Calibration of the Nuclear Associates 07-621 precision photometer.

The spectral response of the Nuclear Associates 07-621 photometer has been measured over an extended range (400-990 nm). The measurements reveal that the photometer shows large deviations from the standard CIE photopic response. In particular it has considerable excess response in the red (650-780 nm) and in the near infra red (780-990 nm). Although the instrument is claimed to have a photometric accuracy of +/- 7% this is only realised when measuring sources, such as tungsten lamps, which are rich in the red and near infra red regions of the spectrum. When used with sources, such as fluorescent lamps, which contain little radiation in the range 650-1200 nm it underestimates the light output by approximately 20%. As a consequence this photometer can only be used in radiology QA for such tasks as measuring view box luminance if the appropriate correction factor is used. This factor should be determined at the outset by comparing the Nuclear Associates 07-621 with a high quality photometer using the same type of light that is emitted by the boxes.

A fast system for reporting the Farnsworth-Munsell 100-hue colour vision test.

We have developed a system for rapidly reporting the Farnsworth-Munsell (FM) 100-hue test using a personal computer and a bar code scanner. The computer generated report duplicates the conventional manual report of the FM 100-hue test so is very familiar to ophthalmologists and optometrists. The new system has proved to be of great assistance both in saving time and in eliminating arithmetic errors in the scoring calculations. The scanner technique produces two reports, one for each eye, within 4 min of the patient completing the test. This compares with the 60 min required by the conventional manual reporting system. In addition, it also gives a statistical analysis of the results in accordance with Verriest norms. The program is very versatile and user friendly, achieving a standard not present in the other FM 100-hue computerised systems currently available. As a consequence it makes this valuable diagnostic test much more accessible to patients and clinicians.

A comparison of two patient-friendly ERG electrodes.

The ideal electroretinography (ERG) electrode does not exist. In deciding which electrode should be used in clinical practice the capacity to provide reproducible waveforms, maximal amplitudes and minimal irritation to the patient's eyes are the most important characteristics. This study tested two patient friendly electrodes, the gold foil (CH Electrodes, UK) and the H-K loop (Avanta, Slovenia). Seventeen normal volunteers were subjected to three standard measurements namely flash ERGs under photopic and scotopic conditions and the transient pattern ERG (PERG). Each test followed the guidelines set by the International Society for Clinical Electrophysiology of Vision (ISCEV). It was found that the mean values of the flash ERG a and b wave amplitudes and the PERG P50 and N95 amplitudes from the gold foil electrodes were approximately a factor of two larger than those from the H-K loop. In addition most of the subjects (13/17) felt less discomfort with the gold foil electrodes. We reached the conclusion that gold foil electrodes are the electrode of choice because they provide good patient comfort, reasonably high amplitudes and relatively reproducible results.

The clinical value of ophthalmic electrodiagnosis in children.

A group of 113 children with poor vision who had been referred to the Electrodiagnostic Clinic over a five year period were investigated for disease of the retina and optic pathway by electroretinography (ERG), electro-oculography (EOG) and visual evoked response (VER). The electrodiagnostic measurements were made using an automated system developed at Christchurch Hospital. The results of these investigations confirmed the clinical value of ophthalmic electrodiagnosis both as an aid in the diagnosis of these young patients and in determining their prognosis. In some cases it permitted an early detection of their condition. In addition the analyses of the ERG into rod and cone mediated responses helped to establish the diagnosis of hereditary retinal disorders and was particularly useful in the case of infants with nystagmoid movements of the eyes who were suspected of having poor vision. Interestingly 21 of the 113 patients were found to have functional visual loss. These patients complained of visual loss but subsequent examinations revealed their ocular findings, EOG, ERG and VER were all normal. The age of this functional visual loss group ranged from 7 to 15 years, with the average being 11.3 years (SD = 2.6 years). Furthermore they were a large group representing 32% of all the children between 7 and 15 years and in most cases were not happy at school.

Pattern VEP for glare sensitivity testing.

Conditions such as optic neuritis and cataract cause a patient to be unduely affected by glare and this occurs even though they may have normal visual acuity. A new test incorporating visual evoked potential (VEP) and glare sensitivity has been developed in Christchurch which shows promise for the objective assessment of such conditions. This report describes the methodology of the new technique and its application to the glare sensitivity testing of fifteen normal volunteers and ten patients with post optic neuritis. The effect of glare was expressed in terms of the glare disability score (GDS). This was defined as the percentage reduction in the amplitude of the P2 peak in the VEP waveform after glare was introduced. In these preliminary results, in spite of relatively good visual acuity, nine out of ten patients with a past history of optic neuritis showed elevated GDS values indicating that they were more sensitive to glare than the normal volunteers. In addition we report a dramatic reduction in the GDS of one patient with a lens opacity following extracapsular cataract extraction and the implantation of an intraocular lens.

A flexible automated data acquisition system for ophthalmic electrophysiology.

An automated system for performing VER, ERG and EOG measurements has been developed and is now in clinical use. Considerable effort has been made to retain the flexibility of non-automated systems while providing an easily followed procedure for standard tests which can be undertaken by staff with minimal training. Clinical experience has shown that the standard parameters for data acquisition which are optimal for normal subjects are not always suitable for patients who are uncooperative or have poor vision. These parameters are under software control and can be amended interactively if necessary. The five main functions of the software, namely data acquisition, data selection and commentary, report generation, patient database operation and waveform archiving are written as separate modules and called as required. During data acquisition the software rejects gross artefacts and in the case of EOG's warns of patient non-cooperation. After an ERG or VER has been acquired the operator identifies features in the waveforms and the computer measures them whereas for EOG's the measurement process has been automated. When the waveforms are subsequently reviewed by the operator they are presented in a logical sequence, a sequence which does not depend on the order in which they were acquired, and this sequence is maintained when they are printed out later in the completely automated report phase.