Test 5

1. The following are true about magnifying glasses: a. the angular magnification of a hand-held magnifier with a power      of +20.00D is 5 X  b. Fixed stand magnifiers are designed to be used with a reading add  c. according to Kestenbaum's rule, a low vision patient with a Snellen      acuity of 6/36 will required +6.00D add for reading  d. the visual field is increased by increasing the lens-eye position  e. the hand-held magnifier is normally placed 25 cm from the object. Answer1.    a.T    b.T    c.T    d.F    e.T Magnifying glasses the hand-held magnifier is normally placed 25 cm from the object and therefore the angular magnification is given by the formula D/4 where D is the dioptre power of the magnifier. Therefore for a +20.00D magnifier, the magnification is 5X the fixed stand magnifiers are designed so that the stand height is less than the principal focal length of the lens. This produces divergent light from the image. In a presbyopic patient this should be used with reading glasses Kestanbaum's rule is used to estimate the power of the addition needed to read ordinary newsprint which is usually N7 or 8 in low vision patients. The power is obtained by diving the denominator the Snellen visual acuity fraction by its numerator. Therefore, a patient with visual acuity of 6/36 will require an add of +6.00D the visual field and magnification are increased when the lens-eye position is reduced. 2. The following diseases are associated with myopia: a. Stargardt's disease  b. Stickler's syndrome  c. juvenile retinoschisis  d. Marfan's syndrome  e. congenital glaucoma Answer2.    a.F    b.T    c.F    d.T    e.T Other diseases associated with myopia include: Down's syndrome Marfan's syndrome homocystinuria Weill-Marchesani's syndrome Ehlers-Danlos syndrome Stickler's syndrome Pierre-Robin's syndrome Pader-Will's syndrome congenital glaucoma 3. The range of stereoscopic vision as measured by the following tests       are true: a. 3000 to 60 seconds of arc with the Frisby's test  b. 3000 to 40 seconds of arc with the Titmus test  c. 480 to 15 seconds of arc with the TNO test  d. 1200 to 600 seconds of arc with the Lang stereostest  e. 3000 to 15 seconds with the synotophore Answer3.    a. F    b.T    c.T    d.T    e.F Stereoscopic vision is the awareness of disparity and therefore depth perception normal is around 60 seconds of arc can be measured by various tests: Frisby's test        600 to 15 seconds of arc Titmus test        3000 to 45 seconds of arc TNO test            480 to 15 seconds of arc Lang stereostest      1200 to 600 seconds of arc synotophore        720 to 90 seconds of arc 4. With regard to the visual field: a. lead poisoning causes cecocentral scotoma  b. tobacco amblyopia typically produces central scotoma  c. optic disc pit causes arcuate scotoma  d. retinoschisis causes binasal hemianopia  e. optic neuritis can cause homonymous hemianopia Answer4.    a.T    b.F    c.T    d.T    e.F Visual fields: cecocentral scotoma is typically seen in toxic optic neuropathy such as tobacco-alcohol amblyopia, ethambutol and lead poisoning optic disc pit can produce arcuate scotoma bilateral retinoschisis in the temporal quadrants can cause binasal hemianopia  homonymous hemianopia suggests retrochiasmal lesion. 5. True statements about ametropia include: a. myopia is commoner among school children than pre-school children  b. the incidence of hypermetrope increases with age  c. the antero-posterior diameter of the eye ball is increased in axial     myopia  d. in refractive hypermetrope the refractive power of the eye is too      strong  e. a hypermetropic patient is unable to focus on as a near a point as      a myopic patient Answer5.    a.T    b.T    c.T    d.F    e.T Ametropia: myopia is commoner among school children than pre-school children the incidence of hypermetropia increases with age in axial myopia, the refractive power is normal bu the antero-posterior diameter is increased. In refractive myopia, the antero-posterior diameter is normal but the refractive power is increased in axial hypermetropia, the refractive power is normal but the antero-posterior diameter is increase. In refractive hypermetrope, the antero-posterior diameter is normal but the refractive power is decreased in hypermetropia, the patient needs more accommodative power to bring a near object into focus and therefore he has a reduced amount of accommodative power to focus on as near a point as a myopic patient

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