Pathology of macular lesions from subnanosecond pulses of visible laser energy.

PURPOSE: To demonstrate how current theories regarding ultrashort laser pulse effects may apply to ocular tissue, a prospective clinicopathologic study of macular lesions from ultrashort laser pulses compared the pathologic effects with the clinical and fluorescein angiographic appearance of the laser lesions. METHODS: Ninety-femtosecond, 3-picosecond, and 60-picosecond laser pulses, throughout a range of energies, were delivered to the retina of Macaca mulatta. Clinical examination and fluorescein angiography were performed at 1 hour in all eyes and 24 hours after exposure in selected eyes. Eyes were enucleated at 1 or 24 hours after lesion placement. The structure and extent of retinal lesions were scored for comparison with the clinical findings. RESULTS: Focal retinal pathologic appearance correlated well with a clinically visible lesion observed 24 hours after laser delivery. Retinal lesions were small foci of retinal pigment epithelium (RPE) and retinal disruption, without choriocapillaris involvement. Lesions that contained focal RPE vacuoles or lifting of the RPE also demonstrated leakage, in fluorescein angiographic studies. Suprathreshold laser delivery frequently caused focal columns of retinal injury and intraretinal hemorrhages from retinal vessel bleeding, with no rupture of choroidal blood vessels. CONCLUSIONS: The retinal response to ultrashort laser pulses at moderate energy followed a pattern of focal damage from laser-induced breakdown without significant thermal spread.

A comparison of retinal morphology viewed by optical coherence tomography and by light microscopy.

OBJECTIVE: To compare the cross-sectional images of primate retinal morphology obtained by optical coherence tomography (OCT) with light microscopy to determine the retinal components represented in OCT images. METHODS: Laser pulses were delivered to the retina to create small marker lesions in a Macaca mulatta. These lesions were used to align in vivo OCT scans and ex vivum histologic cross sections for image comparison. RESULTS: The OCT images demonstrated reproducible patterns of retinal morphology that corresponded to the location of retinal layers seen on light microscopic overlays. Layers of relative high reflectivity corresponded to horizontally aligned retinal components such as the nerve fiber layer and plexiform layers, as well as to the retinal pigment epithelium and choroid. In contrast, the nuclear layers and the photoreceptor inner and outer segments demonstrated relative low reflectivity by OCT. CONCLUSIONS: Retinal morphology and macular OCT imaging correlate well, with alignment of areas of high and low reflectivity to specific retinal and choroidal elements. Resolution of retinal structures by OCT depends on the contrast in relative reflectivity of adjacent structures. Use of this tool will enable expanded study of retinal morphology, both normal and pathologic, as it evolves in vivo.

Argon laser retinal lesions evaluated in vivo by optical coherence tomography.

PURPOSE: To assess the in vivo evolution of argon laser retinal lesions by correlating the cross-sectional structure from sequential optical coherence tomography with histopathologic sectioning. METHODS: Argon laser lesions were created in the retinas of Macaca mulatta and evaluated by cross-section optical coherence tomography, which was compared at selected time points with corresponding histopathology. RESULTS: Argon laser lesions induced an optical coherence tomography pattern of early outer retinal relative high reflectivity with subsequent surrounding relative low reflectivity that correlated well with histopathologic findings. The in vivo optical coherence tomography images of macular laser lesions clearly demonstrated differences in pathologic response by retinal layer over time. CONCLUSION: The novel sequential imaging of rapidly evolving macular lesions with optical coherence tomography provides new insight into the patterns of acute tissue response by cross-sectional layer. This sequential imaging technique will aid in our understanding of the rapid evolution of retinal pathology and response to treatment in the research and clinical setting.