Test 14  (Instruments)

1. The direct ophthalmoscope:

a. gives an angular magnification of 15X

b. gives a real erect image

c. makes the disc of a myope appears larger than that of 
    a hypermetrope

d. makes the disc of a hypermetrope larger than that of an
    emmetrope

e. is better than indirect ophthalmoscope in detecting
    diabetic maculopathy
 

Answera.T   b.T   c.T    d.F   e.F
The direct ophthalmoscope gives an angular magnification of 15X. The image formed is virtual and erect. 
The size of the optic disc when viewed through a direct ophthalmoscope is larger in myope than emmetrope which in turn is larger than in hypermetrope. Diabetic maculopathy is better detected with indirect ophthalmoscope.

 
 

2. When using a direct ophthalmoscope, the field of view:

a. is about 6 degrees 

b. is smaller than that through an indirect ophthalmoscope

c. is larger in an eye dilated with mydriatic

d. is larger in a myope compared with a hypermetrope

e. is larger when the observer moves towards the patient
 

Answera.T   b.T   c.T   d.F   e.F
The field of view refers to the retina that can be seen through the ophthalmoscope. It is about 6 degrees with a direct ophthalmoscope and 25 degrees through an indirect ophthalmoscope. 
The field of view is increased if the pupil is dilated and when the observer moves towards the patients. It is larger in hypermetrope than emmetrope which in turn is larger than in a myope.
 
 

3. The image formed by an indirect ophthalmoscope:

a. is upside down

b. is real

c. is laterally inverted

d. is not affected by the refractive state of the patient

e. is formed between the observer and the condensing lens
 

Answera.T   b.T   c.T    d.F   e.T
The image formed by the indirect ophthalmoscope is real and inverted (both vertically and laterally). It is situated between the observer and the condensing lens. The image formed is affected by the refractive state of the patient but not to the same extent as with direct ophthalmoscope.
a
a

4. In indirect ophthalmoscopy, the field of view is affected by:

a. size of the patient's pupil

b. size of the observer's pupil

c. diameter of the condensing lens

d. power of the condensing lens

e. the refractive state of the observer
 

Answera.F   b.T   c.T    d.T   e.F
The field of view in indirect ophthalmoscopy is affected by:
size of the observer's pupil
diameter of the condensing lens ie. the larger the diameter, the greater the field of view
the power of the condensing lens, a higher power gives a smaller magnification but greater field of view.
The size of the patient's pupil affects the field of illumination.
 

5. The advantages of indirect ophthalmoscope over direct 
    ophthalmoscope include:

a. binocular view

b. larger field of view

c. higher magnification

d. erect image

e. the instrument is smaller size
 

Answera.T   b.T   c.F   d.F   e.F
Direct ophthalmoscope has the following advantages 
over indirect ophthalmoscope:
easily portable
image not inverted
and larger magnification
On the other hand, indirect ophthalmoscope has the following advantages:
binocularity
higher field of view and the presence of teaching mirror

 
 

6. Regarding the condensing lenses used in indirect ophthalmoscope:

a. it is usually aspheric to reduce aberration

b. the image formed is located at or near the first principal
    focus of the condensing lens

c. the stronger the condensing lens used the higher the 
    angular magnification

d. the stronger the condensing lens used the larger the field
    of vision

e. when deliver laser photocoagulation through the 
    condensing lens, the stronger the condensing lens the
     larger the laser spot magnification
 

Answera.T  b.F  c.F   d.T  e.T
Aspheric lens is used to reduce aberration during indirect ophthalmoscope. The image formed is located at or near the second principal focus of the condensing lens.
The stronger the condensing lens used the lower the angular magnification but the larger the field of vision. However, the laser spot magnification increases the stronger the condensing lens used.

 
 

7. During indirect ophthalmoscopy:

a. observer needs to accommodate to see clearly

b. image size in emmetrope remains the same  irrespective 
    of the position of the condensing lens

c. image size in myope increases when the condensing lens
    moves towards the eye of the patient

d. image size in hypermetrope decreases when the 
    condensing lens moves towards the eye of the patient

e. image from myopic retina always falls within the second 
    principal focus of the condensing lens
 

Answera.T  b.T  c.F   d.F  e.T
The image is formed 40 to 50 cm from the observer's eye and therefore accommodation is needed. The image size in emmetrope remains the same irrespective of the 
position of the condensing lens. In myope, the image size increases when the condensing lens moves away from the eye and decreases when the lens moves towards the eye of the patient. The reverse is true for
hypermetrope. 
The image from myopic retinal always falls within the second principal focus of the condensing lens, whereas that of the hypermetrope eye always falls outside the second principal focus of the lens.

 

8. The following are true about the retinoscope:

a. two mirror systems are used: the plane mirror and the
    convex mirror

b. in the UK, most retinoscope gives a plane mirror effect 
    when the condensing lens is moved down the shaft of 
    the instrument

c. scissors shadows are usually seen in patient with widely
    dilated pupil

d. the speed of the reflex increases as the neutralization 
    point is near

e. a myope who accommodates excessively during 
    retinoscopy will result in a more myopic refraction
 

Answera.F  b.T  c.T   d.F  e.T
The two mirror systems used are: the plane mirror and
the concave mirror. In the UK, most retinoscope used gives a plane mirror effect when the condensing lens is moved down the shaft of the instrument. Scissors shadows result from a difference in refraction with the different zone of the pupil and is most commonly seen in dilated pupil.
The speed of the reflex increases as the neutralization point is near. 
Excessive accommodation gives a myopic shift and therefore the result of refraction will be more minus.

 
 

9. When using the plane mirror technique during retinoscopy:

a. a 'with' movement is neutralized with a plus lens

b. an 'against' movement is neutralized with a minus lens

c.  a 'with' movement always indicates hypermetropia

d. an 'against' movement always indicates myopia

e. the neutral point occurs when the patient's far-point 
    coincides with the observer's nodal point
 

Answera.T  b.T  c.F  d.T  e.T
With the plane mirror technique, plus lens is used to neutralize with movement and minus lens for against movement. While an against movement always indicates myopia, a with movement may be seen in myopic patient if the myopia is less than the dioptric value of the observer's working distance (for example at a distance of 2/3 m, a with movement is seen if the myopia is less than -1.50D.
The neutral point occurs when the patient's far-point coincides with the observer's nodal point..
a
a

10. The keratometer:

a. uses the cornea as a convex mirror in the measurement of corneal curvature

b. measures only the central 3 mm of the cornea

c. can be misleading in patients who have had corneal 
    transplantation

d. doubles the central image size to overcome the effect 
    of eye movement

e. is more important in fitting soft contact lens than rigid 
    gas permeable contact lens
 

Answera.T  b.T  c.T  d.T  e.F
The keratometer uses the first Purkinje-Sanson's image. It measures only the central 3 mm and can be 
misleading in patients who had had radial keratectomy 
or corneal transplant. To negate the ocular movement, the central image is doubled during keratometry. 
Keratometry is important for contact lens fitting but more so for rigid gas permeable contact lens than soft contact lens.
a
a

11. The following are true about the keratometer:

a. in the Javal-Schiøtz instrument, the object size is fixed

b. in the Javal-Schiøtz instrument, each step of the mire is 
    equivalent to 1/2 a dioptre

c. Wollaston prism is used in Javal-Schiøtz instrument

d. von Helmholtz instrument uses rotating glass plates to
    double the size of the image

e. the power of the cornea is equal to 337.5 divided by 
    the radius of curvature in mm.
 

Answera.F  b.F  c.T  d.T  e.T
In the Javal-Schiøtz instrument, the object is varied to give a fixed image size. Each step of the mire in Javal-Schiøtz instrument is equivalent to 1 dioptre of corneal power. Wollaston prism is used to double the image formed by reflection on the cornea.
von Helmoholtz instrument uses rotating glass plates to double the image size. 
The power of the cornea is equal to 337.5 divided by the radius of curvature in mm.
 
 

12. The slit-lamp:

a. is a low powered binocular compound microscope

b. contains prisms that shorten and invert the image 

c. incorporates Galilean telescopes that are used to
   magnify the image

d. visualizes vitreous best with blue light

e. can be used to perform Watzke's sign
 

Answera.T  b.T  c.T  d.F e.T
The slit-lamp is a lower powered binocular compound microscope. It contains prisms that shorten the instrument and inverts the image. Galilean telescopes are used to achieve magnification. 
The vitreous is best viewed with green light as it scatters more and allow vitreous to be better visualized. The slit-lamp can be used to detect the presence of macular hole using the Watzke's sign.
 
 

13. The following are true about the techniques used in slit-lamp:

a. uncoupling of the microscope and light source is needed
    in sclerotic illumination

b. specular illumination is best for visualizing the 
    endothelium

c. the light and the microscope are co-axial in 
    retroillumination

d. lateral illumination is best for visualizing the anterior
    capsule

e. diffuse illumination is best for visualizing iris atrophy
 

Answera.T  b.T  c.T  d.F  e.F
In sclerotic illumination, the light and the microscope are uncoupled and the light is focused on the limbus at 3 and 9 O'clock. It is a useful technique for visualizing fine corneal opacity. Specular illumination is useful for viewing endothelium. 
In retroillumination, the light and the microscope are co-axial and it is best for visualizing iris atrophy and iris transillumination as in pseudoexfoliation syndrome and pigment dispersion syndrome.
Diffuse illumination is best for viewing the anterior capsule.
.
 
 

14. The Hruby lens:

a. is a powerful biconcave lens

b. gives a virtual, erect and diminished image

c. is useful for laser photocoagulation of the retina

d. requires a coupling solution in order to visualize 
    the retina

e. forms retinal image between the lens the observer
 

Answera.F  b.T  c.F  d.F  e.F
The Hruby lens is a powerful plano-concave lens which gives a virtual, erect and diminished image. It is difficult to master and the image is too small for reliable photocoagulation.
Coupling solution is not required as the lens does not come into contact with the eye. It is held with the concave side towards the patient. The image is formed within the eye.
.
 
 

15. Regarding the indirect lens

a. 90D has a larger angular magnification than a 78D

b. 90D has a larger field of view than a 78D lens

c. superfield has a larger angular magnification than a 78D

d. panfundoscope gives a larger field of view than a 90D

e. panfundoscope gives a real erect image
 

Answera.F  b.F  c.F  d.T  e.F
78D gives a larger angular magnification than 90D or superfield. Both 90D and superfield has the same angular magnification. The field of view is larger in a 78D than a 90D because the 78D has a larger diameter. The superfield has a larger field of view than 78D or 90D but smaller than panfundoscope. The panfundoscope gives a real inverted image.
 
 

16. The optical pachymeter (pachometer):

a. can be used to measure the corneal thickness as well as
    the anterior chamber depth

b. uses images I and II of Purkinje-Sanson's images to
    measure the corneal thickness

c. is more precise than ultrasound pachymeter

d. gives a larger corneal thickness in the early morning 
    than in the afternoon

e. can be used to decide if the ocular pressure recorded is
    spuriously high
 

Answera.T  b.T  c.F  d.T  e.T
Optical pachymeter can be used to measure both corneal thickness and the anterior chamber depth. Images II and II of Purkinje-Sanson images are used to measure the corneal thickness. Whereas II and III are used for the anterior chamber depth. 
Ultrasound pachymeter is more precise than optical pachymeter. 
The cornea tends to be thicker early in the morning on waking than during the day because of evaporation.
A higher intraocular pressure is associated with a higher ocular pressure reading. Correction can be done if the corneal thickness is known.

 

17. The OCT (optical coherence tomography):

a. uses reflection of infrared light to obtain retinal image

b. provides a three-dimensional picture of the retina

c. can give resolution as small as 10 micrometer

d. can be used to detect subtle macular oedema

e. can be used instead of fluorescein angiography in 
    deciding if a diabetic patient requires macular laser
 

Answera.T  b.F  c.T  d.T  e.F
The OCT works along the same principle as ultrasound scan but uses infrared light instead. It gives a two-dimensional picture of the retina and can have resolution as small as 10 micrometer. It can be used to detect macular oedema such as following cataract 
surgery or diabetic retinopathy. While it can detect subtle macular oedema in diabetic maculopathy, it does not show the leakage point or the integrity of the capillary network. Therefore, fluorescein angiography is still needed to detect the leakage point in difficult cases and the presence of macular ischaemia.
 
 

18. Regarding the autorefractors:

a. which are currently available on the market show large 
    variation in accuracy

b. Schiener double-pinhole principle are used in all 
    modern autorefractors

c. modern autorefractors are useful in checking binocular 
    muscle balance

d. accommodation and the size of the pupil can affect the 
    accuracy

e. photoscreening uses a polaroid camera to screen 
   children at risk of refractive amblyopia
 

Answera.F  b.F  c.F  d.T  e.T
The currently available autorefractors show little variation in accuracy. Schiener double -pinhole principle are used in some autorefractors but not all. Infrared optometers are also used. Binocular muscle balance cannot be measured with autorefractors. The accuracy of autorefraction is affected by the pupil size and accommodation.
Photoscreening with a polaroid camera can be used to detect ametropia in children.

 

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