Varikuti PhD thesis final.pdf - Anglia Ruskin Research Online

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$Repeatability and Validity of the PowerRefractor and the Nidek ...$

Figure 2.2: Schematic showing examples of the SGRL stimuli for the 1.0letter width separation, 0.4 letter width separations and abutting conditions.For each separation condition, as the separation between the lettersdecreases the overall array size decreases.1.0 separation 0.4 separation Abutting73
Three subjects from the main experiment participated in the second controlcondition. The 3x3 array stimuli consisted of a central 3x3 array of the sameletters surrounded by an additional single letter array of randomly allocatedSG letters to maintain equality of contour interaction for the outsiderepeated letters. The stimuli were constructed with two extreme separationconditions which covered the maximum and minimum array sizes, the 1.0letter width separation and the abutting condition (see Figure 2.3). Theangular subtense of the SGRL chart at the other separations (0.8 to 0.2letter separations) will be within the two extreme separation conditions. The3x3 letter array, 1.0 letter width separation, subtended approximately 88 x88 and 17 x 17 min arc at 1.9 m and 9.5 m respectively. The 3 x 3 letterarray, abutting condition, subtended approximately 48 x 48 and 10 x 10 minarc at 1.9 m and 9.5 m respectivelyThe procedure was the same as that used in the main experiment. A 3x3repeat letter array with 1.0 letter width separation and abutting conditionwas presented at a range of the test distances. The subject’s task was toidentify the repeated letter presented in the central 3x3 array of letters. Theresults for the 7x7 array were taken from the main experiment. The visualthresholds for the 3x3 array, 1.0 letter width separation were compared tothe 7x7 array, 1.0 letter width separation. Similarly, the thresholds for the3x3 array, abutting condition were compared to the 7x7 array, abuttingcondition.74
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ANGLIA RUSKIN UNIVERSITYFURTHER INS
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ANGLIA RUSKIN UNIVERSITYABSTRACTFAC
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TABLE OF CONTENTSACKNOWLEDGEMENTS .
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...................................
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Table 4.5(A) and 4.5(B): Depicts th
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Tables 5.8(A) and 5.8(B): Depicts t
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Chapter 1General IntroductionVision
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Visual acuity chartsSnellen chartTh
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Bailey-Lovie LogMAR chartThe LogMAR
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An accurate and repeatable measurem
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elimination of one or more of these
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1985; 1988). Greater crowding in yo
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In order to study the reliability o
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A significant difference in visual
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has gained increased attention foll
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Figure 1.3: Depicts the picture of
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Landolt C surrounded by flanking ba
Page 36 and 37: Figure 1.4: Depicts the picture of
Page 38 and 39: normal vision and at the fovea and
Page 40 and 41: educed at the abutting condition wh
Page 42 and 43: Figure 1.5: Depicts the data obtain
Page 44 and 45: fixations in normal eyes. Further,
Page 46 and 47: Figure 1.6: Example of a Regan repe
Page 48 and 49: and adults had better isolated lett
Page 50 and 51: (Glasgow acuity poorer than the iso
Page 52 and 53: closer separations based on the fin
Page 54 and 55: identify. On the other hand a 10 mi
Page 56 and 57: Figure 1.7: Example of a PVA test c
Page 58 and 59: the inner letters resulting in miss
Page 60 and 61: gaze instability in amblyopes. A se
Page 62 and 63: each letter in the low contrast Sne
Page 64 and 65: 1999a), the findings are contradict
Page 66 and 67: RationaleTo determine the effect of
Page 68 and 69: In most of the studies (Stuart and
Page 70 and 71: study the effect of contour interac
Page 72 and 73: contour interaction effect and not
Page 74 and 75: contour interaction as the Snellen
Page 76 and 77: In this experiment, the effect of l
Page 78 and 79: The final set of experiment will in
Page 80 and 81: Chapter 2The effect of contour inte
Page 82 and 83: laterality (unlike the Illiterate E
Page 84 and 85: ProcedureGeneral conditionSix adult
Page 88 and 89: Figure 2.3: Schematic of the SGRL s
Page 90 and 91: were corrected by adjusting the deg
Page 92 and 93: Figure 2.4: The data shown in the f
Page 94 and 95: thresholds normalised against the i
Page 96 and 97: Table 2.1: (A) Depicts high contras
Page 98 and 99: IH was replaced by his slope value
Page 100 and 101: Table 2.2: Depicts slopes obtained
Page 102 and 103: Figure 2.7: The data shown are a la
Page 104 and 105: Table 2.3: (A) Depicts recognition
Page 106 and 107: Figure 2.9:93
Page 109: Figure 2.1196
Page 112 and 113: Figure 2.13:99
Page 114 and 115: error bars represent ± 1 SD.101
Page 116 and 117: The effect of the relative letter l
Page 118 and 119: Figure 2.15: The graph shows mean l
Page 120 and 121: Normalised recognition thresholds (
Page 122 and 123: DiscussionThe main results of this
Page 124 and 125: Since the experiment of Flom, Weymo
Page 126 and 127: showed that the target flanker simi
Page 128 and 129: gaze instability and attention comp
Page 130 and 131: Chapter 3The effect of contour inte
Page 132 and 133: MethodsMethod of generating low con
Page 134 and 135: the low contrast letters were more
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was the same as that described in C
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isolated letter in each slide was l
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the identification of the isolated
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Threshold of psychometric functions
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The threshold values obtained from
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AB133
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Figure 3.4: Depicts normalised thre
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Slopes of psychometric functionsThe
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Figure 3.5: Average slope of the ps
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esulting in improved threshold visu
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employed the same size target for t
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Chapter 4The effect of contour inte
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Freeman, 1981). As a result of the
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Table 4.1: Depicts the visual featu
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same as that of the main experiment
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Figure 4.2: The recognition thresho
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Table 4.2: Depicts the test distanc
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Figure 4.3: The percentage correct
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2 X contrastSubject Eye Contrast th
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A (amblyopic eyes) B (non-amblyopic
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Figure 4.5: Recognition thresholds
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Figure 4.6(A) shows mean recognitio
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Figure 4.6: (A) Recognition thresho
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Figure 4.7: Depicts normalised thre
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Further, the estimates of slopes ob
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Low contrast conditionFor all the f
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A (non-amblyopic eyes) B (amblyopic
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Figure 4.10: Depicts the layout of
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Figure 4.11(A) shows mean absolute
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A189
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The threshold values of all the sep
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Figure 4.12: Depicts normalised thr
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Further, the estimates of slopes fo
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197
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High and low contrast conditionThe
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DiscussionThe current experiment in
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ecognition thresholds were nearly t
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on the target size and the extent o
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the contrast sensitivity loss was d
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Simmers, Gray, McGraw and Winn, 199
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separations are also immune to the
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SGCI chart was surrounded by an add
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ProcedureGeneral conditionThree adu
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Chapters 2 and 4 where the effect o
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ResultsGeneral conditionFor the 3 n
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The effects of crowding on visual a
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Figure 5.4(A): The top panel depict
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Further, the estimates of slopes ob
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Table 5.4(A) and (B): Depicts the s
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and mean complex interaction thresh
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235
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A (non-amblyopic eyes) B (amblyopic
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Figure 5.8: The difference between
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Std error 0.05 0.06 0.06 0.07 0.07
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For the amblyopic subjects, a three
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Control conditionError analysisData
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249
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DiscussionThe current experiment in
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Based on these findings, we attribu
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and Spowart, 1997), multiple E opto
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Chapter 6Summary and conclusionsThe
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The effect of contour interaction o
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demonstrable at the abutting condit
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SGCI thresholds when measured for s
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REFERENCESABRAHAMSSON, M. and SJOST
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BERNARD, J.B. and CHUNG, S.T.L., 20
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ELLIOTT, D., BULLIMORE, M., PATLA.
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HARIHARAN, S., LEVI, D.M. and KLEIN
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JACOBS, R.J., 1979. Visual resoluti
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LEVI, D.M., KLEIN, S.A. and HARIHAR
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OWSLEY, C., 1994. Vision and drivin
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ROBINSON, D.A., 1964. The mechanics
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SIMMERS, A.J., GRAY, L.S. and WINN,
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AppendicesAppendix 1: Depicts the p
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three and two amblyopic subjects re
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Appendix 3:287
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Appendix 4: The percentage of subst
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Appendix 5: Depicts the letter conf
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