Test 16  (Practical clinical refraction)

1. During clinical refraction:

a. accommodation results in a more myopic prescription

b. the visual acuity is measured binocularly for distance 
    and near

c. occlusion is recommended for patient with nystagmus to
    reduce the ocular movement

d. a high minus lens over the non-examining eye of a 
    patient with bilateral congenital nystagmus can reduce 
    the nystagmus

e. recent wearing of gas permeable lens may give 
    erroneous results 
 

Answera.T   b.F   c.F    d.F   e.T
Accommodation causes myopic shift.
The visual acuity is examined uniocularly for distance and near. 
Occlusion of one eye in congenital nystagmus worsens the nystagmus. Fogging with  a high plus lens is recommended.
Contact lens especially gas permeable lens can cause corneal warpage give false refractive results.
Photostress from bright light may affect the visual acuity and should be performed last.

 

2. The following tests depend on binocular vision:

a. Maddox rod

b. Maddox wing

c. Worth's four dots test

d. Duochrome tests

e. Bagolini's test
 

Answera.T   b.T   c.T   d.F   e.T
Duochrome does not require binocular vision.

3. Fogging::

a. reduces or eliminates accommodation 

b. brings the image behind the retina

c. uses strong plus lenses

d. is achieved by adding minus sphere power to 
    plus corrections

e. is achieved by reducing minus sphere power in minus 
    corrections. 
 

Answera.T   b.T   c.F   d.T   e.T
Fogging is used to reduce or eliminate accommodation. It brings the image in front of the retina so that 
accommodation blurs the image further. It is achieved 
by adding a limited amount of minus sphere power to 
plus corrections or by reducing minus sphere power in 
minus corrections. The end point is the most plus power, or least minus power, that gives the best vision. 

 

4. In objective refraction:

a. accommodation is stimulated if the patient stared at 
    the light from the retinoscope

b. 'with' motion occurs in high myope if the sleeve of the 
    retinoscope is placed in the plano mirror position

c. 'against' motion occurs in hypermetrope if the sleeve of 
    the retinoscope is placed in the concave mirror position

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

e. the power of the working distance lens in dioptres is 
    proportional to the working distance in metres
 

Answera.T   b.F   c.F    d.T   e.F
In objective refraction, accommodation is reduced by getting the patient to look at the distance or using 
cycloplegic drug. 'With' motion occurs in hypermetrope and 'against' motion occurs in high myope if the sleeve of the retinoscope is placed in the plane mirror position. 
The reverse occurs if the sleeve of the retinoscope is placed in the concave mirror position. The power of the working distance lens in dioptre is inversely proportional tot he working distance in metres.

5. Using minus cylinder during refraction :

a. avoids stimulation of  accommodation in young 
    hypermetropic patients

b. may overcorrect hypermetrope in the elderly

c. may overcorrect hypermetrope in cycloplegic refraction

d. may undercorrect myope patients

e. is a major cause of spectacle intolerance
 

Answera.T   b.T   c.T    d.F   e.F
The use of minus cylinder in young hypermetrope 
prevents stimulation of accommodation but may overcorrect hypermetrope in the elderly and when performing cycloplegic refraction. 

6. The following is the power cross of a patient examined at 2/3 meters 
    (before correcting for the working distance):

a. when a streak retinoscopy is used to neutralize the eye 
    at 30⁰  the power of the lens needed is +4.00

b. if the patient were to accommodate the power cross 
    will have a higher plus power

c. if a +5.00DS lens is placed in the trial frame; a 
    -1.00DC is required to neutralize the eye at 120⁰

d. the lens required for correcting this patient's refraction 
    can be +2.50/+1.00 X 30

e. the lens required for correcting this patient's refraction 
    if the working distance is 1/2 m can be 
    +3.00/-1.00X 120
 

Answera.F   b.F   c.T   d.T   e.T
The power is 90 degrees from the axis and when the 
retinoscopy is used to neutralize the eye at 30 degrees, the required power will be +5.00D.
Accommodation causes a myopic shift resulting in a lower plus power during refraction.
The working distance lens is -1.50 for 2/3 metres and -2.00 for 1/2 metres.

 

7. In subjective refraction:

a. the spherical power should be tested before the cylinder

b. the axis of the cylinder should be verified before the 
    power

c. Duochrome test should be only performed when the 
    spherical power is corrected to within 1 D of 
    emmetropia

d. if the letters against the green background appear 
    clearer on the Duochrome test, more plus correction or 
    less minus correction is indicated.

e. Maddox rod test is useful in patients with manifest 
    squint
 

Answera.T   b.T   c.T   d.T  e.F
The spherical power should be verified before the cylinder and the axis of the cylinder should be verified before its power.
Maddox rod is used to check muscle balance for distance.

8. The interpupillary distance:
 

a. can be measured using the corneal reflex

b. can be measured by noting the distance between the 
    nasal limbus of one eye and the temporal limbus of the 
    other

c. used in making spectacle is 1 mm less than the 
    anatomical interpupillary distance

d. for a patient with accommodative esotropia is the 
    distance between the two corneal reflexes without 
    spectacle correction

e. for a patient with intermittent exotropia is the distance
    between the two corneal reflexes when the two eyes 
    are in primary position
 

Answera.T   b.T   c.T   d.F   e.T
The interpupillary distance is important to avoid decentring 
the optical axis which can cause spectacle intolerance. The distance is shorter for reading than distant glasses. 
For a patient with accommodative esotropia, it is important to have the eyes in primary position before measuring the interpupillary distance. This can be achieved with either the correcting lenses in place or using cover test.

 

9. A 42 year-old myopic man recently changes his glasses and 
    find them uncomfortable despite having a visual acuity of 6/6 in 
     both eyes. The following may be responsible:

a. over-correction of myopia

b. onset of presbyopia

c. change of lens form

d. change of axis

e. decentring  of the lens
 
 

Answera.T   b.T   c.T   d.T   e.T
Onset of prebyopia may make reading difficult especially if the patient is over-corrected. Myope tends to be less tolerant of a change in lens form and axis of the cylinder. Decentring of the lens causes prismatic effect.
 

10. Regarding refraction in children:

a. myopia is more common than hypermetropia

b. refractive amblyopia can occur if there is more than 1 
    dioptre of hypermetropic anisometropia

c. increased accommodation is used by children to 
    overcome uncorrected hypermetropia

d. myopia tends to progress as the child grows older

e. correction of hypermetropia can reduce exophoria
 

Answera.F  b.T   c.T   d.T   e.F
Hypermetropia is more common than myopia amongst UK children. It is recommended that hypermetropic anisometropia of more than 1D should be corrected because of the risk of refractive amblyopia. Increased accommodation is used by children to overcome 
uncorrected hypermetropia; as accommodation is associated with convergence accommodative esotropia can result. As children grow older, the axial length of the eye increase leading to more myopia. Correction of myopia can reduce exophoria due to stimulation of accommodation.

 

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