Multispectral diagnostic imaging of the iris in pigment dispersion syndrome

Abstract

Purpose: To determine if wavelength selection with near infrared iris imaging may enhance iris transillumination defects (ITDs) in pigment dispersion syndrome.

Methods: An experimental apparatus was used to acquire iris images in 6 African-American (AA) and 6 White patients with pigment dispersion syndrome. Light-emitting diode probes of 6 different spectral bands (700 to 950 nm) were used to project light into patients' eyes. Iris patterns were photographed, ITD regions of interest were outlined, and region of interest contrasts were calculated for each spectral band.

Results: Contrasts varied as a function of wavelength (P<0.0001) for both groups, but tended to be highest in the 700 to 800 nm range. Contrasts were higher in Whites than AAs at 700 nm but the opposite was found at 810 nm (P<0.001).

Conclusions: Optimized near infrared iris imaging may be wavelength dependent. Ideal wavelength to image ITDs in more pigmented eyes may be slightly longer than for less pigmented eyes.

Figure 1

Infero-temporal position of light probe during imaging.

Figure 2

Example photo showing iris transillumination defect regions of interest (ROIs) (red pixels) and non-iris transillumination defect zones (green pixels), which were used to calculate contrast values. The regions of interest and the surrounding non-iris transillumination defect zones have the same number of pixels. The surrounding regions were automatically selected via computer algorithm.

Figure 3

Right eye images from all of the control and pigment dispersion subjects, obtained using 700 nm for the Whites and 750 nm for the African-Americans. Some show classic mid-peripheral iris transillumination defect spokes but others are more amorphous and/or coalescent.

Figure 4

Near infrared transillumination images of the same iris acquired at different wavelengths for an African-American pigment dispersion subject. Contrast differences can be visualized with the different wavelengths. This subject’s 360° iris transillumination defect pattern was not detectable without near infrared imaging.

Figure 5

Region of interest contrasts grouped by wavelength and subject group for the pigment dispersion subjects (top) and normal subjects (bottom). Boxplots denote the range of contrast values between the 25^th and 75^th percentiles, with whiskers extending to the 10^th and 90^th percentiles. Dashed and solid lines connect mean region of interest contrast values across all wavelengths for the White and African-American groups respectively. Peak contrast occurred at 750 nm for the African-American pigment dispersion eyes, but it was 700 nm for Whites.

Figure 6

Example “mean vs. difference” plots of two selected imaging wavelengths that reflect region of interest contrast results calculated from two separate imaging sessions.