NBEO PART 2 - LOW VISION

What is the definition of legal blindness in terms of visual acuity/VF

Best corrected visual acuity of 20/200 or worse in the better-seeing eye.

Visual field is less than 20 degrees in the better-seeing eye.

What does 1M acuity represent?

20/20 visual acuity and subtends 5 arcminutes.

At what distance is newspaper print typically measured in M-notation?

1M at 40 cm

What is the formula to convert M-Notation to Snellen-Notation?

Test distance / M letter size = 20 ft / Snellen letter size.

What are the typical distances used for measuring distance visual acuity?

4 meters, 2 meters, or 1 meter.

How is the Kestenbaum Equation calculated?

The inverse of the patient's distance acuity is the estimated near add.

Provide an example of the Kestenbaum Equation calculation.

A patient's BCVA is 20/100.

Estimated Near Add = 100/20 = +5.00D.

What formula is used to determine the distance at which a patient needs to hold reading material?

Distance (cm) = 100 / Add Power.

Provide an example calculation for the reading distance.

If a patient requires a near add of +5.00, the distance is 100/5 = 20 cm.

What are the benefits of the ETDRS test?

Lights up for consistent contrast.

Mobile on wheels for any testing distance.

Equal number of letters on each line

What is the Feinbloom Chart, and how is it used?

Smaller and less expensive than the ETDRS.

Common in general practices.

Examiner holds the chart, moves it to any distance, and flips pages for best acuity.

What does the Vistech Contrast Sensitivity Chart utilize?

Uses sine wave gratings.

What is the Pelli-Robson Contrast Sensitivity Chart used for, and how does it measure?

For distance testing at 1 meter.

Uses Sloan Letters of the same size with decreasing contrast sensitivity after each triplet.

What is the Mars Contrast Sensitivity Chart used for, and how does it measure?

For near testing at 40 cm.

Uses Sloan Letters of the same size.

What does the Brightness Acuity Test (BAT) measure?

Measures glare sensitivity in low vision patients.

How is acuity measured in the BAT, and what indicates increased glare sensitivity?

Patient holds the BAT over the eye being measured.

If the patient's BCVA decreases during the test, it indicates increased glare sensitivity.

How is a patient's Just Noticeable Difference (JND) calculated?

Provide an example of calculating JND for a visual acuity of 20/200.

Divide the denominator of their best visual acuity by 100.

JND = 200 / 100 = 2.00D.

What is the purpose of the Tangent Screen?

Measures a magnified view of the patient's central visual field.

Patient fixates on a center target while examiner moves a target from the periphery.

If visual field size is the same at 1 meter and 2 meters, it suggests malingering.

What are the characteristics of the Keplerian Telescope?

Positive ocular and objective lenses.

Power can exceed 4x.

Inverted image.

Exit pupil outside the telescope.

Longer and heavier.

What are the characteristics of the Galilean Telescope?

Negative ocular lens, positive objective lens.

Power up to 4x.

Upright image.

Exit pupil inside the telescope.

Short and light.

How can you remember the lens configuration for Keplerian and Galilean Telescopes?

Keplerian Telescope: Think of the "K" looking like a distorted "+" sign (positive ocular and objective lenses).

Galilean Telescope: The "G" has a horizontal line, resembling a "-" sign (negative ocular lens).

What does "4x25" mean on a telescope marking

4x is the magnification, and 25mm is the objective lens diameter.

How is Exit Pupil Size calculated?

Diameter of the objective lens in mm / magnification

What is a Telemicroscope and why does it need a reading cap?

A telescope used for near viewing.

Requires a reading cap to reduce accommodative demand.

How do you calculate the Dioptric Power of a Reading Cap?

Dioptric Power = 1 / working distance in cm.

What effect does a Reading Cap have on a telescope?

Changes overall power and magnification of the system.

How is Overall Dioptric Power calculated with a Reading Cap?

Overall Dioptric Power = Dioptric Power of Reading Cap * Telescope Magnification.

How do you calculate Overall Magnification of a telescope system with a reading cap?

Overall Magnification = Overall Dioptric Power / 4.

How is Telescope Magnification calculated?

(Power of the Ocular Lens / Power of the Objective Lens) with a negative sign if needed.

How is Distance Magnification calculated?

Current distance BCVA / desired distance BCVA.

How is Near Magnification calculated?

(Current near BCVA / desired near BCVA) * dioptric power of the working distance.

How is Relative Distance Magnification calculated?

Original Distance / New Distance.

How is Relative Size Magnification calculated?

New object size / Original object size.

What are Hand Held Telescopes used for?

Spot viewing distant objects (e.g., scoreboard at a sports game).

What are Center Fit Spectacle Mounted Telescopes used for?

Prolonged distance viewing (e.g., watching a movie).

What are Bioptic Telescopes, and what are they used for?

Mounted to patient's glasses for spot viewing while driving.

Requires thorough training.

What are High Plus Readers, and what do they require due to convergence demand?

Reading glasses with high add power.

Require BI (base in) prism.

How is the BI Prism calculated for High Plus Readers?

BI Prism for each eye = Dioptric Power of the Lens + 2D.

Example: Lens Power OD and OS is +8D, so each eye requires 10Δ BI.

What are Hand Held Magnifiers, and what is a key characteristic regarding near adds?

Do not require a near add.

Patients must learn the proper working distance.

What is a Collimating Magnifier, and what does it create?

Plus lens with an object placed at its focal point.

Creates parallel light, eliminating the need for accommodation (or near add).

How is Magnification calculated for a Collimating Magnifier?

Dioptric Power of the Lens / 4, assuming a distance of 25 cm.

What are Stand Magnifiers, and what is a unique feature?

Require a near add.

Used for stable viewing and continuous reading (e.g., books).

Reduced field of view and use Conventional Magnification.

How is Conventional Magnification calculated?

(Dioptric Power of the Lens / 4) + 1.

What is CCTV in the context of low vision devices, and what are its characteristics?

Electronic magnifier with a camera, monitor, and moveable table.

Maintains contrast sensitivity and provides magnification without peripheral distortion.

Patients without accommodation need an add to use CCTV.

Utilizes relative size magnification.