VT and Accommodation
Accommodation is defined as the act of focusing the eyes to provide an image clear enough for interpretation. Accommodation also refers to the change in the power of the crystalline lens to bring an object into focus when stimulated by the presence of blur or proximity of the object.
Vision Therapy should strive to help patients improve their accommodative efficiency which includes facility (the ease with which a patient can shift from a relaxed posture to a stimulated posture), amplitude (the accommodative range when viewing a near target), flexibility (the ease with which accommodation is achieved), stamina (the ability to maintain accommodative accuracy without breakdown or diminishing the performance) and speed (the ability to quickly and accurately make the appropriate changes in focusing demand).
These facets can affect the three main areas of Accommodation:
• Accommodative facility which is the ability to rapidly jump from different objects of regard at varying distances
• Accommodative posture which is the position of accommodation relative to the object of regard
• Accommodation amplitude which is the maximum amount of accommodative output possible
In our office, we explore accommodation with “real space” activities and “simulated space” in instrument. Since accommodation is intricately linked to the vergence system, via the accommodative-vergence-pupil triad, it is an important goal in vision therapy to call attention to both, even if the activity is monocular. The vergence system is used first to determine first “where is it” to better understand the “what is it” of the accommodative system. It provides feeling tone and increases the speed of response for SILO awareness.
It is also important to use spatial localization and spatial awareness in combination with the blur stimulus to understand where the plane of regard is in space, and where they are looking in relation to that plane. For example, if a minus lens is used to stimulate accommodation, it is useful for the patient to gain the feeling tone of looking closer to help with the ease of making the target clear.
Patient responses to changes in accommodative demand will include a change in pupil size as the accommodative system relaxes or constricts. If the patient is wearing a translucent patch, the Vision Therapist may also see a fusional response with the occluded eye. The patient may also verbalize a change in spatial awareness (SILO), or possibly demonstrate some other discomfort through body language. Under binocular conditions, a fusional (convergence or divergence) response depending on the power of the lens is included.
The beginning of the hierarchy for “real space” near/far shift activities we use in our office include a Bullseye near target and a Far Hart Chart, then changing to a Near and Far Hart Charts, on a monocular level. These activities begin with the patient physically touching the near target (an important step in the patient having a spatial awareness of exactly where the object is in space), and then backing away until they reach the maximum distance from which the patient can still see the letters on the distance chart clearly without guessing. Monocularly, these activities isolate accommodation and eliminate the possibility of diplopia which may be caused by an accommodative-vergence integration weakness. Lenses are introduced to include SILO awareness. Once equality and accuracy is achieved one eye at a time, the activities are repeated binocularly to incorporate a vergence demand.
The demand of an activity can also be changed by increasing or decreasing the distance from the target, the power of the lens or lenses (depending on the activity), the cognitive demand, auditory or anti-gravity load, as well as providing a dynamic target versus a static target.
Other examples of activities used in our office listed from higher level to lower level to assist patients in strengthening their accommodative systems are Wachs Mental Minus, MFBF, and Bifocal Rock, respectively. Wachs Mental Minus works on facility, posture and amplitude and even incorporates a bi-ocular demand with dissociated prisms. MFBF activities done with red/green filters not only provide information about suppression, but also whether the patient can successfully satisfy both the accommodative and vergence demands presented by the situation, effectively calibrate both systems, so they can operate together with freedom and flexibility between them. Bifocal rock asks the patient to learn to appreciate the SILO aspects of a minus lens, which compresses space, brings the target closer, and makes the image smaller. This appreciation of SILO in bifocal rock is important because it demonstrates the patient’s ability to “disconnect” from the logic they posses about the real world (when an object gets smaller, logic tells us it is getting farther away) and allows the opportunity to fully understand and embrace what their visual system is experiencing.