Sir,

Multiple myeloma (MM) is a malignant plasma cell disorder of the bone marrow characterized by high levels of monoclonal serum protein and multiple organ involvement.1 Corneal crystalline deposition is a rarely reported but known ocular manifestation of MM.2 Recent reports have employed in vivo confocal microscopy (IVCM) to investigate MM-associated crystalline deposits.3, 4, 5 However, the pathophysiology of this condition is not fully understood. To objectively quantify the MM-associated corneal changes in differing depths of the cornea, we obtained corneal densitometry data in MM patients using a Scheimpflug camera. A hypothesis for the pathogenesis of this condition is discussed.

Ten MM patients (5 males; 5 females; mean age, 70.1±6.1 years) who were being routinely examined for their systemic disease were referred to the Ophthalmology department from the Hematology department. All patients underwent ophthalmologic screening, including slit-lamp and fundus examination. All eyes were deemed to be clear by slit-lamp examination without abnormal findings. Corneal densitometry measurements from the anterior, central, and posterior cornea within a 6-mm-diameter were attained using a Scheimpflug camera (Pentacam HR; Oculus GmbH). In total, 20 eyes from 10 MM patients were enrolled in this prospective case series. Ten eyes of 10 age-matched patients (mean age, 66.9±6.5 years) undergoing routine examination before cataract surgery served as controls. Table 1 shows the densitometry values of the central 2-mm zone and of the surrounding 2- to 6-mm zone for both groups. MM eyes had significantly greater corneal densitometry values than control eyes in the anterior (P<0.001) and central (P<0.001) layers within a 6-mm diameter of the cornea. There was no significant difference in the posterior corneal layer between both groups.

Table 1 Subclinical corneal densitometry changes in anterior, central, and posterior corneal layers
Full size table

To our knowledge, this is the first report of quantified corneal densitometry in MM. A recent study using IVCM3 reported that MM patients without clinically evident corneal involvement show hyperreflective deposits in the epithelium and stroma as well as corneal structural changes, similar to observations in MM patients with clinically apparent corneal deposits.4, 5 Our results also demonstrate increased corneal densitometry in MM patients who were deemed to be clear by slit-lamp examination.

Crystals are thought to form due to the deposition of immunoglobulin light chain proteins and may diffuse from the tear film or aqueous fluid,3 although the mechanism by which serum proteins in MM patients reach the cornea remains unclear. In the MM population of our study without clinically evident corneal involvement, increased corneal densitometry values were found in the anterior and central cornea. We presume that either of these may be the initial site of corneal immunoprotein deposition in MM patients, suggesting that serum proteins may diffuse from the tear film (anterior part) rather than from the aqueous fluid (posterior part). Future studies with a greater number of patients, varying degrees of corneal involvement, and comparative IVCM images may better our understanding of this pathophysiology.

In conclusion, corneal densitometry has the potential to non-invasively detect subclinical corneal alterations associated with MM and to further develop our understanding of MM-associated corneal deposits.

Author contributions

All authors contributed to patient management and to the writing of the report. All authors approve of the final version of this manuscript.