(The following are answers to the eight stations in mock examination 1. To return to each station, click on the number)

       a. T2-weighted MRI. 
          (This is shown by the high signal of the CSF within the ventricles. 
           In MRI scan of the brain, T1-weighted image is useful for demonstrating anatomical details whereas T2 
           excellent pathology)


        b. The advantages of MRI over CT scan of the brain include:

      •             non-ionising radiation
      •             excellent soft tissue contrast
      •             multiplanar images (axial, sagittal and coronal)
      •             no artefact from the bone and is especially useful for posterior fossa imaging.

        c. High signal lesions within the periventricular white matter of both cerebral hemispheres
            (These represent multiple plaques of demyelination see figure below, these plaques have high water content and 
              therefore appear white on T2-weighted images.) 

The jelly-like nodules above the ventricle
are the plaques seen on the MRI scan

        d. Multiple sclerosis.

        e. Optic neuritis.

         a. B-scan ultrasound.
                 (A-scan gives a one-dimensional images whereas B-scan gives a two-dimentsonal images) 

         b. Higher.

(Ocular ultrasound has a frequency range of 8 -10 MHz compared with abdominal ultrasound which 
has a frequency range of 1 - 5 MHz. The higher frequency in ocular ultrasound produces shorter 
wavelength and therefore better resolution of the small ocular structures. The longer wavelength of 
abdominal ultrasound gives better tissue penetration at the expense of less structural details.)

         c. Retinal detachment.
             (The scan shows a V-shaped image with insertion at the optic nerve head. This indicates a funnel-shaped retinal 


       a. The corneal topography shows corneal steepening with downward displacement of the apex.

       b. Early keratoconus (the maximum power of cone is only 47.50 D)

       c. The following signs may be present in this patient:

      • corneal thinning and steepening of the apex
      • vertical striae
      • Fleischer's ring below the cone


      a. The required spectacle power is calculated using the formula for lens effectivity
          Do = Do / (1-sDo) = -10 / ( 1-0.1) = -11.11D

      b. The change in spectacle magnification is
           = retinal image size with the contact lens / retinal image size with the spectacle
           = power of the contact lens / power of the spectacle
           = -10.00 / -11.11
           = 0.9

           The percentage spectacle magnification change is
           =  (0.9 - 1) 100
           =   -10%

5.       a. 

                                               Fo = objective lens  fo = focal length of the objective lens 
                                               Fe = eye piece        fe = focal length of the eyepiece lens 

          b. 5cm
             (The length of the Galilean telescope is equal to the focal length of the objective lens minus the focal length of 
              the eyepiece lens) 

          c. Magnification of the Galilean telescope = W' / W 
                                                                                = Fe / Fo
                                                                                = fo / fe
                                                                                = 2

         a. Using the IOL formula
               = A - 2.5 (axial length) - 0.9 (average K reading )
               = 118 - 2.5 (23) - 0.9 (43)
               = 21.8 D
              ( As the lens come in step of 0.5 D, the one used would be 22.0D)

          b. Moving the lens forward increases the power of the lens and therefore a weaker lens is needed. This is
              usually 0.5D less than in the bag IOL


a. Venous phase 

b. The following signs are present:

      • extensive areas of hypofluorescence in the posterior pole 
      • dilatation of the veins
      • leakage of dye at the optic nerve head
c. Central retinal vein occlusion (see picture below).




a. The Hess chart shows left inferior oblique underaction with overaction of the contralateral superior 
            (This is best shown in the small squares; the lower fields are normal) 

b. Left Brown's syndrome

c. Congenital (such as short anterior superior oblique tendon sheath or tight superior oblique tendon.)


  •   injury to the trochlea causing scar tissue formation
  •   swelling of the tendon from inflammatory conditions such as rheumatoid arthritis and scleritis.

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