Roger W. West

Measurement of refractive errors in young myopes using the COAS Shack-Hartmann aberrometer.

Purpose. To evaluate the Complete Ophthalmic Analysis System (COAS; WaveFront Science) for accuracy, repeatability, and instrument myopia when measuring myopic refractive errors. Methods. We measured the refractive errors of 20 myopic subjects (+0.25 to −10 D sphere; 0 to −1.75 D cylinder) with a COAS, a phoropter, and a Nidek ARK-2000 autorefractor. Measurements were made for right and left eyes, with and without cycloplegia, and data were analyzed for large and small pupils. We used the phoropter refraction as our estimate of the true refractive error, so accuracy was defined as the difference between phoropter refraction and that of the COAS and autorefractor. Differences and means were computed using power vectors, and accuracy was summarized in terms of mean vector and mean spherocylindrical power errors. To assess repeatability, we computed the mean vector deviation for each of five measurements from the mean power vector and computed a coefficient of repeatability. Instrument myopia was defined as the difference between cycloplegic and noncycloplegic refractions for the same eyes. Results. Without cycloplegia, both the COAS and autorefractor had mean power vector errors of 0.3 to 0.4 D. Cycloplegia improved autorefractor accuracy by 0.1 D, but COAS accuracy remained the same. For large pupils, COAS accuracy was best when Zernike mode Z40 (primary spherical aberration) was included in the computation of sphere power. COAS repeatability was slightly better than autorefraction repeatability. Mean instrument myopia for the COAS was not significantly different from zero. Conclusions. When measuring myopes, COAS accuracy, repeatability, and instrument myopia were similar to those of the autorefractor. Error margins for both were better than the accuracy of subjective refraction. We conclude that in addition to its capability to measure higher-order aberrations, the COAS can be used as a reliable, accurate autorefractor.

The effect of changing from glasses to soft contact lenses on myopia progression in adolescents

At the end of a clinical trial of bifocals as myopia treatment, subjects were allowed to select any type of optical correction they wished and were asked to return in 1 year. This report gives results of that last examination with emphasis on how progression rates differed between those remaining in their original type of glasses compared with those who switched to soft contact lenses. We found that myopia progressed at an age‐adjusted average rate of 0.74 D in 19 children who switched to soft contact lens wear compared with 0.25 D for 24 children remaining in glasses (p < 0.0001). Increased growth of the vitreous chamber appeared to account for much of this excess myopia progression, although the difference in that variable did not reach statistical significance (p = 0.101). We also noted a 0.203 D steepening in the corneal curvature in contact lens wearers compared with spectacle wearers whose corneas steepened very little (0.014 D, p = 0.007). Soft contact lens wear was also accompanied by a greater change in the near‐point phoria which moved 4.5 prism dioptres in the exo direction compared with spectacle wearers who experienced only a 1.4 prism dioptre divergent shift (p = 0.048).

The effect of head turn on the perception of gaze

When subjects viewed straight and turned eyes that were isolated singly or in pairs from a head that was straight or turned, they underestimated their true direction of gaze. They also underestimated the direction of head turn when both eyes were closed. However, the judged direction of gaze was improved when the eyes were layered against the heads. Judged direction of averted gaze was primarily based on the abducting eye. The effect that the deviation between an eyes optical axis and its true direction of gaze (angle kappa) has on its judged direction of gaze is discussed.

Gaze as Depicted in Vermeer's Girl With a Pearl Earring

Ten observers viewed Vermeers painting Girl With a Pearl Earring and estimated her direction of gaze when her eyes were exposed together and separately. The observers also viewed the painting when her eyes were digitally replaced by those of a real person. The authors found that Vermeer painted the girls eyes with a precision that was near the limits of visual acuity. Also, Vermeer included 3 gaze illusions, none of which researchers have documented as known in Vermeers time: (a) when a model whose head is turned to one side gazes at an observer, there is an illusion that she is looking to the side of the observer away from the direction of her head turn; (b) when a models eyes are viewed separately, they appear to gaze outward relative to each other; and (c) when both of a models eyes are viewed, the perceived direction of gaze follows that of the nearer eye.

Redirecting gaze to improve the cosmetic appearance of strabismus.

Purpose. We studied a behavioral technique in which strabismics can reduce the detectability of their eye turn by appropriately redirecting their gaze. We tested the efficacy of this technique for various amounts of strabismus and different positions of gaze. Methods. We took digital images of a model gazing in different lateral directions and digitally edited them to simulate fixation with one eye on different lateral locations whereas the other eye was misaligned from the first by ±0, 6, 12, 18, 24, and 30 &Dgr;. Then we asked 22 lay observers to examine each of the images and to report whether or not they perceived eye contact and normal gaze. Results. The observers reported that our model appeared to look normal and gave them eye contact two-thirds of the time for up to 18 &Dgr; of exotropia and 12 of esotropia when she looked half her prismatic deviation to the side opposite her eye turn. Conclusion. By appropriately directing their gaze, both exotropes and esotropes can improve the cosmetic appearance of their strabismus and increase the perception that they are looking at the observer. This may be useful during job interviews and other social encounters where eye contact and a good impression are critical. A drawback is that large amounts of strabismus may require the gazer to look far to the side of the observer’s head where it may be difficult to maintain gaze and the observer’s facial expression may be hard to read. However, all patients may be counseled on which eye to look at when engaging in conversation, as looking at the appropriate rather than the inappropriate eye can reduce the perceived amount of their strabismus. Also, when their portrait is being taken, the full amount of eccentric gaze could easily be used.

Comparisons of dynamic retinoscopy measurements with a print card, a video display terminal, and a PRIO® System Tester as test targets

BACKGROUND Dynamic retinoscopy is a common clinical test for assessment of visual function in patients with symptoms related to computer use. It has been suggested that performing dynamic retinoscopy with a fixation target resembling a computer screen may be valuable in the examination of computer users. However, such targets differ in luminance and other characteristics from the printed paper test cards typically used for dynamic retinoscopy. METHOD To address the effect of varying test targets on dynamic retinoscopy results, this study compared lag of accommodation results from dynamic retinoscopy with three different fixation targets: (a) a printed paper target, (b) a video display terminal, and (c) the PRIO vision testing device, which is designed to simulate a computer screen. MEM (monocular estimate method) dynamic retinoscopy was performed with the print target and with the PRIO device. RESULTS The difference between results with the different test conditions were generally small, with a statistically significant 0.32 D lower lag found on MEM retinoscopy with the PRIO target IMEM-PRIO) than on MEM retinoscopy with a print target (MEM-PRINT). Mean lag measurements on MEM with a print target and on Nott retinoscopy with the video display terminal (NOTT-VDT) were only 0.04 D different. The 95% limits of agreement for the difference between MEM-PRINT and MEM-PRIO (+/- 0.6 D) was similar to the 95% limits of agreement for the interexaminer reliability of the two procedures (+/- 0.6 D for MEM-PRINT and +/- 0.7 D for MEM-PRIO). CONCLUSION There was a small but statistically significant difference in lag of accommodation measured with MEM dynamic retinoscopy on the PRIO testing device when compared to a print card.

Perceived direction of gaze from eyes with dark vs. light irises.

Purpose. Much of the previous research on the perceived direction of gaze has not specified eye color or pupil visibility. This study tests whether the lightness or darkness of a gazers irises (typically brown vs. blue) affects their perceived direction of gaze. Methods. Twenty-five observers judged the direction of horizontal gaze from a model whose LCD-imaged head gazed toward points on the plane of the observers face. The models head was displayed with its natural brown irises and also with its irises digitally altered to look blue without pupils, blue with centered pupils, and blue with nasally decentered pupils. True gaze location was compared with the judged gaze location for each type of iris. Results. For all iris types, observers judged that monocular gaze was biased outward from its true direction for all gaze locations, including central, whereas binocular gaze was close to centered and had a greater slope. Blue eyes with no pupil and blue eyes with a centered pupil exaggerated this perceived outward deviation for monocular gaze but binocular gaze remained the same. When the pupils were nasally decentered by a typical amount, straight monocular as well as binocular gaze appeared to be centered. Conclusions. The direction of monocular gaze from eyes that differ in the darkness of their irises is perceived differently, and, within the blue irises, small differences in pupil centration made surprisingly large differences in the perceived directions of gaze.

Was Rembrandt strabismic

Purpose We studied a set of Rembrandt’s self-portraits to reassess a previous claim, based on measurements of the centration of his painted irises, that Rembrandt had a large exotropia. Methods Of the 24 self-portraits that Rembrandt painted, with significant ocular detail to give an impression of the direction of his gaze, we scanned 10; the five with the largest difference in centration between the irises and the five with the smallest difference. The right and left eyes in each image were then occluded using Photoshop to produce two additional images that gave monocular gaze. Thirty observers then judged where the portraits appeared to be gazing within the plane of their face. Results Although our observers did judge a significant outward deviation for gaze between the two eyes, part of this was caused by an outward deviation from central by the presumably nonstrabismic eye. Any greater amount of outward deviation from the “strabismic” than the nonstrabismic eye can then be explained by a gaze overshoot induced by head turn, painting with a mirror, and angle kappas. In addition, Rembrandt’s apparent strabismus is seen only in those portraits painted during a few years early in his career, and portraits that Rembrandt and his students produced of other presumably nonstrabismic individuals often give a similar impression of strabismus. Conclusions There are several factors that can explain why some of Rembrandt’s self-portraits make him look strabismic without concluding that he actually was. Rembrandt and his students may also have painted this appearance as an artistic style.

The effect of color on light-induced seizures : A case report

BACKGROUND Two to four percent of epileptics have their seizures triggered by flickering light, an effect which may be wavelength-dependent. We evaluated a patient with a long-standing history of light-induced petit mal seizures to determine if the seizures were triggered more effectively by a particular range of wavelengths and to determine whether this information could be used in the optometric management of such patients. METHODS Flickering lights of different wavelengths but equal luminance were presented while the patients electroencephalogram (EEG) and subjective reports were monitored. RESULTS The EEG results were not significantly different for different wavelengths, but the patient reported that longer wavelength light induced stronger seizures more consistently. Based on these results we concluded that the patient might benefit from spectacles tinted to exclude transmission of red light. The patient was given 4 pairs of 85% transmission spectacles, which differed only in lens tint (red, yellow, green, and blue), to try over a period of time. The patient felt that the tinted lenses were not dark enough to decrease his seizures effectively and he has opted to wear standard sunglasses. CONCLUSIONS We feel this case shows that patients with light-induced seizures can benefit from optometric consultation. Because the patients subjective report identified the clearest wavelength effect, we feel that it is reasonable for the general practitioner to suggest deeply tinted lenses to reduce the frequency of seizures in these patients.

The Effect of Simulated Altitude on the Visual Fields of Glaucoma Patients and the Elderly

We investigated whether mild hypoxia, such as may be encountered in civilian aircraft, causes temporary visual field defects in elderly persons or temporarily increases pre-existing defects in persons with glaucoma. The central 24-2 program on the Humphrey automated perimeter was used to test visual fields in 3 groups of subjects: 6 with glaucoma; 12 age-matched controls, all of whom were over 44 years of age; and 6 normal subjects under 36 years of age. Visual fields were tested at ground level and at simulated 3000 m (10,000 ft) in an alternating sequence. A repeated measures design of multiple analysis of variance was used to analyze the data. Altitude was found to have no effect on the visual fields of subjects with glaucoma, agematched normals, or younger subjects. We found no evidence to suggest a change in the present Federal Aviation Administration (FAA) standards, which allow a special certificate to be issued to persons with glaucoma who wish to obtain medical clearance to operate civilian aircraft, nor have we found any evidence that should discourage glaucoma patients from flying as passengers.