A systems model for low vision rehabilitation. I. Basic concepts.

The basic concepts and structure of a hierarchical systems model for low vision rehabilitation is developed and presented. The model is built on the assumption that the patient has a desired life state, which is not realized because of the visual impairment. Life state is defined as a set of activities that the individual wants or needs to perform. The activities that constitute life state are represented hierarchically in a system called the activity breakdown structure (ABS). The highest level of the ABS represents the objectives served by the activities (e.g., daily living, vocational, recreational, social, and educational objectives). Under each objective is a set of goals and serve that objective. Any goal could serve multiple objectives. The requirements for successfully achieving a goal may vary with the objective that goal serves. The lowest level of the ABS consists of tasks that must be performed successfully to achieve particular goals. Any task could serve multiple goals. Each goal and each task has a value to the patient (i.e., level of importance) and also is associated with a level of difficulty. The need for rehabilitation, which is captured in the formal construct rehabilitative demand, for each goal and its subsidiary tasks, scales with the value of the goal or task and with the difficulty in achieving the goal and/or performing the task. Successful rehabilitation will reduce rehabilitative demand by reducing the level of difficulty associated with the goal or task and/or by reducing the value assigned by the patient to the goal or task (as a result of counseling or of learning alternative strategies). Within the framework of the model, changes in rehabilitative demand define effectiveness of intervention.