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Optometry 662, Spring 2010 Pacific University College of Optometry James Kundart, O.D., M.Ed., F.A.A.O.
1. Why do we see the Purkinje Tree under the slit lamp, but not in the sunshine?
2. Why are flying corpuscles better described as flying spots?
3. Which entoptic phenomena can be used by an observant patient to monitor glaucoma? Which can be used to monitor diabetic retinopathy?
3. What part of the retinal causes the polarization responsible for the Hadinger Brush effect?
4. What is Maxwells spot? When is it seen?
What Are Entoptic Images?
Visual perceptions that are produced or influenced by native structures in your own eyes are entoptic phenomena
For example, you have all seen your retinal vessels when sitting for slit lamp exams. This is called the Purkinje tree.
Why dont you see it all the time?
Why should you care?
We will answer these question today
Why Havent I Heard About This Before?
Its not just because you are second years! Hart and Westheimer (in Adler) say:
Because of their subjective nature, entoptic phenomena require a savvy, articulate patient to observe and describe them.
They also cant be photographed, so I can only show you drawings
We will cover these phenomena from anterior to posterior eye structures
Because entoptic phenomena improve your understanding of the physiology of vision and visual perception, and can sometimes be used to monitor ocular disease
Some Entoptic Phenomena
1. Corneal Mosaic
2. Physiologic Halos
3. Vitreous Floaters
4. Retinal Phosphenes
5. Purkinje Tree
6. Flying Spots
7. Blue Retinal Arcs
8. Haidingers Brushes
1) Corneal Mosaic
You have seen what sodium fluorescein looks like on the tear film of your classmates, and the corneal epithelium by now
Did you know you can see your own corneal mosaic without a slit lamp?
If a small (0.1 mm) pinhole is placed at the spectacle plane (17 mm in front of the eyes) and backlit, you can see your own tear film, and irregularities in the cornea
The resulting image is limited in size by the pupil, not the pinhole
Imagining the Corneal Mosaic
Adler, figure 16-4
What Can Be Seen with the Pinhole Technique?
According to Adler, folds in corneal epithelium appear as horizontal bands
Excessive oil or mucus in the tear film look like bright blobs surrounded by a dark ring which swim up and down on blink
Shallow, linear channels made by ridges in Bowmans membrane can be seen with sodium fluorescein, as are sometimes caused by contact lens wear
Endothelial Dystrophy and the Corneal Mosaic
Tattooing the Cornea
What is the treatment for symptomatic partial corneal scarring where transplants (penetrating keratoplasty or DSEK) are not available?
With a translucent scar, patient symptoms would decrease when the scar was made opaque by surgical tattoo of the cornea
This is because a true opacity reduces the light that reaches the retina, but does not reduce overall contrast like a translucent defect does
Special pigments can be embedded in the cornea to hide corneal scars and to block light from entering the eye through iris defects
2) Physiologic Halos
You may have learned about pathologic halos, such as those from a steamy, edematous cornea, from contact lens overwear or ocular hypertension
Physiologic halos are different -- they are colored rings from chromatic aberration caused by the corneal mosaic -- but they still come from the cornea
They are dimmer, and their size varies with wavelength (color) of the light
All colors of the rainbow are present -- which are smallest, and which biggest? _______________ (Remember: blue bends best!)
Which of These Will Cause a Pathologic Halo?
Nuclear sclerotic cataract vs. corneal opacity
The cornea causes haloes, and the lens
Lenticular Diffraction Spikes
Instead of haloes, the surface of the crystalline lens causes diffraction of pinpoint light, such as starlight
Everyone knows that you dont need a cataract to see starbursts around lights this way, so
They must originate from a healthy lens, too
Physiologic sutre lines are the likely culprit
The same pinhole technique used for the corneal mosaic can be used to image lens opacities, which otherwise simply dampen light
Why Patients Dont See Their Cataracts Directly
Adler, figure 16-4C http://www.flickr.com/photos/whvick/132165203/
Early Cataract as It Appears Through a Pinhole
Adler, 9th edition, figure 15-4 http://www.flickr.com/photos/mak506/283085523/
Please resist temptation to use the
abbreviation cats for cataracts
3) Vitreous Floaters
We are all familiar with the muscae volitantes (flitting flies) that patients believe are in their tear film, but you know are actually in the vitreous
Some of these are remnants of the hyaloid artery that feeds the fetal lens. Others may be due to retinal tears or hemorrhage, like so-called tobacco dust floaters
When they settle to the inferior vitreous due to gravity, we dont see them
Remember, the vitreous never circulates or gets replenished, so floaters are forever. Learn to love them.
Why Patients Do See Vitreous Floaters
Adler, figure 16-4B
Which Floaters Are Harmless?
We quickly become accustomed to reassuring patients that floaters are normal, but sometimes they are not
Familiar, countable floaters can be normal might as well become your friends
Recent-onset, innumerable floaters often are due to retinal tear or detachment
Likewise, large, new spider-shaped floaters can be a retinal hemorrhage, so ask your patients to describe what they see
Will patients with active uveitis see their cells and flare? What about asteroid hyalosis? Why not? ___________
Are These Floaters Symptomatic?
Some Treat Asteroid Hyalosis with Laser
When Do You Expect To See Floaters?
When the lighting is bright and there is stationary background, floaters are most visible
For example, you might see your floaters against the blue sky or snow on the SOA ski trip
As we have seen, they also have to be close to the retina to cause a penumbra (shadow)
Holding a pen tip so that it casts a shadow on a paper gives you an idea, as the shadow fades the further away you hold the pen from the paper
4) Retinal Phosphenes
We are all familiar with the bright glow you see when rubbing your closed eyes
This is known to occur due to increase in vitreal pressure on, and deformation of, the retina
This causes the photoreceptors to fire, and for you to perceive light, especially if you are in a dark room
Why dont you feel pain? Hint: where are pain sensors in the eye? How high does your IOP have to be to feel painful?
These are different than other entopic phenomena as they require a nonlight stimulus -- rubbing or quick eye or head movements (flick phosphenes)
Infants with low vision are thought to rub their eyes incessantly in order to trigger phosphenes and stimulate the optic nerve (this helps diagnosis)
Phosphenes and the B&L Proview Eye Pressure Monitor
Adler, figure 16-6
Moores Lightning Streaks
These are entoptic phenomena that occur at the vitreal-retinal interface
They are most often seen in the temporal visual field and are vertically oriented
They were first described in 1935, but are very common in middle-aged patients
It is now thought that they are brought on by posterior vitreous detachment, or PVD
This is a universal condition that some patients never see because it happens in the periphery
Posterior Vitreous Detachment (PVD) vs. RD
Why Do We Get PVD?
Since the vitreous never replenishes, it degenerates over a lifetime in all patients
Think of it like a bowl of jello left out of the refrigerator on a warm day. What happens?
The jello is the vitreous, and the bowl is the retina from which it can become detached
The jello becomes liquified and separates from the bowl the longer it sits out (or the older your patient is)
This liquefaction is called vitreous syneresis
5) Purkinje Tree The Purkinje tree is a good example of how the
visual cortex separates self from non-self Its there, but we dont see it most of the time,
EXCEPT The retinal arteries (arterioles) and veins
(venuoles) show up in stark relief when you sit in the slit lamp for your classmates. Have you seen it?
Why??? The slit lamp isnt brighter than, say, the s