Keratic precipitates, commonly called KPs, are clumps of inflammatory cells that stick to the inner surface of the cornea during episodes of eye inflammation. They are not a disease on their own but rather a visible sign that something is irritating the inside of the eye, most often a form of uveitis. Their size, shape, color, and distribution on the cornea give ophthalmologists surprisingly detailed clues about what is causing the inflammation, which makes them one of the more useful diagnostic signposts in eye care.
What Keratic Precipitates Actually Are
The inner lining of the cornea is a single layer of cells called the endothelium. During intraocular inflammation, white blood cells and protein debris floating in the fluid behind the cornea (the aqueous humor) settle onto this endothelium the way sediment settles to the bottom of a glass. The deposits tend to collect in the lower third of the cornea because gravity and convection currents in the aqueous push them downward, forming a roughly triangular pattern sometimes called Arlt’s triangle. Confocal microscopy studies have shown that the endothelial cells immediately surrounding a KP look abnormal, with round defects visible at or near the deposit.1PubMed. Evaluation of keratic precipitates and corneal endothelium in Fuchs’ heterochromic cyclitis by in vivo confocal microscopy In other words, KPs are not just sitting passively on the cornea; they interact with and can damage the cells beneath them.
How Size and Shape Point to a Cause
Ophthalmologists broadly sort KPs into two categories based on appearance, and each category narrows the list of possible diagnoses considerably.
Fine or small KPs are tiny, often white or translucent dots. They are typical of non-granulomatous inflammation, the kind seen in many acute or autoimmune forms of uveitis. HLA-B27-associated anterior uveitis, for instance, usually produces a brisk inflammatory reaction with fine KPs rather than large ones.2CRO Journal. HLA-B27 Associated Acute Fibrinous Anterior Uveitis In one cross-sectional study of HLA-B27 uveitis patients, about a quarter had visible keratic precipitates during active episodes.3PubMed Central. Clinical characterization of patients with HLA-B27-associated uveitis and evaluation of the impact of systemic treatment on the recurrence rate
Large, greasy-looking KPs, sometimes called “mutton-fat” KPs because of their waxy appearance, signal granulomatous inflammation. Sarcoidosis is one of the classic causes, where the anterior segment examination may show these granulomatous KPs along with iris nodules and adhesions between the iris and the lens or cornea.4PubMed Central. Ocular Sarcoidosis: New diagnostic modalities and treatment Tuberculosis and syphilis can produce a similar granulomatous picture, which is why ruling them out is part of the diagnostic workup for ocular sarcoidosis.
Then there are some distinctive variants that don’t fit neatly into either camp. Stellate KPs, for example, are small and star-shaped, scattered diffusely across the cornea rather than clustering at the bottom. They are a hallmark of Fuchs uveitis syndrome, where the eye also shows iris color changes and diffuse iris thinning.5PubMed Central. Classification criteria for Fuchs uveitis syndrome Fuchs is unusual in that the inflammation is typically low-grade, painless, and confined to one eye, and the stellate KPs are diffuse and small rather than clumped inferiorly.6Güncel Retina Dergisi (Current Retina Journal). Fuchs Heterochromic Iridocyclitis: Clinic, Diagnosis, and Treatment Another variant, coin-shaped KPs, tends to show up specifically in cytomegalovirus (CMV) anterior uveitis and can help distinguish it from other viral causes.7PubMed. Distinguishing Features of Anterior Uveitis Caused by Herpes Simplex Virus, Varicella-Zoster Virus, and Cytomegalovirus
Viral Causes and How They Differ
Herpes family viruses are among the most common infectious triggers of anterior uveitis with KPs, and different members of the family leave different fingerprints. Herpes simplex virus (HSV) and varicella-zoster virus (VZV) both tend to cause a relatively acute, painful episode with medium-to-large KPs, redness, and cells floating in the anterior chamber.8PubMed. Comparison of the ocular characteristics of anterior uveitis caused by herpes simplex virus, varicella-zoster virus, and cytomegalovirus They often produce posterior synechiae, where the iris sticks to the lens behind it.
CMV anterior uveitis looks and behaves quite differently. It tends to be less painful, the KPs are often small or coin-shaped, the iris may show diffuse thinning, and intraocular pressure frequently rises. Glaucoma surgery ends up being needed more often in CMV cases than in HSV or VZV cases.7PubMed. Distinguishing Features of Anterior Uveitis Caused by Herpes Simplex Virus, Varicella-Zoster Virus, and Cytomegalovirus The pressure elevation in CMV uveitis is a particular concern because it can become chronic and difficult to control, making early recognition of the viral cause critical for management.
Pigmented KPs are another variant worth knowing about. After active inflammation subsides, white blood cell deposits sometimes pick up pigment from the iris and turn brownish. But prominently pigmented KPs appearing early in the course, especially after cataract surgery, can signal an unusual infection. In reported cases of endophthalmitis caused by the slow-growing bacterium Propionibacterium acnes, pigmented KPs and persistent low-grade iritis were the presenting findings; the inflammation only resolved once the artificial lens and its surrounding capsular bag were removed.9PubMed Central. Resolution of Pigmented Keratic Precipitates Following Treatment of Pseudophakic Endophthalmitis Caused by Propionibacterium Acnes
How KPs Are Evaluated
The standard tool is a slit-lamp biomicroscope, the device your eye doctor uses to look at the front of your eye with a bright, focused beam of light. Under the slit lamp, an experienced examiner can note the size, shape, color, and distribution pattern of KPs. Old KPs tend to look glassy or slightly pigmented, while fresh ones appear white and fluffy. This distinction matters because it tells the clinician whether the inflammation is new or has been smoldering for a while.
For more detailed analysis, anterior segment optical coherence tomography (AS-OCT) can image KPs in cross-section. Studies using this technology have found that KPs associated with active, acute inflammation tend to be more reflective (brighter on the scan) than those from chronic or resolving episodes. Highly reflective KPs may also be more common in herpetic uveitis, offering another diagnostic clue.10PubMed. Anterior segment optical coherence tomographic characterisation of keratic precipitates In vivo confocal microscopy goes even further, letting clinicians visualize individual inflammatory cells within a KP and assess the endothelial damage around it.1PubMed. Evaluation of keratic precipitates and corneal endothelium in Fuchs’ heterochromic cyclitis by in vivo confocal microscopy These imaging tools are not available everywhere, but they are increasingly useful in research settings and specialized uveitis clinics.
Treatment Depends on the Underlying Cause
Because KPs are a symptom of inflammation rather than a standalone disease, treatment centers on controlling whatever is driving the inflammation. The approach varies widely depending on the cause.
Corticosteroids for Most Inflammatory Causes
Topical corticosteroid eye drops are the first-line treatment for most forms of anterior uveitis. They quiet the immune response, reduce the number of inflammatory cells entering the aqueous humor, and allow existing KPs to shrink or resolve. For autoimmune-driven uveitis such as HLA-B27-associated disease or sarcoidosis-related disease, steroids are typically paired with a cycloplegic drop that keeps the pupil dilated and prevents the iris from sticking to the lens. In an interesting finding, one study of glaucoma patients whose only sign of inflammation was precipitates on the drainage meshwork of the eye showed that topical steroids alone eliminated the precipitates and lowered eye pressure, even when standard glaucoma medications had failed.11PubMed. Glaucoma associated with precipitates on the trabecular meshwork That finding underscores how easily subtle inflammation can be missed and how directly treating it can resolve seemingly unrelated problems like elevated pressure.
Antivirals for Herpetic and CMV Uveitis
When a herpes-family virus is identified as the cause, antiviral therapy becomes essential. For CMV anterior uveitis specifically, both oral valganciclovir and topical ganciclovir eye drops have shown positive results. Early antiviral treatment reduces the chance that the patient will need glaucoma surgery down the road.12PubMed Central. Cytomegalovirus Anterior Uveitis: Clinical Manifestations, Diagnosis, Treatment, and Immunological Mechanisms However, CMV uveitis has a frustrating tendency to recur. Topical ganciclovir may reduce how often flare-ups happen, though it has not been shown to significantly delay the time until the next recurrence.13PubMed Central. Efficacy and safety of topical ganciclovir in the management of cytomegalovirus (CMV)-related anterior uveitis Extended antiviral courses can help prevent relapses, but courses longer than about six months carry risks of drug resistance and side effects.12PubMed Central. Cytomegalovirus Anterior Uveitis: Clinical Manifestations, Diagnosis, Treatment, and Immunological Mechanisms
For HSV and VZV uveitis, oral acyclovir or valacyclovir is the standard. These cases generally respond more predictably than CMV, though recurrences are still common, and long-term low-dose antiviral prophylaxis is sometimes used to keep the virus suppressed.
Surgical Intervention in Rare Scenarios
Most KPs resolve with medical treatment. Surgery enters the picture only when the underlying cause demands it. In P. acnes endophthalmitis after cataract surgery, as noted earlier, removing the artificial lens and capsular bag was required to clear the infection and its associated pigmented KPs.9PubMed Central. Resolution of Pigmented Keratic Precipitates Following Treatment of Pseudophakic Endophthalmitis Caused by Propionibacterium Acnes In advanced CMV-related disease, glaucoma surgery may become necessary if the pressure cannot be controlled with drops alone.
Corneal Damage and Other Complications
KPs do not just sit harmlessly on the endothelium. The corneal endothelial cells near fresh KPs show measurable changes: they tend to be larger and less densely packed than normal cells in the unaffected eye.14PubMed Central. Evaluation of corneal endothelium and keratic precipitates by specular microscopy in anterior uveitis Since the human corneal endothelium does not regenerate in any meaningful way, repeated bouts of inflammation with KPs can gradually thin out this cell layer. If enough endothelial cells are lost, the cornea loses its ability to pump fluid out and begins to swell, leading to corneal edema and cloudy vision.
This problem becomes especially severe in the setting of corneal transplantation. A case-control study of patients who developed CMV-positive corneal swelling with KPs after corneal transplant found that all of the transplanted grafts ultimately failed, with most patients left with vision worse than 20/400.15PubMed. Cytomegalovirus-positive corneal stromal edema with keratic precipitates after penetrating keratoplasty The combination of a cornea that is already vulnerable (because it came from a donor) and ongoing viral inflammation proved devastating. This highlights why controlling the underlying cause of KPs is so important, especially in people who have had or may need corneal surgery.
Glaucoma is the other major long-term risk. Inflammatory cells and debris can clog the eye’s drainage system, and as mentioned earlier, precipitates can sometimes form directly on the trabecular meshwork even when the rest of the eye looks quiet.11PubMed. Glaucoma associated with precipitates on the trabecular meshwork Chronic or recurrent inflammation, particularly from CMV, carries the highest glaucoma risk among the common causes of KP-associated uveitis.
Keratic Precipitates in Children
Uveitis in children can be tricky because young kids rarely complain of eye pain or redness, and the inflammation is often discovered only on routine screening exams. Juvenile idiopathic arthritis (JIA) is the most common systemic disease associated with childhood uveitis, and the inflammation is traditionally described as non-granulomatous, meaning fine KPs and no large waxy deposits. But that textbook picture turns out to be incomplete.
Studies have found that roughly a third of JIA-associated uveitis patients show granulomatous features at some point. In one cohort, about 32% of children with JIA uveitis had granulomatous signs during their disease course, and the majority of those had bilateral inflammation.16PubMed Central. Granulomatous Features in Juvenile Idiopathic Arthritis-Associated Uveitis is Not a Rare Occurrence A separate study found a similar rate, with about 28% of JIA uveitis patients manifesting granulomatous disease. Interestingly, two-thirds of those classified as granulomatous had so-called “ghost KPs,” which are old, faded deposits left behind after inflammation resolves, rather than the classic mutton-fat appearance.17Journal of the American Association for Pediatric Ophthalmology and Strabismus. Granulomatous inflammation in juvenile idiopathic arthritis–associated uveitis
This matters because finding granulomatous KPs in a child with arthritis-related uveitis could send clinicians down a rabbit hole looking for sarcoidosis or tuberculosis when the cause is actually JIA. Awareness that JIA uveitis frequently takes on a granulomatous appearance can avoid unnecessary workups and delays in treatment.
Ghost KPs and What Old Deposits Tell You
When inflammation resolves, KPs do not always disappear completely. They often shrink, lose their fluffy white appearance, and become translucent or lightly pigmented. These remnants, known as ghost KPs or old KPs, can persist for months or even years on the endothelium. Their presence tells a clinician that the eye has had inflammation in the past, even if it looks perfectly quiet at the time of the exam.
Ghost KPs are clinically significant for a few reasons. First, they help establish a history of uveitis in a patient who may not remember having any eye symptoms, which is particularly relevant in conditions like Fuchs uveitis syndrome or JIA-associated uveitis where symptoms can be minimal. Second, their distribution pattern can still provide diagnostic clues. If old deposits are scattered diffusely rather than clustered inferiorly, that distribution points toward conditions like Fuchs even after the active phase has passed. Third, they serve as a baseline: if a follow-up exam shows fresh, white deposits layered on top of or next to older ghost KPs, the clinician knows that new inflammation has started.
KPs in Animals
Keratic precipitates are not unique to humans. Veterinary ophthalmologists encounter them regularly, especially in cats, where uveitis is common and can be caused by feline infectious peritonitis (FIP), feline leukemia virus, feline immunodeficiency virus, and toxoplasmosis, among other conditions. In a retrospective review of 96 cats with uveitis, KPs were documented in about 40% of cases.18Agriculture and Agricultural Science Procedia. Causes of Feline Uveitis: A Retrospective Study of 96 Cases at the Faculty of Veterinary Medicine Bucharest, 2012-2015 Just as in humans, the presence and character of KPs in an animal eye helps narrow the differential diagnosis. A cat with large, granulomatous KPs might raise suspicion for FIP, whereas a cat with fine KPs and a painful red eye could have toxoplasmosis or a bacterial cause. The same principle applies in dogs and horses, where uveitis from infectious and immune-mediated causes produces KP patterns that guide treatment decisions.