Crystals are seen in subepithelial and/or stromal regions of the cornea. May or may not have an overlying epithelial defect. In the presence of a corneal transplant, the crystalline opacities frequently are localized emanating from an existing suture track (see Figure 4.15.1).
Infectious crystalline keratopathy: Seen in corneal grafts and chronically inflamed corneas. Streptococcus viridans is the most common organism; other organisms include Staphylococcus epidermidis, Corynebacterium species, Pseudomonas aeruginosa, and fungi. Atypical mycobacteria and Alternaria have been reported after LASIK.
Schnyder corneal dystrophy: Slowly progressive, autosomal dominant. Subepithelial corneal crystals in 50% of patients (cholesterol and phospholipids), central and midperipheral corneal haze, dense arcus, decreased corneal sensation. Local disorder of corneal lipid metabolism but can be associated with hyperlipidemia and hypercholesterolemia. Higher prevalence in patients with Swede–Finn descent. See 4.26, Corneal Dystrophies.
Bietti crystalline dystrophy: Rare, autosomal recessive. Retinal crystals (decrease with time) and sparkling, yellow-white spots at the corneal limbus in the superficial stroma and subepithelial layers of the cornea.
Cystinosis: Rare, autosomal recessive, systemic metabolic defect. Infantile form (nephropathic): dwarfism, progressive renal dysfunction, and polychromatic cystine crystals in conjunctiva, corneal stroma (densest in peripheral cornea but present throughout anterior stroma), trabecular meshwork. Intermediate/adolescent form: less severe renal involvement. Adult form: normal life expectancy.
Lymphoproliferative disorders (e.g., monoclonal gammopathy of undetermined significance, essential cryoglobulinemia, or multiple myeloma): Fine or larger crystalline opacities are diffusely distributed throughout the cornea more commonly in the anterior stroma and peripheral cornea than the posterior stroma and central cornea.
Infectious crystalline keratopathy: Culture as outlined in Appendix 8, Corneal Culture Procedure. Obtain mycobacterial cultures/acid-fast bacillus stain (especially in patients with history of refractive surgery).
Fasting lipid profile in patients with Schnyder corneal dystrophy.
Electroretinogram may be decreased in later stages of Bietti crystalline dystrophy.
Cystinosis: Very high level of suspicion required, especially for infantile form, which can be fatal in the first decade of life without a renal transplant. Conjunctival biopsy, blood or bone marrow smear.
If a lymphoproliferative disorder is suspected, consult hematology and consider complete blood count with differential, serum chemistries (including calcium), creatinine, albumin, lactate dehydrogenase, beta-2 microglobulin, C-reactive protein (CRP), serum protein electrophoresis (SPEP), urine protein electrophoresis (UPEP), and peripheral/bone marrow smear.
Infectious crystalline keratopathy: Treat as outlined in see 4.12, Bacterial Keratitis, and 4.31, Corneal Refractive Surgery Complications. If patient is on topical steroid therapy, decrease frequency or steroid strength rather than stopping the steroid abruptly.
Schnyder corneal dystrophy: Excimer laser PTK may be effective for subepithelial crystals. Corneal transplantation for severe cases. Diet and/or medications if associated with systemic dyslipidemia.
Cystinosis: Topical cysteamine drops reduce the density of crystalline deposits and corneal pain. PK for severe cases (although corneal deposits may recur). Patients must get systemic evaluation by primary care physician and/or geneticist.
Lymphoproliferative disorder: Consult a hematologist and/or oncologist.
