Optics: Entoptic Phenomenon Flashcards
Entoptic images are…
Visual sensations that arise from within the eye itself
Entoptic images are __________ as they are only see by the person whose eye it is
Subjective
Most Entoptic images are benign but are important to…
Understand their causes and include them in patients reports
Not all entoptic images arise from characteristic of the optics of the eye, some arise from…
Higher neuronal processes
Small surface changes across the cornea can redirect light ___________ the _______________
Outside the retinal image
Refractive entoptic effects:
-tear film
-corneal corrugations
-shadows
-white blood cells
-blue field entoptoscopy
Entoptic effects in the tear film:
-Eye blinks causing a horizontal ridge of tears that are left momentarily when the lids came together.
-report a shadow effect seen as horizontal striation
Corneal corrugations of entoptic images:
-Squeezing lids tightly cause shadow streaks or monocular diplopia and decreased VA
-can last for more than an hour in some cases
Entoptic phenomenon from shadows:
-Small bright light source close to the eye produces an out-of-focus patch of light on the retina where shadows of objects are formed
Entoptic phenomenon from shadows:
-Small bright light source close to the eye produces an out-of-focus patch of light on the retina where shadows of objects are formed
Types of shadows:
-ocular opacities
-purkinje tree
What factors can cause pt to see shadows?
-corneal scars
-lens opacities
-IO foreign bodies
-floaters
The effect of shadows will be strongest for opacities ___________ to the retina because….
Closer, closer objects are more apt to project an umbra
Anterior opacities may…
Not be seen at all
Astoroid hyalosis in an ________opacity
Anterior
Astoroid hyalosis for doctor looking in
Look bright and make view of fundus difficult due to glare
Astoroid hyalosis for patients looking from retinal side
Look darker and they may not be aware of them
Purkinje tree
Shadows of retinal blood vessels cast out due to the vessels being in front of the photoreceptors
Purkinje tree is normally not seen but a small bright light can reveal them as a…
Branched pattern around fovea
In purkinje vascular test, a patient with a good. Functions macular should be able to see what when the light source is moves?
A negative image of his or her retinal vessels
Entoptic perimetry is a method of measuring…
Entoptic phenomenon
Entoptic perimetry is used for:
-retinal capillary detail
-fovea a vascular zone
-macular blood flow
-diabetic retinopathy
-AMD
When looking at a blue bright background such as the sky a person may see…
Bright spots moving along curved lines
The phenomenon of the blue filed occurs because:
-blue light is absorbed by rbc but not by wbc which creates a gap in the blood column that appear as bright dots
Movement of the dots on the blue background are synchronized with…
Your heartbeat
Diffraction effects for entoptic phenomenon:
-colored halos
-asterisms
Colored halos are caused by
Corneal edema
Corneal edema increases…
Increase IOP that forces water into cornea producing water clefts that act as refractive particles
Patients may report colored halos around small bright light during…
Episodes of acute glaucoma
Colored halos can also be caused by…
Swimming in chlorinated pool and over wear of contact lenses
Asterisms
-Small bright object against dark background that have spikes
-assumed to be due to diffraction of the suture lines of lens
Pressure phosphates of entoptic phenomenon:
-digital pressure
-moores lightening streaks
Digital pressure applied to eyelid with eye closed can cause a…
Bright spot seen in the visual field on the opposite side of the
Why does bright light occur with pressure?
Pressure directly activates the retinal cells and the field reversal due to optical crossed projection
Moores lightening streaks
-vitreous liquefies with ages causing the points of remaining adherence between vitreous and retina to tug during eye movements
-produces pressure phosphernes that appear as lightening streaks
When a patient is seeing moores lightening streaks then you should…
Check carefullat for the possibility of retinal detachments
Effects of entoptic phenomenon due to xanthophyll:
-Maxwell’s spot
-haidinger’s brush
Maxwells spot
Blue filter placed in front of eye as you view and bright background as a dark disc appears in the macular area
Haidinger’s brush
If one looks at a uniform white background through a Polaroid filter, a small yellow hourglass figure appears centered on fixation point
Haidinger’s brush is due to…
Birefringence induced by xanthophyll
Electrical phosphenes and entoptic phenomenon:
-blue arcs on the retina
Blue arcs of the retina:
Red patch of light is projected against a dim background and blue arcs will be seen following direction of optic nerve fibers
Blue arc on the retina effect is due to:
An electrical short circuit between the axons from ganglion cells under the red stimulus and ganglion cells encountered along the path of the axons
