ROUB FINAL PAPER UPDATED QUESTIONS AND
ANSWERS GRADED A+
✔✔What is the term for the capacity of an ultrasound instrument to display two or more
interfaces that are very anatomically close to one another as separate echoes ? -
✔✔Resolution
✔✔How does increasing the gain setting on the biometer affect the displayed echo ? -
✔✔It increases the amount of amplification of the echo
✔✔What is the range of ophthalmic biometry frequencies ? - ✔✔8 to 12 MHz
✔✔How is resolution affected when the gain is set at maximum ? - ✔✔The resolution is
less
✔✔A non-focused sound beam is always utilized by which type of scan ? -
✔✔Diagnostic A-Scan
✔✔What scan is used to obtain a two-dimensional image of the globe ? - ✔✔Diagnostic
B-Scan
✔✔What is the term for a one-dimensional amplitude scan ? - ✔✔A-Scan
✔✔The strength of an echo is dependent on what three factors ? - ✔✔Gain, difference
in density, and proper alignment
✔✔What type of scan uses Prager or scleral shells ? - ✔✔Immersion A-Scan
✔✔How often should the filter of a biometry instrument be vacuumed ? - ✔✔Once a
month
✔✔Measurement of axial length of the eye, thickness of an extraocular muscle, and
tumor height are all within the definition of what term ? - ✔✔Biometry
✔✔What is the leading cause of an unplanned, post-operative refractive error ? - ✔✔An
error in the measurement of axial length
✔✔An error of 0.1 mm in the axial length measurement can result in a post-operative
refractive error of how many diopters ? - ✔✔0.25 D
✔✔If multiple axial length readings are taken from a single eye, each measurement
should be within how many millimeters ? - ✔✔0.2 mm
, ✔✔The difference in axial length between two eyes should measure within how many
millimeters ? - ✔✔0.3 mm
✔✔What are two techniques for measuring axial length ? - ✔✔Contact & Immersion
✔✔When performing contact biometry, steps should be taken to minimize what factors?
- ✔✔Corneal compression and corneal abrasions
✔✔What are possible causes of a short measurement in biometry ? - ✔✔(+) Gain is set
too high
(+) Corneal compression
(+) Air bubble adherent to the transducer
(+) Corneal gate to the right of the corneal spike
(+) Retinal gate too far left of the retinal spike
(+) Lens measured too thin
(+) Misalignment of the sound beam
(+) Low sound velocity
✔✔What are possible causes of a long measurement in biometry ? - ✔✔(+) Gain is set
too low
(+) Fluid bridge (contact method)
(+) Air bubble in fluid bath (immersion method)
(+) Retinal gate too far right of the retinal spike
(+) Lens measured too thick
(+) Misalignment of the sound beam
(+) Sound velocity too fast
✔✔How is corneal compression determined ? - ✔✔AC depth and/or distance between
initial spike and anterior lens spike
✔✔What is more likely to occur during contact (hand-held) method biometry ? -
✔✔Corneal depression
✔✔What are three advantages of A-Scan immersion technique ? - ✔✔(+) Proper sound
beam alignment
(+) No corneal compression
(+) Corneal and crystalline lens thickness measured
✔✔What generally causes short axial length measurements ? - ✔✔An air bubble in the
water of the probe
✔✔What is the correction factor for the normal cornea when measuring axial length ? -
✔✔0.04 mm
ANSWERS GRADED A+
✔✔What is the term for the capacity of an ultrasound instrument to display two or more
interfaces that are very anatomically close to one another as separate echoes ? -
✔✔Resolution
✔✔How does increasing the gain setting on the biometer affect the displayed echo ? -
✔✔It increases the amount of amplification of the echo
✔✔What is the range of ophthalmic biometry frequencies ? - ✔✔8 to 12 MHz
✔✔How is resolution affected when the gain is set at maximum ? - ✔✔The resolution is
less
✔✔A non-focused sound beam is always utilized by which type of scan ? -
✔✔Diagnostic A-Scan
✔✔What scan is used to obtain a two-dimensional image of the globe ? - ✔✔Diagnostic
B-Scan
✔✔What is the term for a one-dimensional amplitude scan ? - ✔✔A-Scan
✔✔The strength of an echo is dependent on what three factors ? - ✔✔Gain, difference
in density, and proper alignment
✔✔What type of scan uses Prager or scleral shells ? - ✔✔Immersion A-Scan
✔✔How often should the filter of a biometry instrument be vacuumed ? - ✔✔Once a
month
✔✔Measurement of axial length of the eye, thickness of an extraocular muscle, and
tumor height are all within the definition of what term ? - ✔✔Biometry
✔✔What is the leading cause of an unplanned, post-operative refractive error ? - ✔✔An
error in the measurement of axial length
✔✔An error of 0.1 mm in the axial length measurement can result in a post-operative
refractive error of how many diopters ? - ✔✔0.25 D
✔✔If multiple axial length readings are taken from a single eye, each measurement
should be within how many millimeters ? - ✔✔0.2 mm
, ✔✔The difference in axial length between two eyes should measure within how many
millimeters ? - ✔✔0.3 mm
✔✔What are two techniques for measuring axial length ? - ✔✔Contact & Immersion
✔✔When performing contact biometry, steps should be taken to minimize what factors?
- ✔✔Corneal compression and corneal abrasions
✔✔What are possible causes of a short measurement in biometry ? - ✔✔(+) Gain is set
too high
(+) Corneal compression
(+) Air bubble adherent to the transducer
(+) Corneal gate to the right of the corneal spike
(+) Retinal gate too far left of the retinal spike
(+) Lens measured too thin
(+) Misalignment of the sound beam
(+) Low sound velocity
✔✔What are possible causes of a long measurement in biometry ? - ✔✔(+) Gain is set
too low
(+) Fluid bridge (contact method)
(+) Air bubble in fluid bath (immersion method)
(+) Retinal gate too far right of the retinal spike
(+) Lens measured too thick
(+) Misalignment of the sound beam
(+) Sound velocity too fast
✔✔How is corneal compression determined ? - ✔✔AC depth and/or distance between
initial spike and anterior lens spike
✔✔What is more likely to occur during contact (hand-held) method biometry ? -
✔✔Corneal depression
✔✔What are three advantages of A-Scan immersion technique ? - ✔✔(+) Proper sound
beam alignment
(+) No corneal compression
(+) Corneal and crystalline lens thickness measured
✔✔What generally causes short axial length measurements ? - ✔✔An air bubble in the
water of the probe
✔✔What is the correction factor for the normal cornea when measuring axial length ? -
✔✔0.04 mm
