Indirect Ophthalmoscopy and Optos Flashcards
image from direct ophthalmoscopy is:
virtual, erect, non reversed
limiting factors to direct ophthalmoscopy are:
- pupil size of patient
- distance to observer
- refractive error
- limited FOV
which is better for getting through very small pupils: DO or BIO?
DO
in DO, high myopia results in _____ field of view
decreased FOV
b/c greater mag
in DO, high hyperopia results in ____ field of view
increased FOV
FOV in DO is about ____-____ degrees in an emmetrope
10 to 15 degrees
FOV is BIO is about ___ degrees
30
in BIO, the image is:
real, inverted, reversed, aerial, and 3D
where is the image located in BIO?
between the patient and the examiner
main advantages of BIO:
- binocular view (resolution and depth perception)
- high illumination (better resolution)
- low mag
- large FOV
failure to do what will result in the view in the lens not “filled” from edge to edge?
failure to hold the lens at its focal point from the patient’s eye
for a 20D condensing lens: the image is about ___cm from the lens
5cm
closer viewing distances in BIO require:
- greater accommodation
- greater convergence
- much more precise alignment of all components
since it is very difficult to maintain a binocular, well-focused, well-illuminated image at closer distances, it is best to stay about ___-__cm from the lens
25 to 30cm
how does the viewing triangle get imaged into the patient’s pupil?
- mirrors in the BIO headset optically shrink the examiner’s PD to ~15-20mm
- condensing lens magnifies the patient’s pupil
clinical keys for small pupil
- switch to small pupil setting to shrink viewing triangle
- higher power condensing lens (magnifies pt’s pupil more)
BIO total mag=
[instrument mag] x [relative distance mag]
instrument mag=
[power of eye] / [power of lens]
relative distance mag=
[std viewing dist (25cm)] / [actual viewing distance]
BIO: factors affecting magnification are:
- patient refractive error
- power of the condensing lens
- examiner to lens distance
in BIO: decreased field of view can be caused by:
- lower power lens
- smaller diameter lens
- high myopia
- closer to patient
- pupil size (if small enough)
procedures to perform before dilation
case history, best corrected VAs, pupils, anterior set (SLE), angles, tonometry
major zones of the retina are
- central fundus (posterior pole and mid-periphery)
- peripheral fundus (equitorial region and oral region)
what is the arbitrary definition for central fundus
that portion of the funds posterior to posterior edges of vortex veins
