The visual pathway,
macula to cortex.
Vision is a relay. Light is focused at the fovea, transduced by photoreceptors, processed across retinal layers, carried by retinal ganglion cells down the optic nerve, and rebuilt in the cortex. A second, older route leaves the same optic tract for the midbrain and moves your eyes toward something before you have consciously seen it. Research here concentrates on the earliest, most metabolically vulnerable links, where the materials studied act.
Macula & Fovea
The core visual center of the retina. Responsible for high-acuity daylight vision, the fovea is highly vulnerable to metabolic energy failure. Epitalon (AEDG) is among the reference standards studied in models of retinal pigment epithelium stress.
Studied Target Reference Standards
Lyophilized Reference Vial
Lyophilized Reference Vial
Lyophilized Reference Vial
The Macula & Central Vision
The pigmented core of the retina, where sharpest sight is built.
Macula lutea
maculaThe yellow-pigmented central retina (~5.5 mm) responsible for high-acuity central and colour vision. Its lutein and zeaxanthin pigments filter high-energy blue light.
Fovea centralis
foveaA 1.5 mm pit at the centre of the macula with the highest cone density in the eye: the anatomical seat of 20/20 (and finer) vision.
Foveola
The 0.35 mm floor of the fovea, containing only cones (no rods): the point of peak visual acuity.
Umbo
The tiny central depression of the foveola, marking the precise centre of the visual axis. Seen clinically as the foveal light reflex.
Foveal avascular zone
FAZThe capillary-free region (~0.5 mm) at the fovea. Photoreceptors here are fed only by diffusion from the underlying choroid, making them uniquely vulnerable to any drop in metabolic supply.
Henle fibre layer
The obliquely running photoreceptor axons of the fovea. Because the inner retinal layers are swept aside to form the pit, foveal cones reach their bipolar cells sideways through this displaced fibre layer rather than straight down.
Photoreceptors & the Outer Retina
Where photons become electrical signals, at enormous energy cost.
Photoreceptors
Light-sensing neurons that convert photons into electrical signals (phototransduction). Their outer segments are continuously rebuilt, making them among the most energy-demanding cells in the body.
Cones
~6 million photoreceptors for colour and high-acuity daylight (photopic) vision. Three types (S, M, L) are tuned to short, medium, and long wavelengths and are concentrated in the fovea.
Rods
~120 million photoreceptors for low-light (scotopic) and peripheral vision. They are absent from the foveola.
Retinal pigment epithelium
RPEA single cell layer behind the photoreceptors that recycles visual pigment, digests spent outer segments, and manages oxidative load. RPE dysfunction is central to age-related macular degeneration.
Ora serrata
dentate processesThe serrated boundary where the neural retina ends and the ciliary body begins. Its tooth-like extensions are the dentate processes, more pronounced on the nasal side, and the retina is thinnest and most firmly attached here.
Inner Retinal Processing
The interneurons that sharpen, time, and route the signal.
Bipolar cells
Relay neurons carrying signals from photoreceptors to ganglion cells. ON and OFF types encode increases and decreases in light.
Horizontal cells
Lateral interneurons that mediate surround inhibition, sharpening contrast and enabling edge detection.
Amacrine cells
Inner-retinal interneurons (over 30 types) that shape temporal and motion signals and contribute to directional selectivity.
Inner plexiform layer
IPLThe synaptic layer where bipolar, amacrine, and ganglion cells connect, stratified into ON and OFF sublaminae.
Müller cells
Müller gliaThe principal glia of the retina, each one spanning its full thickness from the inner limiting membrane, which they form, to the external limiting membrane. They buffer potassium, recycle neurotransmitter, funnel light toward the photoreceptors, and their processes form the sloping walls of the foveal pit.
In zebrafish, Müller glia re-enter the cell cycle after retinal injury and regenerate lost neurons. In mammals they scar instead, which is why they are a standing focus of retinal regeneration research.
Retinal Ganglion Cells
The retina's output neurons, and the heart of our research.
Retinal Ganglion Cells
RGCsThe output neurons of the retina; their axons form the optic nerve. As central-nervous-system neurons with long, energy-hungry axons, they are the cells lost in glaucoma and optic neuropathy.
Midget ganglion cells
P cells~80% of all RGCs. Small receptive fields projecting to the parvocellular pathway; they carry fine spatial detail and red–green colour.
Parasol ganglion cells
M cellsLarge receptive fields projecting to the magnocellular pathway; they carry motion and luminance contrast at high temporal resolution.
Bistratified ganglion cells
K cellsProject to the koniocellular pathway; they carry blue–yellow (S-cone) colour signals.
Intrinsically photosensitive RGCs
ipRGCs · melanopsin cellsA small subset of ganglion cells containing melanopsin, which respond to light directly rather than only through rods and cones. They project mainly to the suprachiasmatic nucleus and the pretectum, driving circadian entrainment and the pupillary light reflex rather than image formation.
Nerve Fibre Layer & Optic Nerve
Where a million axons converge and exit the eye.
Retinal Nerve Fibre Layer
RNFLThe innermost retinal layer of unmyelinated RGC axons converging toward the optic disc. Its thinning is a key biomarker of optic-nerve damage.
Axons
The long projections of RGCs: roughly 1.2 million per eye, travelling unmyelinated within the retina to preserve transparency.
Optic disc
The point where axons exit the eye and vessels enter. It lacks photoreceptors, creating the physiological blind spot.
Lamina cribrosa
A sieve-like collagen mesh in the sclera through which RGC axons pass. A biomechanical stress point strongly implicated in glaucoma.
Optic nerve
Cranial Nerve II · CN IIThe bundle of ~1.2 million RGC axons carrying vision to the brain. Anatomically it is a central-nervous-system tract, not a peripheral nerve.
Myelin
The insulating sheath that speeds axonal conduction. In the optic nerve it begins just behind the lamina cribrosa.
Oligodendrocytes
The CNS glial cells that produce optic-nerve myelin (unlike Schwann cells, which myelinate peripheral nerves).
The Central Visual Pathway
From the chiasm to the cortex by two routes: the one that builds the picture, and the one that moves your eyes before you know why.
The materials studied here act on the retina and its neurons. They are not represented as acting on these central structures, which are included for anatomical completeness.
Optic chiasm
The X-shaped junction where the two optic nerves meet beneath the brain.
Decussation
The partial crossing at the chiasm: fibres from the nasal retina cross to the opposite side while temporal-retina fibres stay ipsilateral, organising the visual fields.
Optic tract
The pathway from chiasm to the thalamus, now carrying combined input from both eyes for one visual hemifield.
Lateral Geniculate Nucleus
LGNA six-layered thalamic relay that sorts input into magnocellular, parvocellular, and koniocellular streams before sending it to cortex.
Optic radiations
Axon bundles carrying signals from the LGN to the visual cortex, including Meyer's loop through the temporal lobe.
Primary Visual Cortex
Striate Cortex · V1 · Brodmann Area 17The first cortical stage of vision in the occipital lobe. It is retinotopically mapped, with the fovea given vastly disproportionate area (cortical magnification).
Superior colliculus
optic tectumA layered midbrain structure receiving a direct retinal projection that never passes through the LGN. It drives reflexive orienting of the eyes and head toward a stimulus rather than conscious image formation.
Pulvinar
The largest nucleus of the thalamus. It takes input from the superior colliculus and projects on to extrastriate visual cortex, skipping V1 entirely.
Tectopulvinar pathway
retinotectal pathwayThe second visual route: retina to superior colliculus to pulvinar to extrastriate cortex, running alongside the geniculostriate pathway and bypassing both the LGN and V1. It is the anatomy usually proposed to explain blindsight, where people with V1 damage respond above chance to stimuli they report not seeing.
Pretectum
A group of midbrain nuclei mediating the pupillary light reflex. Retinal input here comes substantially from melanopsin-containing ipRGCs, which is why a pupil constricts to light independently of whether anything is consciously seen.
Longevity & the Aging Visual System
The systemic processes that erode the pathway over decades, and where the research turns to aging.
NAD⁺ decline
Tissue NAD⁺ pools fall with age, constraining the sirtuin and PARP maintenance enzymes that high-demand retinal and optic-nerve neurons depend on.
Telomere shortening
Protective chromosome end-caps shorten with each cell division, a hallmark of aging that affects long-lived cells across the retina and nervous system.
Telomerase (hTERT) regulation is the central mechanism studied for the AEDG tetrapeptide.
Cardiolipin oxidation
Peroxidation of the inner-membrane lipid cardiolipin is an early step in mitochondrial aging and intrinsic apoptosis, including in retinal neurons.
Mitochondrial-derived peptides
Short peptides encoded within mitochondrial DNA (such as MOTS-c) that regulate metabolic homeostasis; their circulating levels are reported to decline with age.
Cellular senescence
The state in which cells stop dividing yet resist death, accumulating with age and driving tissue decline, including in the retina and RPE.
Neuronal apoptosis
Programmed death of neurons, accumulating with age due to oxidative damage, mitochondrial dysfunction, and caspase activation. In the visual system, RGC loss is the hallmark of glaucoma and optic neuropathy.
Anti-apoptotic and neuroprotective mechanisms are the central focus of EDR (Pinealon) research.
Of the entire pathway, the fovea, photoreceptors, retinal pigment epithelium, and retinal ganglion cells share one trait: a punishing dependence on mitochondrial energy. That is the link the catalogued materials are studied against.
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