Answer three questions out of four questions.

Transcription

1 Ancillary Material: Nil ACADEMIC UNIT OF OPHTHALMOLOGY & ORTHOPTICS Summer Semester 2016 ELECTRODIAGNOSIS 1 Hour 30 Minutes You are advised to use the 4 leaf answer book. There are four questions. Attempt THREE of the four questions only. Each question is of equal weighting. The marks for each part of each question are shown in brackets. Answer three questions out of four questions. 1. a) Explain how the pressure within an eye can be inferred by flattening a known area of the cornea. (20 marks) b) Describe, with the aid of a diagram, why the VEP is usually recorded using three electrodes across the occiput with a common reference electrode on the forehead. 2. a) Explain, with the aid of a sketch, how voluntary horizontal eye movements result in a time-varying voltage measured between two skin surface electrodes: one placed at the inner canthus and the other placed at the outer canthus. What information can such a recording give us? b) Describe two methods by which the VEP can be used to estimate visual acuity in infants. c) A patient with declining visual acuities has subnormal pattern electroretinograms (PERGs) with normal flash electroretinograms (ERGs). Briefly discuss the likely diagnosis. (5 marks) ORT211 1 TURN OVER

2 3. a) Ganzfeld (full-field) stimulation and pupillary dilatation are normally used for the ERG. Why? b) How does age affect ERG amplitude in normal subjects? c) Describe three standard ERG responses in terms of flash luminance, background luminance and the state of retinal adaptation. Explain why they differ for each response. (18 marks) d) What advantage do electrophysiological tests have over imaging techniques such as optical coherence tomography (OCT) when assessing the macula? 4. a) How does the body transmit intensity information down sensory and motor nerve fibres? Why is this method used? b) Describe, with the aid of an annotated diagram, how the conduction velocity of a motor nerve in the arm can be measured. Explain the reason for using two stimulation sites. Explain how age affects conduction velocity in normal subjects. (20 marks) END OF QUESTION PAPER ORT211 2

3 Ancillary Material: Nil ACADEMIC UNIT OF OPHTHALMOLOGY & ORTHOPTICS Spring Semester 2016 ELECTRODIAGNOSIS 1 Hour 30 Minutes You are advised to use the 4 leaf answer book. There are FOUR questions. Attempt THREE of the four questions only. Each question is of equal weighting. The marks for each part of each question are shown in brackets. 1. a) Explain how the pressure within an eye can be inferred by flattening a known area of the cornea. (20 marks) b) Describe, with the aid of a diagram, why the VEP is usually recorded using more than one occipital electrode. 2. a) Explain, with the aid of a sketch, how voluntary horizontal eye movements result in a time-varying voltage measured between two skin surface electrodes: one placed at the inner canthus and the other placed at the outer canthus. What information can such a recording give us? b) Describe two methods by which the VEP can be used to estimate visual acuity in infants. c) A cooperative patient with normal visual acuities has normal pattern electroretinograms (PERGs) but markedly delayed visual evoked potentials (VEPs). Briefly discuss the likely diagnosis. (5 marks) ORT TURN OVER

4 3. a) How do we ensure consistent homogeneous retinal stimulation for the standard electroretinogram (ERG)? b) What effect might increased axial length of the eye (myopia) have on the electroretinogram? c) Describe the electroretinogram response recorded using: i. a bright flash in a dark-adapted eye ii. a bright flash in a light-adapted eye iii. a dim flash in a dark-adapted eye (9 marks) d) Describe how the pattern electroretinogram (PERG) might be affected in: i. cone dystrophy ii. rod dystrophy iii. cataract (9 marks) e) Why do we need electrophysiological tests to assess the macula when imaging techniques such as optical coherence tomography (OCT) show very fine structural detail? 4. a) Describe the way in which intensity information is transmitted down sensory and motor nerve fibres, and explain the advantages of this system. b) Describe, with the aid of an annotated diagram, how the conduction velocity of a motor nerve in the leg can be measured. Explain the reason for using two stimulation sites. Explain how conduction velocity varies with age in normal subjects. (20 marks) END OF QUESTION PAPER ORT211 2

5 Ancillary Material: Nil ACADEMIC UNIT OF OPHTHALMOLOGY & ORTHOPTICS Spring Semester 2015 ELECTRODIAGNOSIS 1 Hour 30 Minutes You are advised to use the 4 leaf answer book. There are FOUR questions. Attempt THREE of the four questions only. Each question is of equal weighting. The marks for each part of each question are shown in brackets. 1. a) With the aid of a labelled diagram, explain the principles of a system commonly used to indirectly measure the pressure within the eye. b) Explain, with the aid of a sketch, how voluntary eye movements during the electrooculogram (EOG) result in a time-varying voltage at the recording electrodes. What information can such a recording give us? 2. a) List three methods for reducing noise in evoked potential recordings. b) A patient has normal vision in his right eye, but complains of having no perception of light in his left eye. Good quality visual evoked potentials (VEPs) were recorded when stimulating either eye with alternating chequers subtending four minutes of arc. What, therefore, is the minimum cortical acuity for each eye, and what does this tell us about his claim that he cannot see through his left eye? c) Why do we place more than one electrode across the occiput when recording the VEP? d) Why are the hexagonal elements of a multifocal electroretinogram (mferg) stimulus scaled to increase in size towards the periphery of the screen? ORT TURN OVER

6 3. a) Why do we use both full-field stimulation and pupillary dilatation for the standard electroretinogram (ERG)? b) Describe the stimuli and the state of retinal adaptation required to record (i) rod, (ii) mixed rod/cone, and (iii) cone ERGs. Explain why the responses differ. c) Describe how the pattern electroretinogram (PERG) might be affected in (i) retinitis pigmentosa (ii) maculopathy (iii) cataract. d) Why do we need electrophysiological tests to assess the macula when imaging techniques such as optical coherence tomography (OCT) show such exquisite detail? (12 marks) (9 marks) 4. a) Describe the way in which intensity information is transmitted down sensory and motor nerve fibres and why this method is used. b) Describe, with the aid of an annotated diagram, how the conduction velocity of a motor nerve in the leg can be measured. Explain the reason for using two stimulation sites. How does conduction velocity vary with age in normal subjects? (20 marks) END OF QUESTION PAPER ORT211 2

7 Ancillary Material: Nil ACADEMIC UNIT OF OPHTHALMOLOGY & ORTHOPTICS Spring Semester 2014 ELECTRODIAGNOSIS 1 Hour 30 Minutes You are advised to use the 4 leaf answer book. There are FOUR questions. Attempt THREE of the four questions only. Each question is of equal weighting. The marks for each part of each question are shown in brackets. 1. a) How does the body transmit intensity information down sensory and motor nerve fibres? Why is this method used? b) Why are two stimulation sites necessary in order to measure conduction velocity along a peripheral motor nerve? c) What voltage is typically required to stimulate a peripheral nerve using surface electrodes, and what may be done to reduce it in order to minimise discomfort? d) How might a demyelinating disorder, such as multiple sclerosis, affect a patient s visual evoked potential (VEP), and why? (9 marks) (9 marks) 2. a) Ganzfeld stimulation and pupillary dilatation are normally used for the elecroretinogram (ERG). Why? b) Describe the flash stimulus, background illumination and state of retinal adaptation required for three standard electroretinogram (ERG) responses, and explain why they differ. (4 marks) (12 marks) c) Explain, with the aid of a sketch, how voluntary movement of the eyes creates a time varying voltage at the recording electrodes. Why is this phenomenon useful in recording the slow changes in corneo-retinal potential that occur during the Arden electrooculogram (EOG)? d) Briefly explain how a patient s pattern electroretinogram (PERG) might be affected by an optic neuropathy? (4 marks) ORT TURN OVER

8 3. a) With the aid of a diagram, explain the principles of applanation tonometry. b) What is the main difficulty in differentiating normal eyes from those with glaucoma? c) List the main confounding factors which may affect measurements of intraocular pressure. (20 marks) (7 marks) 4. a) Describe two methods of estimating visual acuity by recording visual evoked cortical potentials. b) Describe how the elements of a multifocal electroretinogram (ERG) stimulus vary spatially and explain why this is so. c) Evoked potential recordings are often contaminated with electrical noise from tense muscles in the face and neck. What three steps could be taken to reduce this noise? d) A single electrode placed on the occiput just above the inion is well placed to pick-up visual evoked potentials (VEPs) from both hemispheres, so why do we normally place three electrodes across the occiput? (16 marks) (5 marks) END OF QUESTION PAPER ORT211 2

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11 Ancillary Material: Nil ACADEMIC UNIT OF OPHTHALMOLOGY & ORTHOPTICS Spring Semester 2013 ELECTRODIAGNOSIS 1 Hour 30 Minutes You are advised to use the 4 leaf answer book. There are FOUR questions. Attempt THREE of the four questions only. Each question is of equal weighting. The marks for each part of each question are shown in brackets. 1. a) With the aid of a labelled diagram, explain the principles of a system commonly used to indirectly measure the pressure within the eye. b) Explain, with the aid of a sketch, how voluntary eye movements during the electrooculogram (EOG) result in a time-varying voltage at the recording electrodes. Why is this movement necessary? 2. a) Evoked potential recordings are often contaminated with electrical noise from tense muscles in the face and neck. What steps could you take to reduce this noise? b) A patient has normal vision in her left eye, but complains of having no perception of light in her right eye. Robust pattern visual evoked potentials (VEPs) were recorded when stimulating either eye with chequers subtending two minutes of arc. What, therefore, is the minimum cortical acuity for each eye, and what does this tell us about her claim that she cannot see with her right eye? c) A single electrode placed on the occiput, just above the inion, is well placed to pick-up visual evoked potentials (VEPs) from both hemispheres, so why do we normally place three electrodes across the occiput? d) Briefly explain how a patient s pattern electroretinogram (PERG) might be affected by an optic neuropathy. ORT TURN OVER

12 3. a) Why are both full-field stimulation and pupillary dilatation required for the standard electroretinogram (ERG)? b) Describe the stimuli and the state of retinal adaptation required to record (i) rod, (ii) mixed rod/cone, and (iii) cone ERGs. Explain why the responses differ. (4 marks) (12 marks) c) How might a patient s pattern electroretinogram (PERG) be affected by a maculopathy? d) Draw and label a simple box diagram showing the key elements of a system used to record the ERG. e) What main advantage does the multifocal electroretinogram (mferg) have over imaging techniques such as optical coherence tomography (OCT) in detecting zonal retinal dysfunction? (7 marks) (4 marks) 4. a) Why are some nerve fibres coated in myelin? (5 marks) b) Describe the way in which intensity information is transmitted down sensory and motor nerve fibres. Why is this method used? c) Describe, with the aid of an annotated diagram, how the conduction velocity of a motor nerve in the leg can be measured. Explain the reason for using two stimulation sites. END OF QUESTION PAPER ORT211 2

13 Ancillary Material: Nil ACADEMIC UNIT OF OPHTHALMOLOGY & ORTHOPTICS August 2012 ELECTRODIAGNOSIS 1 Hour 30 Minutes You are advised to use the 4 leaf answer book. There are FOUR questions. Attempt THREE of the four questions only. Each question is of equal weighting. The marks for each part of each question are shown in brackets. 1. a) Describe three standard ERG responses in terms of flash, background luminance, and the state of retinal adaptation. Explain why they differ for each response. b) When recording the EOG, why is it necessary for the subject to move their eyes? What is the Arden Index and how is it defined? 2. a) Explain the principles of a system, applied to the cornea, which aims to measure the pressure inside the eye. Sketch a practical configuration of such a system. (20 marks) b) What factors may reduce the accuracy of such measurements? 3. a) Describe, with the aid of a diagram, how a nerve may be stimulated electrically using surface electrodes. Where, approximately, is the site of stimulation and why? Estimate typical currents and durations that would be required. How can the voltage required to achieve stimulation at a given location be reduced? b) How does the body transmit intensity information down sensory and motor nerve fibres? Why is this method used? (20 marks) ORT TURN OVER

14 4. a) What are the key elements of a system used to record the electroretinogram? Show the position of each of these elements in a diagram and describe their function. b) Briefly explain the two methods by which visual evoked potentials can be used to estimate visual acuity in infants. END OF QUESTION PAPER ORT211

15 The University Of Sheffield. ORT 211 Ancillary Material: Nil ACADEMIC UNIT OF OPHTHALMOLOGY & ORTHOPTICS Spring Semester 2012 ELECTRODIAGNOSIS 1 Hour 30 Minutes You are advised to use the 4 leaf answer book. There are FOUR questions. Attempt THREE of the four questions only. Each question is of equal weighting. The marks for each part of each question are shown in brackets. 1. a) Why are Ganzfeld (full-field) stimulation and pupillary dilatation both required for the standard electroretinogram (ERG)? b) Describe the stimulus and the state of retinal adaptation required for recording ERGs exclusively from: i. the rod system ii the cone system c) Why are the hexagonal elements of a multifocal ERG stimulus scaled to decrease in size towards the centre of the screen? d) When recording the Electrooculogram (EOG), why is it necessary for the subject to move their eyes? What is the Arden Index and how is it defined? (5 marks) (5 marks) 2. a) Draw an annotated diagram detailing the components of an applanation tonometer used to measure pressure within the eye. (11 marks) b) Describe the tonometer's principles of operation. (11 marks) c) What factors may reduce the accuracy of the tonometer's measurement? (8 marks) ORT TURN OVER

16 ORT a) Describe briefly how one could measure the conduction velocity of a motor nerve in the arm. Sketch and annotate the position of all electrodes, and explain why two stimulating sites are used. (16 marks) b) Describe how age affects conduction velocity in normal subjects. (4 marks) c) How does the body transmit intensity information down sensory and motor nerve fibres? Why is this method used? 4. a) Describe, with the aid of a diagram, the key elements of a system used to record visually evoked potentials (VEPs) from electrodes placed on the scalp. State the function of each element. b) Describe two methods by which the VEP can be used to estimate visual acuity in infants. (18 marks) (12 marks) END OF QUESTION PAPER ORT 211