Pump-Probe Laser Imaging of Pigment in Conjunctival Melanocytic Lesions

Abstract

 

Purpose

 

To report the use of a novel molecular imaging technique, pump-probe laser microscopy, as an adjunctive diagnostic tool in distinguishing conjunctival melanocytic lesions.

 

Methods

 

Eight patients underwent surgical management of conjunctival melanocytic lesions. Their histopathologic specimens were imaged retrospectively with pump-probe microscope. The technique uses a laser-scanning microscope with a two-color pulsed laser source to distinguish eumelanin and pheomelanin pigment based on differences in excited state photodynamics. The distribution of eumelanin and pheomelanin was acquired and analyzed. Patients’ clinical histories were reviewed, and histopathologic and pump-probe images were correlated (Figure 1, 2).

 

Results

 

The pump-probe laser microscopy images provided clear delineation of conjunctival anatomic features and pathologic benign or malignant areas in all cases. The characteristics, margins or depth of these lesions are illustrated and appearance of benign vs malignant lesions is defined. This initial study demonstrated that there are spectroscopic differences in pigmentation chemistry between nevi, primary acquired melanosis (PAM) and melanomas. There was significant correlation between pump-probe images and histopathologic features, providing a noninvasive confirmation of clinical diagnosis.

 

Conclusions

 

Pump-probe laser microscopy is a novel technique that shows promise as a noninvasive, adjunctive diagnostic tool in evaluation of ocular melanocytic lesions and may serve as an “in vivo” optical biopsy. A significant degree of morphologic correlation with the histopathologic results demonstrates its potential use in clinical and surgical management of conjunctival melanocytic lesions.

 

 

Figure 1: A. 79-year-old female with pigmented conjunctival lesion. B. Nests of markedly atypical melanocytes were seen in substantia propia consistent with invasive malignant melanoma. C. Pump-probe image demonstrated distribution of eumelanin (orange-red) and pheomelanin (camouflage green) pigment with predominance of eumelanin. Surgical ink (teal) pigment is noted.

 

 

Figure 2: A. 55-year-old male with pigmented conjunctival lesion. B. The epithelium was replaced in full-thickness by nests of atypical melanocytes consistent with PAM with atypia. C. Pump-probe image illustrated predominance of pheomelanin (camouflage green) along basal epithelium. Surgical ink (teal) and hemoglobin (pink) pigments were noted.

 

Keywords: 474 conjunctiva • 550 imaging/image analysis: clinical • 589 melanoma