A new tonometer--the pressure phosphene tonometer: clinical comparison with Goldman tonometry.

OBJECTIVE: This study aimed to compare the results of pressure phosphene tonometry, a new tonometric technique, with Goldmann applanation tonometry. DESIGN: Comparative case series. PARTICIPANTS: A total of 100 consecutive patients (192 eyes) without diagnostic specificity, plus a separate subset of 14 eyes with intraocular pressure (IOP) above 19 mmHg, participated. INTERVENTION: Intraocular pressure was measured with Goldmann tonometry by one examiner and pressure phosphene tonometry by a different examiner. There was no communication between the examiners regarding test results. MAIN OUTCOME MEASURES: Intraocular pressure. RESULTS: In the group without diagnostic specificity, the mean difference between the two techniques was 0.3 mmHg. Fifty-one percent of the measurements were within +/-1 mmHg, 74.9% of the measurements were within +/-2 mmHg of each other, and the average deviation for 100% of the data was 1.8 mmHg. For pressure phosphene tonometry, the mean IOP was 15.2 mmHg with a standard deviation of 2.9 and a range of 18 mmHg (minimum, 10; maximum, 28). With Goldmann, the mean was 15.5 mmHg, the standard deviation was 3.1, and the range was 20 mmHg (minimum, 8; maximum, 28). The t test for paired data showed a Gaussian approximation with a P value of 0.05. A comparison between the results of the two techniques gave a correlation coefficient of 0.71. Results for the separate 14 patients with higher IOPs yielded a statistically significant mean difference of 0.1 mmHg between the two techniques (P < 0.05, t test for paired data). For pressure phosphene, the mean was 21 mmHg with a standard deviation of 5.5 and a range of 24 mmHg (minimum, 14; maximum, 38). For Goldmann, the mean was 21.1 mmHg with a standard deviation of 4.7 and a range of 19 mmHg (minimum, 15; maximum, 34). The correlation coefficient was 0.73. CONCLUSIONS: The close agreement between the two techniques suggests that pressure phosphene tonometry offers an alternative method for measuring IOP. It has the advantages that it is simple, noninvasive, and inexpensive. Potential uses of the pressure phosphene tonometer may include self-administered home testing, in outreach clinics by nonophthalmic technicians, and in patients with corneal conditions that preclude the use of Goldmann tonometry.

Measurement of glare susceptibility using low-contrast letter charts.

The Committee on Ophthalmic Procedures Assessment of the American Academy of Ophthalmology suggested either contrast sensitivity or low-contrast visual acuity (VA) measured before and after adding a glare source as a test for assessing overall visual disability from immature cataracts. We have developed a test that follows the Committee's three principles of design, and we report that the effect of glare on VA is considerably greater for recognizing low-contrast letters than for recognizing high-contrast letters. The effect of glare on VA increases progressively as letter contrast is reduced from 96% through 50%, 25%, 11%, and 4%. The 25% chart (and possibly the 11% chart) gives the most suitable sensitivity for eyes with immature cataracts. Neither age-related brunescence and aging itself nor even the presence of a distinct opacity necessarily produces high sensitivity to glare. The test is sensitive enough to detect an ageing effect even before the age of 45 to 55 years and to reveal large intersubject differences among normally sighted 19- to 25-year-old subjects.

Measurement of glare sensitivity in cataract patients using low-contrast letter charts.

The Committee on Ophthalmic Procedures Assessment of the American Academy of Ophthalmology suggested using low-contrast visual acuity measured before and after adding a glare source as a test for assessing overall visual disability from immature cataracts. We have developed a test that follows the Committee's three principles of design, and we report that the effect of glare on visual acuity is considerably greater for recognizing low-contrast letters than for recognizing high-contrast letters. The effect of glare on visual acuity increases progressively as letter contrast is reduced in the stages 96%, 50%, 25%, 11% and 4%. The 25% chart (and possibly the 11% chart) gives the most suitable sensitivity for eyes with immature cataracts. Age-related brunescence and aging itself do not necessarily produce high sensitivity to glare. Sensitivity to glare was markedly different in eyes with different kinds of cataract.

Opaque contact lenses for YAG laser iridotomy occlusion.

Although a laser-produced iridotomy effectively controls angle-closure glaucoma the iridotomy can cause annoying visual effects. One solution is to fit a toric contact lens with an opaque portion to cover the iridotomy.

The persistence of dichoptically presented grating patterns.

A dichoptic viewing device was used to present sinusoidal gratings with interocular asynchrony. The persistence of various spatial frequencies was then determined psychophysically by using blank detection, for near-threshold and suprathreshold contrast conditions and across the contrast range. Greater persistence was evident for higher spatial frequencies, and across all spatial frequencies the values were higher for near-threshold contrast conditions. Contrast specificity was evident, with the low spatial frequencies showing flat contrast functions while the higher spatial frequencies showed a steeper monotonic curve. Intermediate spatial frequencies displayed biphasic properties. In view of the different neural persistence for different spatial frequencies, we investigated the degree of binocular summation for different interocular asynchronies. Binocular summation was predominant for all spatial frequencies where the dichoptic asynchrony was within 25 msec. Binocular summation decreased as a function of asynchrony. The binocular/monocular ratio decreased to a greater extent and earlier for low than for high spatial frequencies.