Final Exam - Entopic Phenomenon

Entopic phenomena

visual effects that originate from within the eye by native structures. They are often harmless, but can sometimes be used to monitor ocular disease and visual function as well.

subjective

Entopic phenomena are completely _____, and cannot be photographed or imaged in any way.

hallucinations

Entopic phenomena should not be confused with _______, which have no obvious structural foundation and are generally psychological distortions due to cortical misinterpretation.

Visual Snow

condition in which people see white or black dots in their vision which is constant and can last years. Often occurs with other types of visual disturbances such as floaters or afterimages and cause trigger migraines. Its cause is unclear, but brain imaging suggests that it is a brain disorder.

retinal function and blood supply

Entopic phenomena can have value in diagnosis because they often relate to

small pupils

Entopic phenomena may appear worse for patients having _____, because the visual effects superimpose on the real image.

Opacities

small refractive anomalies in the cornea that can redirect light over local areas of the retina and causes shadows, reducing the optical clarity of the ocular media.

Tear droplets (oil or mucus)

spots on the cornea that can act as a convex lens and appear as bright spots surrounded by dark margins. They will move upward on the corneas with blinking causing them to appear to float down. Can be visualized by fluorescein staining

Striae

folds in the cornea that can cause horizontal bands of shadows across the visual field due to transient wrinkling of tears.

Opacities

occur in the lens and appear as dark lines radiating inwards and casting shadows on the retina. These phenomena do not move and appear as small round discs with a brighter center (pearl speck of listing)

Floaters

entopic phenomena appearing as slow drifting colorless blobs of varying size, shape, and transparency which move with eye movement. They are most visible when viewing a bright light against a stationary background or a point source very close to the eye

Physiological floaters

floaters that are long standing and tend to disappear when they settle in the inferior vitreous due to gravity. Are caused by remnant of the hyaloid artery embryonic material or proteins of the vitreous. Common in high myopic patients or the elderly.

Pathological floaters

floaters of recent onset that can be distinguished from physiological floaters by examination of the peripheral retina and vitreous. Can be caused by retinal tears, PVD, hemorrhage, infection, or inflammation.

30

percent of the general population having symptomatic eye floaters.

Vitrectomy

removal of the vitreous body which resolves floaters but can bring about other complications like cataracts and possible retinal detachment.

Asteroid Hyalosis

a form of vitreous degeneration in which calcium soaps aggregate in the vitreous body and are visible as small mobile white to yellow opacities. Treatment is not usually necessary, but vitrectomy can be performed in severe cases.

2:1, older

ateroid hyalosis has a male to female ration of ____ and is more common in ____ patients.

DM, HT, and hypercholesterolemia

asteroid hyalosis is thought to be associated with these three conditions

VA

asteroid hyalosis rarely affects..

unilateral

A majority of asteroid hyalosis cases (75-90%) are...

Physiological halos (coronas)

anatomical arrangements of a number of small structures in the eye can cause diffraction gratings dispersing light to create distinct patterns on the retina. Can be caused by cells of the corneal epithelium, pigment of the corneal endothelium, radial fibers of the crystalline lens, and mucous or foreign bodies in the tear film.

diameter of the diffractive particle or spacing of lens fibers

Diameter of a physiological halo varies inversely with the

smaller

Haloes appear (larger or smaller) when nearer to the retina

Conjunctivitis

a pathological cause of halos associated with increased mucous secretion

Angle closure glaucoma

the best known pathological cause of halos. Raised IOP results from a failure of aqueous flow through the trabecular meshwork leads to anterior media edema and therefor light scatter and halos.

Corneal edema

contact lens over wearers can experience halos due to this reason. Haloes appear worse when there is poor endothelial function.

larger, brighter, dimmer

Pathological halos tend to be (smaller or larger), (brighter or dimmer) for the observer, but (brighter or dimmer) via slit lamp examination than physiological halors

Purkinje tree

an image of the retinal blood vessels in one's own eye seen by shining a beam of light through the pupil from the periphery of the subject's vision. Caused by shadows cast on the unadapted portions of the retina. Can also be seen by holding a bright light on the closed eyelid.

neural adaptation

typically images of retinal blood vessels are invisible due to _______. Fast movement of a light (1 Hz) defeats this mechanism.

diabetes

The appearance of a purkinje tree can help patients with _____ self-monitor for retinal hemorrhages at home.

Blue field entopic phenomenon (Scheerer phenomenon)

when looking at a brightly lit blue field with no background, a series of white spots appear to be moving around the field of view in sync with the pulse accelerating at each heartbeat within 15 degrees of the fixation point. This occurs because blue light is absorbed by hemoglobin in RBCs and the white blood cells which are translucent appear as white spots.

inner nuclear and outer plexiform

Blue field entopic phenomenon occurs in the capillary loops of these two layers of the retina

Clinical significant macular edema (CSME)

disease that can be monitors via the blue field entopic phenomenon. Allows for detection of blood vessels in the typically avascular foveal zone.

Haidinger's brushes

the appearance of paired brush like structures seen projected into space when looking at a clear blue sky. Appearances have origin in Henle's fibers in the macular region of the eye.

Henle's fibers

fibers of the eye that connect cone receptor outer limbs and their main nuclei. The origin of Haidinger's brushes. Because the fibers are organized radially they act as a dichroic filter whose absorption is dependent on the plane of polarization of the incident light.

perpendicular

Henle's fibers absorb blue light to a greater degree when light waves are _____ to the direction of the fibers.

parallel

Henle's fibers absorb yellow light to a greater degree when light waves are _____ to the direction of the fibers.

Macular function

can be assessed using Haidinger's brushes in conditions such as advanced cataracts, macular degeneration, or oedema.

amblyopia, aphakic

The appearance of Haidinger's brushes does not depend on VA so even patients with ____ or ____ patients can experience this phenomenon

strabismic

Haidinger's brushes can be used to locate the fovea in _____ patients who have eccentric fixation

central serous retinopathy

Haidinger's brushes are valuable in the detection of ______ where Haidinger's brushes are not visible in light of wavelength longer than 560 nm.

Maxwell's Spots

an entopic experience where a target on a white screen viewed through a deep purple filter is illuminated alternately every two second with yellow and blue light. Eventually, the red spot target will appear to have a blue ring surrounding it and an outer dark red ring. This occurs due to the selective absorption of the yellow macular pigment, xanthophyll. Not everyone will experience this phenomenon because it depends on the degree of pigment.

32 min of arc (2-3 degrees)

the size of the red target used for Maxwell's spots

macular pigment

Size of the Maxwell spot phenomenon depends on how diffuse the ____ is

Protanopes

will see Maxwell spots as blue or dark

Deuteranopes

will not see Maxwell spots at all

Moore's lightning streak

entopic phenomenon characterized by lightening type streaks seen to the temporal side caused by shock waves in the vitreous humor hitting the retina during sudden movement in the dark.

retinal detachment

Typically Moore's lightning streaks are not a cause for alarm if they are momentary, only occur in the dark, and are due to sudden head movements. A referral should be made if there is suspicion of...

Blue arcs phenomenon

entopic phenomenon caused by the nerve fiber layer. Blue arc are seen one above and one below the fixation point when viewing an open fire. This corresponds to the projected path of retinal nerve fibers from the optic nerve.

Distance

______ from the fixation will move blue arcs caused by blue arcs phenomenon further and closer together.

Nasal

viewing gives the best sensation of the blue arcs phenomenon

Electrical discharge of ganglion cells in the Papillo-macular region

the cause of the blue arcs phenomenon

an ophthalmoscope using red free light

The Papillo macular bundle responsible for the blue arc phenomenon can be seen with..

dim grey

blue arcs phenomenon is seen as ______ in the dark

bright blue

blue arcs phenomenon is seen as ______ in the light

Prolong dark adaptation

ruins the effect of the blue arc phenomenon

Phosphenes

a phenomenon characterized by the experience of seeing light without light actually entering the eye. A vague visual sensation arising when the retina is stimulated by energy other than light. Ie) mechanical stimulation of the retina during retinal detachment causes the appearance of flashing lights.

electrical charge in the retina, breakdown of visual pigment, and activity of the cortical areas

phosphenes can be caused by these three things

visual cortical neurons

phosphenes can be caused by direct electrical stimulation of ____ during brain surgery, including patients that have no sight

accommodation, eye movement, respiratory rate

sensation of phosphenes fluctuates base on these three body changes

cataract surgery

phosphenes Can indicate residual retinal function in patients having retinal degeneration and therefore indicate the potential benefit, or lack of, for...

Troxler's effect

a peripheral afterimage that is slower with respect to the central fovea after image. Involve activity of the parvocellular and magnocellular pathways. Mid-brain or cortical explanations are also possible. Occurs due to the difference in retinal adaptation between the central and peripheral retina.