conditions and specific infectious diseases.
Non-infectious causes often involve systemic autoimmune disorders that mistakenly target the eye’s tissues. Examples include uveitis associated with conditions like sarcoidosis, juvenile idiopathic arthritis (JIA), or HLA-B27 related diseases such as ankylosing spondylitis.
Infectious causes involve pathogens that have entered the eye, triggering a localized immune reaction. Specific pathogens can include viruses like the Herpes Simplex Virus or Varicella Zoster Virus, or bacteria responsible for conditions such as tuberculosis or syphilis.
Detection and Clinical Assessment
A patient experiencing an inflammatory episode may notice symptoms such as ocular pain, redness, increased sensitivity to light, or blurred vision. These symptoms prompt an eye examination where KPs are identified. The primary tool for detection is the slit lamp microscope, which allows an ophthalmologist to direct a thin beam of light into the eye.
This magnified, three-dimensional view makes the tiny, translucent KPs highly visible against the dark background of the pupil. The clinician assesses the deposits based on their size, shape, color, and location on the corneal endothelium. The morphology of the KPs provides a significant diagnostic clue, helping to narrow the list of potential underlying causes.
Treatment and Management
The management strategy for keratic precipitates is centered entirely on treating the underlying intraocular inflammation. Since the KPs are merely a sign of the immune response, they cannot be treated directly. The goal of therapy is to suppress the uveitis, thereby preventing the migration of inflammatory cells and allowing the existing deposits to naturally dissipate.
The standard medical approach for non-infectious uveitis involves anti-inflammatory medications, most commonly corticosteroids. These are often administered as topical eye drops to achieve high concentrations within the anterior chamber of the eye. If the inflammation is severe or involves systemic disease, oral or injected corticosteroids may be necessary to control the immune response.
If the uveitis is determined to be infectious, treatment requires a targeted approach using specific antimicrobial, antiviral, or antiparasitic agents to eliminate the pathogen. Topical steroids may still be used alongside these agents, but only after the infection is adequately managed. Once the inflammation is controlled, KPs will slowly resolve, although older deposits may leave behind pigmented spots on the cornea, which generally do not affect vision.