COA/A-scan Biometry, Basic,

The audible signal on a A-scan instrument may be able to: A. indicate contact with the cornea B. indicate axial alignment C. guarantee an accurate measurement D. all except B E. all except C

E. all except C

Corneal compression, caused by excessive pressure from the probe, will: A. have no affect on the measurement B. cause an artificial shortening of the axial length C. cause an artificial lengthening of the axial length D. distort the lensE. damage the probe

B. cause an artificial shortening of the axial length

The optical axis is a line that runs through the _____ to the ______ . A. iris, lens B. corneal apex, fovea C. anterior sclera, posterior sclera D. nasal fornix, temporal fornix E. check-out desk, optical shop

B. corneal apex, fovea

For A-scans, the velocity of sound through the vitreous is considered to be the same as through the: A. cornea B. aqueous C. lens D. retina E. orbital fat

B. aqueous

An error due to corneal compression is most likely with which method or mode? A. tonometer mount method B. hand-held method C. immersion method D. automatic mode

B. hand-held method

The echoes of an A-scan that are being measured are identified by the instrument by means of: A. a mm scale B. measuring gates C. the gain D. identifying any spike above the baseline E. none of the above

B. measuring gates

To obtain an accurate axial length measurement the A-scan probe must be aligned _______ to the corneal apex. A. obliquely B. at a 45 degree angle to C. perpendicular D. any of the above

C. perpendicular

When performing A-scan biometry, a one diopter IOL power error could result from an axial length error of: A. .4 mm B. .04 mm C. 4 mm D. 4 cm E. 4 meters

A. .4 mm

The axial length probe is directed toward: A. the macula B. the optic nerve C. any part of the retina D. the orra serrata E. the superior arcade

A. the macula

An A-scan retinal spike cannot be identified as a macular echo unless: A. there are orbital fat echoes present B. there are no orbital fat echoes present C. there are two lens spikes D. there is a posterior lens spike E. there is no posterior lens spike

A. there are orbital fat echoes present

Which is the least effect method for disinfecting the probe tip? A. wipe with distilled water B. wipe the tip with alcohol C. soak the tip in 3% hydrogen peroxide D. soak the tip in a 1:10 bleach solution

A. wipe with distilled water

Consecutive A-scans should have total length readings within ______ to be considered to have good reproducibility. A. 20 mm B. 2.0 mm C. .20 mm D. .02 mm E. 2.0 cm

B. 2.0 mm

Corneal compression can result in an erroneous axial length measurement. This is caused by: A. the gain set too high B. probe pressure on the cornea C. improper probe alignment D. gates improperly set E. the patient wiping their eyes

B. probe pressure on the cornea

Applying too much pressure to the cornea with an A-scan probe will: A. patient discomfort B. result in a shorter axial length C. result in a longer axial length D. cause a corneal ulcerhave no affect

B. result in a shorter axial length

An A-scan echo that is perpendicular to the retina will produce a relatively _______ spike: A. short B. tall C. bright D. dim E. thick

B. tall

The echo from a strongly reflecting surface will produce a spike on an A-scan that is relatively: A. short B. tall C. bright D. dim E. none of the above

B. tall

Which drop is used immediately prior to performing an axial length measurement? A. phenylephrine B. tetracaine C. tropicamide D. fluorescein E. cyclopentolate

B. tetracaine

The speed of ultrasound through vitreous is: A. 153.2 m/s B. 15.32 m/s C. 1532 m/s D. 15.32 cm/s E. 153.2 mm/s

C. 1532 m/s

Which of the following echoes will always be absent in the axial length scan of an aphakic patient? A. cornea spike B. posterior lens capsule spike C. anterior lens capsule spike D. retina spike E. B and C

C. anterior lens capsule spike

It is more difficult to align an A-scan with the macula in an aphakic patient because of the absence of: A. the cornea echo B. anterior chamber echoes C. lens echoes D. vitreous echoes E. the retina echo

C. lens echoes

The axial length probe is aligned with: A. the central cornea B. the center of the lens C. the optic nerve D. A and B E. all of the above

D. A and B

A-scan alignment with the optical axis of the eye will be indicated by: A. a tall anterior lens spike B. a tall posterior lens spike C. a tall retina spike D. all of the above

D. all of the above

Corneal compression can be monitored by comparing _____ readings between scans. A. corneal thickness B. iris thickness C. lens thickness D. anterior chamber depth E. posterior chamber depth

D. anterior chamber depth

When measuring the axial length of an eye that has no lens, which mode should be used? A. pseudophakic B. cataract C. dense cataract D. aphakic E. phakic

D. aphakic

An axial length measurement measures the eye from the _______ to the _______. A. anterior lens posterior lens B. lens retina C. cornea lens D. cornea retina E. none of the above

D. cornea retina

Which A-scan factor can be controlled by adjusting a setting on the instrument? A. perpendicularity B. reflectivity C. compression D. gain E. all of the above

D. gain

Which solution would not provide disinfection for an A-scan probe tip? A. alcohol B. 3% hydrogen peroxide C. bleach 1:10 dilution D. sterile saline E. all would provide disinfection

D. sterile saline

When performing an IOL measurement, which step should be performed first? A. axial length measurement B. keratometry C. instill a topical anesthetic D. tell the patient what you will be doing

D. tell the patient what you will be doing

If an ultrasound beam strikes a surface in a perpendicular fashion, ______ will be produced. A. a hole B. no spike C. a negative spike D. a low spike E. a high spike

E. a high spike

An ultrasound beam will not travel through: A. water B. the retina C. the iris D. the cornea E. air

E. air

An A-scan measurement with the echo perpendicular to the retina will produce a retina spike that will: A. be a sharply rising spike B. be a tall spike C. have no smaller spikes preceding it D. have a 90 degree angle to the baseline E. all of the above

E. all of the above

The normal vitreous produces _______ echoes on an A-scan. A. tall B. short C. one D. multiple E. no

E. no