Test one

1. True statements about the circle of least confusion include: a. it is the clearest image that a spherocylindrical lens can      produce  b. it is located at a point corresponding to the spheroequivalent      of a spherocylindrical lens  c. it is in the mid point of the Sturm's interval  d. it is increased if the distance between the two focal lines      of a spherocylindrical lens is increased  e. the shape of the circle of least confusion is influenced by the      shape of the spherocylindrical lens Answer1.    a. T    b.T    c.T    d.T    e.T Circle of least confusion is the clearest image that an astigmatic eye or a spherocylindrical lens can produce is located at the point corresponding to the spherocylindrical lens is situated between the two focal lines of a spherocylindrical lens and therefore mid-point of the Sturm's interval is increased in size if the distance between the two focal lines of a spherocylindrical lens is increased its shape is influenced by the shape of the spherocylindrical lens. The circle is circular if the lens is circular otherwise it will takes on the shape of the lens   2. The following are true: a. simple myope can be corrected fully with      minus sphere only  b. simple myopic astigmatism can be corrected fully      with a minus sphere lens and a minus cylindrical lens  c. compound myopic astigmatism can be corrected      fully with a plus sphere lens and a minus cylinder  d. simple hyperopic astigmatism occurs when one      principal meridian is on the retina and the other is      behind the retina  e. mixed astigmatism occurs when one principal meridian      is on the retina and the other is behind the retina Answer2.    a.T    b.F   c.F    d.T    e.T Simple myopia correctable with minus sphere lens only Simple hyperopia correctable with plus sphere lens only Simple myopic astigmatism correctable with plano sphere with minus cylinder Simple hyperopic astigmatism correctable with plano sphere with plus cylinder or plus sphere of same power as minus cylinder Compound myopic astigmatism correctable with minus sphere with minus cylinder Compound hyperopic astigmatism correctable with plus sphere with plus cylinder or plus sphere with minus cylinder of less magnitude than the sphere Mixed astigmatism correctable with plus sphere with minus cylinder of greater magnitude than the sphere   3. True statements about ultrasound include: a. the ultrasound used in diagnosis has a frequency of greater      than 20 kHz  b. piezoelectric effect is used to emit ultrasound as well      as analysing the echo  c. ultrasound is propagated as a transverse wave through      a medium  d. ultrasound travels faster through vitreous than the lens  e. ultrasound with longer wavelength penetrates the tissue      deeper than one with shorter wavelength Answer3.    a.T    b.T    c.F    d.F    e.T Ultrasound: acoustic wave with frequencies greater than 20 kHz the transducer of the ultrasound contain a crystal which emits the sound wave when excited by an electrical signal (piezoelectric effect), the sound emitted is reflected by the body tissue which then acts on the crystal to produce an electrical signal (again a piezoelectric effect). The signal is analysed by a computer to produce an image it is propagated a a longitudinal wave consisting of alternating compression and rarefraction of molecules as it travels through a medium the velocity is dependent on the medium and is faster in solid than liquid medium with longer wavelength penetrates deeper into the tissue but has a poorer resolution than shorter wavelength   4. The following are true about Hess's test: a. ocular dissociation is necessary  b. it can be used to calculate the amount of ocular deviation  c. a visual acuity of better than 6/12 is essential      for the testing  d. the eye with restricted movement usually has a smaller      field on the the Hess's chart  e. it can be used to test the field of binocular single vision. Answer4.    a.T    b.T    c.T    d.T    e.F Hess's test: used to measure and classifying ocular movement disorders can be used to calculate the amount of ocular deviation because each small squares on the Hess's chart subtends 5 degrees at a working distance of 50 cm  foveal fixation is necessary for the test and therefore a visual acuity of better than 6/12 is essential restricted eye movement gives rise to smaller field on the Hess's chart   5. True statements about dissociated vertical deviation include: a. it is unilateral in 90% of the cases  b. it is associated with infantile esotropia  c. it is caused by inferior oblique overaction  d. it can be diagnosed with Bielschowsky darkening      wedge test  e. it can be demonstrated with Bagolini filter bar Answer5.    a.F    b.T    c.F    d.T    e.T Dissociated vertical deviation: describe the elevation of the eye when the light entering it is reduced it is associated with infantile esotropia and is bilateral in the majorityof the cases though asymmetrical the cause is unknown it can be diagnosed by cover test in which the occluded eye showselevation but returns to its original position when the occluder is removed. Bielschowsky darkening wedge test and Bagolini filter bar can also be used as they reduced the amount of light entering the eye

1

Click here to return to Contents