Optometric management of Alzhiemer's and Parkinson's diseases.
Assessment of the visual field in patients with AD or PD should involve a technique that assesses magno-cellular function. (1) The usefulness of frequency doubling technology (FDT) as employed by the Zeiss FDT screener has previously been described, (2,3) whilst other techniques include the Bjerrum (tangent) screen and campimeter, which assess the initial perception of a moving target to which the magno-cellular system is most sensitive. Such methods may reveal a constricted field and accompanying enlarged blind spot. (4) However, practitioners should beware that it can be difficult to accurately assess visual fields in patients with AD or PD using automated threshold methods, due to poor fixation/attention. As such, some alternative and inexpensive methods can be adopted instead.
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Temporal hand confrontation
Face the patient and ask them to look at your nose binocularly (the nose acts as a septum so there is no need to occlude one eye). Hold your hand close to the side of your face and ask the patient if they can see it. If they can, slowly move your hand away to the side, asking the patient to notify you if the hand disappears. When it does disappear, move the hand out further and then bring it in slowly until the patient tells you they can see it again. Repeat for both eyes and compare to the expected range. Repeating the test with fingers spread apart, and asking the patient to tell you when they are aware of the separated fingers, helps to assess the ability to process detail within the peripheral field; this field can be quite small. (5)
Laser pointer on wall
The patient sits one metre from a plain wall and is asked to fixate a mark directly in front of them (eg, a pin or a cross on a post-it note). Testing monocularly, the patient fixates this as you move a laser pointer light towards the fixation target from various peripheral directions. (6) Results are compared akin to the Bjerrum chart or the Fincham Sutcliffe chart; these charts are more useful as they have the degree markings written on the screen. In either case, the measured visual field can be very restricted if compared to static threshold visual fields. In addition, comparing this field to that found using the Fincham Sutcliffe chart in its conventional flashing light mode will demonstrate a significant difference. Indeed, though they may have identified the correct number of lights, their awareness of stimulus location is poor (difference between static and motion processing). This demonstrates one of the causes of mobility problems that people with PD and AD can have along with difficulties with reading and posture (downward head tilts are common). (7)
Awareness of Practitioner
This is a very simple test of peripheral awareness that requires no specialist equipment or training and can be used by a doctor or nurse in a person's home. Stand three metres in front of the patient and ask them to fixate your nose. The patient is asked to report how much of the practitioner's body they are aware of. As the practitioner is looking at their patient, they can monitor fixation and compare the patient's field to their own (Figure 1).
Optometrists will commonly assess a near reading addition power but often overlook the available range of clear vision (accommodative flexibility; af), which can actually be reduced due to the visual field and affects on the magno-cellular (kinetic or awareness) pathway. (4,8,9) This was confirmed by a retrospective study during a six-month period, revealing a direct relationship between the near range of vision and the visual field assessed using the awareness of practitioner technique; patients wore a +2.25DS near add and had normal near visual acuity (VA) (Figure 2). From this relationship, it can be seen that a typical awareness field of a patient with PD that reaches "down to the waist", corresponds to a clear range of reading (af) of only 15 cm. (10) Therefore, adding these simple tests, which take very little time, can alert the optometrist to potential visual processing problems that require further investigation.
Eye tracking and ocular motility
Patients with dementia have significantly worse smooth-pursuit tracking movements than people with either pseudodementia or elderly normal controls. (11,12) It is postulated that the ocular motor changes seen in PD are contingent upon functional dopamine levels in the basal ganglia. Clinical improvement with dopaminergic drugs has shown an improvement of saccadic accuracy and smooth pursuit gain. (13)
As such, it is important to assess ocular motility, looking for head movements, loss of fixation, jerky eye movements, postural instability, and reduced convergence.
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Visual acuity and contrast sensitivity
Though VA in patients with PD and AD is initially normal, it may reduce gradually through disease processes such as cataract and age-related macular degeneration (AMD), bringing with it associated effects on the visual field eg, general reduction in sensitivity (consider this as Traquair's "Island of vision" sinking into the sea, with a higher island peak corresponding to a better VA). (14) Furthermore, there can be a reduction in contrast sensitivity, indicating a need to assess this using, for example, the Vistech chart or Bailie Lovie charts, and to monitor for progressive changes in AD and PD. (15)
Visual mid-line shift syndrome
Some patients with AD and PD experience difficulty with walking in a straight line, often associated with head tilts/turns and postural problems that affect the shoulders, lower back and neck. These symptoms can be due to a condition called visual mid-line shift syndrome, where objects directly in front of an individual are perceived to be offset to the side; (16) typically the shift is in the same direction as the head tilt/turn eg, if the patient has a head turn to the left, the object will be perceived as being offset to the left of centre (Figure 3). Visual mid-line shift syndrome results from dysfunction of the ambient magno-cellular system, which causes a shift in their concept of the visual mid-line. (17) This condition can be elicited by a test similar to confrontation. Have the patient stand as for a motility test, hold your fixation target off to the side and move it slowly across in front of them. The patient is required to tell you when the target is in front of their nose. Check the position and if it is not centred, a visual mid-line shift can be identified. When carrying out the test, do not stand directly in front of the patient, as this will give them a centring reference. Repeat from the other side too. Also assess the patient's posture, looking for head tilt, whether the shoulders and pelvis are level, and if the spine is curved to the side or forward (particularly seen in PD).
Visual mid-line shift can also be evaluated with the Van Orden star (18) and the VTE Spatial Localisation Board (18) (Figure 4). The latter allows the optometrist to quickly assess a patient's spatial localisation in real space and time; determine x, y and z axis spatial warps in nine primary meridians and record patient responses for pre- and post-test data (especially good for documenting visual mid-line shifts in mild traumatic brain injury) and quantify immediate effects of lenses and prisms. (19,20,21)
People with AD may experience loss of blue/violet sensitivity, which may be associated with damage to the koniocellular system. Such defects are not adequately detected by the Ishihara test and so the Farnsworth D15 or the City University (TCU) tests ought to be used instead (see previous articles in Optometry Today for details on colour vision testing). (22,23)
Retinal abnormalities in early AD and PD include a specific pattern of retinal nerve fibre layer (RNFL) loss, (24) narrowing of veins, and reduced blood flow. Loss of retinal ganglion cells may reflect degenerative change in the brain in these conditions. (24) As software for digital retinal cameras and optical coherence tomography (OCT) improves, a greater understanding of these early changes will be obtained.
As glaucoma can develop faster in patients with AD or PD (causing damage to magno-, parvo- and konio-cellular nerve fibres), careful investigation of this potential condition should be undertaken, with regular monitoring of the optic nerve head appearance and visual fields; the latter should include magno-cellular assessment, as mentioned earlier, along with static threshold tests for monitoring progression.
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Treatment regimes for patients with AD and PD are not aimed at treating the medical condition but rather to reduce stress and visual problems encountered, in order to improve quality of life. For example, patients with tremor may not be able to hold a book to read comfortably and so one can prescribe a lower reading add, advise good lighting and/or suggest the use of non-visual aids eg, placing the book on a table. Many optometric assessments will require reliance on objective techniques such as retinoscopy and Sheridan-Gardner VA testing, due to the difficulty in obtaining accurate subjective responses.
Patients with dementia are typically less likely to have regular eye exams, increasing the consequent risk of sight loss from typical age-related sight problems. Assessment of these patients under mydriasis is therefore essential to identify sight-threatening disease. Where possible, treatment of these problems can improve quality of life by helping mobility and posture. Improving functions such as motion awareness, contrast, VA, and colour vision can enable a person to look at magazines and watch TV too.
The near range of clear vision can be modified with the prescription of yoked prisms, typically 2A base down each eye, (25) which will increase the functional near visual field, improve the near point of convergence and improve reading speed and comprehension. Base down prisms will also have the effect of "lifting the environment", aiding those patients with "head down" postural problems. Base up prisms can also be helpful but may increase the tendency for head down posture. (19-21) Horizontal yoked prisms can help with mid-line shift syndrome. (26,27)
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Consideration should be given to the possibility that postural problems and visual field deficits may impair the effective use of varifocal spectacle lenses and so single vision lenses ought to be preferred, especially for mobility and reading. (28) An alternative option is a degressive varifocal lens, such as Rodenstock Ergo, Sola Access, or Varilux computer 2V, especially for those people who are using a VDU. (25) Photochromic or contrast enhancing lenses may also be considered for patients with photophobic or contrast problems, respectively, and for protection from ultraviolet (UV) light.
A new visual field test, the Motion Displacement Test (MDT) (Figure 5), is currently in development at Moorfields Eye Hospital and The Institute of Ophthalmology, UCL, in collaboration with City University, London. This computer-based test works primarily on the "awareness of movement displacement" associated with the magno-cellular pathway. Therefore it may prove useful to identify and monitor these deficits. However, present research has concentrated on glaucoma detection only. (29)
Results obtained with the City University CAD test, developed in association with the Civil Aviation Authority, provide an efficient means of detecting and classifying even minimal deficiencies in colour vision, by evaluating red/green and blue/yellow colour detection thresholds using an internationally recognised colour system. As such this can be used to monitor changes in colour perception, disease progression, and/or therapy outcomes. However, the cost of this test suggests it may only be appropriate in specialist clinics. (30)
Optometric vision therapy
Techniques used to develop the visual system in children with learning difficulties and in adults with mild traumatic brain injury could also be applied to improving visual function in people with AD and PD. Based on the Skeffington concept (see part 1 of this series, Optometry Today January 14 2011), optometrists can train specific elements of the visual processing system:
1. Anti-gravity--to improve posture, balance, and postural/primitive reflexes
2. Centring--to improve pursuit & saccadic eye movements, convergence, and accommodation
3. Identification--to improve visual discrimination, closure, perception, and memory
4. Speech/auditory--to improve visualisation, sequencing, laterality, and developing ideas/concepts
Optometric phototherapy (syntonics)
Syntonics or optometric phototherapy is the branch of ocular science dealing with the application of selected light frequencies through the eyes (31) to improve cortical processes such as in cases of brain injuries, emotional disorders, (32) and seasonal affective disorder (SAD). A number of studies have shown expansion of visual fields in children with learning difficulties (33-34,35) and similar changes could be expected of people with PD (36) as a result of improved form and motion coherence processing, through inhibition of melatonin. (37) Green light (505nm) is the most effective for suppressing melatonin production and is utilised in Sunnex Biotechnologies Lo-LIGHT lamps. (38) Light therapy was reported to slow "cognitive deterioration" by 5% and depressive symptoms fell by 19%, (36) however, further research in this area is required.
Within the panoply of age-related disease, AD and PD are serious conditions that significantly affect a person's quality of life. Knowledge of the visual problems associated with these conditions, and how simple changes such as improving contrast in the home or prescribing different lens forms, might help to extend quality of life for these patients. Eye care professionals need to consider a variety of tools at their disposal to do this and it is hoped that these articles will stimulate further research.
See http://www.optometry.co.uk clinical/index. Click on the article title and then download "references"
For the module questions to this article, please turn to page 49.
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|Title Annotation:||CET: CONTINUING EDUCATION & TRAINING|
|Date:||Feb 25, 2011|
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