Can “perceive” avascular fovea with steady fixation  area that “spots” never enter.Field divided into quadrants by large cross-hair “reticle”.Brightly back-illuminated blue filter viewed through magnifying eyepiece.Diagnostic device to detect/monitor retinal pre-occlusive and occlusive conditions.37īlue Field Entoptoscope - Optimized Viewing Conditions Leukocytes transmit blue  light interruptions on dark background.Erythrocytes absorb blue  create a dark background.Origin: leukocytes in pre-retinal capillaries.Optimum Conditions: view uniform, bright, blue background  dark spots against blue background.View a uniform white background  see yellow spots moving in short, arcuate patterns in paracentral visual field.Luminous Darting Points - Yellow Dancing Spots Can “map” foveal diameter by entoptic perimetry

Purkinje Tree - Optimum Conditions Directional light shone into eye (point source at first focus)  perceive retinal vessels down to capillary level Avascular fovea visible (“no branches”). Purkinje Tree See projection of larger vessels with penlight

Projected into visual field based on inverted receptor map.

See shadows of retinal vessels entoptically.

keep light moving to prevent adaptation.

shine light into eye at a very oblique angle.

Can overcome normal adaptation that prevents us seeing shadows of retinal vessels:.

“Switches off” our perception of pre-retinal vessels (cast very distinct shadow on retina) under normal conditionsĮntoptic Perception of Retinal Vessels.

View center of pattern with one eye for ~ 30 seconds Fig 2.23.

Larger receptive fields in peripheral retina  will see retinal adaptation here first with very steady fixation.

High cone density Central Retina Peripheral Retina Thick ganglion cell layer

Receptive fields much larger in peripheral retina  many cones feeding into a single ganglion cell.

Retinal receptive fields smallest at the fovea  1:1 correspondence cone  ganglion cell.

“Receptor” stimulation therefore constantly changing:.

Result  images always moving over retina.Attempted steady fixation  eyes in constant motion:.Retinal receptors (actually receptive fields) require constantly changing stimulus.

Entoptic phenomena macular pigment