BIOPHYSICS OF VISION THEORY OF COLOR VISION ELECTRORETINOGRAM Two problems: All cows are black in dark! Playing tennis in dark with illuminated lines, rackets, net, and ball! Refraction media of the human eye D eye = 63 diopter, D cornea =40, D lens = 15+ Human eye has complicated lens systems Normal eye, Nearsightedness myopia, Farsightedness hyperopia Astigmatism need for a cylinderic lens Cornea the main focusing element Lens adjustable focusing Iris adjust sensitivity and depth of focus Retina photosensitivity and much, much more lens
The human eye has a complicated lens systems Photoreceptors (rods, cones) Normal eye Myopia nearsightedness corrected farsightedness corrected Hyperopia (Astigmatism -- cylinderic lens) Simplified eye Astigmatism tangential image (focal line) Sagittal image (focal line) tangential plane Optical axis saggital plane It can be applied when objects are farther than 5 meter object lens paraxial focal plane
Structure of photoreceptors cones ~(30 2-4) micrometer (color vision) rods ~(60 1-2) micrometer (light sensing) Distribution of photoreceptors Sensitivity (1-2 photons for rods) (3-5 receptors) Adaptation (10-9 10 5 lux) Resolution (70 micrometer at 25 cm) (two different receptors, between them one resting receptor) Localization of rhodopsin Pigmented epithelium Outer segment rods Rods ~(60 1-2) micrometer (light sensing) Rods nd cones Inner segment cones Cones ~(30 2-4) micrometer (color vision) Bipolar neurons Müller-cell Ganglion cells Optical nerves
Distribution of photoreceptors nasal temporal Receptor density 10 3 /mm 2 150 100 50 Rods cones 90 60 30 30 0 blind spot fovea centralis 60 90 visus sensitivity in darkness (%) visus 80 1/1 60 40 20 1/2 1/4 1/8 90 60 30 0 30 60 90 90 60 30 0 30 60 90 blind spot fovea centralis blind spot fovea centralis Vavilov experiment E n =, error = n (Poisson distribution) hf E ΔE = hf n = hf = hf Ehf Δ E Ehf hf = = = 1 E E E n Rods are able to detect one or two photons
Current (pa) Rod 860 photon 2 2 In dim light only rods can work. There is no color vision. Light retinal opsin* transducin PDE cgmp 1:1 1:1 1:500 2:1 1:million 3 photon Cone 36000 photon 2 190 photon Response of cones is faster and shorter. Cones are able to follow fast movements. Na + channels close hyperpolarization transmitter release is decreased (glutamate inhibitor) stimulus (Hundreds of Na + channels close, a million Na + ions will not enter.) E light = 1.5-3 ev, E ion = 6 x 10 3 6 x 10 4 ev, Time (s) Amplification = 2 x 10 3-2 x 10 4 Adaptation (10-9 10 5 lux) a. Pupilla reflex (~16 ) b. Concentration of photopigment (dim light, high pigment concentration) c. Spatial summation (dim light, many receptors per a single nerve cell) d. Temporal summation (dim light, longer time to induce stimulus) e. (intracellular concentration of calcium ion)
Absorbed photon serves as a trigger Through the wizardry of biochemistry, sodium channels close Light impulse Resting potential A= arrestin, GC= guanylate cyclase, PDE= phosphodiesterase, Rh= rhodopsin, T= transducin Time (s)
COLOR VISION THEORY OF COLOR VISION Different cones (blue, green, red) (same retinal, different opsins) Young-Helmholtz theory X = rr + bb + gg (Monochromatic color, mixed color) (Color blindness) COLOR VISION ELECTRORETINOGRAM Electric properties of human eye Retina is at 6 mv potential compared to cornea. Electrotinogram (ERG) Early phase (ERP, Early Receptor Potencial) Late phase a b c waves Dark adaptation (up to 30 minutes) wavelength (nm) Lack of vitamin A, night-blindness.
ELEKTRORETINOGRAM BASIC PRINCIPLES OF GEOMETRIC OPTICS Biphasic wave incident light ray normal to surface reflected light ray Snellius - Descartes ERP Pigment layer a receptor cells, hyperpolarization medium a medium b ab switch out peak b Müller cells depolarization Time (ms) in out Light refracted light ray BIOPHYSICS OF VISION BASIC PRINCIPLES OF GEOMETRIC OPTICS THEORY OF COLOR VISION ELECTRORETINOGRAM Two problems: All cows are black in dark! Playing tennis in dark with illuminated lines, rackets, net, and ball!
BASIC PRINCIPLES OF GEOMETRIC OPTICS Image formation of thin lenses 1 f 1 1 = + i o D ( diopter) = 1 1 = ( n 1) f R1 + 1 f 1 R 2 Monochromatic Aberration 3 5 i i sin i = i + 3! 5! Spherical aberration Coma Astigmatism Field curvature Distortion i 7! Chromatic Aberration Longitudinal chromatic aberration Lateral chromatic aberration 7 9 i + 9!... BASIC PRINCIPLES OF GEOMETRIC OPTICS Paraxial light rays object Major planes 1 f 1 = ( n 1) R1 Image formation of thick lenses 2 1 ( n 1) + + R2 n d R R 1 2 Real image formation Paraxial focal plane Spherical aberration image longitudinal spherical aberration transverse spherical aberration
Astigmatism Object point Coma tangential image (focal line) Sagittal image (focal line) tangential plane Image Optical axis saggital plane object lens paraxial focal plane Coma Astigmatism Coma is when a streaking radial distortion occurs for object points away from the optical axis. If a perfectly symmetrical image field is moved off axis, it becomes either radially or tangentially elongated.
Spherical focal surface Cause: refractive index depends on wavelength dispersion Light is bent and the resultant colors separate (dispersion). Red is least refracted, violet most refracted. Distortion Longitudinal chromatic aberration object pincushion distorted images barrel white light ray blue light ray red light ray blue focal point red focal point blue light ray white light ray red light ray Longitudinal chromatic aberration
Lateral chromatic aberration Ocular electric potentials ELEKTRORETINOGRAM red light Lateral color white light ray blue light object focal plane BIOPHYSICS OF VISION BASIC PRINCIPLES OF GEOMETRIC OPTICS THEORY OF COLOR VISION ELECTRORETINOGRAM Two problems: All cows are black in dark! Playing tennis in dark with illuminated lines, rackets, net, and ball!