This document provides an overview of various ophthalmic instruments used in eye examinations, including: 1. Direct and indirect ophthalmoscopes are used to examine the interior of the eye. Indirect ophthalmoscopy uses a condensing lens to form an erect, magnified image of the retina. 2. The slit lamp examination uses different illumination techniques like diffuse, direct, and retroillumination to examine the anterior segment of the eye including the eyelids, cornea, iris, and lens. 3. Indirect techniques like specular reflection and optical sectioning are used to examine corneal structures at high magnification. 4. A lensometer is used to measure the refractive power of correct

1. OPHTHALMIC INSTRUMENTS
(direct and indirect ophthalmoscopy, slit lamp examination,
lensometer)
PRESENTER- DR SHWETA
MODERATOR- DR AJAY KUMAR SINGH

2. Babbage and his ophthalmoscope

3. Hermann von Helmholtz

4. Distant Direct Ophthalmoscopy
• Performed with the help of self illuminating ophthalmoscope
or a plane mirror with a hole in centre
• Distance – 20 to 25 cm
• Applications-
1. To diagnose opacity in the refractive media
2. To differentiate between a mole and a hole of the iris
3. To recognize detached retina or a tumour arising from the
fundus

5. DIRECT
OPHTHALMOSCOPY

6. OPTICS

7. • Image – erect, virtual,14-15 times magnified emmetropes
(more in myopes and less in hyperopes)
• Field of vision is always smaller than field of illumination.
• Factors affecting it are-
 Directly proportional to size of pupil
 Directly proportional to axial length
 Inversely proportional to the distance between the observed
and the observer’s eye

8. PROCEDURE
• Performed in a semidark room with the patient seated and
looking straight ahead and observer standing to the side of the
eye to be examined.
• The observer should reflect beam of light from the
ophthalmoscope into the patient’s pupil.
• Once the red reflex is seen, the observer should move as close
to the patient’s eye as possible.
• Once the retina is focused, the details should be examined
systematically.

9. INDIRECT
OPHTHALMOSCOPY

10. • Introduced by Nagel in 1864
• Indirect Ophthalmoscopy (IDO) involves making the eye
highly myopic by placing a high power convex lens in front of
the eye so that a real, inverted and laterally reversed image is
formed close to the principle focus of the lens, between the
lens and the observer
• The technique is called Indirect because the fundus is seen
through a condensing lens.

11. Optical system of binocular indirect
ophthalmoscope
• Binocularity is achieved by reducing the observer’s
interpupillary distance from about 60mm to approximately
15mm by prism/mirror

12. Image formation
emmetrope
hypermetropes
myopes

13. • Image- real, inverted, magnified.
image magnification=power of eye/power of condensing lens
• Magnification of image depends upon
diopteric power of convex lens
position of lens in relation to the eyeball
refractive state of eyeball
• Field of observation is always greater than field of illumination

14. SIZE OF THE IMAGE IN DIFFERENT REFRACTIVE
STATE (EMMETROPIC, HYPERMETROPIC AND
MYOPIC EYE)

15. Procedure
• The practitioner should first illuminate the patient’s pupil area
by pointing the head and hence the illumination towards the
patient’s eye.
• Interpose the condenser lens close to the eye about 2 cm, and
centre the lens on to the pupil. The lens should be held with the
more convex side towards the practitioner.
• Pull back the lens away from the patient’s eye, at the same time
taking care to keep the illumination centered on the pupil. Whilst
withdrawing the lens, the practitioner will find a distance that
provides an optimum field of view. This should be approximately
at the focus of the lens, i.e. 5cms from the pupil using a +20D
lens
• Having obtained an image filling the BIO lens, the fundus may
then be examined by moving around the patient if reclining, or by
redirecting the patient’s fixation if seated

16. Scleral indentation
• Done with the depressor placed on the patient’s lid
• It should be moved in a direction opposite to that in which
examiner wants the depression to appear
• It should be rolled gently and tangentially over the eye surface
• Superonasal quadrant is most sensitive to scleral depression

17. COMPARISON WITH DIRECT
OPHTHALMOSCOPY

18. ADVANTAGES OF IDO
• Larger field of view
• Lesser distortion of retinal image
• Easier to examine if patients eye movements are present and
with high spherical or astigmatic refractive errors
• Useful in hazy media due to its bright light and optical
property
• Can be used intraoperatively
• Vitreous can be examined easily and various vitreous
abnormalities diagnosed through this

19. DISADVANTAGES
• Difficult to learn
• Less magnification, therefore details of a small lesion not
visualized properly
• Impossible with very small pupils
• More uncomfortable to the patient

20. FUNDUS DRAWING
• It is made on special Amsler’s
chart, which has 12 clock hours
marked and has 3 concentric
circles
• Vortex veins ampulla seen along
the equator
• Long ciliary vein- 3 and 9 o’clock
• Branching vessels

21. COLOUR CODING OF RETINAL DRAWING
red Optic disc, retinal artery, hemorrhage, attached
retina, retinal neovascularisation
blue Retinal vein, detached retina, retinal oedema
green Media opacities, vitreous hemorrhage
yellow Retinal an choroidal exudates
brown Pigmented lesion, choroidal dethachment
Red line with
blue
Retinal breaks

24. SLIT LAMP EXAMINATION

25. • The slit lamp facilitates an examination which looks at anterior
segment of the human eye, which includes the
– Eyelid
– Cornea
– Sclera
– Conjunctiva
– Iris
– Anterior chamber
– Natural crystalline lens and
– Anterior vitreous.

26. HISTORICAL LANDMARKS
• De Wecker 1863 devised a portable ophthalmomicroscope .
• Albert1891,developed a binocular microscope which provided
stereoscopic view.
• Gullstrand ,1911 introduced the illumination system which had
for the first time a slit diaphragm in it
– Therefore Gullstrand is credited with the invention of slit
lamp.

27. • Operational components of slit lamp biomicroscope essentially
consist of:
• Illumination system
• Observation system
• Mechanical system

28. OBSERVATION SYSTEM

29. ILLUMINATION
SYSTEM
1- light source
2-condenser lens
3- slit diaphragm
4- filters
5- projection lens

30. MECHANICAL SUPPORT SYSTEM

31. METHODS OF ILLUMINATION
1- DIFFUSE ILLUMINATION
• Angle between microscope and illumination system should be
30-45 degree.
• Slit width should be widest.
• Diffusing filter is used.
• Magnification: low to medium
• Illumination: medium to high
 Applications:
General view of anterior of eye: lids,
lashes, sclera, cornea ,iris, pupil,
Gross pathology and media opacities
Contact lens fitting.
Assessment of lacrimal reflex.

32. 2- DIRECT ILLUMINATION
• Involves placing the light source at an angle of about 40-50
degree from microscope.
• This arrangement permits both light beam and microscope to
be sharply focused on the ocular tissue being observed.
• It is particularly suitable for assessment of cataracts, scars,
nerves, vessels etc.
• It is also of great importance for
the determination of stabilization
of axis of toric contact lens.

33. PARALLELOPIPED
Constructed by narrowing the beam to 1-2mm in width to
illuminate a rectangular area of cornea.
Microscope is placed directly in front of patients cornea.
Light source is approximately 45 degree from straight ahead
position.
Applications:
• Used to detect and examine corneal structures and defects.
• Used to detect corneal striae that develop when corneal
edema occurs with hydrogel lens wear and in keratoconus.
• Corneal scars and infilterates appears brighter than
surrounding because they have more density.
• Cells and flare in anterior chamber can be graded.

34. CONICAL BEAM
• Produced by narrowing the vertical height of a parallelopiped to
produce a small circular or square spot of light.
• Light source is 45-60 degree temporally and directed into pupil.
• Biomicroscope: directly in front of eye.
• Magnification: high(16-25x)
• Intensity of light source to heighest setting.
• Focusing: Beam is focused between cornea and anterior lens surface
and dark zone between cornea and anterior lens observed.
• Principle is same as that of beam of sun light streaming through a
room ,illuminating airborne dust particles.
• This occurance is called tyndall phenomenon.
• Most useful when examining the transparency of anterior chamber
for evidence of floating cells and flare seen in anterior uveitis.

35. OPTICAL SECTION
• Optic section is a very thin parallelopiped and optically cuts a
very thin slice of the cornea.
• Axis of illuminating and viewing path intersect in the area of
anterior eye media to be examined.
• Angle - 45 degree.
• With narrow slit the depth and portion of different
objects(penetration depth of foreign bodies, shape of lens etc)
can be resolved more easily.
• Magnification- maximum
• Used to localize:
– Infiltrates
– Cataracts
– AC depth.

37. SPECULAR REFLECTION
• microscope and slit beam should be at equal angles from normal to cornea.
• Angle of illuminator to microscope must be equal and opposite.
• Angle of light should be moved until a very bright reflex obtained from
corneal surface which is called zone of specular reflection.
• Irregularities ,deposits in these smooth surface will fail to reflect light and
these appear darker than surrounding.
• Under specular reflection anterior corneal
surface appears as white uniform surface
and corneal endothelium takes on a mosaic
pattern.
• Uses:
a) Evaluate general appearance of corneal
endothelium
b) Lens surfaces
c) Corneal epithelium

38. INDIRECT ILLUMINATION
• The beam is focused in an area adjacent to ocular tissue to be
observed.
• Main application:
Examination of objects in direct vicinity
of corneal areas of reduced transparency
e,g infiltrates, corneal scars, deposits,
epithelial and stromal defects
• Illumination:
Narrow to medium slit beam
Decentred beam
• Magnification: approx 12x

39. RETROILLUMINATION
• Light is reflected off the iris or fundus, while the microscope is
focused on the cornea.
• 2 types-
DIRECT RETROILLUMINATION
• Observer is in direct pathway of
light reflected from structures.
• Pathology is seen against an
illuminated background

40. INDIRECT RETROILLUMINATION
• Observer is at right angle to the
observed structure and, therefore,
not in line with light.
• Pathology is seen against dark
background.

41. SCLEROTIC SCATTER
• Light beam is focused at limbus.
• Because of the phenomenon of total internal reflection, rays of
light pass through the substance of cornea and illuminate the
opposite side of limbus.
• Any corneal opacity becomes visible because it scatters the
rays of light.
• Magnification- 6-10 times

42. LENSOMETER

43. • It is a device designed to measure the refractive power
prescription of a unknown lens.
• 2 types-
1. Manual-
• Manual lensometer gives the accurate
power of a lens and were used in optical
industries.
• A manual lensometer is portable and
can be carried anywhere
• But a person needs to have a better
idea to measure the power of a lens.
(specially in case of a toric lens)

44. 2-Automated lensometer
• It is a fully automatic well programmed
device mostly used in clinics.
• It is easy and faster and can print
prescription.
• It is less accurate when compared to
manual lensometer.

45. Steps to neutralize spectacle lenses in
manual lensometer
• Calibration:- Adjusting the device to perform smoothly in
order to get accurate power of the lenses.
• Eye piece should be focused manually.
• Power drum should level zero.
• All the knobs should be placed
rightly and the device should be
neat and clean to avoid errors.

46. ADJUSTMENT OF EYEPIECE
• It is very important to focus the eye piece so that the
observer’s eye is relaxed and to avoid errors.
• In adjusting the eye piece the blurred black protractor is
focused.
• At first the eye piece is rotated completely Anti-clock
wise, the protractor views blurred.
• Then slowly rotate the eye piece clock wise and stop at
once where it is sharp and clear.
• Now the eye piece is set and focused.

47. Placing the spectacle lenses on the device
• Placing the spectacles lens on the device with its front surface
facing towards the eye piece.
• There are 2 knobs on the lensometer:-
1-Lens stop (holds the lens/
frame in place)
2-Frame leveling knob (makes
sure that the frame is leveled
and helps in accurate axis
measurement)

48. TARGET
• It is green in colour and appears when the device is switch on.
• It shows the position of the optical center of the lens.
• There is a ring of round dots at the centre of the target.
• This represents the power orientation of the lens as it rotates
with the lens rotation
• These round dots become small
lines oriented in one direction in
case of a toric lens

49. ANALYZING THE SPHERICAL LENSES
• Move the lens such that the target is exactly at the centre.
• Rotate the power drum until target is clear and sharp (all the
dots at the center should be separate & sharp)
• Stop rotating the power drum when the target is sharp for the
first time.
• Always count the upper mark on the power scale for accuracy
of the spherical power of the lens.

50. ANALYZING THE CYLINDRICAL LENS
• The process of Neutralizing a toric lens when compared to
spherical lens is completely a different concept.
• The key and the most important thing to remember is the
central orientation of the dots.

51. Process of toric lens neutralization
• Step 1:-
• Move the lens so that the target is at the centre of the protractor.
• This gives the optical centre location.

52. • Step 2-
• Rotate the power drum so that the central lines (oriented in one
direction) are sharp

53. • Step 3 -
• Rotate the axis wheel so that one meridian of the target is
parallel to the orientation of the central lines.
• Note that only one meridian of the target will be sharp.
• As the 180° meridian is sharp in this picture, we will write the
power and the axis as 180°
• Ex: ---DC X 180s°

54. • Rotate the power drum so that the opposite meridian in the
target is sharp.
• Note that the central lines will change in direction and will be
oriented in the opposite direction.
• As the 90° meridian is sharp in this picture, we will write the
power and the axis as 90°
• Ex: ----DC X 90°
• Writing the power
• As the Lensometer gives the readings of a toric lens power in 2
cylinder format, we need to transpose the power and write in
sphero – cylindrical format
• The power which we got in the example shall be written as:
• -----DS/----DC X 180°