Introduction of the instrument - Aesthesiometer and its procedure, types, with description of pros and cons

1. CORNEAL
AESTHESIOMETER
Presented by :
Simanta Borah
B.Optom 3rd Year
RCOJ

2. Objectives
Introduction
History
Uses
Corneal sensitivity
Key points to note about ocular sensation include
Methods :
 Qualitative method
Quantitative method

3.  Draw back of cochet-bonnet aesthesiometer
 Electromechanical aesthesiometer
 Causes of corneal hypoaesthesia and differential diagnosis
 Testing of corneal hypoaesthesia
 Advantages & disadvantages
 References

4. Introduction
An Esthesiometer (British spelling Aesthesiometer) is a device used to measure tactile
sensitivity of the cornea
The measure of degree of tactile sensitivity of the cornea is called Corneal
Aesthesiometry

5. History
 The first aesthesiometer was described in 1894, by Von Frey
 In 1932 Franches chetti, improved on von Frey’s version and then in 1956
Boberg-Ans reports a device using a single nylon thread with a constant
diameter but variable length
 Cochet-Bonnet improved on the Boberg-Ans version and developed two
different models. One model uses a diameter of 0.08 mm which allows
pressure of 2 to 90 mg/0.005 mm2 and the second model uses a diameter
of 0.12 mm with pressure ranging from 11 to 200mg/0.0113 mm2

6. Uses
 Corneal esthesiometry is typically used clinically to evaluate for
neurotrophic keratopathy
 In research, esthesiometry has been used for various purposes to include
recording the duration of an analgesic on the cornea or indicating the
corneal health in long-term contact wearers
 Can be used pre-operative or for post-operative recovery

7. Corneal sensitivity
 The sensitivity of the cornea is a protective mechanism. The ophthalmic
branch of the fifth cranial nerve (trigeminal) carries sensory fibers for
the cornea
 If the cornea senses stimulation (ranging from mild irritation to intense
pain), then the eyelid will close, providing protection to the cornea and
distribution of tears
 As the corneal sensitivity is decreased, then the blinking/tearing
mechanism will decrease, leaving the corneal epithelium exposed to
dehydration

9. Key points to note about ocular sensation
include:
 Greatest in the central cornea except in elderly patients where it is
more sensitive in the periphery
 Drops rapidly as distance increases from the limbus
 Falls with increasing age and is not affected by iris color
 More sensitive in the temporal limbus than the inferior limbus
 Reduction has been reported in Diabetes Type I and II

10. Methods
Qualitative
method
Quantitative
method

11. Qualitative method
 The most commonly used method in clinical practice which is qualitative in
nature, is the use of a cotton-tipped applicator
 Topical anesthetics should not be used prior to testing corneal sensation
 It is recommended to approach the patient from the side and test all four
quadrants. Record the sensation in each location as normal, reduced, or
absent

12. Cotton wisp test
 This is a gross test of
corneal sensitivity that
would be used if a
Cochet-Bonnet
instrument was not
available
 The basic idea is to touch
the cornea with a wisp of
cotton to determine
sensation of the patients
cornea whether he can
feel or not

13. Note:
 To create the tool, use your fingers (after washing them) to tweeze some
fibers from the end of a cotton tipped applicator. Twirl the fibers to create
a single strand. If the strands is too thin at the end, use scissors to shorten
it

14. Procedure
 Explain to the patient that the test is not painful
 Touch the cornea with the fibers and the patient is to signal when
sensation occurs
 Have the patient fixate straight ahead
 Touch the central cornea with the wisp in a perpendicular orientation that
is slightly below the line of sight. Continue to touch, moving slowly toward
the cornea, until the patient signals, or until the wisp bends slightly. The
patient might blink or tear before signaling
 Test the other eye, asking the patient to compare the two. The test can be
repeated as necessary

15.  The results are based upon two responses from the patient
 Do you feel the sensation?
 Is there a difference between the two eyes?
Do not use a blink reflex as a response, because a
blink may occur normally

16. Notes
 Anaesthetics should not be used before the testing
 Ideally, should not use any drops before testing. If there is corneal
disease present, be sure to use a separate wisp for each eye

17. Quantitative method
 There are various quantitative methods that are typically reserved for
research or complicated cases. The most common quantitative method is
the handheld esthesiometer (Cochet-Bonnet). Other methods reported
include:
A.Noncontact air puff technique
B. Chemical stimulation using capsaicin
C. Thermal stimulation with a carbon dioxide laser

18. Quantitative methods
Cochet-Bonnet aesthesiometer(Handheld
aesthesiometer)
Non-contact corneal aesthesiometer

19. Cochet-Bonnet aesthesiometer
 Instead of a cotton wisp, the C-B
aesthesiometer uses a nylon
monofilament (similar to fishing
line) to stimulate the cornea The
stiffness of the filament is controlled
by changing the length of the
filament with a slider on the side of
the pen
 As the length of the line decreases,
pressure increases from
11mm/grms to 200mm/grms
slider

20.  A cornea that requires a greater pressure to elicit a response would be less
sensitive. The procedure is similar to that described above
 If we want to start with low "pressure" (greater length of line) and decrease
the length of the line until sensation is reported
 Record the scale reading as the result. If no sensation is reported, then
record that there was no response at the highest scale reading
(200mm/grms)

22. Non contact corneal
aesthesiometry(NCCA)
 NCCA uses controlled pulses of air of pressures to stimulate the cornea
 It measures the threshold sensitivity to a composite stimulus consisting of
air pressure along with tear film evaporation and disruption
 Measurements are made in millibars of air pressure required

23. Drawback of cochet-bonnet
aesthesiometer
 The patient is usually afraid when he sees a hand holding a black rod
advancing toward his eye
 The examiner cannot tell when the tip has touched the cornea except by
observing the change in the bend of the hair. This reduces the accuracy of
the measurement, particularly as the hair is very fine and thus difficult to
see
 The force applied to the cornea is measured indirectly. The operator must
notice when the hair bends and this is the indication that a force has been
applied
 The nylon hair cannot easily be sterilized

24. Electro mechanical corneal
aesthesiometer

25. Larson-Millodot
aesthesiometer(1969)
 The probe tip is made of fine platinum wire bent double so that the tip has
known and reproducible dimensions. This wire may be flame-sterilized as is
the practice in microbiology
 The probe is automatically advanced toward the eye at a constant rate
upon the operator's command. When the cornea is touched with a force
equal to the test force, the probe is retracted quickly and automatically

26.  The force applied to the cornea can be set at any value within the range of
this instrument and this force will not be exceeded. The range of settings
for practical purposes is from 1 to 200mg., and any force within these
limits can be set with an accuracy of ±5 mg Operation

27. Fig: L-M aesthesiometer being used to check C-B instrument

29. In which condition corneal
sensation is lost?
 Herpes simplex keratitis
 Herpes zoster ophthalmicus
 Diabetic condition
 Corneal ulcers

30. What are the causes of corneal
hypoaesthesia
 As a result of reversal reaction in the trigeminal nerve (V cranial nerve)
 As a result of exposure of the cornea in lagophthalmos
 As a result of severe scleritis and damage to the ciliary nerves (often
bilateral)
 As a result of bacterial infiltration and secondary atrophy of ciliary and
corneal nerves (often bilateral)

31. Corneal Hypoesthesia Differential
Diagnosis
Corneal hypoesthesia can occur from any etiology that
causes CN V damage. Important etiologies to
consider include:
 Herpes simplex keratitis
 Herpes zoster ophthalmicus
 Surgical trauma (PK, LASIK, large limbal incisions, ablation of the trigeminal
ganglion)

32.  Topical medications (anesthetics, NSAIDs, ß-blockers, and carbonic
anhydrase inhibitors)
 Tumors (acoustic neuroma, neurofibroma, or angioma)
 Multiple sclerosis
 Hansen disease (leprosy)
 Hereditary causes - Familial dysautonomia (Riley-Day syndrome)
 Cocaine abuse
 Cerebrovascular events
 Aneurysms

33. Testing of Corneal Hypoasthesia
 Corneal hypoaesthesia is done by observation of blinking; if regular, there
is no reason for testing
 If in doubt, or in the case of lagophthalmos, corneal sensitivity is tested
with a whisp of clean cotton wool, touching the cornea from the side and
observing the blink reflex

34. Advantages
 It is a easy process to check the sensitivity of the cornea
 Take less time to test
 Easy to carry this instrument

35. Disadvantages
It does not give the accurate result

36. References
 http://www.west-op.com/aesthesiometer.html
 https://www.youtube.com/watch?v=owiljey1ol8
 https://en.m.Wikipedia.org.aesthesiometer
 www.prohealthcareproducts.com/blog/von-frey-hair-aesthesiometer

37. Thank You