OPHTHALMOSCOPE Discreption in detail .ppt

Ophth

1. Prof A E OMOTI
MBBS, FWACS, FMC(Oph), FIPMD, FIMC, CMC, MD
CONSULTANT
DEPT OF OPHTHALMOLOGY
UBTH

2. An instrument used for investigating the state of the
fundus and in the detection of opacities of the ocular
media. It also provides some information on the
refractive state of the eye.
Direct: the fundus is viewed directly, no intermediate
image is formed.
Indirect: observer views an intermediate fundal image
which is formed by an ophthalmoscope lens between
the subject and the observer.

3. A small portable instrument which consists of a
system of converging lenses which focus light
on to a reflecting surface which diverges the
beam to illuminate the subject’s eye.

5. Apertures which control diameter of beam
Filters which control wavelength
Graticles which measure fundus components
A slit used for evaluating retinal lesions such as
depressions eg macular hole, or elevations
such as macular cysts
A system of focusing lenses

7. This is the area of the retina which can be seen at
any one time.
Factors affecting field of view include
1.Projected image of sight-hole on the retina- the hole
in ophthalmoscope mirror or observer’s pupil
whichever is smaller
2.State of refraction of patient’s eye
3.Size of patient’s pupil (larger if dilated)
4.Proximity of observer to patient. The closer observer
is to the patient, the larger the field of view

9. Image of sight hole
 Rm R Rh pupil sight-hole

11.  image R P sight-hole

13. Long distance
Close to pupil

15. Optics is best constructed with knowledge of
patient’s far point.
Far point of distinct vision is the position of an
object such that it’s image falls on the retina of
the relaxed eye.
NB. A ray from the top of the image at the far
point through the observers nodal point will
locate the image on the observers retina.

16. Emmetropic far point is at infinity
FP N Fa No
 R P Po Ro

17. Image is smaller than in emmetropia
 far point R P Fa Po Ro

18. Image is larger than in emmetropia
 R N P Fa Po Ro FP

20. Emergent rays from emmetropic patients are
parallel & will be brought to a focus in
emmetropic observer’s retina without
accommodative effort.
Hypermetropic observer needs to accommodate
or rack up appropriate correcting convex lens
Myopic observer needs to rack up appropriate
correcting concave lens.

22. Emergent rays of hypermetropic eyes are divergent so,
emmetropic observer needs to accommodate or use
convex lens
Emergent rays from myopic eyes are convergent so
emmetropic observer needs to use correcting concave
lens
Aim of correcting lens is to render the rays parallel so
that an emmetropic observer can form a focused
image on his retina.

23. virtual image is behind the observer's eye
FP R P Fa Po Ro VI

25. observer can form focused image on retina
 FP R P convex Po Ro
 lens

26. Converging rays are focused in the vitreous
R N P Fa Po f Ro FP

28. Image is formed on the retina
lens FP

30. Observer uses the dioptric power of the
patient’s eye as a loupe.
Dioptric power of the eye is about +60D
Magnification formula is M= F/4, where F=
dioptric power of loupe.
Thus magnification of direct ophthalmoscope is
about X 15.

31. Principle- makes eye highly myopic by placing a
strong convex lens in front of it
Results in real inverted image of the fundus
between the convex lens & observer
Problem encountered with earlier instruments
was corneal reflex which interfered with
visualization of the fundus

32. BIO has become an indispensable tool to
diagnose and manage a variety of vitreoretinal
disorders.
Sophisticated additions to the basic technology
include high–magnification lenses built into the
ophthalmoscope, video adapters that facilitate
patient and student education as well as open
up an array of telemedical possibilities, and
laser photocoagulation systems mounted onto
the indirect ophthalmoscope to treat peripheral
tears through a 20 diopter lens.

33. The ophthalmoscope was invented by Hermann
von Helmholtz in the 19th century.
Helmholtz was able to do this by gluing a lens,
microscope cover glasses, and cardboard to
create the first ophthalmoscope in 1850.
hundreds of variants have been described and
produced, and many of them have been
commercially available.
The successful variant is the binocular indirect
headband ophthalmoscope, first described by
Charles Schepens in 1945.

35. Gullstrand simply separated the illuminating and
viewing paths as they pass through the cornea
and lens.
Henker modified this by introducing a horizontal
slit in the illuminating system and a circular
aperture in the viewing system, which are
imaged at different positions in the subjects
plain.

37. The condensing lens converges the rays from
the light source to form a real image in the
vitreous from which light diverges to strike the
retina
Factors affecting the field of illumination include
The state of refraction of the eye. It is largest in
myopia and smallest in hypermetropia.
The size of the subjects pupil. The wider the
pupil, the larger the field of illumination.

38. Subject’s eye condensing
M E H p P lens

39. The condensing lens causes a reduced image of the
observers pupil to be formed at the subjects pupillary
plane. The image of a 4mm pupil is approximately
0.7mm.
Factors affecting the field of view include
1.The sight hole which is the observers pupil. This is
because only the rays that leave the subjects eye via
the area of the image of the observers pupil can be
seen by the observer
2.The aperture of the condensing lens. The wider the
condensing lens, the wider the field of view. The field
of view is approximately 25
0

40. Subject’s observer’s
pupil pupil

41. Effect of wider pupil and
wide lens aperture
Effect of smaller lens
aperture and smaller
pupil

42. The image from an emmetropic eye is located at the
second principal focus of the condensing lens
because all rays emerging from it are parallel.
On the other hand, rays emerging from a
hypermetropic eye are divergent and therefore brought
to a focus outside the second principal focus
While the convergent rays emerging from a myopic eye
forms its real image within the second principal focus
of the condensing lens.

43. Image from emmetropic eye is located at 2
nd

principal focus of condensing lens
M E H P M E H

44. It can be shown mathematically, that both the
linear and angular magnification of a +13D
lens is about x 5, a +20D lens is about x3 and
a +30D lens is about x2.

46. BN is the distance between the nodal point and
the retina of the subject's eye.
If this distance BN is taken to be 15 mm, the
linear magnification is equal to the focal length
of the lens (in mm) divided by 15.
Thus, the linear magnification of a +13 D lens
(f = 75mm) is approximately × 5, while the
linear magnification of a +20 D (f = 50 mm)
lens is approximately × 3.

47. Movement of the condensing lens alters the
image size.
In emmetropia, the image size is the same in
all positions of the condensing lens.
The image size increases in myopia and
reduces in hypermetropia as the condensing
lens is moved away from the eye.

48. Condensing lens F1 behind Fa. Hyperopic
image largest
M E H P Fa CL M E H

49. F1 coincides with Fa. Image size same in all
refractive states

50. F1 in front of Fa. Myopic image largest
M E H P Fa F1 M E H

51. The basis for this is “Effectivity of the lens”.
A convex lens becomes more effective when
you move it away from the eye.

53. Incorporates a +2.00 D lens to facilitate viewing of
image at 40-50 cm.
Incorporates prisms which serves to
Forms reflective mirror which represents the teaching
facility
Directs rays to observer by total internal reflection
because angle of incidence is approx 45 degrees
which exceeds the critical angle for glass:air interface
which is 41 degrees.

54.  rays from subject to observer
To
student

55. DIRECT INDIRECT
IMAGE
VIEWED
No intermediate
image formed
Intermediate
image formed
Image
orientation
Not invertedVertically &
horizontally
inverted
Size of
instrument
Small and
portable
Usually large
Field of view Small. About 6
0
Large. About
25
0

56. Magnification Large (x15 )Small x2 to (x5)
Binocularity Not available Stereopsis
Corneal reflexMarked Negligible
refractive error Marked Minimal
Illumination Moderate Very high
Teaching facility None Teaching mirror

57. Peripheral
retina view
Impossible Possible with
indentation
Surgical use Useless Useful in retina
detachment
surgery
Laser use Useless Useful
Number of
units
Single unit Multiple units

58. 1.In viewing the appearance of the fundus: The optics
of this has already been described. In addition to
white light, many modern instruments also have a
red-free filter which causes microaneurysms to show
as black dots against a green background.
2.Also used as a self illuminating loupe for viewing the
anterior segment of the eye such as the detection of
lens opacities with + 10D correcting lens.

59. 1.Can be used as a light source in place of a pen torch.
2.Assists in determination of refractive state of the eye
and can give a rough idea as to the patients
refractive error. This is judged by noting the power of
the correcting lens used assuming the observer is
emmetropic and neither patient nor observer is
accommodating.
3.Determine the presence of any opacity in the
transparent media of the eye including the vitreous.
4.Elevation of the optic disc in papilloedema

60. Today’s indirect ophthalmoscopes come with a
myriad of features, which may include
adjustable interpupillary distance, portable
power packs, adjustable mirrors, dust sealed
optics, and red-free and cobalt blue filters.
Video capture capabilities built into some
indirect ophthalmoscopes allow the patient to
see his or her fundus on video and, in some
instances, in real time.

61. Magnification lenses built into BIO allow
enlarged, but more restricted views of the
retina through the 20 diopter lens
Since these lenses can usually be flipped into
and out of the indirect’s axis of focus, they
allow the ophthalmologist to first visualize the
diseased area of the fundus in low
magnification, then zoom into the area at high
magnification.

62. The New Vantage Plus.
The PLUS gives you:
P Premium intelligent
optics
L Lighter weight and
brighter images
U Unique wireless
patented technology
S Smaller and more
compact size

63. The TruFocus™ Laser Indirect
Ophthalmoscope (LIO) is ideal
for patients who are best
examined and treated in a
supine position. It is recognized
as the industry standard -
unique optical design eliminates
the need for laser focus
adjustments and
accommodates a wide range of
working distances.(Dual
532/810 nm, 810 nm, and 810
nm large spot models available)