Macular function tests


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Macular function tests

  1. 1. Abubaker AhmedM.Sc Ophthalmolgy
  2. 2.  Macula is a round area at the posterior pole temporal to the optic disc 5.5mm in diameter It is yellowish color derived from the presence of xanthophyll pigment
  3. 3.  Densest concentration of cones a one to one photoreceptor- ganglion cell relationship Cones more elongated and slender Absence of rods at the foveola RPE cells are taller, thinner and deeply pigmented Presence of xanthophyll pigment
  4. 4. This special anatomy enable the fovea for: highest discriminative ability(VA) colour perception
  5. 5. Uses of macular function tests Diagnosis and Follow up of macular diseases For evaluating the potential macular function in eyes with opaque media such as cataract and dense vitreous hemorrhage
  6. 6. Symptoms• Central vision impairment• Metamorphopsia• Micropsia• Macropsia
  7. 7.  MFT With clear media MFT With opaque media
  8. 8.  Visual acuity  Amsler grid Contrast sensitivity  Microperimetry Slitlamp  FFA biomicroscopy  OCT Photostress test Colour vision
  9. 9.  Maddox rod test Focal ERG VEP Laser interferometry Potential visual acuity meter test Entoptic phenomena B scan
  10. 10.  V/A is measured by the visual resolution of a letter, symbol or a pattern under conditions of maximal contrast In pts with macular disease VA is frequently worse when the pt looks through a pin-hole
  11. 11.  Contrast sensitivity is a measure of the minimum amount of contrast needed to distinguish a test object indirectly assesses the quality of vision Can detect early/subtle visual loss when VA is normal
  12. 12.  To detect retinal conditions like DR, ARMD and other retinal, macular and optic nerve diseases Optical conditions like refractive error, refractive surgery, cataract and intraocular lens implantation and normal aging of the eye
  13. 13.  Is an effective test for monitoring potential decreases in contrast sensitivity function over time.
  14. 14. With a strong convex lensaffords excellent visualizationof the macula
  15. 15.  PRINCIPLE : The test involves exposing the macula to a light source bright enough to bleach a significant proportion of the visual pigments. Return of normal retinal function and sensitivity depends on the regeneration of the visual pigments
  16. 16.  pathological states that affect the photoreceptors,Bruchs membrane, chorio- capillaries or choroid can prolong visual recovery time. no such prolongation is observed in diseases affecting the neural conducting pathways
  17. 17.  Evaluates the 10 ̊ of visual field centered on fixation Used in screening and monitoring macular diseases square 10*10 cm divided into 400 5*5 mm squares to be held at 30 cm
  18. 18.  reading glasses, cover 1 eye Pt asked to see the central spot Presence of abnormalities like blurred areas, holes, distortions, or blank spots Pt with maculopathy reports that the lines are wavy whereas pt with optic neuropathy remarks some lines are missing or faint
  19. 19.  Colour vision is the function of three populations of retinal cones Blue ( tritan) 414-424 nm Green ( deuteran) 522-539nm Red (protan) 549-570nm Normal person possess all these three cones and called trichromat
  20. 20.  Acquired macular diseases tends to produce blue yellow defects and optic nerve lesions red green defects Deutran anomaly is the most common and those subjects can not differentiate between red and green colours
  21. 21.  Farnsworth-Munsell 100 Hue test is the most sensitive but seldom used
  22. 22.  The principle of microperimetry rests on the possibility to see —in real time— the retina under examination (by infrared light) and to project a defined light stimulus over an individual, selected location
  23. 23.  SLO microperimetry was the first technique which allowed to obtain a fundus-related sensitivity map SLO uses a near infrared diode laser (675nm)beam that rapidly scan the posterior pole. The reflected light is detected by a confocal photodiode and the digitized image is stored in a computer
  24. 24.  SLO fundus perimeter did not allow to perform fully automatic examination. Moreover, automatic follow-up examination to evaluate exactly the same retinal points tested during baseline microperimetry was not available with this instrument.
  25. 25.  The limitations of SLO have been overcome by MP1 microperimetr a recently developed automatic fundus perimeter MP1 microperimeter automatically compensates for eye movements during the examination via a software module that tracks the eye movements
  26. 26.  Dark appearance of the fovea on FFA is caused by FAZ and blockage of the choroidal background by xanthophyll and dense RPE FFA is a very useful tool in diagnosing macular disorders e.g. diabetic maculopathy, CSR , CNVM and can reveals the functionality of the lesion e.g. ischemic maculopathy
  27. 27.  OCT it is non invasive noncontact imaging that produce high resolution cross sectional image Useful in diagnosing macular disorders and to delineate retinal layers and detect subtle anatomical changes
  28. 28.  Maddox rod Focal ERG VEP Laser interferometry Potential visual acuity meter test Entoptic phenomena Preferential hyperacuity perimeter (PHP) B scan
  29. 29.  Simple and reliable test and can be used in semi opaque media Pt is asked to fixate light at a distance of 1/3m through M.R. with opposite eye occluded Any breaks/holes; discoloration/distortion indicates a macular lesion
  30. 30.  ERG is only abnormal when a large area of retina is functionally impaired Focal ERG needs a stimulus localized to one area without scattering of light to stimulate the rest of the retina
  31. 31.  It is a hand held foveal ERG It employs a 3-4 degrees whit flickering light focused on the fovea with a 10 degrees annulus of constant white light to desensitize surrounding retina
  32. 32.  VEP Measure of the electrical potential generated in response to a visual stimulus it represents integrity of entire visual pathway from retina to occipital lobe so can not differentiate between macula ,ON and cortical pathology
  33. 33. Two types of stimulus eitherby flash of light or bypatterned stimuliIf the issue is the V/A thenthe amplitude is measuredIf the issue is the lesion inthe visual pathway then thelatency is measured
  34. 34.  Utilizes coherent white light or helium-neon laser generated interference stripes or fringes that are projected onto the retina through the ocular media Brightness increased in pts with dense cataracts The laser interferometer resolving power converted to standard V.A
  35. 35.  1. subjective 2. Laser fringe vision>vision of letter acuity. 3. over predicts visual potential in amblyopes
  36. 36.  PAM introduced in1983 This is attached to a slit lamp and projects a reduced Snellen’s chart via narrow beam of light through a pinhole clear area in the cataract towards the macular region The resulting potential acuity is the smallest line where the patient was able to read three characters
  37. 37.  Subjective methods that require an alert and cooperative patient and skilled compassionate examiner But it is easier than laser interferometry
  38. 38.  It is refer to visual perceptions that have their origin in the structure of an observers eye Three types are used for testing the macula in opaque media 1/ PURKINJE VASCULAR E.P 2/ Flying spot( blue field entoptic phenomenon) 3/Haidinger’s Brushes
  39. 39.  The Purkinje’s vascular entoptic test is a simple method which elicits the response by placing a penlight against a closed eyelid or the globe and moving it back and forth, creating images of the patient’s retinal vascular tree
  40. 40.  Blue field entoptoscopy relies on the observation of leucocytes flowing in the macular retinal capillaries. The leucocytes appear as ‘Flying Corpuscles’ when the retina is diffusely illuminated with a bright blue light.
  41. 41.  Subject looks at a surface illuminated with blue light through a polarizer hourglass shaped yellowish brushes seen radiating from the point of fixation. On rotating polarizer, brushes rotate
  42. 42.  Phenomenon caused by variations in absorption of plane polarized light by oriented molecules of xanthophyll pigment in foveal retina Used to sensitize the fovea in amblyopic child with eccentric fixation
  43. 43.  limited by the patient’s subjective interpretation May yield false negatives if the retina cannot be sufficiently illuminated through a dense cataract
  44. 44.  PHP relies on the concept of hyperacuity which is the ability to discern a subtle misalignment of an object. This can be explained by the fact that an extended edge will stimulate an array of cones and when there is a break in this line the fovea can perceive it.
  45. 45.  if the patient’s photoreceptors are slightly misaligned due to macular lesion (e.g. drusen) then this misalignment can be perceived by the patient and recorded by the PHP.
  46. 46.  This gives a gross idea about the anatomic normalcy of the eye, and rules out pathologies like vitreous hemorrhage, retinal detachment, optic nerve anomalies, etc Scanning does not offer any information on macular function
  47. 47.  Evaluation of the macular function of a patient with opaque media is a challenging problem commonly faced by us No single test is infallible