DISTANCE ACUITIES & VISUAL FIELDS
By: Carmen Willings
As part of the Functional Vision Evaluation, it is necessary to assess the student's distance visual acuities (including their intermediate and distance responses) as well as their visual fields. The technique used will vary depending on the students cognitive abilities.
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Distance Visual Acuity
Assess the student's distance vision using a combination of informal and formal devices. Assessment should include classroom activities, such as reading the chalkboard, as well as activities that take place outside the classroom, such as reading a banner in a hallway, catching a ball in a PE class, or identifying the bus after school. A formal distance-screening procedure should be included in the functional vision assessment to act as a comparison with clinical measures provided in the report of the clinical low vision specialist. Functional tasks using distance vision should include familiar an unfamiliar ones under different lighting conditions.
Depending on the results of the Distance Visual Acuity, the following strategies, recommendations, and accommodations may be necessary to meet the students unique visual needs:
The central visual field is the "what" system, while the peripheral visual field is the "where" system. The visual field is the entire area of vision that can be used without shifting the eyes or moving the head, encompassing 180 degree arcs. Assess the student's visual fields including the student's preferences or limitations. Observe the students response to materials presented in the central visual field and to the peripheral visual fields. Note where the student responds to materials. Estimate the number of degrees from the nose.
Note other signs of possible field loss including: over-scanning; eccentric viewing; holding object to the side, up, or down to inspect it; stumbling over low-lying objects; functional peripheral vision is often a source of distractibility. A student's scanning of an array of objects or looking for a missing object can demonstrate his functional visual field at near point. For example, a compensatory head turn suggests a peripheral field loss to the side of the head turn, since the student has learned to compensate by moving the usable visual field toward the side where information is missing.
The performance of activities, such as scanning a map or doing a word-search puzzle, can also suggest where scotomas (areas of absent vision) may be located, because if students are asked to keep their heads perfectly still while doing them, they may miss information in some areas of the tasks. Students who walk with their heads turned slightly to one side may be compensating for a difference in visual fields. Eye preference, evidenced in typical tasks, can also be evaluated.
Observe special visual behaviors and repetitive behaviors including eccentric viewing, stereotypical behaviors, and fluctuating visual abilities. Observe whether the student uses corrective lenses and tolerates them. Also indicate if the student has received Orientation and Mobility services. Note how the student currently travels indoors, outdoors, in familiar and in unfamiliar environments.
The absence of a full (180 degrees) peripheral field may cause difficulty in sports and social difficulty due to not seeing those in their visual field or by using an odd posture in order to see. They also may not see downward flight of stairs or a curb. It also may limit the amount of letters/words can see at a time.
Depending on the results of the Visual Fields Testing, the following strategies, recommendations, and accommodations may be necessary to meet the students unique visual needs: