However, despite some attempts at segmentation of the choriocapillaris or CSJ, 40 — 43 none have yet to become widely accepted owing to their variable and often ambiguous appearance in human subjects. Our study of choroidal morphology in rhesus macaques showed a very clearly defined choriocapillaris and poor visualization of the CSJ, likely due to the abundance and darker pigmentation of uveal melanocytes in these animals.
Future studies on the relationship between melanin pigment and ocular imaging may improve the development of segmentation algorithms and interpretation of OCT findings in retinal and choroidal diseases. GY is supported by the E. No funding organizations had any role in the design or conduct of this research. The content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agencies. Disclosure: G. Vuong , None; S. Oltjen , None; D. Cunefare , None; S.
Farsiu , None; L. Garzel , None; J. Roberts None; S. Thomasy None. Nickla DL, Wallman J. The multifunctional choroid. Prog Retin Eye Res. Enhanced depth imaging spectral-domain optical coherence tomography.
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Arch Ophthalmol. A well was created to simulate a fluorescein-filled choroid. The fluorescence of each tissue and combinations of tissue atop the well was determined using a fluorescence microscope. The percent reduction in the fluorescence of each, relative to the baseline fluorescence of the well alone, was calculated. Macular NR demonstrated lower fluorescence than peripheral NR in all but one subject.
The anatomic basis for this phenomenon has been a source of controversy. Some authors have concluded that this phenomenon is primarily due to xanthophyll pigment in the neurosensory retina NR of the macula, which acts as an optical filter of the exciting blue light. These conclusions are based largely on clinical and histological observation. We are aware of only 2 studies 11 , 12 that actually addressed the issue of macular hypofluorescence in a quantitative manner. They did not simulate the in vivo situation in which exciting blue light passes through the NR and RPE, sodium fluorescein is stimulated in the choroid, and emitted green light returns through the RPE and NR.
Using donated human tissue, we developed a model of clinical fundus fluorescein angiography to determine quantitatively the relative contributions of the NR and RPE to macular hypofluorescence. For the purposes of this study, macula is defined as the central 1 mm 2 , ie, a circle centered on the fovea with a radius of 0. We selected 10 eyes from 10 deceased human donors 5 women, 5 men; 5 white, 5 of unknown race ranging in age from 5 to 67 years.
Donors with a history of or dissecting microscopic evidence for diabetic retinopathy, macular degeneration, vascular occlusion, or retinal detachment were excluded. Attempts at dissecting RPE from fresh, unfixed eyes were unsuccessful owing to tissue fragility. After coronal transection at the level of the equator, the vitreous was removed from each globe using a cotton-tipped applicator and Westcott scissors. The RPE and choroid were removed from the globe as a unit by creating a flap of tissue and peeling it from the sclera.
Care was taken to lyse the short posterior ciliary arteries. A fluorescence microscope Olympus BH-2; Olympus Corporation, Lake Success, NY with a to nm bandpass excitation filter and a nm low-pass ie, passing longer wavelengths barrier filter was used. To simulate the human choroid, a well was designed to serve as a fluorescein reservoir. The well consisted of a 2.
The well was filled with 0. This arrangement of lighting, filters, tissue, and fluorescein is analogous to that used in clinical fundus fluorescein angiography, ie, both the exciting and fluorescing light each must pass through and be partially absorbed by the retina NR and RPE Figure 4. The emitted light from the well alone including the filtering effect of an overlying glass slide, coverslip, and a thin layer of cyanoacrylate adhesive was measured with a broad-range, photographic light meter placed in the trinocular tube of the fluorescence photomicroscope.
The digital camera was removed from the trinocular tube during these measurements. The sensitivity range of the digital camera was limited; consequently, it was necessary to employ 2 levels of exciting light produced by using neutral density filters : a high intensity for measuring the RPE and a low intensity for the NR. The emitted light levels of the well alone no tissue—only a slide, glue, mounting medium, and a coverslip were The average gray-scale luminance value of the central 1.
A calibration curve was generated using light within the sensitivity range of the digital camera so that its arbitrary luminance values could be converted to lux. Subsequently, the filtering effect, as a percent reduction of the emitted light, by any piece or combination of tissues could be determined. Since the measured values of luminance were dependent on the strength of the light source, they had only relative significance.
The results were therefore expressed as a percent reduction of light reaching the digital camera owing to a specific tissue or tissues compared with the well alone. Adding macular NR to macular RPE, thus simulating the natural superposition of the 2 tissues, resulted in only a 3.
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Finally, when macular RPE and macular NR were compared, the former had a markedly greater effect on fluorescence than the latter Note that filters combine in a multiplicative not additive manner. No clearly defined age-related effects were evident Figure 6 , Figure 7 , Figure 8 , and Figure 9. Our model for testing the filtering effects of retinal tissue shows significantly greater reduction of fluorescence by both the macular RPE and the macular NR compared with their peripheral counterparts. These data also indicate, regardless of location, a markedly greater reducing effect produced by the RPE than by the NR.
In the macula, the RPE causes a Combining these 2 tissues reduces choroidal fluorescence by only 3. We therefore conclude that the RPE is responsible for most of the macular hypofluorescence so commonly seen with fluorescein angiography. This study did not address the effects of the lack of retinal vascular fluorescence seen in vivo. We would expect this to contribute to macular hypofluorescence as well. The choroid has melanocytes that partially block fluorescence from the deeper vessels. In principal, this could affect the relative fluorescence of the macula compared with its surrounds if the pigmentation were greater centrally.
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