Low Vision Exam - Part 2

What does lensometry measure?

Back vertex power

How do you do "speed" retinoscopy?

Only 3 things to see:
1. With
2. Against
3. Not with or against

Only 3 things to do:
1. Add plus
2. Add minus
3. Quit

- Add by 4.00D increments until reversal
- Cut diopters by half each reversal with "definitely with" and "definitely against"

What is a good test to run if not red reflex is observed during retinoscopy?

Keratometry! Pt may have significant corneal astigmatism (albinism, KCN, aniridia, post keratoplasty)

What is the preferred method of subjective refraction in LV?

Trial frame refraction

What are the advantages of trial frame refractions? (5)

1. Allows patient to utilize EV
2. Nystagmus/null point can be used
3. More natural viewing position
4. Allows for easier comparison of larger power differences
5. Allows for use of auxiliary lenses (telescopic, microscopic)

_________ trial lenses are recommended for TF refractions

Large diameter

List the TF refraction steps (4)

1. Prep TF and determine JND using BCVA
2. Test sphere
3. Test cyl axis and power using hand-held JCC
4. Re-test sphere

What are the 2 options for initial set up of TF in LV refractions?

1. Clean patient's Rx and attach Halberg or Janelli clips
2. Put starting Rx in TF using patient's habitual Rx, retinoscopy, or lensometry

How do you adjust the TF on the patients face before starting your refraction?

TFs should be adjusted and snug with a small amount of pantoscopic tilt to decrease vertex distance and reduce glare

See diagram on slide 230

What is the JND?

Dioptric value needed to elicit an appreciable change in acuity or blur

What are the 2 ways to classify the JND?

1. The total dioptric value the patient needs to appreciate a difference
2. The power of the lenses to be bracketed (+ and - value)

How do you calculate JND using the 20 ft acuity?

The denominator is the full JND. Divide by 2 to determine +/- lens powers to bracket

Ex) 20/60 = JND of 0.60 or +/- 0.30 (round up to +/-0.50

How do you calculate JND using the 10 ft acuity?

The denominator/100 gives you the bracketing values

Ex) 10/30 = JND of +/-0.30D
10/100 = JND of +/- 1.00

How do you find the best sphere power if the patient's BCVA in the better seeing eye has a JND value = 2.00 (3 steps)

1. Ask the patient to compare +1.00sph to -1.00sph over the trial frame. If patient states that +1.00sph is clearer, place +2.00sph in the TF (FULL JND VALUE)
2. Again, ask the patient to compare +1.00sph to -1.00sph, this time through the +2.00sph in the TF. If the patient still prefers the plus lens to the minus, replace the +2.00 in the TF with a +4.00sph (FULL JND VALUE)
3. Again, ask the patient to compare +1.00sph to -1.00sph this time through +4.00sph in the TF. If they now prefer -1.00 to the +1.00, this is called a REVERSAL and you now know the "best sphere" is more than +2.00 and less than +4.00. You can enter a +3.00 in the TF and continue refining the best sphere by letting the patient compare the JND lenses in front of the +3.00 sphere in the TF

Why is it important to continue to check VA as you go when doing a TF refraction?

If the acuity improves, the JND will change too!

How do you find the cyl power using a TF refraction?

Use a hand-held JCC, works the same as in the phoropter! Chase the red

Handle = axis
Slash marks = power

How do you find the amount of cyl/axis using a stenopaeic slit?

Slit is put into the TF and patient rotates slit until preference is reached. Slit is now aligned with the MINUS cylinder axis. Now 2 principal meridians are refracted separately with slit in place. After best VA is achieved, +0.50D is added

Why is binocular balance not commonly performed in LV refractions?

The Rx between eyes is often not equal

List the disadvantages of telescopic refraction (2)

1. Reduced field of view of telescopes
2. Reduced illumination through telescopes

Review slide 241

How do you perform a telescopic refraction?

1. Insert a full diameter 2.2-2.5x telescopic trial lens in front of the distance Rx
2. Occlude the opposite eye
3. Place a reading cap or trial lens above the telescope (+0.75Dsph if the chart distance is 20 ft or +1.25sph if the chart distance is 10ft)
4. Introduce trial lenses behind the telescope and ask for the patient's subjective response

What is equivalent power (Feq)?

The power of an optical system in diopters

In LV, we calculate a prediction of the Feq a patient might need to resolve ________

1M print

Hand and stand magnifiers, high plus readers, electronic magnification systems are interchangeable when the ____________ of each device is the same

Equivalent power

What is Kestenbaum's Rule?

Using best corrected DVA, divide the denominator by the numerator to get dioptric power to read 1M print (20/50)

Review example on slide 248

What is acuity reserve?

How much "more" the patient needs to read fluently and comfortably

How do you calculate Feq?

Feq = letter size in M/test distance in m

What things should you take into consideration when fine tuning the add on LV patients?

1. Patient's functional goals
2. Motivation
3. Reading ability
4. Acuity and acuity reserve
5. Contrast
6. VF, scotomas
7. Sensory and motor fusion and coordination

What are the goals of LV management? (4)

1. Functionality (make the most of remaining vision)
2. Independence (initiate self-determination and adaptive skills)
3. Support (community and social resources)
4. Education (goals/expectations; family/support system)

List the different types of near magnification devices (6)

1. Spectacles/microscopes (high adds)
2. Clip-on loupes
3. Handheld magnifiers
4. Stand magnifiers
5. Telemicroscopes
6. Video/electronic magnifiers

What is another name for high plus spectacles?

Microscopes

Spectacles/microscopes can range from +______D to +________D

+5.00D to +64D

_________ provide the WIDEST FOV of LV optical devices

Microscopes

What are the advantages of microscopes/high plus spectacles? (4)

1. Hands-free
2. Wide FOV
3. Small, portable
4. Can maintain binocularity <+10

What are the disadvantages of microscopes/high plus spectacles? (4)

1. Requires close working distance so training/reinforcement often needed
2. May be difficult to use task-lighting due to reduced working distance
3. Not ideal for reading heavy books/novels
4. Must add BI prism for adds >+4 due to convergence demand (if pt is binocular)

How much BI prism is added per eye to maintain binocularity with microscopes?

Add power + 2pd BI per eye

List the advantages of clip-on loupes (4)

1. Allow correction of higher distance refractive error and astigmatism
2. Hands free
3. Small, portable
4. Good for task-specific goals (reading music, computer)

List the disadvantages of clip-on loupes (4)

1. Can be heavy on frames
2. Require dexterity to clip on
3. FOV can seem smaller, binocularity limited
4. Training/reinforcement often needed (attaching unit to frames, focal distance, adaptation to clip bar in FOV)

Clip on loupes come in powers ranging from ___x to ____x and can come in a fitting set

1.7x - 3x

What is a hand-held magnifier and what is it typically used for (give examples)?

Simply a plus lens with a handle typically used for brief spotting tasks

Ex) reading price tags, labels, menus, telephone numbers

HHM come in powers ranging from ___x to ___x

2x to 14x

Why is there a functional limit in higher powered HHM?

Because usable field is so small

List the advantages of HHM (4)

1. Familiar for many patients
2. Can use with or without add
3. Small, portable
4. LED options

List the disadvantages of HHM (4)

1. Requires manual dexterity and hand control
2. Not hands free
3. Smaller FOV than spectacles
4. Training/reinforcement often needed (use with bifocals? Depends on where it is held)

True or false: when HHM is held at the anterior focal length of the magnifier, patient should use distance portion of Rx

False; can use either distance OR bifocal/add

True or false: if a HHM is held farther from the anterior focal length, patients should use distance portion of Rx

True

What type of image does a stand magnifier create?

Virtual, erect, and divergent image

The location of the image from a stand magnifier determines how much ____________ is required to resolve it

Accommodation or add

The powers of stand magnifiers range from ___x to ___x

2x to 12.5x

List the advantages of stand magnifiers (4)

1. Stable hand position (SM always maintains contact with page, good for pts with tremors)
2. Helpful for longer periods of reading (fixed locus)
3. Very easy to use (if patient understands fixed focus)
4. LED options

List the disadvantages of stand magnifiers (4)

1. Requires accommodation or near add (see below)
2. How hands free, not as portable - pt must be made aware of fixed focus
3. Writing difficult
4. Smaller FOV than spectacles (can increase FOV using a reading stand)

In order for a pt to see with a stand magnifier, what 3 corrected options must the pt use?

1. Add or bifocal
2. Uncorrected myopia
3. Own accommodation

What is a telemicroscope?

Multi-unit magnification system with a telescopic correction and reading cap

In a telemicroscope, the WD is equal to the focal length of the ___________

Reading cap

List the advantages of telemicroscopes (3)

1. Longer working distance (focal length of reading cap)
2. Hands-free
3. Excellent optics

List the disadvantages of telemicroscopes (3)

1. Requires steady reading material
2. Can be heavy and expensive
3. Might require assembly

How do you calculate the Feq of a telemicroscope?

Feq in D = Power of telescope (in x) x Reading cap power (in D)

List the advantages of electronic magnification (3)

1. Longer working distance
2. Excellent contrast (option for reverse polarity)
3. Excellent optics and high magnification options

List the disadvantages of electronic magnification (3)

1. Requires steady reading material
2. Not hands-free (non-desktop EM)
3. Can be expensive

How do you calculate electronic magnification?

Feq = Screen magnification (in x) x Accommodation (or add) (in D)

List the different types of distance magnification LV devices (3)

1. Hand held telescopes
2. Spectacle mounted telescopes (focusable, fixed-focus)
3. Electronic distance units

What are the main uses of telescopes and what are they NEVER used for?

Mainly for distance spotting (street signs, bus numbers, TV, facial detail recognition), but can be used for continuous tasks

NEVER used for mobility (very dangerous)

Telescopes range in power from ___x to ___x

1.7x to 14x

List the advantages of hand held telescopes (4)

1. Wide range of focus
2. Fairly inexpensive, durable
3. Portable, useful for spotting
4. Clip-on option available for longer viewing periods

List the disadvantages of hand held telescopes (4)

1. Limited FOV
2. Need for external illumination
3. Requires good manual dexterity to focus
4. Not for mobility

How do you predict the distance magnification needed (calculation)?

Divide the denominator of DVA by the denominator of goal DVA

Ex) can see 20/200 but wants to see 20/40; 200/40 = 5x

List the advantages of spectacle-mounted telescopes (4)

1. Both hands-free
2. Can be used for longer viewing periods (TV, sporting, theater events)
3. Binocular or monocular
4. Wide range of magnification

List the disadvantages of spectacle-mounted telescopes (4)

1. Limited FOV
2. Appearance, can be heavy
3. Requires good manual dexterity to focus if unit is focusable
4. Not for mobility, but some states allow bioptic driving

What are reverse telescopes and what are they used for?

Telescopes that are turned around backwards with the objective lens close to the observer's eye. The image is smaller but the FOV is increased.

Helpful as an orientation tool if VFs are constricted (more about this when we talk about managing visual field constriction)