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11-cis-retinal is a geometrical form of retinal with a cis configuration at the carbon-11/carbon-12 double bond. In vertebrate rod rhodopsin, it acts as the bound chromophore that absorbs light. Photoisomerization toward all-trans-retinal triggers a change in the receptor's state, linking molecular geometry to photoreceptor signaling.^[ref]

The name identifies a configuration, not a different number of atoms. 11-cis-retinal and all-trans-retinal have the same molecular composition but differ in the arrangement around a double bond. Replacing a cis arrangement by trans is therefore an example of cis-trans isomerism, rather than cleavage of the retinal molecule into smaller fragments.

The $2.8$ angstrom rhodopsin crystal structure showed the retinal-binding pocket in the dark-state receptor. Bound 11-cis-retinal helps maintain its inactive arrangement; its behavior depends on the surrounding protein, so free retinal and retinal inside a receptor need not have identical optical properties.^[ref]

The visual cycle regenerates the usable 11-cis supply. In RPE65-deficient mice, 11-cis retinoids and normal rod pigment were absent despite retained rod opsin. This distinguishes making the receptor chain from supplying the correctly configured light-sensitive component.^[ref]

A representation of position or orientation in an external reference frame. Transforming a retinal direction to a world location generally needs eye position, head orientation, self-location and depth or scene geometry. A label in world coordinates is a description of the code, not an explanation of how it develops.

All-trans-retinal is the geometrical form of retinal whose relevant chain double bonds have trans configurations. In rod vision it is formed from the bound 11-cis-retinal chromophore after light absorption by rhodopsin. The change in geometry helps initiate receptor activation, while later processing of retinal participates in the visual cycle.^[ref]

“All-trans” describes cis-trans isomerism. It does not mean that the entire molecule is a perfectly straight, rigid line, or that the double bonds have become single bonds. The carbon skeleton and elemental composition are preserved during the idealized isomerization; arrangement changes.

The visual system must subsequently restore a pigment-compatible retinal supply. After bleaching, the retinal-derived material undergoes biochemical processing involving the photoreceptor and retinal pigment epithelium; rebuilding rod rhodopsin requires 11-cis-retinal, not merely any molecule labeled retinal. The RPE65 knockout illustrates the dependence on chemical form: all-trans retinyl esters accumulated while 11-cis retinoids were absent and normal rod responses were lost.^[ref]

Retinyl esters are distinct chemical species from all-trans-retinal. The experiment demonstrates a disrupted conversion pathway; it should not be paraphrased as though the accumulated ester and the newly photoisomerized aldehyde were the same compound.

An amacrine cell is a retinal interneuron that modifies signaling in the inner retina, including interactions between retinal bipolar cells and retinal ganglion cells. Different types contribute different spatial, temporal and inhibitory interactions.

This diversity makes the label an anatomical and circuit category rather than one universal computation. Comparing responses before and after a specific connection is perturbed can test a proposed function more directly than observing that an amacrine cell responds to moving light.

An ocular refractive error in which a point object cannot be brought to one sharp retinal focus by a single spherical correction. Regular ocular astigmatism has perpendicular principal meridians of unequal power; irregular departures require a more general description.^[ref]

A light-driven proton pump with a seven-helix membrane-spanning structure and a retinal chromophore. Its mechanical unfolding involves membrane anchoring as well as protein and lipid interactions.

A bipolar neuron has two main processes extending from its soma, conventionally an axon and a dendrite. Retinal bipolar cells provide a sensory example connecting photoreceptors to downstream retinal circuitry. The anatomical label does not mean that the biological cell has two axons, and it does not imply that every signal must be an action potential.^[ref]

The central retinal artery enters the retina through the optic-nerve route and supplies much of the inner retinal tissue. The outer retina depends strongly on the choroidal circulation. Separating these supplies explains why retinal layers need not respond identically to one vascular interruption.

A channelrhodopsin is a light-gated ion channel associated with a retinal chromophore. Absorbing light changes the protein's conducting state, connecting photoreception directly with ion movement across a cell membrane. Naturally occurring members in Chlamydomonas reinhardtii participate in responses to illumination.^[ref]

The landmark channelrhodopsin-2 study expressed the protein in Xenopus laevis oocytes and mammalian cells and recorded light-evoked electric currents. Altering ionic conditions showed passage of multiple cations; continued illumination produced an initial response followed by a smaller sustained conductance. Expressing the channel in another cell type helped establish that light gating was a property of this molecular machinery.^[ref]

In an illustrative Ohmic model with outward-positive electric current, $I=g(V-E_{\mathrm{rev}})$. If light produces $g=1\mathrm{nS}$ at $V=-60\mathrm{mV}$ and $E_{\mathrm{rev}}=0$, then $I=-60\mathrm{pA}$: net inward positive electric charge. These invented values illustrate the driving force. Light opens a route whose direction depends on membrane potential and ionic conditions, a principle used in optogenetics.

The choroid is the vascular and pigmented layer between the retina and sclera. It supports the outer retina and helps limit stray light. Its position distinguishes it from the retinal vessels supplying other parts of the sensory tissue.

A researcher who coauthored maps of human photoreceptor topography. Measuring receptor distributions connected retinal structure with variation across visual locations instead of assuming a spatially uniform sampling array.^[ref]

A vertebrate retinal photoreceptor class important in photopic vision and colour discrimination.

A researcher who coauthored physiological and morphological identification of a blue-on opponent retinal pathway. Combining cellular shape with responses connected a particular ganglion-cell class to a measured color signal.^[ref]

A central retinal region specialized for detailed vision, with a dense cone mosaic and a rod-free central region. Receptor density, optical blur and downstream sampling jointly constrain spatial resolution; visual sensitivity is not uniform across the retina.

A researcher who coauthored adaptive-optics imaging and densitometry of human cone mosaics. Measuring variation among individuals connected retinal sampling with trichromatic vision without assuming one fixed cone ratio for every observer.^[ref]

A retinal interneuron contributing lateral interactions among photoreceptor signals and spatial context. Its participation in a circuit does not imply that every perceptual surround effect originates at that one cell type.

Krzysztof Palczewski is a researcher in the molecular basis of vision. In a 2000 collaborative study, he helped determine the X-ray crystallography structure of rhodopsin at 2.8 angstrom resolution. Rhodopsin is a light-sensitive G protein-coupled receptor; the structure showed its seven membrane-spanning alpha helices and the buried binding environment of retinal.^[ref]

The structure connected architecture with a signaling problem: how can a light-driven change near retinal influence the intracellular surface that activates a G protein? Locating the binding pocket, connecting loops and contacts between alpha helices constrained possible mechanisms. The measured inactive-state structure supplied a starting configuration for testing those mechanisms; it did not by itself record the complete time-dependent activation process.^[ref]

A thalamic visual structure receiving retinal input and participating in pathways to visual cortex. Chromatic nulling experiments constrain how particular cells combine cone signals, while recurrent and descending interactions complicate a pure feed-forward relay description.

A retinal ganglion-cell type whose central retinal circuitry can support fine spatial sampling and cone-opponent responses. Functional spatial and chromatic roles need not correspond to entirely separate anatomical channels.

Parallel retinal pathways emphasizing increments and decrements in stimulation. Their sign differences depend on synaptic transformations of photoreceptor output; an ON pathway is not simply a photoreceptor that depolarizes to light.