Dean A. VanNasdale

The use of forward scatter to improve retinal vascular imaging with an adaptive optics scanning laser ophthalmoscope

Retinal vascular diseases are a leading cause of blindness and visual disability. The advent of adaptive optics retinal imaging has enabled us to image the retinal vascular at cellular resolutions, but imaging of the vasculature can be difficult due to the complex nature of the images, including features of many other retinal structures, such as the nerve fiber layer, glial and other cells. In this paper we show that varying the size and centration of the confocal aperture of an adaptive optics scanning laser ophthalmoscope (AOSLO) can increase sensitivity to multiply scattered light, especially light forward scattered from the vasculature and erythrocytes. The resulting technique was tested by imaging regions with different retinal tissue reflectivities as well as within the optic nerve head.

Mobile personal health records: An evaluation of features and functionality

PURPOSE To evaluate stand-alone mobile personal health record (mPHR) applications for the three leading cellular phone platforms (iOS, BlackBerry, and Android), assessing each for content, function, security, and marketing characteristics. METHODS Nineteen stand-alone mPHR applications (8 for iOS, 5 for BlackBerry, and 6 for Android) were identified and evaluated. Main criteria used to include mPHRs were: operating standalone on a mobile platform; not requiring external connectivity; and covering a wide range of health topics. Selected mPHRs were analyzed considering product characteristics, data elements, and application features. We also reviewed additional features such as marketing tactics. RESULTS Within and between the different mobile platforms attributes for the mPHR were highly variable. None of the mPHRs contained all attributes included in our evaluation. The top four mPHRs contained 13 of the 14 features omitting only the in-case-of emergency feature. Surprisingly, seven mPHRs lacked basic security measures as important as password protection. The mPHRs were relatively inexpensive: ranging from no cost to

In vivo adaptive optics microvascular imaging in diabetic patients without clinically severe diabetic retinopathy

9.99. The mPHR application cost varied in some instances based on whether it supported single or multiple users. Ten mPHRs supported multiple user profiles. Notably, eight mPHRs used scare tactics as marketing strategy. CONCLUSION mPHR is an emerging health care technology. The majority of existing mPHR apps is limited by at least one of the attributes considered for this study; however, as the mobile market continues to expand it is likely that more comprehensive mPHRs will be developed in the near future. New advancements in mobile technology can be utilized to enhance mPHRs by long-term patient empowerment features. Marketing strategies for mPHRs should target specific subpopulations and avoid scare tactics.

Mueller matrix retinal imager with optimized polarization conditions.

We used a confocal adaptive optics scanning laser ophthalmoscope (AOSLO) to image the retina of subjects with non-proliferative diabetic retinopathy (NPDR). To improve visualization of different retinal features, the size and alignment of the confocal aperture were varied. The inner retinal layers contained clearly visualized retinal vessels. In diabetic subjects there was extensive capillary remodeling despite the subjects having only mild or moderate NPDR. Details of the retinal microvasculature were readily imaged with a larger confocal aperture. Hard exudates were observed with the AOSLO in all imaging modes. Photoreceptor layer images showed regions of bright cones and dark areas, corresponding in location to overlying vascular abnormalities and retinal edema. Clinically undetected intraretinal vessel remodeling and varying blood flow patterns were found. Perifoveal capillary diameters were larger in the diabetic subjects (p<0.01), and small arteriolar walls were thickened, based on wall to lumen measurements (p<.05). The results suggest that existing clinical classifications based on lower magnification clinical assessment may not adequately measure key vascular differences among individuals with NPDR.

The Association Between the Foveal Avascular Zone and Retinal Thickness

A new Mueller matrix polarimeter was used to image the retinas of normal subjects. Light from a linearly polarized 780 nm laser was passed through a system of variable retarders and scanned across the retina. Light returned from the eye passed through a second system of retarders and a polarizing beamsplitter to two confocal detection channels. Optimization of the polarimetric data reduction matrix was via a condition number metric. The accuracy and repeatability of polarization parameter measurements were within +/- 5%. The magnitudes and orientations of retardance and diattenuation, plus depolarization, were measured over 15 degrees of retina for 15 normal eyes.

Imaging polarimetry in patients with neovascular age-related macular degeneration

PURPOSE To investigate the association between the size and shape of the foveal avascular zone and retinal thickness in healthy subjects. METHODS In vivo imaging of the foveal microvasculature was performed on 32 subjects by using an adaptive optics scanning laser ophthalmoscope (AOSLO). Motion contrast maps of the AOSLO images were used to generate a montage revealing the foveal capillary network. Foveal avascular zone (FAZ) diameters along the horizontal (FAZH) and vertical (FAZV) meridians were measured on the montages. An asymmetry index (AI) of the FAZ was then computed as the ratio of the FAZH to FAZV. Retinal thickness was investigated by using spectral-domain optical coherence tomography (SDOCT). Inner retinal layer (INLFAZ) thickness and outer nuclear layer (ONLFAZ) thickness were measured at the edges of the FAZ on the horizontal and vertical SDOCT scans on the same eye. RESULTS The foveal capillary network was readily visualized in all subjects. As expected there was individual variation in the size and shape of the FAZ. Along the horizontal and vertical meridians, the mean±SD (μm) of the FAZ diameter was 607±217 and 574±155, respectively. The INLFAZ thickness was 68±9 and 66±9, and the ONLFAZ thickness was 103±13 and 105±11, respectively. The mean±SD of the AI was 1.03±0.27. The difference between FAZH and FAZV decreases with increasing FAZ area (P=0.004). Mean ONLFAZ was negatively correlated with FAZ effective diameter (P<0.0001). No significant correlation was found between mean INLFAZ and FAZ effective diameter (P=0.16). CONCLUSIONS Despite large individual variations in size and shape of the FAZ, the INLFAZ has a relatively constant thickness at the margins of the FAZ, suggesting the presence of retinal capillaries is needed to sustain an INLFAZ thickness greater than 60 μm. A smaller FAZ area is associated with a vertically elongated FAZ.

Foveal phase retardation changes associated with normal aging

Imaging polarimetry was used to examine different components of neovascular membranes in age-related macular degeneration. Retinal images were acquired with a scanning laser polarimeter. An innovative pseudocolor scale, based on cardinal directions of color, displayed two types of image information: relative phases and magnitudes of birefringence. Membranes had relative phase changes that did not correspond to anatomical structures in reflectance images. Further, membrane borders in depolarized light images had significantly higher contrasts than those in reflectance images. The retinal birefringence in neovascular membranes indicates optical activity consistent with molecular changes rather than merely geometrical changes.

Spatial distribution of macular birefringence associated with the Henle fibers

This study quantified normal age-related changes to the photoreceptor axons in the central macula using the birefringent properties of the Henle fiber layer. A scanning laser polarimeter was used to acquire 15° × 15° macular images in 120 clinically normal subjects, ranging in age from the third decade to the eighth. Raw image data of the macular cross were used to compute phase retardation maps associated with Henle fiber layer. Annular regions of interest ranging from 0.25° to 3° eccentricity and centered on the fovea were used to generate intensity profiles from the phase retardation data, which were then analyzed using sine curve fitting and Fast Fourier Transform (FFT). The amplitude of a 2f sine curve was used as a measure of macular phase retardation magnitude. For FFT analysis, the 2f amplitude, as well as the 4f, were normalized by the remaining FFT components. The amplitude component of the 2f curve fit and the normalized 2f FFT component decreased as a function of age, while the eccentricity of the maximum value for the normalized 2f FFT component increased. The phase retardation changes in the central macula indicate structural alterations in the cone photoreceptor axons near the fovea as a function of age. These changes result in either fewer cone photoreceptors in the central macula, or a change in the orientation of their axons. This large sample size demonstrates systematic changes to the central cone photoreceptor morphology using scanning laser polarimetry.

Corneal epithelial bullae after short-term wear of small diameter scleral lenses.

The spatial distribution of macular birefringence was modeled to examine the contribution from the foveal Henle fiber layer, particularly cone axons. The model was tested in 20 normal subjects, age 17-55yr. Phase retardance due to Henle fibers was modeled for rings increasing in radius around the fovea, using a sinewave of two periods (2f). The 2f sinewave amplitude increased linearly with eccentricity for each individual, (p<0.004) in 19 of 20 subjects. A good fit to linearity implies regular cone distribution and radial symmetry, and the uniformly excellent fits indicate no effect of age in our sample. The peak of the 2f sinewave amplitude varied across subjects from 1.06 to 2.46deg. An increasingly eccentric peak with increasing age would indicate a relative decrease of cone axons in the central fovea, but the location of the peak was not associated with age for our sample, which did not include elderly subjects.

Foveal localization in non-exudative AMD using scanning laser polarimetry.

Complications of scleral lens wear are not well documented or understood. While multiple studies focus on oxygen transmission during scleral lens wear and associated corneal swelling, little is known about the effects of varying scleral lens fitting relationships, especially when there is corneal interaction. Scleral lenses, by convention, are designed to completely clear the corneal surface and rest on the conjunctival and scleral tissue. However, some designs maximize oxygen transmission by reducing the lens diameter, thickness, and recommended corneal clearance.While the modifications increase oxygen transmission in any scleral lens design, they also distribute the lens mass closer to the limbus and make visualization of corneal clearance, especially narrow in the limbal region, more difficult. The sequelae from mechanical interaction between scleral lenses and the ocular surface, in particular the cornea, remain uncertain. This case series will describe corneal epithelial bullae, molding, and epithelial erosions as unintended scleral lens complications. These corneal changes corresponded to areas of contact lens-corneal bearing confirmed utilizing a combined scanning laser ophthalmoscopy (SLO) and anterior segment OCT. This case series will discuss epithelial bullae detection, their etiology, and suggestions for application of this information into scleral lens fitting protocols.