Telescope Low Vision P3

Increasing angular subtense

Unlike spectacle magnifiers, telescopes primarily work by:

Ability to magnify distant objects

The key advantage of telescopes over spectacle magnifiers is:

Restricted field of view

Which of the following is a major disadvantage of telescopes?

Incoming and outgoing rays are parallel

Telescopes are considered afocal because:

Convex objective and concave eyepiece

A Galilean telescope is composed of:

Galilean

Which telescope natively produces an erect image?

The image is inverted

The Keplerian telescope typically requires prisms because:

Better image quality

Compared to Galilean telescopes, Keplerian telescopes generally have:

Galilean

Which telescope is shorter and lighter?

External to the telescope

The exit pupil of a Keplerian telescope is:

The eyepiece must be stronger than objective

For magnification to occur in a telescope:

3×

A Galilean telescope is clinically limited to about:

Darker image

High magnification in Keplerian telescopes often results in:

Highly divergent

When a distance telescope is used for near without modification, the exiting light is:

Accommodate excessively

Using a distance telescope at near requires the eye to:

Longer working distance

The primary reason telemicroscopes are prescribed is:

Longer working distance

Compared with a spectacle magnifier of equal power, a telemicroscope provides:

Refocus the tube

If a telescope has adjustable focus, the preferred method for near viewing is to:

Bright circle leaving eyepiece

Exit pupil refers to:

As close as possible to eyepiece

To maximize field of view, the patient’s eye should be:

Angular subtense

Name of method by which telescopes magnify without reducing working distance.

Afocal system

Optical system where incoming and outgoing rays are parallel.

Galilean telescope

Telescope using a convex objective and concave eyepiece producing an erect image.

Keplerian telescope

Telescope using two convex lenses that produces an inverted image.

Porro/roof prisms

Components used in Keplerian telescopes to erect the image.

Exit pupil

Bright circle of light leaving the eyepiece and entering the eye.

Dynamic magnification

Apparent increase in speed of moving objects through a telescope.

Telemicroscope

Telescope modified for near viewing to provide longer working distance.

Reading cap

Plus lens placed over the objective to allow near viewing.

Tube length adjustment

The name of the method of compensating refractive error by physically changing telescope length.

Vignetting

Crescent-shaped shadow caused by exit pupil misalignment.

Working distance

Distance between the device and the object being viewed.

20 cm

A low-vision patient is prescribed a Keplerian telescope for distance spotting. The optical design uses an objective lens with a focal length of +15 cm and an eyepiece with a focal length of +5 cm. What is the physical tube length of this telescope?

10 cm

A compact Galilean telescope is being designed for a patient who prefers lightweight devices. The objective lens has a focal length of +15 cm, and the eyepiece has a focal length of −5 cm. Determine the required tube length of this telescope.

2× inverted

A patient is fitted with a Keplerian telescope for distance viewing. The objective lens power is +20.00 D, and the eyepiece power is +40.00 D. Calculate the angular magnification and state the image orientation.

2× upright

Another patient is prescribed a Galilean telescope with an objective power of +20.00 D and an eyepiece power of −40.00 D. Determine the magnification and image orientation.

4 mm

A clinician is evaluating whether a telescope will provide adequate brightness. The device is labeled 4×16. What is the diameter of the exit pupil?

Not physiologically possible — requires optical modification (54D)

A patient attempts to use a 6× distance telescope to view reading material positioned at 66 cm. Calculate the accommodative demand required and determine if this is physiologically possible.