Midterm 2: Ophthalmoscopy

Question 1

During Direct O, if the patient is myopic, what kind of lens would the doctor need to use if the doctor is emmetropic to view the retina?

Answer 1

Minus. Since eye has stronger plus, rays will be converging before doctor’s eye

Question 2

During Direct O, if the patient is hyperopic, what kind of lens would the doctor need to use if the doctor is emmetropic to view the retina?

Answer 2

Plus. Rays will be diverging before reaching doctors eye.

Question 3

When do you need to vertex adjust when using Direct ophthalmoscopy?

Answer 3

Vertex adjust when you get further away from patient.

Question 4

During direct, if both patient and doctor are myopic, how much minus does the lens have to be to work?

Answer 4

equivalent to their refractive errors. Then vertex depending on where doctor is positioned.

Question 5

The further away the doctor gets during Direct, would the doctor need to add more or less minus if the patient is myopic and the doctor is emmetropic?

Answer 5

More minus.

Question 6

If the patient is hyperopic during Direct, would the emmetropic doctor need more or less plus as they move further away?

Answer 6

More plus

Question 7

What must the lens power in the direct ophthalmoscope be equal to?

Answer 7

Equal to the sum of the doctor and patient’s prescription. But then may slightly change due to vertex distance.

Question 8

Why do you find equivalent power when adding lenses to direct ophthalmoscope?

Answer 8

You find equivalent power because using two lenses changes the magnification. Find equivalent power by…..

Fe= F1 + F2 - d(F1)(F2)

F1= power of eye
F2= lens added
d= distance separating them

Question 9

The average angular mag for both emmetropic patient and doctor during DO

Answer 9

15x at 25 cm

Question 10

If the patient is myopic in DO, do you have more or less magnification?

Answer 10

More magnification

Question 11

If the patient is hyperopic in DO, do you have more or less magnification?

Answer 11

less magnification

Question 12

Describe differences in Direct ophthalmoscope magnification between axial myope and refractive myope.

Answer 12

Refractive myopes will have more magnification since the power of the eye is actually changing. Axial myope mag still changes, just not as much.

Question 13

Describe differences in Direct ophthalmoscope magnification between axial hyperope and refractive hyperope.

Answer 13

Refractive hyperopes will have less magnification since the power of the eye is actually changing. Axial hyperope mag still changes, just not as much.

Question 14

How large is normal FOV for Direct?

Answer 14

3mm or 1.5 disc diameters

Question 15

The rays that make it to your retina during Direct have to go through what? What do you call this?

Answer 15

Rays have to go through the exit pupil of the patient and through the entrance pupil of the doctor’s eye to make it to the image plane.

CascadeOptical system

Question 16

What limits field of view in DO?

Answer 16

Pupils not being able to be on the same plane.

In other words….

Because exit pupil of patient and entrance pupil of doctor are not lined up

Question 17

How to find angular mag in DO?

Answer 17

Angular mag = power of eye / 4 (being at standard distance, 25 cm)

Question 18

Is IO or DO more commonly used?

Answer 18

Indirect

Question 19

Describe what “the cartoon” shows for indirect ophthalmoscope features

Answer 19

• image inverted
• pupil dilated
• light shined into the eye
• doctor eye aligned with patient pupil plane

Question 20

Advantages of Indirect

Answer 20

Much larger FOV than Direct (8 disc diameters)

Doctor able to use steropsis

Question 21

Describe image of indirect

Answer 21

upside down, inverted

Question 22

Where do we perceive the image to be when doing Indirect? Where is it actually?

Answer 22

We perceive it to be inside the condensing lens. It is actually floating in space between you and condensing lens.

Question 23

For indirect ophthalmoscope, the closer the doctor is to the image, the more the doctor will have to _________.

Answer 23

Accommodate.

Question 24

When could you use a monocular indirect opthalmoscope? What advantage does the monocular have?

Answer 24

When patient pupils are smaller.

Instead of it being inverted, it re-inverts and is upright while maintaining the same FOV and magnification.

Question 25

Where does the light of Indirect focus?

Answer 25

Focuses on patients pupil plane.

Question 26

How do you find lateral mag of indirect?

Answer 26

Lateral Mag= (-) Patients eye power/ condensing lens power

or

image height/ object height

or

image distance / obeject distance

Question 27

What has a higher magnification in indirect, 20D or 30D condensing lens?

Answer 27

20D because later mag is -60/ 20 = -3x compared to -60/ 30 = -2x

Question 28

What does axial magnification measure in Indirect? How do you find it?

Answer 28

Depth of image. Perceived depth is exagerrated.

Axial mag = (lateral mag)^2

Question 29

Why do we not perceive axial magnification as much as we should in indirect?

Answer 29

Are pupil distance is made smaller using the headset for indirect.

Smaller PD results in less stereo acuity so we cant perceive as much depth.

Question 30

How to find total angular mag for indirect

Answer 30

Angular mag = Lateral mag x RDM

-assume 25 cm (reference distance) and 40 cm (from doc to image) for RDM

Question 31

If you have 8 times more less magnification, how much more area can you see?

Answer 31

64x more

Question 32

What limits FOV for indirect?

Answer 32

Amount of rays that are caught in the condensing lens

Question 33

Where is condensing lens held for indirect?

Answer 33

About 1 focal distance away from exit pupil of patient