Near dissociated phoria measurements are effected by a variety of variables including accommodation, testing conditions, and procedures. Several studies have compared various techniques and repeatability of near phoria measurements. However, previous studies have not assessed target manipulation to determine how the phorias may be affected. The intention of this study was to evaluate if a change in card design has any influence on the outcome of near dissociated phoria measurements. Forty volunteers between the ages of 20 and 40 years were used to assess near point phorias using the von Graefe method. Phorias were measured with a standard near point card and an experimental near point card which eliminated most  white space  on the card. Two near phoria measurements per card per subject were performed independently by three examiners. The results showed a mean near phoria using the standard card was 3.730A exophoric and the mean phoria using the experimental card was 4.607A exophoric. Based on these values alone a statistical difference does exist. However, when interexaminer variability was taken into account a statistical difference does not exist between the standard and experimental near phoria targets. This was due to the large range of measurements between examiners

Anderson, Traci

Fischer, Beth

Wurst, Sandy S

English

CommonKnowledge

Pacific University 
CommonKnowledge 
College of Optometry Theses, Dissertations and Capstone Projects 
5-2001 
Differential near phoria measurements between standard and 
experimental targets 
Traci Anderson 
Pacific University 
Beth Fischer 
Pacific University 
Sandy S. Wurst 
Pacific University 
Recommended Citation 
Anderson, Traci; Fischer, Beth; and Wurst, Sandy S., "Differential near phoria measurements between 
standard and experimental targets" (2001). College of Optometry. 1360. 
https://commons.pacificu.edu/opt/1360 
This Thesis is brought to you for free and open access by the Theses, Dissertations and Capstone Projects at 
CommonKnowledge. It has been accepted for inclusion in College of Optometry by an authorized administrator of 
CommonKnowledge. For more information, please contact CommonKnowledge@pacificu.edu. 
Differential near phoria measurements between standard and experimental 
targets 
Abstract 
Near dissociated phoria measurements are effected by a variety of variables including accommodation, 
testing conditions, and procedures. Several studies have compared various techniques and repeatability 
of near phoria measurements. However, previous studies have not assessed target manipulation to 
determine how the phorias may be affected. The intention of this study was to evaluate if a change in 
card design has any influence on the outcome of near dissociated phoria measurements. Forty volunteers 
between the ages of 20 and 40 years were used to assess near point phorias using the von Graefe 
method. Phorias were measured with a standard near point card and an experimental near point card 
which eliminated most "white space" on the card. Two near phoria measurements per card per subject 
were performed independently by three examiners. The results showed a mean near phoria using the 
standard card was 3.730A exophoric and the mean phoria using the experimental card was 4.607A 
exophoric. Based on these values alone a statistical difference does exist. However, when interexaminer 
variability was taken into account a statistical difference does not exist between the standard and 
experimental near phoria targets. This was due to the large range of measurements between examiners. 
Degree Type 
Thesis 
Degree Name 
Master of Science in Vision Science 
Committee Chair 
Scott C. Cooper 
Subject Categories 
Optometry 
This thesis is available at CommonKnowledge: https://commons.pacificu.edu/opt/1360 
Copyright and terms of use 
If you have downloaded this document directly from the web or from CommonKnowledge, see 
the “Rights” section on the previous page for the terms of use. 
If you have received this document through an interlibrary loan/document delivery service, the 
following terms of use apply: 
Copyright in this work is held by the author(s). You may download or print any portion of this 
document for personal use only, or for any use that is allowed by fair use (Title 17, §107 U.S.C.). 
Except for personal or fair use, you or your borrowing library may not reproduce, remix, 
republish, post, transmit, or distribute this document, or any portion thereof, without the 
permission of the copyright owner. [Note: If this document is licensed under a Creative 
Commons license (see “Rights” on the previous page) which allows broader usage rights, your 
use is governed by the terms of that license.] 
Inquiries regarding further use of these materials should be addressed to: CommonKnowledge 
Rights, Pacific University Library, 2043 College Way, Forest Grove, OR 97116, (503) 352-7209. 
Email inquiries may be directed to:.copyright@pacificu.edu 
DIFFERENTIAL NEAR PHORIA MEASUREMENTS BETWEEN 
STANDARD AND EXPEFSh4ENTAL TARGETS 
TRACI ANDERSON 
BETH FISCHER 
SANDY S, WURST 
A thesis submitted to the faculty of the 
College of Optometry 
Pacific University 
Forest Grove, Oregon 
For the degree of 
Doctor of Optometry 
May 2001 
Advisor: 
Scott C. Cooper, O.D., M.Ed. 
DIFFERENTIAL NEAR PHORIA MEASUREMENTS BETWEEN 
STANDARD AND EXPERIMENTAL TARGETS 
d u r n  
TRACI ANDERSON 
4 3. U k u b ~  
SANDY S. WURST 
ADVISOR 
Traci Anderson 
Traci Anderson was born and raised in Spokane, Washington. She graduated from 
Pacific University for her undergraduate work. While a student at Pacific University 
College of Optometry Traci was involved in Amigos Eyecare, Student Optometric 
Association (SOA), American Optometric Student Association (AOSA), and also served 
as a class officer. 
Beth Fischer 
Beth Fischer was born in Garrison, North Dakota. In 1997 she received a Bachelor of 
Science degree in Zoology with a minor in Chemistry from North Dakota State 
University in Fargo, North Dakota. She is currently attending Pacific University College 
of Optometry in Forest Grove, Oregon. 
Sandy S. Wurst 
Sandy S. Wurst was born in Harrisonville, Missouri. She attended Central Missouri State 
University and graduated with a BS in Finance. She was employed as an associate bank 
examiner with the U.S. Treasury for five years. She is currently attending Pacific 
University College of Optometry. Future plans include working in a group practice 
consisting of optometrists and ophthalmologists with emphasis in corneal disease and 
refractive surgery. 
Differential Near Phoria Measurements Between Standard and Experimental Targets 
ABSTRACT 
Near dissociated phoria measurements are effected by a variety of variables including 
accommodation, testing conditions, and procedures. Several studies have compared 
various techniques and repeatability of near phoria measurements. However, previous 
studies have not assessed target manipulation to determine how the phorias may be 
affected. The intention of this study was to evaluate if a change in card design has any 
influence on the outcome of near dissociated phoria measurements. 
Forty volunteers between the ages of 20 and 40 years were used to assess near point 
phorias using the von Graefe method. Phorias were measured with a standard near point 
card and an experimental near point card which eliminated most "white space" on the 
card. Two near phoria measurements per card per subject were performed independently 
by three examiners. The results showed a mean near phoria using the standard card was 
3.730A exophoric and the mean phoria using the experimental card was 4.607A exophoric. 
Based on these values alone a statistical difference does exist. However, when inter- 
examiner variability was taken into account a statistical difference does not exist between 
the standard and experimental near phoria targets. This was due to the large range of 
measurements between examiners. 
Differential Near Phoria Measurements Between Standard and Experimental Targets 
NrnODUCTION 
"The phoria position of the eyes is the position taken by the two visual axes with respect 
to one another when all stimuli to fusion have been eliminated" ( 1 ). Although near 
phorias exhibit much variability between individuals, and slightly between normative 
data bases, the average near phoria measurement has been cited as 3 exophoria ( 2 ) when 
measured using standard phorometric methods. Factors that affect near phoria 
measurements include accommodative vergence, proximal vergence, and tonic vergence ( 
3 ). Other factors that may impact phoria measurements include pre-testing activities, 
positions of gaze, testing distance, testing material (size of letters), illumination, and 
proprioception of the near point target. 
Many experiments have compared the variability in phoria measurements, testing 
conditions, and techniques. A recent study by Rainey, et, al. evaluated near phoria 
testing techniques including estimated cover test, prism neutralized objective cover test, 
prism neutralized subjective cover test, the von Graefe - continuous presentation, von 
Graefe - flash presentation, Thorington, and modified Thorington methods ( 4 ). Each of 
the above tests has different methods for establishing dissociation, controlling 
accommodation, and target image and size, therefore making the results difficult to 
compare clinically. Additionally, variables such as proprioceptive feedback when the 
patient holds the near target further confound single comparisons of techniques. 
As mentioned previously, various factors can impact the phoria measurement. No studies 
have looked at the impact of the near point card design on near phoria data. The purpose 
of this study is to determine whether a significant difference exists between lateral near 
phorias measured with a standard near point card versus an experimental near point card 
that provides more normal peripheral visual cues by eliminating excessive card material. 
METHODS 
Forty subjects between the ages of 20 and 40 volunteered for this study. Inclusion 
criteria included best corrected near visual acuity of at least 20120 without the use of a 
bifocal. In addition, any history of amblyopia, pathology of ocular media, eye surgery, 
accommodative dysfunction, or binocular dysfunction including strabismus or 
suppression resulted in exclusion. 
Subjects were tested using a prescription not older than one year. The subject's near 
pupillary distance (PD) was measured with a pupilometer and the near PD and the 
habitual prescription were established in the phoropter. Subjects were not allowed to use 
contact lenses during testing. 
The method used to test the near phorias consisted of the von Graefe technique. This 
method was selected for its routine clinical use and high reliability. ( 5 ) The initial 
dissociating prisms consisted of 12A base in over the right eye and 6A base up over the left 
eye. The standard or experimental card was placed on the nearpoint rod 40 cm from the 
patient. Standard room illumination was used with an additional nearpoint lamp using a 
40-watt incandescent light bulb located 20 inches from the nearpoint card. ( 1 ) 
The standard near point card displayed a vertical row of 20/20 letters. The experimental 
card was created from the same standard near point card with all excess "white
yy 
material 
removed, leaving a "T" shaped experimental card. 
Figure 1 : A drawing of the experimental card. 
: 
The shape of the card allowed placement on the near point rod. By removing as much of 
the "non print'karea as possible, only the 20120 letters were exposed, leaving most of the 
testing room's background visible during phoria measurements. 
Major variables were controlled due to the following features. Proximal vergence was 
conlrolled since it should be consistent with both cards. Accommodative vergence was 
controlled with 20120 print letters on both cards. Position of gaze was controlled by 
n~aintaining a 40cm testing distance in primary gaze. 
C 
P 
'I' 
PI 
R 
S 
U 
- 
- 
The following instruction set was read to each subject before each phoria measurement. 
"Do you see two lines of letters? Is the lower set to the left? Keep watching the letters 
on the bottom row and keep them as clear as you can. The top row is going to move 
across and it will never stop completely. When it lines up directly over the bottom row 
say 'Now'. You should always see double but keep the lower image clear. Here we 
go". After the first measurement was found, the following instructions were given. 
"Once again, when they pass directly above each other from the other direction say 
'Now"'. 
To reduce variability among the three examiners, the two testing cards were used in 
random order for each subject. Each examiner performed two phoria measurements per 
card per subject for a total of twelve measurements per subject, also in random order. 
The measurements consisted of alignment from the base in direction and then a second 
alignment from the base out direction. Only one examiner was present during data 
gathering and results were not revealed until all testing was complete. All testing was 
completed in a single visit for each subject. 
RESULTS 
A within-subjects design paired t-test showed a statistically significant difference 
between the phoria measurements using the standard and experimental cards. 
l ~ a n ~ e  Experimental I -3.86 2.394 
Table 1 : The mean and range for the standard and experimental cards. 
The mean phoria using the standard card was 3.730" exophoric with a standard deviation 
of 5.1 90". The mean phoria using the experimental card was 4.607" exophoric with a 
standard deviation of 5.5 10". The mean difference between the two cards was 0.877. 
Using a two-tailed T-test with 0.05 confidence level, a p-value of 0.0006 was identified. 
This value indicates that a statistical difference exists between measurement taken with 
these targets. 
To account for inter-examiner variability, the ranges of phoria measurements obtained in 
this experiment were compared. The range is defined as the most esophoric measurement 
to the most exophoric measurement for a given subject. An average range of 3.3" and 
3.8" were found for the standard and experimental cards, respectively. A p-value of 
0.1206 was found indicating that a statistical difference in the range of collected data 
does not exist. This also makes sense clinically based on the large range of measurements 
recorded between examiners and the standard deviations found under each testing 
condition. 
DISCUSSION 
There are numerous variables that affect the near point phoria. This experiment 
controlled as many variables as possible to isolate one element, the amount of "real 
space" visible during near point phoria testing. Unfortunately, we were not able to control 
the subject's pre-testing activities. However, with testing randomization and relatively 
short data collection time, this should not have been a significant problem. 
The standard von Graeffe testing condition simulates a two-dimensional situation with a 
small amount of print in a comparatively large white field. This is a significantly 
different target than typically used with other phoria measurements (cover test, Maddox 
rod, Modified Thorington, etc.). The peripheral cues available by the experimental card 
allow the benefits of a three dimensional environment visually accessible to a person on a 
daily basis. Without prompting, various subjects made comments about the ease of 
aligning the experimental card compared to the standard card. This may be due to the 
small margin surrounding the letters on the experimental card. This margin may have 
created better contrast with the "natural" background or made the subject aware of the 
color and detail rich background elements peripheral to the 20120 letters coming into 
alignment during the test. If this is the case, the peripheral cues may have prevented the 
subject's accommodation from fully or consistently responding to the 40cm stimulus, or 
perhaps having more of the full testing room visible altered the subject's tonic 
innervation ( 6 ). It is assumed these cues account for the larger exophoric posture and 
standard deviations found in this study. 
There are many variabIes that impact phsria measurements including tonic vergence, 
proximal vergence, accommodative vergence, pre-testing activities, positions of gaze, 
testing distance, testing material (size of letters), and illumination. 
This study has now identified another element that impacts phoria measurements. By 
changing the shape of the testing card and allowing more of the testing room to be seen, 
we found an exophoric shift of the near pl~oria measurement. These results show how 
easily one can manipulate the phorias md the expected standard deviations by the 
slightest change in testing conditions. 
Further studies could be done to investigate the impact of this experin~ental card on 
vergence ranges and similar card designs could be applied to associated phoria 
measurements. Further study may demonstrate analytical benefit to near point testing 
with targets that create a more "normaI" visual environment. If sirniIar resuIts are found 
in future studies, it is suggested this experimental card be used as a standard near target in 
order to simulate a more natural testing environment. 
REFERENCES 
1. Grosvenor TP. Primary Care Optometry. 3'd Ed. Newton, MA: Butterworth- 
Heinemann, 1996:309-3 12. 
2. Goss D. Ocular Accommodation, Convergence, and Fixation Disparity: A Manual of 
Clinical Analysis. 2nd Ed. Boston, MA: Butterworth-Heinemann, 1995 :63. 
3. Jackson T, Goss D. Variation and correlation of standard clinical phoropter tests, 
phorias, vergence ranges, and relative accommodation in a sample of school-aged 
children. Journal of the American Optometric Association 1991;62:540-546. 
4. Rainey By Schroeder T, Goss D et al. Inter-examiner repeatability of heterophoria 
tests. Optometry and Vision Science 1998;75(10):719-726. 
5. Schroeder T, Rainey By Goss D et al. Reliability of and comparisons among methods 
of measuring dissociated phoria. Optometry and Vision Science 1996;73 :3 89-397. 
6. Chiu N, Rosenfield M. Dark Accommodation, Dark Vergence and Surround 
Propinquity. Supplement to: Optomedry and Vision Science - Academy '93 Edition 
1993;70:15. 


Differential near phoria measurements between standard and experimental targets

https://commons.pacificu.edu/cgi/viewcontent.cgi?article=1249&amp;context=opt

Differential near phoria measurements between standard and experimental targets

Abstract

Similar works

Full text

Available Versions

CommonKnowledge