Fig 1.
Identification of the RPE/choriocapillaris and neural retina.
(A) A low-power histological view of the sample, stained with autometallography/hematoxylin (AMG/H), shows the sclera, choriocapillaris (*), RPE (arrow), neural retina (#), and optic nerve head. The RPE is artefactually separated from the neural retina. The area corresponding to this histological image is shown in the dashed boxes in the LA-ICP-MS images below. Optic nerve head anatomical regions are NF: superficial nerve fibre layer, PL: prelaminar region, LC: lamina cribrosa, and RL: retrolaminar region. (B) LA-ICP-MS of an adjacent section shows iron (Fe) in the RPE/choriocapillaris (*), and in the optic nerve head (O). (C) LA-ICP-MS for phosphorus shows the high cellularity of the neural retina (#), and the lower cellularity of the RPE (*) and optic nerve head (O). The separation of the RPE and the neural retina, and a smaller separation within the neural retina (to the right of the #), can be seen.
Fig 2.
LA-ICP-MS of three eye samples.
The histological images at the top of the figure, stained with autometallography/hematoxylin (AMG/H), are from sections adjacent to the LA-ICP-MS samples. The areas corresponding to these histological images are shown in the dashed boxes in the iron (Fe) and phosphorus (P) LA-ICP-MS images. The toxic metals sampled are presented below in alphabetical order. The location of the toxic metals in the eye can be assessed by reference to the iron image (high levels in the RPE/choriocapillaris) and to the phosphorus image (high levels in the neural retina, low levels in the RPE/choriocapillaris). The optic nerve head (O) is not included in the R3 AMG image. Scale = counts per second (proportional to abundance).
Fig 3.
LA-ICP-MS of four eye samples.
The histological images at the top of the figure, stained with autometallography/hematoxylin (AMG/H), are from sections adjacent to the LA-ICP-MS samples. The areas corresponding to these histological images are shown in the dashed boxes in the iron (Fe) and phosphorus (P) LA-ICP-MS images. The toxic metals sampled are presented below in alphabetical order. The location of the toxic metals in the eye can be assessed by reference to the iron image (high levels in the RPE/choriocapillaris) and to the phosphorus image (high levels in the neural retina, low levels in the RPE/choriocapillaris). Scale = counts per second (proportional to abundance).
Table 1.
Elements found by LA-ICP-MS in the posterior segment of seven adult eyes.
Fig 4.
Autometallography of the retina and choriocapillaris of R6.
(A) In the section stained with autometallography/hematoxylin, small black autometallographic grains are seen in most retinal pigment epithelium (RPE) cells. Brown-coloured melanosomes can also be seen in some of these cells. No black grains are seen in the pigmented cells of the choriocapillaris, in the retina, or in the sclera. Red blood cells (*, pale yellow) are seen in capillaries. The photoreceptor layer (PRL) of the outer neural retina is artefactually fragmented. (B) In an adjacent section stained with hematoxylin only, normal brown melanosomes, but no black grains, are present in the RPE. Red blood cells (*, pale yellow) are seen in capillaries. BM: Bruch’s membrane.
Fig 5.
Hypothesis of toxic metal-induced age-related macular degeneration.
(A) Exposure to a variety of toxic metals results in these metals entering capillaries of the choriocapillaris. Toxic metals are normally filtered by the retinal pigment epithelium (RPE) to prevent them entering the neural retina. The RPE is overwhelmed by toxic metals when these accumulate during aging. Synergistic effects between different toxic metals, and genetic susceptibilities, augment these toxic effects. Damage to the RPE is via multiple mechanisms, chiefly oxidative stress. Injury to RPE cells reduces its varied functions protecting the outer neural retina, and allows the entry of toxic metals into the outer neural retina, with subsequent age-related macular degeneration. (B) Toxic metals can enter the outer neural retina by transcellular and paracellular routes. Left: When the concentrations of a few circulating toxic metals (red circles in choriocapillaris capillaries) are low, they are filtered by binding to RPE melanosomes (grey rounded rectangles), and prevented from entry to the neural retina by apical tight junctions (black boxes). Right: With high levels of multiple toxic metals (red and blue dots in choriocapillaris capillaries), damaged melanosomes allow freed toxic metals to pass through the cell. Damaged RPE tight junctions allow toxic metals to pass between the cells, into the outer neural retina, contributing to AMD.