A simplified method of identifying the trained retinal locus for training in eccentric viewing.
It has been reported that persons with AMD can unconsciously adopt an eccentric area of the uncompromised retina, allowing them to achieve better vision. This eccentric area acts as a pseudo-fovea and is termed the preferred retinal locus (PRL) (Schuchard, 1995; Timberlake et al., 1986). Although useful, this spontaneous choice of location may not provide optimal vision for individuals to perform various visual tasks, such as reading, recognizing faces, or performing activities of daily living. Optimizing the location of the retinal area used can be addressed with formal training in eccentric viewing to teach individuals to use a more suitable part of their retina to see by introducing a trained retinal locus (TRL) (Culham, Silver, & Bird, 1990; Fletcher, Schuchard, & Watson, 1999; Nilsson et al., 2003; Vukicevic & Fitzmaurice, 2005, 2009). Although there are many methods for training eccentric viewing, the fundamental principles are equivocal and involve two stages:
1. Identification of the residual areas of the healthy retina by mapping the individual's visual field and
2. Location of the most suitable area to be used as the TRL on the basis of the proximity to the fovea.
A number of methods and apparatuses are available to chart the visual field, but the preferred method is by microperimetry with such devices as the Macular Integrity Assessment Microperimeter (CenterVue SpA, Padova, Italy) or the Nidek MP-1 Micro Perimeter (Nidek Technologies Srl, Padova, Italy). Alternately, the visual field can be mapped by tangent screen perimetry, such as the Bjerrum tangent screen. Microperimetry allows clinicians to precisely delineate the borders of the scotoma and the corresponding visible pathology on the retina. The technique is also capable of displaying direct, real-time observation of the retina, and stimuli can be placed on the retina for the purposes of training in eccentric viewing. For this reason, microperimetry is useful (Sunness, Bressler, & Maguire, 1995; Timberlake et al., 1986). Nevertheless, microperimetry is not widely used clinically because it is considered to be the least popular method of identifying the retinal locus for eccentric viewing training (Weisser-Pike, 2008). Low vision practitioners have reported that microperimeters are difficult to use and difficult for clients to understand how to perform the required task. The preference is for simpler methods, such as the Amsler grid or the Bjerrum tangent screen. Clinicians' preference is not the only issue that restricts the clinical use of microperimetry in a low vision setting: it is expensive equipment and hence is generally reserved for research purposes (Manivannan et al., 2001).
Low vision practitioners commonly use the Bjerrum tangent screen as a method of mapping the central visual field or the central scotoma or both. The Bjerrum tangent screen is a black felt screen that evaluates the central 30 degrees of the retina at a one- or two-meter (about 3 feet or 6.5 feet) testing distance. The Bjerrum has statico-kinetic properties that allow the borders of the scotoma to be accurately charted (kinetically) and individual test points to be grossly quantified (statically). The Bjerrum tangent screen can also be modified using a white cross for persons with central field defects to assist them to fixate centrally and steadily (Garber, 1994; West, 1988). Although the Bjerrum tangent screen is still considered a valuable tool in clinical settings, the large dimensions of the test screen and the need for an accurate setup each time render it difficult to use during domiciliary visits when this information is required by low vision therapists for mapping the field for training in eccentric viewing.
Limited portability and the lack of access to a microperimeter or a tangent screen have led to the development of more simplified methods of testing the boundaries of a central scotoma for training in eccentric viewing. Wright and Watson (1996) developed the "clock face" method to determine the size of a scotoma and to assist in determining the direction of the TRL. The desk-based California Central Visual Field Test (Mattingly Low Vision, Escondido, California), which uses laser dots of various brightness to map central scotomas has been developed. Because of import restrictions in Australia, this tool was unavailable to the researchers during the time of data collection. Another method is contained in the Eccentric Viewing Resources Kit (EV Kit) (Fitzmaurice, 2002), which was also developed to address the issue of portability and ease of use in determining the TRL. The test consists of three screening cards that help identify the retinal locus closest to the fovea that the low vision practitioner can use for teaching eccentric viewing. The test has been reported to be useful in determining the TRL, and individuals who received training in eccentric viewing after the TRL was identified using this kit made significant improvements in their near vision, reading speed, reading comprehension, and performance of activities of daily living (Vukicevic & Fitzmaurice, 2005, 2009). The consistency of the EV Kit tools compared to conventional perimetry tests has not yet been substantiated. (The EV Kit is available from Associate Professor Kerry Fitzmaurice, e-mail: <k. firstname.lastname@example.org >).
The EV Kit contains a smiley face card (see Figure 1a) made from an A4 size laminated card with two perpendicular lines bisecting each other to form a cross. A smiley face (15 mm, or about 0.6 inch, in diameter) is situated at the end of each line. When the card is held at the testing distance of 30 centimeters (about 12 inches), the distance between each face and the center of the cross corresponds to 7 degrees eccentricity from the fovea. Each eye is tested independently, and the person is asked to look at the center of the card, using the lines as a guide to where the center is. The person should be aware of the faces above, below, and to the side. If the person can see any of these faces, he or she then determines which is the clearest. The clearest smiley face should give an indication of the best area for the TRL. For example, if the person indicates that the top smiley face is the clearest, this is the area to be stimulated, so the person will be required to look approximately 7 degrees inferiorly for the purposes of training in eccentric viewing.
The girl's face card (see Figure 1b) is comprised of two separate laminated strips with the dimensions of 80 millimeters by 300 millimeters (about 3 inches by 12 inches). Each card contains a black-and-white photo of a girl's face centered on top of a 260-millimeter (about 10-inch) black line. Markings on either side of the picture extend out to 20 degrees and are placed at 10-degree increments along the line. Both cards are essentially the same but are oriented perpendicular to each other to allow testing of the vertical and horizontal retina. The individual is asked to look at the lines away from the girl's face to identify the best gaze position that allows him or her to see the girl's face most clearly.
[FIGURE 1 OMITTED]
The aim of the study was to compare the results of the smiley face and the girl's face to estimate an appropriate TRL with that of the Bjerrum tangent screen. We did not have access to a microperimeter for comparison.
The participants were recruited by convenience criterion sampling from a private ophthalmology clinic in Melbourne, Australia. They all had an absolute central scotoma as a result of unilateral or bilateral atrophic AMD, which was diagnosed by an ophthalmologist. There were no restrictions on the level of visual acuity required for the study. The participants were excluded if they presented with another ocular pathology or with visual field loss from an ocular disease other than AMD. All the procedures in the study were approved by the La Trobe University Faculty Human Ethics Committee (08/32), and all the participants gave written consent prior to participation.
The participants' best-corrected distance acuity was measured using a rear-illuminated Snellen chart at 6 meters (about 20 feet, or closer if the participant was not able to read the 6/60 optotype) and converted to LogMAR notation for the purposes of analysis. Near vision was tested at 40 centimeters (about 1.3 feet) using the Bailey-Lovie Word Reading Chart (Bailey & Lovie-Kitchin, 1980). Perimetry was performed using a 1-meter Bjerrum tangent screen to map the border of the participant's central scotoma and blind spot. Because of the loss of central vision, it was difficult for the participants to locate and steadily fix at the middle target on the Bjerrum screen. The screen was therefore adapted by placing two white strings in a cross over the chart to provide a guide for the center.
Tangent screen perimetry was performed using the smallest white stimulus that the participant could see, ranging from 1 to 7 millimeters (about 0.4 to 0.27 inch; M = 3.75 millimeters, or about 0.15 inch). Central field loss was determined kinetically. The blind spot was mapped first to provide the participants with an understanding of the concept of a missing area in the field (Bailey, 1978). The scotoma was then mapped by randomly assessing each meridian (every 15 degrees). The peripheral visual field was charted at every second meridian (every 30 degrees). The Bjerrum visual field results were shown to an experienced clinician who was not related to the study, and she was asked to select the preferred area for training the TRL by placing a cross on the visual field recording. The area selected was identical to that of the researcher, thus only one set of results for this variable are included. No participants were found to have a preferred TRL in a diagonal location using the Bjerrum. The testing order with the smiley face card, the girl's face card, or Bjerrum tangent screen was randomized.
Nine participants (14 eyes) were recruited for the study; the participants' demographic data and visual acuity are shown in Table 1. An example of the results for the Bjerrum, girl's face card, and smiley face card are shown in Figures 2a-c. The "X" indicates the most optimal area on the Bjerrum recording selected by the examiner and the preferred area chosen by the participant on the screening cards (see Figure 2a). With the girl's face card (Figure 2b), the scotoma is placed on the 10-degree line inferiorly, and the girl's face falls onto the healthy area of the retina (denoted by the "X"). Conversely, with the smiley face card (see Figure 2c), the scotoma is placed in the center of the cross (at the "X"), and the superior smiley face falls onto the healthy area of the retina.
Table 2 shows the results for each eye for all three tests. A high degree of agreement was found between the location of the best retinal area, as defined by the Bjerrum tangent screen and that of the smiley face card (13/14, 92.8%), and between the Bjerrum tangent screen and the girl's face card (11/14, 78.6%). A kappa statistic was also calculated for each comparison to the Bjerrum tangent screen. The kappa statistic is a measure of interrater reliability that takes into account chance agreement (Cohen, 1975). According to the results of the kappa statistic, there was a statistically significant level of agreement between the Bjerrum and the smiley face (kappa = 0.90, p < .001) and between the Bjerrum and the girl's face (kappa = 0.71, p < .001). According to Landis and Koch (1977), a kappa statistic of kappa = 0.90 for the smiley face is regarded as almost perfect agreement, while a kappa statistic of kappa = 0.71 for the girl's face is regarded as substantial agreement.
[FIGURE 2 OMITTED]
This study showed a high degree of reliability between using the tools from the EV Kit to identify a TRL and mapping the central scotoma with a Bjerrum tangent screen. A definite advantage of both the smiley face card and the girl's face card is that they are portable, easily administered by a low vision practitioner, and easy for a person to understand. Nevertheless, there are disadvantages, which include the inability to identify a TRL in a diagonal location and a gross estimation of the best area on which to place the TRL. The kit identifies an approximate location in terms of superior, inferior, nasal, or temporal, but is less sensitive to locating the optimum degree for the TRL. Some persons require the TRL at a closer or further proximity to the fovea than what the EV Kit tools can identify. However, this tool, like the clock face method, is not meant to be used in isolation. In a previous study (Vukicevic & Fitzmaurice, 2005), when the TRL was identified with the smiley face card, the distance from the fovea was refined using the EccVUE computer-generated method for training eccentric viewing (Fitzmaurice, Kinnear, & Chen, 1994), and the participants significantly improved on all the parameters that were tested (near vision, reading speed, reading comprehension, and performance of activities of daily living). In conclusion, the almost-perfect agreement between the Bjerrum tangent screen and the smiley face card and the substantial agreement with the girl's face card that were found in this study indicate that these tools from the EV Kit are a useful resource for low vision practitioners who are training persons with a bilateral absolute central scotoma in eccentric viewing, especially if the assessment and training occur outside the clinical environment.
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Meri Vukicevic, Ph.D., academic lecturer, Department of Clinical Vision Sciences, La Trobe University, Kingsbury Drive, Melbourne (Bundoora), 3086, Australia; e-mail: <m.vukicevic@ latrobe.edu.au>. Anh Le, B.Orth., Ophthalmic Sci., orthoptist, Department of Clinical Vision Sciences, La Trobe University, Kingsbury Drive. Melbounce (Bundoora), 3086, Australia; e-mail: <email@example.com>. James Baglin, B.App.Sc. (Psych.-Hons.), doctoral candidate, School of Mathematical and Geospatial Sciences, RMIT University (formerly known as Royal Melbourne Institute of Technology), Plenty Road, Bundoora, 3083, Australia; e-mail: <james. firstname.lastname@example.org>.
[check] EARN CEUs ONLINE by answering questions on this article. For more information, visit: <http://jvib.org/CEUs>.
The authors thank Charlotte Lowry, Teresa Lacy, Sara Fowler, and Katie Fowler for their assistance at the Alabama School for the Blind. We also thank Sharteedra Grace and Holly Smith for their efforts in entering the copious amounts of data. Last, the first author thanks the University of Alabama Huntsville Office of Research for its support of his unique research agenda through a Junior Faculty Distinguished Research grant.
Table 1 Demographic data and visual acuity. Eye Age Sex Distance visual acuity Right = 9 74-88 Female = 6 0.5-1.8 Left = 5 (M = 81; SD = 5) Male = 3 (M = 1.01, SD = 0.3) Eye Near visual acuity Right = 9 12/5/1980 Left = 5 (M = 38.7, SD = 20.8) Table 2 Results for all three tests for each participant. Bjerrum tangent screen: Location of Smiley face card: Girl's face card: the best retinal Location of the Location of the Eye area best retinal area best retinal area 1 Right Right Right 2 Superior Superior Superior 3 Right Right Right 4 Inferior Inferior Inferior 5 Left Left Left 6 Right Right Right 7 Left Left Superior 8 Left Right Inferior 9 Left Left Left 10 Bottom Bottom Superior 11 Right Right Right 12 Superior Superior Superior 13 Left Left Left 14 Left Left Left
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|Title Annotation:||Research Report|
|Author:||Vukicevic, Meri; Le, Anh; Baglin, James|
|Publication:||Journal of Visual Impairment & Blindness|
|Article Type:||Clinical report|
|Date:||Sep 1, 2012|
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