OMI 10

Question 1

what does confocal principle mean?

Answer 1

when a single point of specimen can be illuminated by a point light source while simultaneously imaged by a camera in the same plane.

so an image with a high resolution and magnification forms but no field of view due to a single point of illumination and detection.

Question 2

what can you do to expand the field of view with high resolution and magnification, when illuminating a point of specimen confocally?

Answer 2

instrument needs to instantaneously illuminate and image a region of specimen (tissue) by scanning the tissue with 1000s of tiny spots of light which are then reconstructed to create a usable field of view with high resolution and magnification

Question 3

give an example of an optical equipment that uses the confocal principle to image a specimen?

Answer 3

a slit lamp- you view a small area but by scanning across the eye you can view it in great detail.

Question 4

what is tomography?

Answer 4

imaging by sections or sectioning through the use of any kind of penetrating wave

Question 5

How does a confocal detection unit work?

Answer 5

• The reflected radiation is focussed in a plane optically conjugate with the illuminated plane.
• Scattered (stray) radiation and reflections from planes that are not in focus are blocked by a diaphragm at the conjugate plane. This ensures that only radiation originating from the illuminated focal plane is detected.
• The reflected radiation at each point in the scan that is detected confocally is displayed as a single pixel on a monitor.

Question 6

what is the typical scan depth in confocal laser scanning tomography?

Answer 6

0.5 to 4mm in 0.5mm steps

Question 7

what is shown by the z profile in confocal laser scanning tomography?

Answer 7

the z profile shows that each pixel series has a varying brightness.

Question 8

how is the height of each pixel of an image in confocal laser scanning tomography determined?

Answer 8

determined by the position of the profile maximum which gives the height of each profile.

Question 9

what is the field size of the Heidelberg retinal tomograph (HRT) ?

Answer 9

field size= 15º x 15º

Question 10

how many pixels does each image have in Heidelberg retinal tomography (HRT)

Answer 10

384 x 384 = 147,456 pixels

Question 11

what is the wavelength and type of laser used by HRT?

Answer 11

He-Ne laser

670nm

Question 12

what is the X-Y resolution and the Z-plane resolution of the HRT?

Answer 12

X-Y resolution = 7-10 micrometres

Z-plane resolution= 25-50micrometres

Question 13

how many 2D images are scanned per 1.5 seconds retinal tomography

Answer 13

32 2D images are scanned in sequence (1.5seconds)

Question 14

how can excessive eye movements be analysed in retinal tomography?

Answer 14

the 32 2D images can be viewed as a movie.

Question 15

how can a 3D image be made in retinal tomography?

Answer 15

the 32 retinal images are combined to make a single 3D topographic image which can be analysed.

Question 16

What does moor fields regression analysis compare?

Answer 16

compares the rim area of the imaged optic nerve head to a normal database

Question 17

how many disc sectors are determined by moor fields regression analysis?

Answer 17

6

Question 18

in moor fields regression analysis, what is linear regression analysis carried out on?

Answer 18

Linear regression analysis carried out on the relationship between normal disc parameters and optic disc area to develop 99% normal prediction intervals

Question 19

in moor fields regression analysis, what has the greatest predictive ability?

Answer 19

log neuroretinal rim area had the greatest predictive ability

Question 20

what is only available on HRT II?

Answer 20

Moorfields regression analysis

Question 21

what is developed from 51 glaucomatous and 80 normal eyes?

Answer 21

moorfields regression analysis.

Question 22

what are the layers of the cornea?

Answer 22

(a) superficial epithelium
(b) Basal membrane
(c) Bowman’s layer
(d) anterior stroma
(e) posterior stroma
(f) Endothelium

Question 23

how can you assess the anterior segment or eye?

Answer 23

OCT

Question 24

only the _____ few mm of cornea can be considered ______.

the human cornea is a complex shape resembling an ______.

Answer 24

central
spherical
ellipse

Question 25

how can the shape of the cornea be quantified? what is the procedure called.

Answer 25

by shinning a placid disc onto the cornea and assessing the shape of the reflected image this procedure is called keratoscopy

Question 26

name a corneal topographer

Answer 26

medmont corneal topographer

Question 27

how is corneal topography changing over time?

Answer 27

as we age, the radius of curvature of cornea decreases. it is at peak at the age of 30 years.

Question 28

what is the difference between topography image and reflectance image?

Answer 28

topography image shows height differences of retina and not in much detail reflectance image is in detail and clearer than topography image.

Question 29

what is the double hump curve?

Answer 29

can be seen in retinal tomography , produced because retina is thicker in some places than others

Question 30

in retinal tomography, what structure is a circle drawn around ?

Answer 30

optic nerve head

Question 31

what does a topographic image show?

Answer 31

surface structure and curvature across the surface of the cornea

Question 32

why is the cornea cone shaped in keratoconus?

Answer 32

cornea becomes thinner and the pressure of aqueous humour turns it into a cone shape.

Question 33

what kind of astigmatism does keratoconus patient have? | how is it corrected?

Answer 33

irregular ( so meridians aren't 90º apart) | corrected using special contact lenses

Question 34

which technique can quantify and localise the irregular elliptical rings of the cornea in keratoconus

Answer 34

topography