Since the inclusion of Visual Field testing in the schedule of Medicare items for optometrists, there has been much debate over visual field analysers. Fortunately for optometrists there is now a viable alternative to the older generation of Humphrey and Medmont visual field screeners that are now becoming outdated technology.

So what’s important in a new visual field screener?
• There are no moving parts. Many of the problems associated with the older projection-type of perimeters were caused by failure of the mechanism used to move the light stimulus around the bowl, not to mention the filters that had to be placed in front of the source to achieve the required luminosity. The latest perimeter has an array of LEDs in the bowl which are extremely reliable.
• Stimuli should be presented in arcuate format, to most accurately resemble the actual pattern of receptor cells that make up the neural architecture of the retina. This is far more sensible than the alignment of stimuli in a fixed, square grid pattern as seen in older perimeters.
• Obviously the perimeter should be easy to use and easy to customise. Firstly, the practitioner does not want to waste time on slow methods of data entry and recall such as primitive touch screens and floppy disc drives and secondly the array of testing procedures should be easy to select from and relevant to the needs of the practitioner when testing each individual patient.
• The perimeter is one instrument which should certainly interface with your practice PC, as it must be able to be upgraded when future enhancements are made, particularly within the software of the instrument. In addition to this, the perimeter should streamline the comparison of old patient data with new, allowing easy assessment of changes in the patient’s field with time.
• Flicker perimetry must be available as a testing regime within the perimeter, and ideally the frequency of the flicker should be chosen by the practitioner. This is essential due to the variation in flicker sensitivity from the macula to those retinal cells in the periphery.
• There should be a reliable method of not only monitoring a patient’s fixation but also of disregarding any measurements that have been taken when the patient’s fixation has moved. Obviously the Heiji-Kraku method was an effective way of monitoring fixation in the past, but the advent of digital eye tracking has revolutionised the accuracy of modern perimetry by using video technology to monitor the patient’s fixation during every stimulus presentation and automatically disregarding any measurements taken when the patient’s fixation has moved.

Enter the Opto AP-100 and AP-200 Computerised Perimeters. These instruments are the first of the new generation of visual field screeners that stands alone in satisfying the above criteria of what’s important in perimetry. They have been designed with accuracy, reliability and patient comfort in mind. The stimulator bowl houses an arcuate array of long-life LED targets and has an open design which enhances ventilation and reduces the claustrophobic nature of perimetry for the patient. There are neither motors nor fragile mechanical parts, thus eliminating the need for routine maintenance.

Multiple test capabilities are available for the practitioner to choose from and both screening and fast threshold strategies are included to minimise examination time. Flicker perimetry is available on all tests at a frequency that is chosen by the practitioner. Furthermore, Opto’s award-winning software allows complete analysis of results including regression analysis of patients’ fields and allows results to be immediately displayed and printed if required in colour or black & white exactly as desired by the practitioner, either singly or in multiple (combo) formats.

What really sets these perimeters above all others on the market however is the Automated Eye Tracker System. This system utilises the internal camera in the bowl to indicate and to monitor the position of the patient’s eye during examination and immediately announce any movements in fixation visually and audibly. Any stimulus that is reported as being seen while fixation is incorrect is automatically excluded from the results of the test. Thus every test of every patient yields extremely accurate results.

The recent research that suggests that instruments with SWAP (Short Wavelength Automated Perimetry), also known as blue-on-yellow perimetry, are far more sensitive in detecting early glaucoma than conventional perimeters is catered for in the AP-200, which also has an internal PC and an electric chin-rest.

The Opto Automated Perimeters represent the 2008 benchmark in visual field screeners worldwide and are available exclusively from Optical Manufacturers