The eye blink electro-oculogram.

An electro-oculogram (EOG) was derived from potentials recorded from electrodes placed above and below the eye during voluntary vertical eye movements. Concurrent measurement of the amplitude of eye blink potentials recorded from the same electrodes produced curves which were highly correlated with the EOG measured from stereotyped eye movements. Recordings from a patient with a missing globe, owing to trauma, revealed eye movement and blink responses only from the intact side. A patient with no light perception showed blink responses which were less variable than responses measured during attempts voluntarily to move the eyes vertically in 60 degrees excursions. An EOG calculated by measurement of eye blink potentials may be possible in clinical situations where traditional electro-oculography techniques are not feasible.     

The relation between saccadic eye movements and electrooculogram during light and dark adaptations]

The relation between the amplitudes of saccadic eye movements and the resting potential changes detected around human eyeballs under light and dark adaptations was clarified by means of simultaneous measurements of electrooculogram (EOG) and eye movements. The authors previously reported that the potential changes are proportional to the horizontal saccadic eye movements within +/- 15 degrees (visual angle) under conditions of the room light of approximately 60 lux. There are few reliable data indicative of the presence of the above relations under light and dark adaptations. The result of the simultaneous measurements of EOG and eye movements during the light and dark adaptation at 2-minute intervals in 9 normal subjects showed that the resting potential changes were in direct proportion of the amplitudes of the saccadic eye movements at any time within +/- 20 degrees. In these experiments, the eye positions were monitored with the eye mark recorder during the eye movements. In case the eye positions excursioned from a target, the exact EOG was calculated by measuring eye positions and correcting the EOG errors.     

Rotation of Listing's plane with convergence: independence from eye position

PURPOSE: To determine whether asymmetrical vergence results in a rotation of Listing's plane independent of vergence-associated changes of eye position in the orbit. METHODS: Six normal subjects were required to fixate on a 3x3 array (40 degrees on a side) of light-emitting diodes arranged on a flat screen 124 cm from the subject. Disparity-induced vergence was elicited with a horizontal Fresnel prism (30 cm/m, approximately 17 degrees) placed in front of one eye. In four subjects accommodative vergence (10 degrees to 15 degrees) was produced by placing a minus spherical lens in front of one eye while the other eye was covered. Eye position was measured binocularly using three-axis search coils. Control data were collected without prisms during monocular and binocular viewing. For all data a planar regression was used to fit torsional eye position as a function of horizontal and vertical position to calculate the horizontal and vertical primary positions that define the orientation of Listing's plane. RESULTS: In the prism experiment, the horizontal primary position of the eye not wearing the prism rotated temporally by 3.9 degrees +/-1.7 degrees compared with the both eyes viewing control condition. The rotation of the prism eye was in a similar range (3.4 degrees +/-2.0 degrees). With accommodation, the horizontal primary position of the viewing eye rotated temporally by 4.4 degrees +/-1.4 degrees compared with the monocular viewing control. In both the accommodation and the prism paradigms there was usually a rotation of vertical primary position downward. CONCLUSIONS: Vergence-induced changes in Listing's plane can be independent of changes in orbital position associated with vergence. This finding supports a role for changes in central innervation in the elaboration of Listing's law.     

The "Ring Test" for evaluating eye dominance

A horizontal diplopia is produced with prisms whose bases are nasal or temporal. The subject has to fixate a circle, now seen double, alternately with his left and right eye and touch the center of the circle with a finger. Of one hundred subjects thus examined, 85 located the circle accurately every time when the one eye was fixating it and always missed when fixating with the other eye. This appears to prove that dominance of one eye also means that it is preferred for binocular spatial orientation.     

Peripheral refraction measurement: does it matter if one turns the eye or the head?

It has been suggested that, following eye movements, the changing pressures exerted by the extraocular muscles and the lids might distort the shape of the eyeball and alter refraction across the visual field. To confirm or refute this hypothesis, the pattern of monocular peripheral refraction in the right eyes of 10 healthy young adults was measured either by turning the eye to fixate a series of horizontally spaced targets or by turning the head to view the same targets while maintaining central fixation and the eye in its primary position. In each case a fixed Shin-Nippon autorefractor was used to measure peripheral refraction at 5 degrees intervals over the central +/-30 degrees of the visual field. The duration of any eye turn was < or =1 min. Repeated-measures analysis showed no significant differences between the spherical equivalents of peripheral refraction measured under the two conditions (p = 0.223). A further study of five subjects involving 2.5-min periods of fixation with an eye or head turn of 25 degrees also showed no significant refractive differences. Thus, within the conditions of the study (eye-turn durations and field angles < or =2.5 min and 30 degrees respectively), the results fail to confirm the occurrence of large differences in peripheral refraction when measurements are made with eye turn rather than head turn.     

Technical notes on peripheral refraction,peripheral eye length and retinal shape determination

Purpose

To give an overview of the misconceptions and potential artefacts associated with measuring peripheral refractive error and eye length, the use of these measures to determine the retinal shape and their links to myopia development. Several issues were identified: the relationship between peripheral refractive error and myopia development, inferring the retinal shape from peripheral refraction or eye length patterns, artefacts and accuracy when measuring peripheral eye length using an optical biometer.

Methods

A theory was developed to investigate the influence of artefacts in measuring peripheral eye length and on using peripheral eye length to make inferences about retinal shape.

Results

When determining peripheral axial length, disregarding the need to realign instruments with mounted targets can lead to incorrect field angles and positions of mounted targets by more than 10% for targets placed close to the eye. Peripheral eye length is not a good indicator of the effects of myopia or of treatment for myopia development because eyes of different lengths but with the same retinal shape would be interpreted as having different retinal shapes; the measurement leads to overestimates of changes in retinal curvature as myopia increases. Determining peripheral eye length as a function of estimated retinal height rather than field angle will halve the magnitude of the artefact. The artefact resulting from the peripheral use of biometers with an on-axis calibration is modest and can be ignored.

Conclusion

There are significant issues with peripheral measurements of the refractive error and eye length that must be considered when interpreting these data for myopia research. Some of these issues can be mitigated, while others require further investigation.     

A new method for determining squint angle in primary and all secondary positions using the first and fourth Purkinje images

A new objective method is presented for measuring the squint angle in all gaze positions. While the subject fixates an object at a distance d, his eyes are illuminated one at a time from above or from the side with a collimated infrared beam. A high-sensitivity infrared camera observes the first and fourth Purkinje images from below. Camera and light source are mounted on the same holder, which can be turned around horizontal and vertical axes. The examiner turns the holder while observing the Purkinje images on a TV monitor until both images lie either on a vertical line (to measure a horizontal deviation) or on a horizontal line (to measure a vertical deviation). In either of these cases the direction of the incident light, which is determined by the position of the holder, and the direction of the optical axis of the eye coincide. Advantages of the method include: the angle between the optical axis and the fixation line can be easily determined; the subject does not have to fixate with both eyes; and the accuracy is +/- 1 degree.     

Behavior of the other eye in measuring fixation disparity

In the subjective measurement of FD, the proband fuses contours presented in the peripheral macular areas of both eyes ('fusion lock'). The position of both eyes relative to each other is monitored by means of two haploscopically seen vertical lines presented in the central visual field, one above and one below a binocularly seen horizontal line. The subject is instructed to shift one of the vertical lines horizontally until the two are aligned, while fixating their intersection with the horizontal line. It has recently been questioned whether the foveolae really are pointed at the perceived intersection. To investigate this matter, we registered the position of one eye while intermittently covering the fellow eye, while the subject maintained fixation of the intersection. We found slight differences in monocular eye position depending on the presence or absence of fusion in the macular periphery, confirming earlier findings in part. These differences were more pronounced in the nondominant eye.     

Task demands and binocular eye movements

Humans make rapid movements of their eyes several times a second that enable them to examine objects located at different positions in space with both of their eyes. Much of our understanding of these binocular movements comes from studies using experienced observers performing repetitive, unnatural tasks. But what eye movements are made when na?ve observers perform tasks demanding specific binocular visual information? We examined the binocular eye movements produced by observers performing two tasks differing in the visual information needed for their completion. Our motivation for doing this was to examine the role and function of binocular eye movements when making decisions. We considered the fixation strategies adopted by observers, the effects of the task on the dynamics of saccadic eye movements, and the combination of vergence and version in gaze shifts. We report that the task-dependent use of visual information can have a strong influence on the patterns of fixations, whilst not influencing saccade dynamics. Our data provide some support for the notion that observers choose and fixate a notional reference point in the scene when making judgments about depth structure.     

Covering one eye in fixation-disparity measurement causes slight movement of fellow eye

In the subjective measurement of fixation disparity (FD), the subject fuses contours presented in the peripheral macular areas of both eyes (fusion lock). The position of the eyes relative to each other is monitored by means of two haploscopically seen vertical lines presented in the central macular area, one above and one below a binocularly seen horizontal line. The subject is instructed to shift one of the vertical lines horizontally until the two are aligned, while fixating their intersection with the horizontal line. It has recently been questioned whether the foveolae really are pointed towards the perceived intersection. In this study, we monitored the position of one eye while intermittently covering the fellow eye, while the subject maintained fixation of the intersection of the remaining vertical line and the horizontal line. We found slight differences in position of the measured eye, depending on whether the other eye was covered or not, i.e. depending on the presence or absence of fusion in the macular periphery. These differences were more pronounced in the non-dominant eye.Presented in part at the Fifth European Conference on Eye Movements, Pavia, September 1989, at the 15th Seminar Week of the Berufsverband der Augenärzte Deutschlands, Arbeitskreis Schielen, Munster, June 1989 and at the meeting of the Schweizerische Ophthalmologische Gesellschaft, Crans Montana, September 1990.     

A test eye for wavefront eye refractors

PURPOSE: A multi-site study was conducted to test feasibility of a modified automatic refractor style test eye as a test device for wavefront refractors of various types and to determine whether a) they could be measured and b) when measurements could be made, to see if they were similar. This study did not attempt to assess which instrument most accurately measures the aberrations of the test eye or human eye. METHODS: Three automatic refractor style test eyes were modified for use as test devices for wavefront refractors. One had a simple spherical front surface, and two had additional aberrations added. The test eyes and holder were circulated to 11 test sites where attempts were made to measure them with eight different wave-front refractor systems. RESULTS: Eight (100%) of the eight wavefront refractor systems tested successfully measured the test eyes. The systems did not give similar results for the same test eye. In some cases, coma was reported where none was present. Differences in reported defocus values reflect different approaches for compensating for the dispersion of the eye. A corneal topography system could measure and recognize the aberrations of the test eyes as well as the wavefront refractor systems tested. Interferometry, on the other hand, did not prove to be a successful method to assess the surface of the test eyes. CONCLUSIONS: The test eye design may be used as a test device for wavefront refractor systems. This type of test eye can detect systematic differences between various wavefront refractors and can serve as a useful calibration and comparison tool.     

Scanpaths in saccadic eye movements while viewing and recognizing patterns

Subjects' eye movements were recorded while they viewed and then recognized patterns. Viewing conditions of marginal visibility forced the subject to fixate directly each feature to which he wished to attend. Thus his eye movements revealed the sequence of internal processing. During initial viewing the subject's eye usually scanned over each pattern following, intermittently but repeatedly, a fixed “scanpath” characteristic of that subject viewing that pattern. When later presented with the same pattern for recognition, his first few eye movements usually followed this same scanpath. These results are consistent with a serial theory of pattern learning and recognition previously proposed.     

Automatic testing of the visual field using electro-oculographic potentials

The central visual field is tested using static perimetry on a tangent screen located 1 m from the patient. During the test electro-oculographic (EOG) potentials, associated with eye movements, are recorded. For this purpose two pairs of electrodes are placed in such a way that one pair records the vertical and the other the horizontal component of the EOG potential. The EOG signals that are produced when the tested eye moves toward the light target on the screen are digitized and fed into a computer programmed to relate each pair of signals to the specific lamp on the tangent screen. The results of the test appear on a computer-printed chart that shows the distribution of the lamps on the testing board together with the information whether the lamp was seen by the subject. This method of visual field testing is both objective and automatic.Supported in part by the Swiss Fund for Research in Ophthalmology and by the Rogoff Foundation.     

Wavefront aberrations associated with the Ferrara intrastromal corneal ring in a keratoconic eye

PURPOSE: To describe the optical implications of the aberration pattern of a keratoconic eye implanted with an intrastromal corneal ring (Ferrara ring). METHODS: A 32-year-old man with bilateral keratoconus had a Ferrara intrastromal corneal ring implanted in his right eye. Surgery was uneventful and both uncorrected (UCVA) and best spectacle-corrected (BSCVA) visual acuity improved. Corneal topography was performed before and after surgery. Wavefront measurements were performed 1 month after the procedure in both eyes for comparison. The point spread function, modulation transfer function (MTF), and convolved acuity chart were analyzed. RESULTS: The right eye--implanted with the intrastromal Ferrara ring--had high root-mean-square (RMS) values for higher order aberrations. The left eye-keratoconus without an intrastromal ring-had moderate values. Point spread function, MTF, and convolution acuity charts are presented for each eye, with the latter two showing improved visual function in the implanted eye, despite a higher aberration value. CONCLUSION: The wavefront measurement device captured aberrations even in a highly aberrated eye. Despite better UCVA and BSCVA, the Ferrara ring notably increased higher order aberrations compared to the fellow eye, but with a more uniform central pattern. In this case, the larger RMS value was a poor predictor of good visual function; other metrics better predicted the patient's subjective response. Metrics other than RMS error may be necessary to better correlate aberration value with visual satisfaction in some eyes.     

Directionalization of visual targets during involuntary eye movement

Perceived visual direction with respect to one's self (egocentric direction) depends upon the retinal location of a target's image (its oculocentric direction) and concurrent information about the position of the eyes in the head. Information about eye position is presumably obtained from efference copy signals. However, in order to explain illusory target motion that can occur during reflexive eye movements (e.g., post-rotary nystagmus), these signals have been suggested to accompany only voluntary oculomotor responses. In the experiment reported here, manual pointing was used to assess the perceived direction of targets flashed during optokinetic afternystagmus, an involuntary movement of the eyes that occurs in darkness following optokinetic stimulation. Egocentric directionalization was essentially veridical, indicating that accurate eye position information is available during optokinetic afternystagmus. A model is proposed that accounts for illusory target motion during involuntary oculomotor responses by the cancellation of efference copy information about these eye movements with signals of oppositely directed head motion.     

The application of a new continuous functional visual acuity measurement system in dry eye syndromes

PURPOSE: To evaluate the efficacy of a new continuous functional visual acuity measurement (FVAM) system for the assessment of dry eye patients. DESIGN: Prospective comparative study. METHODS: Monocular recognition acuity measured continuously by the FVAM system during a 30-second blink-free period was defined as functional visual acuity (FVA). Examinations using the FVAM system were conducted in 35 eyes of 20 healthy controls and 19 eyes of 13 dry eye patients. Tear function examinations including the Schirmer test, tear film break-up time, and fluorescein and Rose Bengal staining were performed in all subjects. Functional visual acuity and tear functions were also examined before and after insertion of punctum plugs in dry eye patients. Functional visual acuity results at 10, 20, and 30 seconds were compared. RESULTS: Functional visual acuity in dry eyes were significantly lower than control subjects at all time points (P < .05). Functional visual acuity after punctum plugs insertion improved significantly at all time points (P < .05). CONCLUSIONS: FVAM system seemed not only to be an effective tool in the assessment of dynamic visual acuity changes in dry eye and normal subjects but in evaluating the outcome of management of dry eye disease by punctum plugs.     

Saccade latency toward auditory targets depends on the relative position of the sound source with respect to the eyes

The latency of saccadic eye movements evoked by the presentation of auditory and visual targets was studied while starting eye position was either 0 or 20 deg right, or 20 deg left. The results show that for any starting position the latency of visually elicited saccades increases with target eccentricity with respect to the eyes. For auditory elicited saccades and for any starting position the latency decreases with target eccentricity with respect to the eyes. Therefore auditory latency depends on a retinotopic motor error, as in the case of visual target presentation.     

Smooth pursuit eye movements in response to predictable target motions

The human smooth pursuit eye movement system has a latency of about 150msec. However, this study shows that humans can learn to perform zero-latency tracking of targets that move with continuous velocity and amplitude-limited acceleration. Superposition of eye velocity and target velocity records, for our unique target waveforms, demonstrated that the subject was using the correct waveform and not just approximating it with a sinusoid or some other simple waveform. Calculation of the mean square error between target and eye position gave a quantitative measure of how well the human can track. The mean square error between target and eye position was 0.32 deg² for one thousand seconds of steady-state tracking by seven subjects. For several cycles at a time all subjects were able to reduce this error to less than 0.1 deg².     

Change of eye position in patients with orthophoria and horizontal strabismus under general anesthesia

We studied the relationship between eye position in the awakened state and in the surgical plane of anesthesia in orthophoric and horizontal strabismus patients. We classified 105 orthophoric and horizontal strabismus patients into 5 groups, measured the eye position at the primary position by photographic measurement of the corneal reflex positions and undertook a quantitative study of eye position. Under general anesthesia, the mean divergence was 39.7+/-8 PD for the esotropia group, 36.6+/-11.7 PD for exophoria, 27.4+/-8.1 PD for orthophoria, and 11.1+/-10.2 PD for exotropia I (< or =30 PD). Therefore, the esotropia group had the largest amount of divergence among the groups, but the eye position of the exotropia II (>30 PD) group was rather convergent at 11.0+/-6.5 PD. According to the eye position of the fixating and nonfixating eyes in the esotropia group, both eyes converged with an angle deviation of 14.4+/-4.8 PD divergent and 14.1+/-4.8 PD divergent, respectively (P=.71). In the exotropia groups (I, II), the fixating eye diverged but the nonfixating eye rather converged. Therefore, the angle deviation was 19.0+/-2.1 PD divergent for the fixating eye and 18.2+/-6.4 PD divergent for the nonfixating eye (P=.68). In conclusion, under general anesthesia, eye positions in the awakened state and in the surgical plane of anesthesia were convergent or divergent, and showed a tendency to converge into the position of 25-35 PD divergent. Therefore, we could not distinguish fixating eye from nonfixating eye under general anesthesia.