ophthalmoscopy seeing the eye from greek: ophthalmos - the eye skopeos to see

structure principles of fundus examination direct ophthalmoscopy indirect ophthalmoscopy magnification in ophthalmoscopy field of view in ophthalmoscopy

classic article

principles of ophthalmoscopy in the emmetropic patients, light rays emanating from a point in the fundus emerge as a parallel beam if this beam enters the pupil of the observer, the rays are focussed on his retina and an image is formed

principles of ophthalmoscopy so why do we generally not see the fundus when looking directly into a patient s pupil?

principles of ophthalmoscopy problem: fundus of patient not illuminated light source required pupillary axis of observer must be aligned with incoming light rays from light source to allow observation of the fundus limiting factor patient s pupil size

principles of ophthalmoscopy in large animals or patients with extremely dilated pupils, it may be possible to observe the fundus by simply aligning a bright light source with your visual axis

principles of ophthalmoscopy direct ophthalmoscopy indirect ophthalmoscopy key-hole view aerial image

direct ophthalmoscope first developed by Charles Babbage 1847 failed to prove its function when showing to eminent ophthalmic surgeon and abandoned project http://www.college-optometrists.org/

direct ophthalmoscope clinical use introduced by Hermann von Helmholtz 1851 initially called Augenspiegel (eye mirror) within 10 years physicians using it call themselves ophthalmoscopists first fundus photograph 1864 http://www.college-optometrists.org/

direct ophthalmoscope Helmholtz principles of direct ophthalmoscopy a source of illumination a method of reflecting the light into the eye an optical means of correcting an unsharp image of the fundus greatest improvements made were re. source of illumination candle oil burning wick development of incandescent bulbs halogen.led light source

direct ophthalmoscopy

direct ophthalmoscopy advantages real, upright image high magnification does not require full dilation cheap and mobile disadvantages closeness to patient required small field of view no stereoscopy poor penetration of cloudy media

direct ophthalmoscope head observer s view hole fast diopter switch diopter dial diopter indicator

direct ophthalmoscope head observers viewing aperture shutter light reflecting mirror slit beam setting various sizes round beam red free light

direct ophthalmoscopy light filters green filter (red free light) blood (vessels) appear black grid pattern facilitates lesion documentation slit beam evaluate surface topography of retina and optic nerve

Direct ophthalmoscope head Observers viewing aperture Shutter Light reflecting mirror Slit beam setting Various sizes round beam Red free light

Direct ophthalmoscope on a slit

direct ophthalmoscope if patient and observer are emmetropic, no lenses required to focus on retina why are lenses used? lenses can be used to correct known refractive error of observer

direct ophthalmoscope if observer and patient are emmetropic, lenses can be used to move the point of focus onto structures posterior to the retina or structures more anterior within the eye

direct ophthalmoscope negative lenses can be used to focus onto structures posterior to the retina colobomata, areas of scleral ectasia, cupped disc

direct ophthalmoscope positive lenses can be used to focus onto structures more anterior within the eye lens, iris, cornea, adnexa 0 8 12 20 courtesy J Mould

Mirror

12 dioptre lens Mirror

15 dioptre lens Mirror

20 dioptre lens Mirror

direct ophthalmoscope diopter equivalent distance (in mm) the focal moves anterior/posterior within the eye per diopter change

0 D = focus on retina focus on ONH on + 6 D

Diopter equivalent - clinical

direct ophthalmoscopy how to do it align ophthalmoscope with your visual axis dim light beam to minimal intensity gain control over patient s head with your free hand pick up fundus reflex at arms length (compare fundus reflex of both eyes) following the fundus reflex, come close to the eye until the fundus becomes visible search fundus in reproducible manner

Tora

Fig. 1.12a-c Milk bottles

direct ophthalmoscopy apply a replicable, systematic approach to the assessment of the fundus keep landmarks in mind consider that varying species may require a varying routine!

indirect ophthalmoscopy

indirect ophthalmoscopy http://medical- dictionary.thefreedictionary.com/_/viewer.aspx?path=elmill&name=f0o-01- S2958.jpg

light options

all pupil setting

indirect ophthalmoscopy advantages larger field of view stereoscopic (with head mounted) penetrates opaque media better disadvantages limited magnification inverted & upside down image

celebrity eyes

condensing lenses acrylic or glass glass superior optics biconvex coated to reduce reflections variety of strenghts most commonly used 2.2 pan-retinal 20 D 30D

high power condensing lenses

image direct vs indirect

magnification and field of view magnification process of enlarging something only in appearance but not in physical size field of view (angular or linear or areal) extent of the observable world that is seen at any given moment

magnification and field of view of the fundic image depend on two main factors optical properties of the eye to be examined small eyes = high dioptric power large eyes = less dioptric power form of ophthalmoscopic technique employed direct ophthalmoscopy = high magnification, small field of view indirect ophthalmoscopy = low magnification, larger field of view

magnification optical properties of the eye to be examined small eyes = high dioptric power high magnification large eyes = less dioptric power low magnification

optical properties of the eye to be examined small eyes = high dioptric power high magnification large eyes = less dioptric power low magnification

ophthalmoscopy - magnification lateral magnification magnification of an area axial magnification magnification in depth

lateral magnification magnification across an axis perpendicular towards viewing e.g. left-right, dorsalventral with regards to fundus exemplified by action of slide projector throwing a much magnified image onto a screen

lateral magnification direct ophthalmoscopy the magnification M of a direct ophthalmoscope is equal to M = F e /4 where F e is the total refractive power of the eye. e.g. horse 8 dog 17 cat 20 Rat 77

lat magnification indirect ophthalmoscopy dependent on lens power and eye to be examined lat magnification of a lens = total refractive power of eye/power of lens

lateral magnification - indirect ophthalmoscopy power of lens inversely related to magnification high power = low magnification

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axial magnification describes magnification in depth precisely, the ratio of the distance along the optical axis between two points in image space (A B ) to the distance along the optical axis between the corresponding two points in object space (AB) this magnification is useful when considering an image in its three dimensions

axial magnification magnification along the axis of viewing e.g. elevation of optic nerve head, colobomata

axial magnification axial magnification is approximately the lateral magnification squared (axial) = (lateral) 2 e.g. lateral magnification = 2 means axial magnification = 4

indirect ophthalmoscopy in any given species, the dioptric power of lens used determines magnification field of view

axial magnification in diff. species

axial magnification in diff species

field of view - direct ophthalmoscopy field of view in direct ophthalmoscopy is determined by pupil size of examiner patient size of light beam

indirect ophthalmoscopy in any given species, the dioptric power of lens used determines magnification field of view

image direct vs indirect direct: 2.5 mm 20D lens: 13 mm

indirect ophthalmoscopy high diopter large field of view, (low magnification) low diopter small field of view (high magnification)

hand held PanOptic cross between direct and indirect ophthalmoscope increased field of view 25 degree vs. 5 degree increased magnification (by 26% compared to direct ophthalmoscope) virtual upright image greater working distance monocular view

hand held PanOptic http://www.welchallyn.com