OPB201: Foundations of Optometric Practice - Introduction to Visual Science

Comprehensive vocabulary flashcards covering fundamental optical and visual science concepts from Lecture 1, including photoreceptor properties, dark and light adaptation, spatial and temporal summation, visual acuity, and contrast sensitivity.

Visible Light

The segment of the electromagnetic spectrum detectable by human vision, consisting of a stream of photons or waves with wavelengths ranging from $400\,\text{nm}$ (violet) to $700\,\text{nm}$ (red).

Retinal

An aldehyde of vitamin A that functions as the light-absorbing chromophore common to all four human visual photopigments.

Opsin

A large, clear protein component of visual photopigments that does not absorb visible light on its own and whose amino acid sequence varies across rod and cone photopigments.

Rhodopsin

The visual photopigment located within the free-floating discs of rod outer segments, composed of opsin bound to retinal, with a peak absorption at approximately $507\,\text{nm}$.

Cyanolabe

The short-wavelength-sensitive cone visual photopigment, with an absorption peak at approximately $426\,\text{nm}$ (or $420\,\text{nm}$).

Chlorolabe

The middle-wavelength-sensitive cone visual photopigment, with an absorption peak at approximately $530\,\text{nm}$ (or $540\,\text{nm}$).

Erythrolabe

The long-wavelength-sensitive cone visual photopigment, with an absorption peak at approximately $552\,\text{nm}$ to $557\,\text{nm}$ (or $570\,\text{nm}$).

Duplex Retina

A retina containing two anatomically and functionally distinct photoreceptor systems—rods and cones—enabling the visual system to operate across a broad luminance range of approximately $10\,\text{log units}$.

Scotopic System

The rod-dominated visual system operating under low-light conditions, characterized by high sensitivity to dim light, absence of color perception, poor spatial resolution ($20/200$), and a critical flicker fusion (CFF) of $20\,\text{Hz}$.

Photopic System

The cone-dominated visual system functioning under bright illumination, characterized by color discrimination, high spatial resolution ($20/20$), a CFF of $70\,\text{Hz}$, and an overall peak sensitivity at $555\,\text{nm}$.

Mesopic Vision

Intermediate visual function occurring at twilight or moderate light levels where both rod and cone photoreceptors simultaneously contribute to vision.

Absolute Threshold

The minimum light energy required for an observer to detect a stimulus against a dark background, representing the mathematical inverse of visual sensitivity.

Dark Adaptation

The progressive recovery of visual sensitivity (decrease in detection thresholds) that occurs over time when the visual system is placed in darkness following exposure to a bleaching light.

Dark Adaptation Curve (First Branch)

The rapid initial phase of dark adaptation lasting $5\text{--}10\,\text{minutes}$, mediated by cone recovery and resulting in an approximate $500\times$ increase in visual sensitivity.

Dark Adaptation Curve (Second Branch)

The slower second phase of dark adaptation occurring from $10\,\text{minutes}$ to $30\text{--}45\,\text{minutes}$ (flattening off at $25\text{--}30\,\text{minutes}$), mediated by rod recovery and yielding an approximate $10{,}000\times$ increase in visual sensitivity.

Purkinje Shift

The shift in maximum spectral sensitivity of the eye from longer wavelengths ($555\,\text{nm}$) to shorter wavelengths ($507\,\text{nm}$) as ambient illumination decreases from photopic to scotopic conditions.

Increment Threshold ($\Delta L$)

The minimum luminance difference between a test target and its background ($L$) necessary for the target to be detected as just noticeable.

Weber's Law

The psychophysical principle stating that the increment threshold ($\Delta L$) is directly proportional to background luminance ($L$), manifesting as a constant ratio ($\Delta L / L$) and a slope of $1$ on a log-log light adaptation curve.

Perimetry

A clinical examination of the visual field that measures differential light increment thresholds ($\Delta L$) against a constant background luminance ($L$).

Spatial Summation

The visual system's capacity to integrate photon energy across a specific spatial area (critical area), which enhances detection sensitivity at the cost of spatial resolution.

Neural Convergence

The synaptic pooling of signals from multiple photoreceptors onto a smaller number of ganglion cells, a wiring pattern prominent among peripheral rods that promotes spatial summation.

Temporal Summation

The process by which the visual system accumulates light stimulus energy over a fixed integration window known as the critical time ($T_c$).

Visual Acuity (VA)

A measurement of spatial vision defined as the smallest spatial detail that can be resolved using high-contrast ($100\%$) optotypes.

Snellen Acuity

A clinical visual acuity notation formulated as $d/D$, where $d$ is the testing distance and $D$ is the distance at which the critical detail of the target subtends $1'$ (one minute) of arc.

logMAR

A spatial resolution metric defined as the base-$10$ logarithm of the minimum angle of resolution in arcminutes ($\log_{10}(\text{MAR})$), widely used in clinical research and low vision assessment.

Contrast Sensitivity (CS)

The ability to detect subtle luminance differences between adjacent areas, quantified mathematically as the reciprocal of contrast threshold ($1/\text{contrast threshold}$).

Contrast Sensitivity Function (CSF)

A curve describing visual sensitivity across a spectrum of grating spatial frequencies; adult human photopic CSF exhibits a bandpass profile peaking around $4\,\text{cycles/degree}$ with a high-frequency cut-off.

Pelli-Robson Chart

A clinical contrast sensitivity chart composed of letters of uniform physical size arranged in triplets whose contrast diminishes incrementally down the chart.

Melbourne Edge Test

A clinical contrast sensitivity test presenting circular targets containing edges at various orientations with progressively diminishing contrast steps.

Vision Contrast Test System (Vistech)

A chart-based diagnostic tool displaying rows of circular sine-wave grating patches that vary in spatial frequency across rows and decrease in contrast across columns.

Retinal Eccentricity

The angular distance measured in degrees from the center of the fovea ($0^\circ$), which directly influences cone density, spatial summation, visual acuity, and the peak of the contrast sensitivity function.

Lateral Geniculate Nucleus (LGN)

The thalamic relay station receiving retinofugal axons through the optic tracts and relaying visual signals via optic radiations to the primary visual cortex.