Merrick J. Moseley

ACCURACY OF GOLDMANN TONOMETRY IN CLINICAL PRACTICE

Abstract The intra‐ and inter‐observer variability of Goldmann applanation tonometry was studied in 8 hospital tonometrists, 4 of whom received brief revision training in tonometer use. Intraocular pressure (IOP) measurements were obtained from 16 glaucoma patients. Over a series of four readings taken from individual eyes, intraocular pressure did not significantly vary. However, a decline in IOP was observed when a second tonometrist obtained a further series of four readings from a previously measured eye. Mean pressures recorded by tonometrists who had received revision training were greater than those obtained by the untrained observers though this could be accounted for by two highly experienced individuals in the untrained group who tended to record low pressures. Comparisons of average readings obtained by two observers on the same eye showed that approximately one‐quarter of measurements differed by 2 or more mmHg and approximately one‐fifth by 3 or more mmHg.

Visual acuity: Calculating appropriate averages

ABSTRACT Controversy surrounds the averaging of visual acuity scores We examine this debate and provide a series of guidelines and worked examples to enable investigators to select an average (eg arithmetic mean, geometric mean, median) appropriate for their data

Visual acuity and contrast sensitivity in cataract: summation and inhibition of visual performance.

Patients exhibiting uniocular cataract often report an improvement in vision on closing their cataractous eye. Such qualitative evidence suggests the presence of binocular inhibition—the converse of binocular summation (that is the normal superiority of binocular over monocular vision). To quantify the extent of inhibition in cataract, binocular and monocular visual acuity and contrast sensitivity were measured in 28 patients. Twelve patients showed binocular inhibition for visual acuity whilst 11 showed inhibition for contrast sensitivity measured at four cycles per degree (c.deg-1). Contrast sensitivity for 8 c.deg-1 targets was further recorded in a subset of 14 patients in whom seven showed inhibition. In patients who demonstrated inhibition, the mean decrement in performance for visual acuity was 13%. For contrast sensitivity at 4 and 8 c.deg-1 the mean decrement was 25% and 32% respectively. The clinical significance of these findings is discussed with respect to the assessment of visual function and management of the cataract patient.

Preferential Looking — Clinical Lessons

Preferential looking-based tests of acuity have been available for over a decade. The authors discuss their use in clinical practice, particularly in three groups in whom acuity could not be quantified by traditional means: normal infants, and young children who are either mentally retarded, or who have visual disorders. Preferential looking (PL) testing has increased our understanding of the natural history of visual pathway disorders and has revealed certain patterns of acuity development. Early acuity development may be normal, delayed, or stationary, while in later infancy and childhood the following abnormal patterns have been identified: asymptotic, parallel, catch-up, or regressing. While this information has introduced a degree of complexity hitherto unknown which, if misunderstood, can lead to test misinterpretation, it offers the clinician invaluable information to improve patient care, and may also offer clues to the fundamental mechanisms of visual development.

Non-contact tonometry

Anyone who has undergone the procedure of conventional IOP measurement will vouch for the fact that it is a very uncomfortable procedure. Comfort and the fact that contamination between patients is minimized is what makes non contact tonometers, “the coolest!”. It uses an “air puff” to measure IOP, but is different from the pneumatic tonometers where there is contact between the tonometer and the patients eye.

Development of pupillary responses to grating stimuli

Pupillary responses to stationary, achromatic sine wave gratings were measured in adults and in 1- and 3-month-old infants. Measurements of behaviourally determined contrast sensitivity were also obtained from the infant subjects. Contrast sensitivity functions were typical of those previously described: band-pass in nature with sensitivity increasing markedly with age. The pupil grating response amplitudes also exhibited a spatial frequency and age dependence similar to that observed for contrast sensitivity. These findings provide further evidence that the neural mechanisms which underlie visual sensitivity to contrast also mediate pupillary responses to spatial structure.

Binocular inhibition of visual performance in patients with cataract. The influence of test reliability.

Abstract Patients with cataract may show binocular inhibition: their sight improves on closing the eye in which vision is poorer. Of 36 patients questioned, one‐third reported this to be the case. To quantify this phenomenon, all patients undertook a battery of tests of spatial visual performance and, in an attempt to define the reliability of their scores, were tested on two separate occasions. Patients generally performed inconsistently: at best, of 8 patients who demonstrated inhibition on a single test, only 5 did so again when re‐tested after a short interval. In general, the magnitude of inhibition was less than that which could be reliably detected using the test battery. In addition, self‐reported inhibition was not predictive of inhibition measured psychophysically. It is concluded that clinical tests of form vision lack either the necessary reliability or sensitivity to identify patients with cataract who report inhibition of binocular visual function.