OPHTHALMOLOGY INSTRUMENTS FOR NEET PG REVISION NOTES

Opthal instrument
TONY SCARIA 2010 KMC

Examination of retina
• Indirect opthalmoscope  to visulaise peripheral retina
• Direct opthalmoscope,90 D used to visualise posterior pole
• Goldmann 3 mirror lens

Direct opthalmoscope

Indirect ophthalmoscope

Indirect opthalmoscope

Direct ophthalmoscope Indirect opthalmoscope
Magnification 15 times 5 times
Field of vision Limited to 2 disc diameter Large upto ora serrata
Hazy media Not useful Useful because of bright
illumination
Type of image Virtual & erect Real & inverted

Goldmann 3 mirror lens

Goldmann 3 mirror
Central part To visualise the posterior pole
Equatorial mirror To visualize area surrounding equator
Peripheral mirror To visualise peripheral retina up to ora serrrata

Gonioscopy

Gonioscopy
• Goniolens is used to divert the beam of light and this technique of
biomicroscopic examination of the angle of anterior chamber is called
gonioscopy

Principle of gonioscope

Gonioscopic view

Structures visualised in gonioscopy
• Root of the iris,
• Anteromedial surface of the ciliary body (ciliary band),
• Scleral spur,
• Trabecular meshwork and Schlemm’s canal and
• Schwalbe’s line

Contast sensitivity testing

Contrast sensitivity testing
• Letter contrast sensitivity
• Pelli-Robson and Regan charts are most commonly used.
• Standard Snellen type
• contrast sensitivity gratings
• Cambridge contrast sensitivity gratings

Contrast sensitivity is affected in
• early cataract
• after refractive surgery
• measure of optic nerve disease
• optic neuritis,
• multiple sclerosis,
• papilloedema and
• possibly glaucoma TONY SCARIA 2010 KMC

Investigations for cornea

Pachymeter Measures corneal thickness
Specular microscopy Photographs corneal endothelium and delineates
various cellular characteristics, like size, shape, density
and distribution
Keratometry Measures corneal curvature
Scrapings and Stain • Flourescein stains corneal defects, ulcers
• Rose bengal stains mucus and dead & damaged
cells
Corneal biopsy
Cochet bonnet anesthesiometer Qualitative assessment of corneal sensation

Pachymeter

Corneal thickness can be measured by
• USG
• OCT
• Optical low coherence reflectometry
• Optical slit lamp pachymetry
• Scanning slit based Orb scan

SPECULAR MICROSCOPY  TO VISUALISE
CORNEAL ENDOTHELIUM

Fixed frame method to assess endothelial
count

Keratometry  corneal curvature

Keratometry

Keratometry
• keratometry’ or ‘ophthalmometry’
• Objective method of estimating the corneal astigmatism by
measuring the curvature of central cornea.
• 2 types of tonometer
• Javal-Schiotz model and
• Bausch & Lomb model

Fluoroscein stain for corneal ulcer
Rose Bengal stain for corneal
keratinisation dessication

Confocal microscope to study all layers of
cornea

Anesthesiometer for corneal sensation

Placido disc/ keratoscope
Used to assess anterior surface
of cornea

Placido disc in keratoconus

Slit lamp examination

slit-lamp examination
• Examination of anterior chamber

Tonometry

Direct measure of IOP Manometry
Indirect method of
measuring IOP
Indentation (impression
tonometry)
• Most commonly used
• Schiotz tonometer
Applanation tonometry • Goldmann  most accurate
• Tonopen
• Perkin

Schiotz tonometry
Reading is affected by scleral rigidity

Applanation tonometry
• based on Imbert Fick law which states that the pressure inside a
sphere (P) is equal to the force (F) required to flatten its surface
divided by the area of flattening (A); i.e., P = F/A

Goldmann tonometer • Most popular and accurate tonometer
• double prism mounted on a standard slit-lamp
• Gold standard
Perkins handheld diameter • Used mainly in children
Tono-Pen • computerised pocket tonometer .
• Used in irregular cornea
• microscopic transducer which applanates the
cornea and converts IOP into electric waves
Mackay Marg • Irregular cornea
Maklakov tonometer • Variable applanation area & fixed force
Pneumotonometry • Non contact tonometry based on applanation
• central part of the cornea is ﬂattened by a jet of air
rather than a prism
• No anesthesia is required

Rebound tonometer
• involves a 1.8 mm plastic ball
attached to a wire; deceleration
of the probe upon contact with
the cornea is proportional to
IOP.
• Anaesthesia is not required.
The instrument can be used for
self-monitoring – a tailored
personal version is available –
and for screening in the
community

Tonopen
hand-held electronic contact tonometer (a modifed version of
the older Mackay–Marg
tonometer). The probe tip contains a transducer that
measures applied force. Besides portability, its main
advantage is the facility to measure IOP reasonably
accurately in eyes with distorted or oedematous corneas, and
through a soft contact lens.

Perimetry

• The extent of normal visual field with a 5 mm white colour object is
• superiorly 50,*
• nasally 60*
• inferiorly 70*
• temporally 90*

Central visual field Peripheral visual field
Central field includes an area from the fixation
point to a circle 30° away. The central zone
contains physiologic blind spot on the temporal
side.
Peripheral field of vision refers to the rest of the
area beyond 30° to outer extent of the field of
vision.

Perimetry
Kinetic perimetry Static perimetry
In this the stimulus of known
luminance is moved from periphery towards the
centre to establish isopters.
This involves presenting a
stimulus at a predetermined position for a preset
duration with varying luminance
• confrontation method,
• Bjerrum screen
• Lister’s perimetery,
• tangent screen scotometry
• Goldmann’s perimetry
• Goldmann perimetry,
• Friedmann perimetry,
• Automated perimetry
Combined kinetic & static perimetry in goldmann perimetry

Tangent screen scotometry

Listers perimeter

Goldmanns perimeter

Humphreys automated perimeter

Assesment of colour vision

Test for colour vision
• Ischihara chart
• Anomaloscopes
• The lantern test
• Holmgren wools
• Farnsworth-Munsell 100-hue test

Lantern test

Holmgren wools

Ishihara colour plates

Farnsworth-Munsell
100-hue test.

Anomaloscope

• Diagnostic ultrasound is useful in patients with opacification of ocular
media or with problems of orbit.
• Ultrasound waves of 10 MHz frequency are used in ophthalmic
diagnosis.

A-scan (Time amplitude) B-scan (intensity modulation)
Axial length
Amplitude spikes
B-scan produces twodimensional dotted section of the
eyeball. The location, size and configuration of the
structures is easy to interpret

A scan
The height of the spike
indicates the strength of
the tissue sending back the
echo. The cornea, lens
and sclera produce very high
amplitude spikes, while
the vitreous membrane and
vitreous haemorrhage
produce lower spikes.

Electroretinogram

ERG waves
a wave • negative wave
• representing the activity of the rods and cones
b wave • Positive wave
• arising in the inner retinal layers (bipolar cells)
• large positive wave which is generated by Muller
cells, but represents the acitivity of the bipolar
cells
c wave • not to visual processes but to retinal metabolism,
associated particularly with the pigmentary
epithelium

Results of ERG
extinguished when there is complete
failure in the function of the rods and cones
(pigmentary
retinal dystrophy c/omplete occlusion of the retinal
artery/
complete old retinal detachment or advanced
siderosis)
subnormal in those conditions in which a large area
of the retina does not function;
negative in gross disturbances of the retinal circulation

Electro-oculography

EOG electrode placement

Electro-oculography
• the ratio of the light peak over the dark trough is known as the Arden
index.
• A value above 185 is normal,
• Below 150 abnormal
• 150-185 borderline

VER
• EEG recorded at the occipital lobe
• VER represents the macula-dominated response
• d/t large projection of the macular area in the occipital cortex
• only clinically objective technique available to assess the functional
state of the visual system beyond the retinal ganglion cells

2 modes of testing of VER
Flash VER Pattern reversal VER
it is recorded by using an intense
flash stimulation.
It merely indicates that light has been perceived by
the visual cortex.
It is not affected by the opacities in the lens and
cornea.
It is recorded using some
patterned stimulus, as in the checker board. In it the
pattern of the stimulus is changed
• (i) It can assess the integrity of macula and visual
pathway in infants, mentally retarded and aphasic
patients.
• (ii) It can distinguish between cases of organic and
psychological blindness (e.g.,malingering and
hysterical blindness).
• (iii) It can detect visual potentials in eyes with
opaque media

Pattern reversal VER

Purkinje images

• four purkinje images are produced by reflection from:
• Anterior surface of cornea
• Posterior surface of cornea
• Anterior surface of lens
• Posterior surface of lens

I Anterior surface of cornea Virtual & erect
II Posterior surface of cornea Virtual & erect
III Anterior surface of lens Virtual & erect
IV Posterior surface of lens Real & inverted

Number
Aphakia 2 1 & 2
Pseudophakia / normal 4 1,2,3 & 4
cataract 3 1,2&3

P4 is real & inverted

Binocular vision is studied by synaptophore

Synaptophore

CAM stimulator therapy in amblyopia

Examination in case of heterophoria
• Cover-uncover test
• Prism cover test
• Maddox rod test
• Maddox wing test

Cover uncover test
in heterophoria

Prism cover test in heterophoria

Maddox rod test in heterophoria

Maddox wing test

Tests for binocular vision in
manifest squint

Worths 4 dot test

patient wears
goggles with red lens in front
of the right and green
lens in front of the left eye

Right suppression Normal Left suppression
If the patient sees only three
green lights, he has
right suppression
If the patient sees all the four
lights in the
absence of manifest squint, he
has normal
binocular single vision
When the patient sees only two
red lights, it
indicates left suppression

Macular function test

Macular function test
• 1. Two light discrimination test
• 2. Pinhole test
• 3. Maddox rod test
• 4. Amsler grid test
• 5. Based on entoptic phenomenon
• 1. Purkinje vessel shadow
• 2. Blue field entoptoscope- flying corpuscle test
• 6. PAM – potential visual acuity metre
• 7. Laser Interferometry
• 8. ERG- Electro retinogram
• 9. VEP-Visual Evoked Potential

Amsler grid is a macular function test

Retinoscopy
• skiascopy or shadow test
• objective method of finding out the error of refraction by the method
of neutralization

Results of retinoscopy
No movement of red reflex With movement of red reflex along
the movement
of the retinoscope,
Against movement of red reflex to
the movement
of the retinoscope
myopia of 1D either emmetropia or
hypermetropia or myopia of less than
1 D.
myopia of more than
1 D

Computerised autrorefractometer

Instruments

Wire speculum
Helps to retract eyelids

Strabisumus hook/muscle hook
To hold EOM during
squint surgery

Lacrimal probe

OPHTHALMOLOGY INSTRUMENTS FOR NEET PG REVISION NOTES

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OPHTHALMOLOGY INSTRUMENTS FOR NEET PG REVISION NOTES