Examination of low vision patient

History taking , Visual acuity , refraction , visual field , contrast sensitivity of low vision patient

1. Examination of Low Vision Patient : Visual Acuity Refraction & Visual Field Moderator Presenters Dr. Sanjeev Bhattarai Aayush Chandan Kamal Luitel

2. Low Vision WHO Definition Defined as the impairment of visual functioning even after treatment and /or standard refractive correction and has a visual acuity of less than 6/18 ( 20/60) to light perception or a visual field of less than 10 deg from the point of fixation , but who uses or is potentially able to use vision for the planning and /or execution of a task

3. Visual acuity Visual acuity is the assessment of the finest spatial detail that the visual system can resolve measures minimum angular size of detail that can be just resolved

4. Objectives of VA in Low Vision Evaluation Provides the examiner with baseline information from which the course of pathology may be monitored Essential for calculating a patient’s magnification Provides the patient with an appreciation for residual vision Documents a level of VA that may establish eligibility for services , benefits and even driving privileges

5. Visual Acuity Charts

6. contd Multitude of VA charts are available to the low vision practioner VA may actually vary from chart to chart Number of optotypes presented per line of acuity Spacing between optotypes & between rows of optotypes Configuration of optotypes Contrast of charts It is therefore important to use the same chart for each visit to monitor visual acuity status .

7. Distance VA charts Projector Charts Snellen’s Chart 2 . Printed Visual acuity Charts F einbloom distance test chart F erris-Bailey ETDRS chart C hronister pocket acuity chart Keeler A series charts Sloan distance acuity charts Bailey– Lovie charts Waterloo charts Symbol charts

8. Snellen’s projector Chart Most commonly used chart in assessement of distance visual acuity Not recommended for low vision patients Luminance level of the chart is generally fixed and not easily varied during examination Large gradation of acuity P oor contrast levels Unequal spacing between the letters and lines No geometric progression of letter size Unequal number of letters in each line Difficult to measure acuity at various distance

9. Feinbloom distance test chart Consists of numeric optotypes Calibrated for 20ft but may be used at any distance As the size of optotypes decreases , more numbers are added to each row Because of the reduced number of optotypes , numerals are easier to guess than letters

10. Ferris-Bailey ETDRS chart Consistent number of letters i.e 5 in each row Separation between optotypes and between rows of optotypes are proportional to the size of the optotype Results in smaller spacing in the higher visual acuity levels , giving the chart its characteristics triangular configuration Geometric ( logMAR ) progression of size difference between lines Optotypes on each line are 0.1 log unit or 25% larger than the preceding line

11. Logarithmic progression and proportional spacing of optotypes allows for consistent and accurate evaluation of visual acuity levels May be used at any distance , but testing distance are typically 4m or 2m Available in Landolt C configuration , LEA symbol test system , HOTV chart for pediatric low vision patient

12. Chronister pocket Acuity Chart Uniquely designed for use with patients during “out of office” examinations in hospitals and nursing homes , and during home visits and screening Calibrated for 20ft but may be used at any distance Also contains a near acuity test in log-MAR format Can be recorded in reduced snellen at 40cm or in the meter system

13. Keeler A series charts Designed by Charles Keeler based on a logarithmic (constant ratio) scaling system 20 different series of letters, ranging from A1 (6/6 [ LogMAR 0.0 ] equivalent ) to A20 (1/60 [ LogMAR 1.9] equivalent ) Each line differed from its nearest neighbour , in size, by a factor of × 1.25 Near equivalents, also calibrated in A series format

14. Sloan distance acuity charts American equivalent to the Keeler chart U ses the ‘M’ or metric series notation N ever achieved worldwide usage Best known for its use in the assessment of near acuity System is linear so that 3M letters are exactly three times larger than the 1M letters

15. Bailey- Lovie Charts Based on logarithmic basis Same no. of letters in each row Separation between optotypes and between rows of optotypes are proportional to the size of the optotype Equal legibility for optotypes at each level Clinical scoring is reliable as each letter is given a score

16. How Are Bailey- Lovie Charts and ETDRS different? Bailey- Lovie charts incorporate the European design of LogMAR , where letter sizes are rectangular instead of square For example, a 20/20 ETDRS letter is square, 5 minutes of arc by 5 minutes of arc . For the Bailey- Lovie Chart Design, a 20/20 letter is rectangle, 4 minutes of arc by 5 minutes of arc

17. Waterloo charts Canadian charts Similar in design and concept to the Bailey– Lovie charts letters are oriented such that letters of equal size are placed in columns rather than rows . An additional feature of the Waterloo chart is the inclusion of interactive surround bars, which ensure that letters at the start and finish of each line are as difficult tread as those within the lines.

18. Symbol charts Have been developed for paediatric use but equally useful when assessing the visual status of those with learning disability

19. Prospective evaluation of visual acuity assessment : A comparison of snellen versus ETDRS charts in clinical practice (AN AOS THESIS) Peter K Kaiser MD Trans Am Ophthalmol Soc 2009;107:311-324 Purpose : The purpose of this study was two fold : first, to prospectively compare visual acuity (VA) scores obtained with Snellen charts versus Early Treatment Diabetic Retinopathy Study (ETDRS) charts and second, to see if there was a difference in visual acuity measurements obtained with ETDRS charts starting at 4 or 2 meters Methods : Prospective, consecutive evaluation of patients who underwent best-corrected visual acuity testing of their right eye performed at a single seating by the same experienced, certified vision examiner in the same room with standardized low light conditions using a projected Snellen chart at 20 feet, and two different back-illuminated ETDRS charts placed 4 and 2 meters from the patient .

20. Results: One hundred sixty-three eyes were included in the study The mean Snellen VA was 0.67 logMAR (20/94), ETDRS VA at 4 meters was 0.54 logMAR (~20/69), and ETDRS VA at 2 meters was 0.51 logMAR (~20/65 ). The mean difference was 6.5 letters better on the ETDRS chart (P=.000000001). As the VA worsened, there was increased variability between the charts and the mean discrepancy between charts also increased. Subgroup analysis revealed the greatest difference between charts was in the poor vision subgroup (<20/200) with a difference of 0.2 logMAR (10 letters; P=.0000002). Patients with exudative age-related macular degeneration (AMD) had the greatest disparity on vision testing, but patients with dry AMD and diabetic retinopathy also exhibited significant differences.

21. Conclusions : Visual acuity scores were significantly better on ETDRS charts compared to Snellen charts. The difference was greatest with poor visual acuity (<20/200) and in patients with exudative AMD. Thus, caution should be exercised when comparing data using the different charts

22. Distance acuity specifications Snellen Acuity most universally accepted Metric units = 6/3 6/6 6/9 6/12 6/60 English units = 20/10 20/20 20/30 20/40 20/200  

23. Decimal Acuity Calculated by dividing the numerator of snellen fraction by its denominator. 6/12 = 0.5 6/4 = 1.5 Specification of acuity in this way is, however , regrettable as results can easily be confused with LogMAR results, which are unrelated.

24. Percentage Acuity Decimal acuity multiplied by 100

25. Minimum Angle of Resolution ( MAR) Reciprocal of Snellen fraction e.g. 6/24 MAR = 4 i.e. a patient is unable to resolve a gap or stroke of less than 4’ of arc LogMAR is simply the logarithim to the base of 10 of the ‘MAR’ (6/6 = MAR 1 = LogMAR 0).

26. Visual Acuity Rating (VAR) VAR = 100 – (50 * logMAR ) 6/6 → 100 6/60 → 50

27. Near Acuity Charts Single letter charts Reduced snellen’s chart Sloan M series charts N system chart Reduced Ferris Bailey ETDRS chart Word and continuous text charts Jaeger chart Lighthouse game card Lighthouse continuous Text card MNREAD card

28. Reduced snellen’s Chart designed such that a 20/20 letter subtend a 5’ angle at a given distance (typically 40cm) As in standard snellen distance charts , the levels of acuities are limited

29. Sloan M series charts A 1M optotype will subtend 5’ of arc at 1m . A 1M letter viewed at 1m may be equated to snellen acuity in the following manner 1.00/1M = 20/20 snellen equivalent Because near acuity is frequently measured at 40cm , 1M is equivalent to 20/50 at 40cm Testing may occur at any distance Recorded as E.g 3M at 25cm would be recorded as 0.25/3 M  

30. N system chart An 8-point optotype (N8) suntends 5 minutes of arc at 1m viewing distance N notation may be converted to M notation by dividing by 8 E.g N4 is equivalent of 0.5M print

31. Reduced Ferris Bailey ETDRS chart Maintains a constant number of letters in each row As in the distance ETDRS chart , there is a geometric progression of size differences between lines Consistent and accurate evaluation of visual acuity levels May be used at any distance . Provides snellen equivalent acuities for 40cm and 20cm

32. Jaeger chart Paragraphs are numbered from J1 TO J20 with J1 representing the smallest print size The character and form of the type varies from edition to edition Rows of letters were of unequal height and diameter when compared from edition to edition No predictable relationship between the rows of jaeger letter e.g J4 is not necessarily twice as large as J2

33. Lighthouse Game Card Uses the same geometric progression as the single letter chart with each three row progression representing a halving or doubling of VA levels at any viewing distance VA obtained with this chart may be poorer than that obtained from a single letter ETDRS chart due to the presence of increased contour interaction between letters of each word May be used at any distance , but the snellen equivalent provided are calculated at 40cm

34. Lighthouse Continuous Text Card Follows same geometric progression as the lighthouse Game card Recorded VA may be poorer than single-letter VA , especially in cases in which central scotomas are present Snellen equivalent noted on the testing card are calculated for 40cm

35. MN Read C ard Combines a quick reading performance assessement with a reading acuity assessement Reading passages are printed in decreasing M sizes in logarithmic progression from 8.0 M to below 0.2M Each three-line sentence has an identical no. of characters ( letters & spaces) Enables the examiner to determine optimal print size for fluent reading tasks

36. Distance Visual Acuity Testing Procedure Acuity should be tested until threshold is reached Progression of testing distance for the ETDRS chart is typically 4m , 2m ,1m . When testing at closer distance the patient should be corrected for the accommodative demand induced by the viewing distance It is not acceptable to record acuities as finger counting.It is frequently demoralizing to a patient to be asked to count fingers as opposed to identify optotypes on a chart

37. It is far more effective to bring an appropriate chart to the equivalent viewing distance and obtain a standardized and reproducible visual acuity The examiner should isolate the optotype to determine if resolution is enhanced .This may provide higher level of acuity ,as counter interaction is eliminated Measurement of acuities with pinhole may reveal the presence of uncorrected refractive errors or significant media abnormalities

38. The examiner should record whether a patient consistently loses his or her place or omits sections of the chart . Such information is helpful in establishing strategies for instruction in the use of optical devices and for overall enhancement of visual skills

39. Near V isual Acuity Testing Procedure Single letter acuities should be evaluated until threshold is reached Eccentric fixation positions should be explored and recorded if present Isolation of letters and words through the use of a typoscope VA should be recorded with any near magnification devices that the patient brings to the office

40. Refraction in Low Vision

41. What is Refraction in Low Vision means ?  Refracting the low vision patient is not simply a matter of asking the patient to discriminate clarity between two lenses, but the integration of the following measurements and information which direct the examiner towards the refractive error and finally the lens prescription. A careful refraction is the single most important test in the sequence of the low vision evaluation

42. Refraction In Low vision Patient Is it necessary? They tend to have high prevalence of uncorrected error.  certain ocular pathologies have characteristic refractive findings that may be undetected or change more rapidly compared to healthy eyes. For example , ‘cataract there may be 10D myopic shift and in diabetic 2D or more myopic shift some individuals may overlook their own visual needs, perhaps accepting their blurred vision as a result of their ocular pathology or as a natural consequence of aging.(they think its common) many patients referred for this service have come from settings where refractive care is simply not emphasized, or is performed by unqualified personnel.

43. The basic techniques of refraction of low vision persons are not too different Although specialized techniques like bracketing and over- refraction are commonly used. The refraction is performed both objectively and subjectively. In both procedures it is important to adjust procedures according to the eye condition if each individual client.

44. Bracketing Types of Subjective refraction Mostly used in low vision patient In which large and equal steps of dioptric changes are made above and below the presumed correct answer and then reducing the size for the dioptric changes and shifting the center of the range , until the finest and Just detectable blur is induced by equal steps above and below the refractive error

45. Just Noticeable difference The amount of spherical lens power needed to elicit an appreciable change in clarity or blur is called the Just noticeable difference The lower the acuity , the larger the JND(means patient having low VA needs more spherical lens )  The denominator of the 20 foot Snellen acuity is a good rule-of-thumb estimator of the JND for a given eye. For example, a 20/150 eye will be sensitive to a lens change of approximately 1.50 dioptres using this rule.

46. Significant refractiive findings. In certain disorders? Pseudophakia- (3-4) of ARA due to surgery Cataract – up to 10D of myopia shift Diabetes – fluctuation mostly myopic shift depends on blood glucose level Degenerative myopia – progressive higher degree of up to -35D PK – higher corneal astigmatism up to 12D seen at any axis Albinism – (3-4) of CA(WRA) and usually symmetrical in BE

47. Predictable pattern? ROP- myopia & Keratoconus Coloboma & Microcornea- hyperopia Lenticular Subluxation- Aphakia & myopia

48. Basic for Low vision Refraction Hand held trial lenses are more comfortable than phoroptor Large jump in lens power for JND ‘ Vertex distances play the major role Use hand held cross- cyl of +/- 1.00D Try concave and plano -mirror illumination Refraction over spectacles- Haldberg or Janelli clips

49. Should make the following six adjustments of the trial frame in LV: temple length bridge height pupillary distance pantoscopic tilt horizontal tilt(level) vertex distance

50. Vertex Distance Take note of the vertex distance in prescriptions over +,-10.00D. Small errors in the estimation of vertex distance create clinically significant differences in refractive corrections.

51. Pantoscopic tilt is defined as a lens tilt about the horizontal axis, with respect to primary gaze of a subject. In a simple way, it can be explained as “The rotation of lens bottom towards the cheeks”. Typically these tilts range from 0-12 degrees, and tilt up to 3-7 degrees are considered normal. 

52. Subjective refraction Find the best sphere Test for astigmatism Retest for the best sphere

53. Find the Best Sphere The first step in subjective testing is to find the best sphere. The starting lens in the trial frame(spheres in the back barrel, cylinders in the front) should be the retinoscopy finding, or if unobtainable, the patient's past spectacle prescription. If this is also unavailable, use your best judgment based on their eye history and entering acuities.

54.  Direct the patient's attention to a line large enough to maintain fixation but small enough to detect differences in blur. Present the patient with the JND interval using a plus and minus lens of equal absolute value and ask to compare the clarity. For example, a 20/200 eye with a JND of 2.00D should be shown a +1.00 sphere and a -1.00 sphere sequentially(total lens change = 2.00D). If they have a preference for either lens, change the sphere in the back barrel of the trial frame in the appropriate direction. A reasonable amount of change would be the JND.

55.  Example:   Patient A        Entering acuity, OD=20/200, OS=NLP          retinoscopy unobtainable          old glasses unavailable          JND = 2.00D          Trial frame has no lenses in it

56. Find the best sphere: 1. Ask the patient to compare +1.00sph. To -1.00sph. Patient states that +1.00 sph . is clearer. Place +2.00sph. in the trial frame. 2. Again ask the patient to compare +1.00sph. to -1.00sph, this time through the +2.00 sph . in the trial frame. If the patient still prefers the plus lens to the minus, replace the +2.00 in the trial frame with a +4.00sph.

57. Again ask the patient to compare +1.00sph. to -1.00sph this time through +4.00 sph . in the trial frame. If they now prefer the -1.00 to the +1.00, this is called a reversal and you now know the "best sphere" is more than +2.00 and less than +4.00. You can enter a +3.00 in the trial frame and continue refining the best sphere by letting the patient compare the JND lenses in front of the +3.00 sphere in the trial frame.  Notice that you are determining   the best sphere by bracketing around it with stronger and weaker lenses. In this way, the refractive error can be arrived quite accurately and reliably in patients with significant loss of sensitivity to blur.

58. Test for astigmatism  After finding the best sphere, test for astigmatism. If the K reading or retinoscopy indicate astigmatism, refine axis first, then power using a hand held Jackson cross cylinder, its strength chosen using the same JND rule of thumb.  Use  a  +,-1.00 JCC to test the patient.

59. Retest for the Best sphere After the test for astigmatism, the final step in the subjective is to retest for best sphere with the JND lenses. using the bracketing method

60. Be sensitive to the patient's heightened anxiety for the subjective test; test slowly and carefully, giving the patient enough time to discriminate blur. Repeated presentations to certain patients are necessary to yield valid results.      The effective prescription and ultimate use of low vision devices is usually dependent on the accuracy of the refraction. Careful and logical technique will improve the validity of this challenging and important test, with improved visual function for your patient as the great reward.

61. Decision to change Rx Discuss with clients to change the glasses VA may not improve signigicantly give Rx on the basis of visiability of everyday objects. Face of acompaiined person is the best object to make patient compare about the vision by new Rx If feels not much of diggerece not to change If feels a bit better than that could be of great help

62. Ancillary refraction techniques Radial retinoscopy – if the media is unclear Keratometry - find high cylinder Five diopters step to cover broad range of powers quickly Placido disc Stenopaic slit Is use for high astigmatism Pinhole useful but decrease illumination Current glasses – starting point Ophthalmoscopy Autorefractors may not be reliable in opacities and irregularities reveal high cylinder

63. Visual Field In Low Vision

64. Assessment of visual field Normal extend Superior field = 60°-70° Inferior field = 70°-75° Temporal field = 90°-110° Nasal field = 60°-65° Low vision < 20° or 10° in either side of fixation

65. Uses of Visual Field in Low Vision To document visual field parameter for legal Blindness To fulfill the eligibility criteria for those states which require a minimum visual field To provide objective information about scotoma in visual field which may explain unexpectedly poor performance Orientation & Mobility : learn skills and influence plan for rehabilitation To follow disease progression

66. Various Diseases related to Visual field Defect Glaucoma: it includes paracentral scomata ,arcuate scotomas nasal steps and temporal wedges. ARMD : a central or paracentral scotoma with normal peripheral findings RP: visual field loss begins in the midperiphery , extending inward and outward creating a donut- shaped field defect Diabetic retinopathy: in PDR , retinal ischemia , laser scars and RD can causes corresponding field loss RD: VF defects develop corresponding to the site of RD ROP: VF defects are variable , most common nasally Macular hole: result in dense central scotomas Optic Atrophy: Central vision affected , paracentral cecocentral or central scotomas may present

67. Cataract : central and peripheral field defect Multiple sclerosis: several patterns of field loss occur in patients . Central and cecocentral scotomas may be present although altitudinal defects occur most commonly Myopic Degeneration : high degree of myopia can result in central ring shaped scotoma as well as hemianopia and quadratic defect .

68. Glaucoma ARMD Types of visual field loss

69. How Visual field defects affects in Low vision Patient Patient report running into objects Tripping, falling Being startled by objects or people that suddenly appear in front of them Difficult to detect objects, movements orientation Patient often loose their place while reading

70. Central visual field loss is the main cause of Low vision

71. Central field testing Amsler’s grid Tangent perimeter ( E.g Bjerrum’s screen) Arc perimeter Automated perimeters Goldmann perimeters Goldmann perimeter Automated perimeter Confrontation method Peripheral field testing Various Devices for measuring VF in low vision patient PLPR

72. Amsler Chart Measures central 20 degrees (Macula) Only one eye at a time Look for distortion Uses reading glasses

73. It consists of seven grid like charts each with slightly different patterns It is mounted on stiff cardboard in a ring binder. When held at 30 cm from eye, allow assessment of central 20 degree This corelates anatomically with area just inside the temporal vascular arcades not including optic disc Cont..

74. Amsler chart design ∙ All charts in the shape of square covering an area of 100 cm square ∙Each square measures 5 mm and when the grids are held at 30 cm from the patient each square subtends 1 degree on the retina

75. Designed by Marc Amsler These charts consists of a series of seven grid like charts designed for evaluating the central visual field, mounted on stiff cardbord in a ring binder 20 degree visual field Performed at 30cm First uniocular then binocular

76. Types of distortions that patients would report: Chorioretinal scar Central scotoma Arcuate scotoma Macropsia Micropsia Metamorphopsia metamorphopsia

77. indication Unexplained visual acuity loss Report of a visual disturbance in or near the fixation area A questionable appearance of macular area in ophthalmoscopy

78. 2. Tangent screen Only measures central 30 degrees Testing distance in30 cm Varying size of target (increased sensitivity)

79. 3. Confrontation Illuminated targets Non illuminated target

80. Confrontation visual field exam: a simple and preliminary test extent of visual field tested by this method is 120̊ examiner separated with the patient by a distance of about 60cm and asked to cover one eye and stare at the examiner

81. when the patient covers their right eye, the examiner covers their left eye, and vice versa. The examiner will then move his hand ( or some other test object )from a position as far as possible from the line of sight inward until patient reports seeing it Cont.. this process should be repeated in each of the four quadrants the target should be moved in a plane equidistant from the examiner so that the examiner may compare the patient's visual field with his.

82. Arc perimeter It provides a quick estimation of the extent of peripheral field constriction With this test the practitioner can evaluate all mericians but typically only 45, 90,135, 180 Degree meridians are evaluated

83. 4. Goldmann Perimetry Evaluate both the central and peripheral visual field the standard test performed by most perimetrists Test Targets: dots of Varying size and illumination

84. Goldmann Perimetry : target size Sizes of Stimuli [0...V scale] Each size increment equals a two fold increase in diameter and a fourfold increase in area Diameter (mm) Area (mm 2 ) 0.28 1/16 I 0.56 ¼ II 1.13 1 III 2.26 4 IV 4.51 16 V 9.03 64

85. 5. Automated visual fields Static perimetry Measurement of threshold values Statpac (HFA)- comparison to normative data Inbuilt program for analysis- diagnosis and progression

86. Advantages of AVF… Removal of examiner variability More sensitive to subtle field defects Reproducibility Restests abnormal points automatically Has relaiablity parameters

87. PLPR When none of the test show result and the visual field is very low , we can do PLPR test just to get a gross idea of whether the light perception is present in any of the four quadrants