optics combined1
Rank purkinje images in terms of brightness
1 > 2 > 3 > 4
How do purkinje images move with accommodation?
3 moves forward, 4 moves backwards
Estimated amp based on age
18.5 - 0.3(age) 14D at 10yo 11D at 20yo <2D at 50yo
M notation
A 1 M optotype subtends 5 arcminutes at 1 meter and is equivalent to 20/20 at 1 meter. 1 M = 1.45 mm in height. Most newspaper is 1 M at 40 cm, which is equivalent to 20/50. Just set it up like distance/optotype so like .40 m/1 M
Telescope labeling
A X B, where A s the mag and B is the objective lens diameter
What is a slit lamp system referred to as? Components?
A compound microscope Keplerian telescope = eyepiece Inverting prism (makes img upright) Galilean telescope = to magnify img Objective lens Illuminating system Binocular viewing system
Reading cap
Acts as a hand held magnifier, power of reading cap is so that the object is at its primary focal point, thus parallel light is leaving the reading cap into the objective lens. Referred to as a telemicroscope
STYCAR
Acuities for children Child holds a key card, uses it to point to whichever letter is being presented Similar to HOTV
Cortical blindness
Acute, bilateral blindness due to damage to visual cortex rather than damage to eyes themselves. Common causes are stroke, trauma, surgery, lesions and congenital issues
Manifest hyperopia
Amount present at the subjective
Latent hyperopia
Amount uncovered by cycloplegia
Moore's lightning streaks
An entopic phenomenon - vertical flashes in light seen in peripheral visual field; may indicate a potential problem in periph retina
Formula for lensometry
x = Ft / Fs^2 x = distance target moved Fs = standard lens Ft = test lens
HHM and field of view
Angular mag does not increase but linear field of view increases as the lens is brought closer to the eye.
Source, properties and brightness of purkinje image 1
Anterior cornea Virtual, upright, small Very bright
Source, properties and brightness of purkinje image 3
Anterior lens Virtual, upright, LARGE Dim
Best corrected VA in low vision
Assess central and eccentric viewing at distance and near. Use Feinbloom, ETDRS (lighthouse) and the Bailey-Lovie. These are more helpful because they can be used at closer distances
Keplarian mag
Available in higher mags than galilean.
General blur
Can be caused by corneal scarring or cataracts. At distance and near, poor contrast and may have mobility issues. May require mag, lighting, glare control and contrast enhancement.
Reading cap advantages
Can have longer working distances than hand held or stand magnifiers and also good for hands free work
Prism for VF enhancement
Can relocate missing visual field into pts line of sight or can be used for visual field expansion. Can be bino, mono, cover the entire lens or just a portion. [[Base is always towards the defect.]] 1 degree = 2 pd
Limitations of mohindra ret
Can't identify those with >3.00D hyperopia or >1.00D astig
What do +78/+90 lenses create?
Real, inverted image It becomes the object for the objective of the slit lamp to view
Types of acuity
Resolution acuity - cutoff usually around 40-60cpd Recognition acuity - snellen Minimum detectable acuity - thinnest possible wire visible? Pretty high (1 arcsec) Hyperacuity - seeing if two lines are parallel, etc. A measure of higher cortical processing
What is the criteria/defn of a correcting lens?
Secondary focal point coincides with far point of the eye
Maxwell's spot
Shine a purple light on retina --> pt will report seeing red spot Blue is absorbed by macular pigment
Galilean tube length
Shorter, thus lighter, thus better for LV.
FOV and telescopes
Dependent on diameter of exit pupil and diameter of entrance pupil of eye. So, increase entrance pupil, (objective lens diameter,) increases the exit pupil and thus the FOV. FOV will increase until the exit pupil becomes larger than the pupil. FOV can also be increased by aligning the exit pupil of the scope with the entrance pupil of the eye
Telescope mag
Depends on angular mag, retinal image size with telescope compared to retinal image size without telescope. M = -Foc/Fob or M = dent/dex (diameter of entrance pupil and exit pupil.)
Relative distance mag
Due to change in object distance. Mag increases as object comes closer. Pts with low vision bring things closer to increase RDM. M=O/N
Relative size mag
Due to change in object size, mag increases as size increases. Large print books
Nott retinoscopy
Dynamic ret - move the ret backwards until see neutral
High plus readers evaluation
Easy to use and cosmetically acceptable. Over +4.00 requires the BI prism, power + 2. Stronger lenses require a closer working distance and thus less FOV
Stand mag evaluation
Easy to use, available in stronger powers and built in illumination, FOV may be reduced, pts have to wear an add. Good for continuous reading
Hand held evaluation
Easy to use, portable, available with built in illumination, no add required, have to get the holding distance down, bad for people with tremors or dexterity issues. Good for spot reading, like menus.
Entrance and exit pupils in telescopes
Entrance pupil is usually the objective lens and exit pupil is the image of the objective lens created by the ocular lens
Reverse telescopes
Expand the FOV for pts with constricted VF (RP, advanced GLC.) Just turn the scope around. Minify the image to get larger FOV. Pts need to have good VA. Most often hand held and used for spotting
How to convert from keratometer r finding to power?
F = 337.5/r
Center fit spec mounted scope
Fit on line of axis, allows for continuous viewing, ideal for sports and TV. Minimal training, so good for MR patients or handicapped, cognitive issues. Pts should not walk around while wearing these
Allen vision test
For children >2yo Show child images at near, then occlude one eye, determine longest distance child can resolve images Reported as x/30 (x = dist in feet)
Determining mag for low vision
For distance use current BCVA/goal BCVA. For near, do the same thing but multiply by their working distance. Goal is usually 1 M at 40 cm which is equal to 20/50
Setup of lensometer
Standard lens Test lens at the standard lens's focal length Target is at the standard lens's primary focal length Move the target back and forth until the rays coming out of the test lens are parallel
Telescopes general
Telescopes are used to magnify distance objects. Incoming rays are assumed to be plano. Primary focal point of the ocular lens coincides with the secondary focal point of the objective lens, thus plano waves leave the ocular lens
Facultative hyperopia
The amount of hyperopia found after fogging the pt
Absolute hyperopia
The amount of hyperopia not covered by accommodation
Far point defn
The point conjugate to the axial retinal point
What does the red dots on JCC represent?
The positive power, or the axis for the negative power
Models of the eye
Gullstrand's - has 6 refracting surfaces, 4 chambers with different ns Reduced - single refracting surface with n = 1.33, anterior/primary focal point 16.67, posterior/secondary 22.22 (retina), eye power 60
Acceptable VF tests for legal blindness
Humphrey or goldmann and vision dics (maybe)
How to predict if a hyperopic child will remain hyperopic?
Hyperopic at 14yo if hy >1.5D at 5yrs Emmetropic if between 0.5-1.25 Myopic if <0.5D
Eccentric viewing
This is a good thing, using a retinal point other than the fovea to view an object. This point is known as the preferred retinal locus
Stand magnifiers
Lateral mag and RDM come together to create angular mag. Mt = mM, where Mt is total angular mag, m is lateral mag and M is relative distance mag. Object is INSIDE THE FOCAL POINT SO THERE IS DIVERGING LIGHT LEAVING SYSTEM AND THUS AN ADD IS REQUIRED.
Mohindra ret
Near/dynamic ret to determine DISTANCE Rx Done in the dark, monocularly
Limitation to duochrome check
Need BCVA 20/30 or better
Visual field enhancement
Needed for either hemianopsia or visual neglect due to stroke *or* for VF constrictions
Classifying vision
Normal = 12 - 25 Near normal = 30 - 60 Moderate low = 70 - 160 Severe low = 200 - 400 Legal blindness = Worse than 20/100 in better eye or VF diameter is 20 degrees or less in better seeing eye Profound low = 500 - 1000 Near blindness = Worse than 1000 Blind = NLP
Rank purkinje images in terms of size
Normal: 3 > 1 > 2 > 4 Accommodating: 1 > 2 > 3 > 4
Mirrors for VF enhancement
Primarily for pts with temporal visual field loss, mirror is placed on nasal side so temporal field is reflected into the mirror. Can cause confusion because everything is reversed. Actually decreases FOV by creating a scotoma, because mirror is in the way of their working field. Can also get nausea and comsesis problems, thus they have a low rate of success
What if lens n doesn't match the lens clock n?
Proper F = FLC (nL-1) / (nLC - 1) FLC = power from lens clock nL = n of lens nLC = n of lens clock
Peripheral vision loss
RP or advanced GLC. Hemianopsias or visual neglect. Have problems with mobility, poor night vision and glare. Pts may require visual field awareness, relocation and expansion, orientation and mobility training and tints to minimize glare.
What is a radiuscope for? How does it work?
Radius of curvature for RGP Clear image is seen at two points - at surface of lens + at center of curvature Difference between these distances = radius
Telemicroscope
Will have divergent light leaving lens. To combat this, either adjust the tube length or add a reading cap to the objective side of scope.
Location of purkinje images
2, 1, 4 are anterior to lens 3 is posterior to lens
Trial frame refraction
Better for low vision. Has the ability to show JND, Dr. can watch patient's eyes (eccentric viewing, nystagmus, strab,) pts can easily turn their head to use eccentric viewing and results are more accurate and realistic.
Tools necessary to elicit Hadinger's brush
Blue object Rotating polaroid
Keplarian
Bot objective lens and ocular lens are plus. Makes the scope longer and weight more. Final image is magnified and inverted, so LV keplarian scopes have a third inverting lens.
Lateral mag
Compares the object size and image size formed by optical system
Principles that Keratometry is based on, formula
Cornea acts as a convex mirror Project a mire onto the cornea (h) Measure the height of the reflection (h') r = -2(h'/h) b b = distance from mire to pt's cornea
Angular mag
Increase of retinal image size due to introduction of optical system. Hand held mags, stand mags and telescopes. Compares the old retinal image size and new retinal image size
Cause of night myopia
Increased spherical aberration Light levels are too small to fully relax accomm when viewing distance objects
Type of image formed in BIO
Intermediate, inverted, real
How to find the far point of an eye?
Inverse of the eye's Rx
Galilean exit pupil
Is inside the lens, resulting in a smaller field of view. But the exit pupil is larger, thus you get a brighter image and alignment is less critical.
Tube length
Is obviously the sum of the focal distances of the two lenses. d = fob + foc
JND
Just noticeable difference. Denominator divided by 100. So cut that in half to decide what lenses to use. For 20/400, JND = 4, so use +/- 2.00 D lenses, because there is 4.00 D of difference between these. As their acuity increases, recalculate the JND
Kestenbaum's rule
Just take inverse of best corrected acuity to determine add power. So 20/200 would be a +10.00 add. Not very accurate because distance vision is a poor indicator for near visual function
Bioptic fit spec mounted scope
Mounted on the upper portion and used for spotting, for classroom work, driving. Requires significant training, not good for pts with poor dexterity or cognitive issues. Can add a reading cap to either of these
With higher powered fundus lenses, what happens tot he mag/field?
Lower mag Increased FOV
Total mag of stand magnifier, add combo
M = Fe/4, where Fe is the equivalent power of the stand mag and add.
Central vision loss
Macular disease, central scotoma, difficulty with near tasks and recognizing faces. Require mag, proper lighting, glare control, enhancement of contrast and eccentric viewing training.
Max mag with a stand magnifier
Max mag is achieved when the eye is as close to the lens as possible, going to need a larger add here. Mmax = F/4 + 1. Assumes standard working distance of 25 cm.
Lighthouse method
Measure the near acuity in M units at 40 cm, then multiply by 2.50 D, for the 40 cm working distance. Both methods are starting points, pts may need more add because of contrast issues
Hand neutralization - what motion to expect with a minus/plus lens
Minus - would see with (add plus to neutralize) Plus - would see against (add minus to neutralize)
Hand held mag general
Object is at primary focal point, thus light leaves the lens parallel, making this a COLLIMATING magnifier. Since plano waves are entering eye, accommodation is not necessary and an add is not necessary.
Galilean scope
Objective is plus and ocular is minus. Plus objective forms a real image that becomes a virtual object for the ocular lens. Final image is upright and magnified.
HHM and object distance
Once the object is at the primary focal point, you can move the object and lens anywhere and still get the same mag. As the lens to eye distance changes, the spec mag changes but is compensated for by the relative distance mag.
Galilean mag
Only available up to 4X due to limitations of tube length. Increasing power of ocular lens increases mag but decreases tube length, so there is a point where the lenses will be touching
Keplarian exit pupil
Outside the scope, allowing for a larger field of view because the exit pupil can be more easily aligned with the entrance pupil of the eye. But the exit pupil is small so the image appears dim, proper alignment is critical.
For very high powered readers
Over +4.00, use some BI to reduce the convergence demand. BI per eye is 2 + D (sphere power of lens)
Defn of near point
Point conjugate to the retina when eye is maximally accommodated
Source, properties and brightness of purkinje image 2
Posterior cornea Virtual upright, very small Bright
Source, properties and brightness of purkinje image 4
Posterior lens Real, inverted, smallest Very dim
JND
The just noticeable difference that a pt can discriminate Uncorrected VA denominator / 200
HHM and effective mag
The mag of the magnifier depends on the original object to eye distance. Standard working distance is 25 cm, so this is usually used in the equation to get the magnifiers effective mag. m = F/4
Left or right scotomas
To the left means they can find the start of text, like the next line, means they lose their spot. Scotoma to the right means they can't find the next word, so they are slow readers
Low vision case history
Visual goals, ocular disease history, co morbidities (dexterity issues.)
Rule of 30
When doing fan chart Pt reports the clearest line in clock hours - multiple the lower number by 30 to get the correcting axis If pt reports two oclock to 8 oclock are the clearest - 2x30 = axis 60
Far point sphere defn
When the eye rotates --> far point traces out to a sphere Center of curvature of the sphere is the center of rotation of the eye
How does stenopaic slit work
Wherever the slit is clearest --> this is their axis If the slit is oriented 180, you're correcting the 180 deg meridian Add SPHERES to the refraction
n of keratometer
n = 1.3375