1. E LECTRORETINOGRAPHY E LECTRO - OCULOGRAPHY V ISUAL E VOKED P OTENTIAL Dr. Puneet Kumar Srivasatava

2. O CULAR E LECTROPHYSIOLOGY T ESTS These test give a recording that helps to know the functional integrity of various layers of retina & ant visual pathways Rationale: These tests help to detect & categorize the site of lesion in the visual pathways (layers of retina to optic nerve & brain cortex) Helpful in: Vascular pathology / Drug toxicity / Paediatric visual assessment / cause of poor vision in infants.

3. ELECTRORETINOGRAPHY

4. Principles: The electroretinogram is the record of an action potential produced by the retina when it is stimulated by the light of adequate intensity. It measures the electrical responses of the light- sensitive cells (rods,cones & inner nuclr layers). The ERG is recorded using stimuli delivered by an integrating sphere (Ganzfeld) & contact lens electrode that the subject wears while watching the stimuli.

5. ERG RECORDING ELECTRODES Two types: Bipolar & Non – Bipolar. a) Some are speculum structures that hold the eye open and have a contact lens with a wire ring that "floats" on the cornea supported by a small spring. b) Some versions use carbon, wire or gold foil to record electrical activity.

6. ERG RECORDING ELECTRODES

8. Reference electrode: May be incorporated into the contact lens-speculum assembly or can be placed near each orbital rim temporally or forehead as a reference for the corresponding eye. Ground electrode: A separate skin electrode should be attached to an indifferent point (forehead or ear) and connected to ground.

9. F LASH STIMULUS CHARACTERSTICS Flash of 5 ms duration (each flash is shorter than the integration time of any photoreceptor) Standard Flash strength (SF): one that produces a stimulus strength (in luminous energy per square meter) at the surface of the Ganzfeld bowl of 1.5 to 4.5 photopic cd.s.m2 (candela-seconds per meter square) Stimulator must be capable of producing a steady & even, white background luminance of 17-34 cd.m2 across the full field.

10. C LINICAL PROTOCOL (ISCEV) Pupil max dilated Pt placed in completely dark room for 30 mins Record scotopic responses to weak flashes, followed by mixed responses & oscillatory potential to bright SF Rod are suppressed by 17-34 cd.m2 for 10 mins then record the cone ERG Last flicker response

11. Normal ERG is biphasic:  a-wave: initial fast negative deflection (directly generated by photoreceptors)  b-wave: next slower positive deflection with larger amplitude (generated from fluxes of potassium ions within & surrounding of Muller’s cells)  b-wave: consist of : 1. b1- wave: represents both rods & cones activity 2. b2-wave: represents mainly cones activity  c-wave: represents retinal metabolism (pigmentary epithelium)

13. Two principal measures of the ERG waveform are taken: The amplitude (a) from the baseline to the negative trough of the a-wave The amplitude of the b-wave measured from the trough of the a-wave to the following peak of the b-wave The time (t) from flash onset to the trough of the a- wave and the time (t) from flash onset to the peak of the b-wave

14. N ORMAL ERG Consist of 5 recordings: First 3 are elicited after 30 mins of dark adaptation (Scotopic) Last 2 are recorded after 10 mins of adaptation to moderately bright diffuse illumn (Photopic)

15. S COTOPIC ERG  Rod responses are elicited with a very dim flash of white light(2.5 log units below white SF) – Large b-wave & small or non recordable a- wave  Combined rod & cone response are elicited with a very bright white flash – Prominent a- wave & b-wave  Oscillatory potentials are elicited by using a bright flash & changing the recording parameters(high pass filter - 75 to 100 Hz) Oscillatory wavelets occur on the ascending limb of the b-wave (generated by cells in inner retina)

16. P HOTOPIC ERG  Single flash Cone response are elicited with a single bright flash – An a-wave & b-wave with a small oscillations  Cone flicker used to isolate cones by using a flickering light stimulus at a frequency of 30 Hz to which rods cannot respond – Provides a measure of the amplitude & implicit time of the cone b-wave.

17. R ESPONSES Extinguished: complete failure in function of the rods & cones Seen in :Pigmentary retinal dystrophy Complete occlusion of the retinal Art. Complete old retinal detachment Advanced siderosis Sub normal: cond in which large area of retina does not function. Negative: in gross disturbance of retinal circulation.

18. T HE PATTERN ELECTRORETINOGRAM Response to central retina to an iso-illuminant stimulus, usually a reversing black & white checkboard. Measure central retinal function & retinal ganglion cell function Diff between optic nerve & macular dysfunction.

19. R ECORDINGS & MEASUREMENTS Without mydriasis, with refractive correction, non-contact lens electrodes. Reference electrode is placed on outer canthus Binocular stimulus except squint Diurnal variation & test retest variability may be imp in longitudinal studies Transient & steady state PERG recorded Transient: P50 – macular function N95 – ganglion cell function

20. M ULTIFOCAL ERG Method of producing topographical maps of retinal function. The stimulus is scaled for variation in photoreceptor density across the retina. Fovea – High density Periphery – Low density

21. With ERG many types of measurements can be made at individual locations. The informations can be summarized in the form of 3-D plot. The technique can be used for almost any disorder which effect retinal function.

22. ELECTRO - OCULOGRAPHY

23. Principle: Measures the standing potential between electrically positive cornea & electrically negative back of the eye. It reflects the activity of the RPE & interaction between RPE & photoreceptors. This means that an eye blinded by any lesion proximal to the photoreceptor will have a normal EOG.

24. This positive potential behaves as if it were a single dipole oriented from the retina to the cornea. Such corneoretinal potentials are well established and are in the range of 0.4 - 1.0 mV. Eye movements thus produce a moving (rotating) dipole source and, accordingly, signals that are a measure of the movement may be obtained.  The chief application of the EOG is in the measurement of eye movement.

25. T ECHNIQUE Performed both in light- & dark- adapted states. a. Electrodes are attached to the skin near the medial & lateral canthi. b. The pt is asked to look rhythmically from side to side, making excursions of constant amplitude. Each time the eye moves the cornea makes the nearest electrode positive with respect to other. c. Potential difference between the two electrodes is amplified & recorded. The movement of the eyes produces a voltage swing of approximately 5 millivolts between the electrodes (chloride-coated silver skin) on medial & lateral canthi

28. Pt makes fixed 30` lat eye movements (using diode fixation lights) for 20mins dark adaptation. 12 -15 mins period of light adaptation. Eye movement are made every 1 - 2sec for 10 secs every min.

32. Typically the voltage becomes a little smaller in the dark reaching its lowest potential after about 8-12 minutes, the so-called "dark trough.“ When the lights are turned on the potential rises, the light rise, reaching its peak in about 10 minutes. When the size of the "light peak" is compared to the "dark trough" the relative size should be about 2:1 or greater. A light/dark ratio of less than about 1.7 is considered abnormal.

33. A BNORMAL EOG Best’s Vitelliform macular dystrophy RPE & Rod receptor disorders: Retinitis pigmentosa Choroideremia Stargardt’s disease Age-Related Macular Degeneration Choroidal melanomas Drug toxicity against RPE

35. VISUAL EVOKED POTENTIAL

36. V ISUAL E VOKED P OTENTIAL T EST (VEP) It is similar to an electroencephalogram (EEG) in that it records brain waves. It differs in that it focuses specifically on the parts of the brain that involve vision. Since the visual nerves run the entire length of the head, this test can evaluate a large part of the brain. VEP is a sensitive indicator of optic nerve function.

37. B ASIC T ECHNOLOGY 1. Stimulus parameters A. Flash stimulus B. Pattern stimulus i. Pattern reversal stimulus ii. Pattern onset/offset stimulus 2. Electrodes A. Electrode Placement 3. Recording parameters A. Amplification (20,000–50,000 times) and averaging systems B. Analysis time

39. The standard flash used in ERG recording can be used for flash-VEP The Pattern stimulus consists of a checkboard or grating of various spatial frequencies The anterior-posterior midline measurements are based on the distance between the nasion, inion & vertex.  Active electrode is placed on the midline over the visual occipital cortex  Reference electrode at the frontal pole  Ground electrode is at the forehead or earlobes.

40. R ECORDING Done with refractive correction Without mydriasis Monocular stimulation

41. Pre-chaismal lesions are reliably detected by Pattern reversal stimulation Flash stimulation is used in difficult and uncooperative pt, with dense media opacities & very poor vision Pattern onset / offset are especially useful in Malingerers & pt with Nystagmus (due to short stimulus duration)

42. N ORMAL W AVEFORMS Flash VEP: consist of a series of positive & negative peaks that are designated in numerical sequence (most common component recorded areN2 &P2 at 90 & 120 msec, resp.) Pattern reversal VEP: peaks are named as positive & negative followed by latency (most common wave used is P100 component; positive peak at100msecs) Pattern onset / offset VEP: three components described are C1 (positive at 75msec), C2 (negative at125msecs), C3 (positive at 150msecs)

44. S OME SPECIALIZED TYPES OF VEP Steady state VEP Sweep VEP Motion VEP Chromatic (Color) VEP Binocular (dichoptic) VEP Stereo-elicited VEP Multi-channel VEP Hemi-field VEP Multifocal VEP Multi-frequency VEP LED Goggle VEP

45. C LINICAL USEFULNESS OF VEP S INCLUDES THE FOLLOWING : More sensitive than MRI or physical examination in prechiasmatic lesions Objective and reproducible test for optic nerve function Abnormality persists over long periods of time Inexpensive as compared with to MRI Under certain circumstances, may be helpful to positively establish optic nerve function in patients with subjective complaint of visual loss; normal VEP excludes significant optic nerve disorder

46. DD OF ABNORMAL VEP Optic neuropathy Optic neuritis Ocular hypertension Glaucoma Diabetes Toxic amblyopia Leber hereditary optic neuropathy Aluminum neurotoxicity Manganese intoxication Retrobulbar neuritis Ischemic optic neuropathy Multiple sclerosis Tumors compressing the optic nerve - Optic nerve gliomas, meningiomas, craniopharyngiomas, giant aneurysms, and pituitary tumors

47. Normal VEP virtually excludes an optic nerve or anterior chiasmatic lesion. Summary: The VEP is preferable in optic nerve and anterior chiasmatic lesions, while MRI is clearly superior in retrochiasmatic disease. VEP is nonspecific as to the underlying etiology and pathology.

48. THANK YOU….

49. TestLocation/ Information Conditions investigated Pattern ERGAmacrine & ganglionic cell Glaucoma Diabetic retinopathy Early maculopathy Traction of macula Optic nerve ds a-wavePhotoreceptorsRetinitis pigmentosa b-waveMuller cells Bipolar cells Disorders of negative ERG (CSNB, retinoschisis, quinine toxicity) c-waveHyperpolarisation of apical membrane Diffuse RPE ds EOGRPE