An Optometrists observations of functional visual field problems in adults

Introduction

Following research into the problems of children with specific learning difficulties, it became apparent that a number of adults encountered similar problems and knowledge of visual processing "see sawed" between these two groups. Research in the USA and confirmed by ourselves in the UK indicated that as many as 20 % of children in education have restricted functional fields.

A Functional Field is that peripheral field to which we can react to a given moving stimulus as opposed to an Absolute Visual Field, which is the threshold field of reaction of the eye to a flashing stimulus. A Functional Visual Field relates to the brains processing function of the visual image. An Absolute Visual Field relates to the ability of the eye to respond to a stimulus and send that information to the brain. Dr Wayne Pharr from Okechobee in Florida introduced me to the concept of functional visual field testing with an instrument called a Campimeter.

The Campimeter

As a result of this introduction, I initially compared my results of testing between the Campimeter and Bjerrum screen whilst gaining confidence and experience with this new instrument. The Campimeter is an instrument that is rather like a miniature Bjerrum screen which is focused through a plus lens for clarity and comfort. The Targets like those used on a Bjerrum screen are made with White, Red, Blue and Green targets of various sizes, the major difference being that the target is inset into a black ring.

The Wayne Pharr method of Campimetry with the three levels of testing

Level 1 The Available field of visual processing.

The field is plotted by moving the 5mm (2 degree) white target in towards the centre from non-seeing to seeing with the patient advising as soon as they first see the test target whilst concentrating on a small cross at the centre of the target. The point at which they first observe the target is marked on the chart . The vertical, horizontal and oblique meridians are measured. This is the field that you have the potential to use at this time - that is wired up to the brain for use!

Level 2 The Awareness field

Place the target near the centre and ask the patient to notice that there is a black ring around the target. Explain that their job this time is to again concentrate on the centre, but as they notice the white spot coming in, they are to tell you when they are first aware that the white spot has a black edge to it. Mark the chart and continue to test as before. This is the field you use when walking, being aware of things and reacting to them, mind that dog, where is the kerb, etc.

Level 3 The Activation level

Place the target near the centre and ask the patient to notice that there is a black ring around the target. Explain that their job this time is to again concentrate on the centre, but as they notice the white spot coming in, they are to tell you when they are first aware that the white spot has a complete black ring around it This is the field that is used for detailed viewing such as reading. In a normal field combination levels 1, 2, & 3 are generally reduced about 5 degrees between each level with the diameter of level 1 about 55 degrees.

4) The Physiological Blind Spot

The blind spot is in the temporal field and relates to the area of insertion of the optic nerve into the back of the eye. The 1degree white target is moved out from the fixation point in a temporal direction whilst the patient fixates the central cross until the spot disappears. The area of the blind spot is then measured from non-seeing to seeing. In cases of restricted functional fields, the blind spot is often enlarged. It is believed that is is due to oedema at the optic nerve head. The blind spot may also be displaced, see dural torque. How is this relevant to childrens vision?

Focus Limitations

As a result of this work I became aware that those children that had a small level 3 field also had a restricted depth of focus. Over the years it has always been a puzzle to me that presbyopic patients requiring the same add had different depths of focus. On examining their functional fields, it became apparent that those with a large Level 3 field had a good depth of focus whilst those with a small Level 3 had a very restricted range. This therefore indicates that functional fields are 3 dimensional. A small level 3 functional field is an indication of a difficulty with reading, an inability to scan read a restricted depth of focus, and is likely to be a varifocal "grief" case.

Pre presbyopia

It is generally considered that presbyopia starts to become a problem at around age 45, however, we all experience those in their 30s, for example, with these problems. These patients will, in general, also be found to have restrictions in Level 2 and Level 3 testing

Varifocal Intolerances

In the past patients with a restricted depth of focus with bifocals would be considered an ideal candidate for varifocal lenses, however these same people were often intolerant and complained of difficulty finding the right part of the lens to use, would often use odd head postures, and complained of only being able to read a small area of print. These same patients may have large normal level 1 fields but level 2 or 3 may be severely restricted to sometimes as little as 2 - 3 degrees! i.e. suffering from a restricted narrow field and restricted depth of focus.

Subnormal VA's

6/6 or 20/20 vision is considered normal. When the VAs are 6/9 (20/30) or below with no obvious reason, the functional fields will frequently be restricted

Eye diseases

Some patients with eye diseases of maturity, cataract, macular degeneration, Glaucoma, etc., may experience greater difficulty than would be expected from their observed condition. If their functional fields are examined, they may be found to be substantially reduced.

Closed head brain injuries

Various functional field problems may be encountered from restrictions at all levels to reduction in levels 2 and/ or 3. As an example, patients who have suffered closed head brain injuries may experience difficulties with reading following their accident. Investigation of some of these

patients has also indicated restrictions in Level 2 and Level 3 fields despite the Level 1 field being normal. Dural torque may also be present

Dural Torque

On examining the blind spots of some patients, it will be observed that the physiological blind spot is misplaced. It is believed that this displacement is due to a tightening of the dura mater covering the brain and spinal cord. Following cranial manipulation, releases the tension in the skull and the duramater allowing the position of the physiological blind spot to revert to normal. Research in this area has been undertaken by Drs. Wayne Pharr, Dale Fast and myself.

So What?!

If we check the functional fields of adult patients when they experience difficulties not expected for their age or visual potential, we can at least have an idea of the origin of their difficulty and take steps to remediate the problem

Treatment regimes

Functional fields can be expanded by the appropriate use of lenses, yoked prisms, vision therapy and syntonic photo therapy.

One of my major concerns is the indiscriminate use by lens manufacturers in supplying "thinning" (or yoked) prisms without it being prescribed! In some cases the uses of prism in this way with a patient with restricted field will increase their intolerance risk. I have often found existing varifocal wearers intolerant to new lenses have been supplied with a different thinning (yoked) prism. It seems to be exceeding difficult to obtain varifocals without these prisms! (This seems to be an area we need more research on).

Syntonic Phototherapy

The College of Syntonic Photo therapy has been promoting the provision of "light" therapy to help expand functional visual fields for over 70 years. I have been using their techniques to good effect over the past 2 1/2 years. Having successfully treated many children with learning difficulties with a combination of syntonic photo therapy in association with vision therapy, I recently examined a 78 year old patient diagnosed >5 years ago with macular degeneration and registered partially sighted. Her vision standard was RE counting fingers, the LE just hand movements both at 1/2 metre. There was early bilateral cataract and "early" macular degenerative changes. Her peripheral retina looked normal. Her functional visual field was too small to measure. Following 12 x 20 minute,(interestingly after just 4 sessions, we were able to record a small "spiral" field!), sessions of syntonic photo therapy, her field expanded to normal and in doing so improved her acuities to R 6/9, L 6/12 and reading N6.

From this exceptional case it can be readily seen the importance of assessing this aspect of vision and the effect of its’ remediation. Examining these different functional fields of other patients with Glaucoma, Retinitis Pigmentosa and Macular Degeneration have also indicated that there may, in the right situation, be improvements possible. It should however be pointed out that we are not treating the condition of, for example macular degeneration, but the brains ability to process the visual information that is available to it.

Recommendation

All patients whatever their age whose vision appears to be less efficient than would be normally expected should undergo functional field testing and if a appropriate, a suitable regime of therapy be considered