Tina Romanay gives an assessment of the Oculus Easyfield and describes some cases of its use on patients in City University's new clinic. Of particular interest is whether it may address some of the challenges of the disability discrimination legislation.
0ptometrists have carried out examination of the visual field for many years, either routinely or for further investigative purposes.
Perimetry is the measurement of the differential light threshold, ie the minimum light threshold necessary to evoke a response.
Most visual field screeners offer quick screening and/or advanced threshold strategy programs, to enable detection or assessment of a defect. Unfortunately most screeners, which tend to be big, bulky, non-portable, expensive and time consuming, are not easily accessible to those practitioners outside hospital-based or private practice, and therefore visual field examination is often omitted.
Implementation of section 21 of the Disability Discrimination Act 1995 as of October 1 1999, requires healthcare providers to take all reasonable steps to ensure that the services they provide are as accessible to disabled people as they are to the general population. Either providing extra help or making changes to the way they provide their services and auxiliary aids may affirm this.
SERVICE PROVIDERS' DUTY
WHAT IS AN AUXILIARY AID?
The duty to provide auxiliary aids or services requires the service provider to take such steps as is deemed reasonable to make its services accessible to disabled people. What might be reasonable for a large service provider (or one with substantial resources) might not be reasonable for a smaller service provider.
The service provider will have to consider what steps it can reasonably take. How effectively it is able to do so will depend largely on how far it has anticipated the requirements of disabled customers.
The Act leaves open to interpretation what particular auxiliary aids or services might be provided in specific circumstances. Disabled people may be able to help the service provider to identify difficulties in accessing the service and what kind of auxiliary aid or service will overcome them.
The instrument comprises the Oculus Easyfield Perimeter, an Easyfield control unit, tabletop power supply unit, patient response button and set-up disc software.
Easyfield control unit
Underneath the screen there is a control knob and two push buttons. The push buttons are 'enter' and 'cancel' keys, while the control knob allows you to alternate between different functions. In most situations the cancel key is made
The compact size of the Oculus Easyfield makes it attractive for domiciliary work redundant and this is particularly advantageous to avoid deleting complex information during an examination.
The control unit has a 40,000 patient data base facility which is remarkable for a small unit. Patient details are entered on to the data management system by using the control knob. It records the first name, surname, date of birth and date of examination.
An advantage of the control unit is that patient data can be exchanged between the PC and the unit. This makes it possible to save copies of examination results (which would allow for comparisons of data to be made against future tests), to import examination data and to update the software of the control unit.
The control unit also has the facility of an integrated printer, which prints the results of the examination in a compact readable form, the size of a till receipt.
Oculus Easyfield Perimeter
The cone has a vertical adjustment making it advantageous for those patients who are unable to adjust their height. I found this particularly useful for a patient that was wheelchair bound. The perimeter was placed on a desk that was at a good height for the patient, and adjustments were made to the funnel to allow for patient comfort. This was in comparison to another popular field analyser, where the patient was unable to rest their chin on to the rest comfortably with the instrument in its lowest position. There is a headrest, which is adjustable horizontally to allow for changes in position when testing the left/right visual field. A disadvantage found in this, however, is that the instrument does not allow for a large nose.
A lens mount can be fitted to the aperture to correct for distance and near refractive error, taking into account the fixation distance of the perimeter. This attachment sits almost flush with the viewing aperture, and is slightly smaller in size thereby minimising visual field defects that may be caused by lens artifacts. A patient response button is also located on the perimeter, which the patient holds during the examination, in order to respond to the stimuli presented. The response button has the facility to pause the test during an examination.
The perimeter may be used irrespective of ambient luminance, and this is very useful in situations where lighting cannot be controlled, for example in domiciliary work.
Examination: This gives you the option to load pre-existing
examinations, print results and create new patients.
Program: This selects pre-defined programs, for example: screening,
standard, macula and glaucoma. This is very useful when you want an
examination to begin as quickly as possible.
Statistics and display: These compare statistics and display standard,
relative, grayscale, 3D and sectional profiles on threshold related
Settings: This allows you to adjust the instrument's settings to your preference, for example: brightness of the camera and display, print format.
Although pre-selected examination parameters may have been chosen, the instrument gives you the flexibility to adjust the examination to your requirements.
Here you can adjust:
The option to specify your own testing points in the single points option is very useful, so that specific points can be examined further.
One of the disadvantages of these tests is that the pre-specified points cannot be extended. Therefore to examine more points you would need to use a 'user defined, program.
In all the tests the initial 'expected' brightness is determined by measuring the threshold of the retina centrally and peripherally to give an approximate estimate of the peak of the 'hill of vision'.
The Oculus Easyfield offers five examination strategies.
These are as follows:
The advantage of suprathreshold method of testing is that rather than determining the LDS at each point it localises defects by identifying deviations from the normal course of the test during an initial examination, therefore making it possible to measure lots of points in a short space of time. An advantage of this method of examination according the Easyfield manual is that it makes it possible to reveal small scotomas
Quick start programs
These tests are a combination of the examination parameters available. The idea of these pre-defined programs is to offer quick and reliable tests to save time and fatigue. One disadvantage noted, however, was the limitation of the tests. For example, if the 'screening' program was chosen which measures 55 points and a defect was found, there was no option to extend the testing points to investigate the defect further. Therefore to do this, 'user-defined' program has to be utilised.
Using the 'user-defined' program' you first select a patient in the 'Go to, list. Select 'Start' where you specify the area and the points to be tested. This can then be saved under 'User' in the 'Program' option. Four user-defined programs can be stored In the Easyfield.
I found the advantage of this program is that it allows you to adapt, create and modify a test to your requirements and needs. For example, measuring specific points in the visual field or extending and concentrating on test points that may have been missed in the quick start programs.
SPEED OF TEST
I chose to use the pre-determined programs to give some examples of examination results obtained using the Oculus Easyfield. I asked each patient for comment and will now relate some of the more significant results.
The patient found the screening test quick, comfortable and easy to understand.
Patient name: Ms GE
The patient found the test quick and easy to understand. A criticism noted by the patient was that she did not like the way in which her nose hit the side of the viewing aperture, ie there was no allowance for facial features.
The patient found this test quick and easy to follow.
Patient name: Mrs LH
The patient found the test quick and easy. She liked the appearance and size of the instrument and particularly liked that fact that she was not restrained to a chin rest.
In the fast threshold strategy, shortterm fluctuation was calculated and appeared on the printout in brackets. This is a value for the retest variability of the sensitivity results, ie the reliability of the results according to the patient's responses. This result is then shown in the form of a Bebie curve.
The threshold strategy results are also viewed in the form of a grayscale, and deviation from age-related values can also be examined.
The patient found this test to be long, but liked the option of being able to 'pause' the test during the examination when feeling fatigue.
Patient name: Mr PS
The patient liked being able to do the test with the lights on. This made him feel more relaxed and in a more natural environment. A symptom noted by the patient due to the duration of the test was the entoptic phenomena seen on the white bowl and feeling 'starry eyed'.
Patient name: Ms AN
The patient was very impressed with the size and appearance of the instrument.
The patient reported that she did not like the fixation target in the shape of a diamond, as she was not sure where exactly she should be looking and would have preferred a single dot for fixation.
This gave me the flexibility to define my own program in order to investigate more test points and desired area.
According to the Act, an auxiliary aid may be a special piece of equipment or simply extra assistance to a disabled person.
I feel that the Oculus Easyfield from Birmingham Optical provides such an alternative for perimetry. For example, I examined a patient who was wheelchair bound and unable to reach a screener based on a hydraulic table comfortably without propping cushions under him. The Easyfield, however, could be positioned at a more reasonable height, was more comfortable for the patient and therefore did not create any artificial defects due to incorrect positioning or fixation.
The Easyfield has the advantage of being compact, therefore making it very attractive to practitioners working in a confined space.
The instrument could also be useful for housebound elderly patients who require domiciliary visits, as it is portable and an optional carrying case is also available. This would be particularly good, as we know that the elderly most frequently develop visual field defects, and should be subjected to visual field examinations.
The Easyfield control unit has a large patient database, which is remarkable for such a small unit. Patient details and examinations can be exchanged between a PC and the unit. This is particularly useful to allow comparisons to be made against future examination results.
The perimeter can be used irrespective of ambient light, and I found this very beneficial in situations where I could not control the lighting.
The predefined programs allow you to begin the examination as soon as possible.
The user-defined programs allows you to specify your own program, by choosing your own area, strategy and fixation of a test. This gives you the flexibility to adapt a test to your requirements.
The Oculus is compact and competitively priced at £4,150 plus VAT. I would highly recommend this to practitioners who are looking for a portable, compact and user-friendly perimeter.
Advantages of the Oculus Easyfield
Disadvantages of the Oculus Easyfield
The equipment was kindly loaned by Birmingham Optical.
Tina Romanay is clinic manager, Department of Optometry and Visual Science, City University
Reprinted from Optician 23rd March 2001