Relations between individual differences in oculomotor resting states and visual inspection performance

Management of digital eye strain

Digital eye strain, an emerging public health issue, is a condition characterised by visual disturbance and/or ocular discomfort related to the use of digital devices and resulting from a range of stresses on the ocular environment. This review aims to provide an overview of the extensive literature on digital eye strain research with particular reference to the clinical management of symptoms. As many as 90 per cent of digital device users experience symptoms of digital eye strain. Many studies suggest that the following factors are associated with digital eye strain: uncorrected refractive error (including presbyopia), accommodative and vergence anomalies, altered blinking pattern (reduced rate and incomplete blinking), excessive exposure to intense light, closer working distance, and smaller font size. Since a symptom may be caused by one or more factors, a holistic approach should be adopted. The following management strategies have been suggested: (i) appropriate correction of refractive error, including astigmatism and presbyopia; (ii) management of vergence anomalies, with the aim of inducing or leaving a small amount of heterophoria (~1.5^Δ Exo); (iii) blinking exercise/training to maintain normal blinking pattern; (iv) use of lubricating eye drops (artificial tears) to help alleviate dry eye-related symptoms; (v) contact lenses with enhanced comfort, particularly at end-of-day and in challenging environments; (vi) prescription of colour filters in all vision correction options, especially blue light-absorbing filters; and (vii) management of accommodative anomalies. Prevention is the main strategy for management of digital eye strain, which involves: (i) ensuring an ergonomic work environment and practice (through patient education and the implementation of ergonomic workplace policies); and (ii) visual examination and eye care to treat visual disorders. Special consideration is needed for people at a high risk of digital eye strain, such as computer workers and contact lens wearers.

Effect of artificial tears on tear stress test

PURPOSE

To determine the effect of two artificial tears of different viscosities in the relief of environmental dry eye induced with a novel tear stress test (TST).

METHODS

A novel TST was developed and validated. The following four test conditions were evaluated in 12 healthy normal subjects in a cross-over and subject masked study; unprotected (no test solution used), relief (test solution instilled just after application of TST), immediate protection (test solution instilled just before application of TST), and chronic protection (1 week prophylactic use of the solution). The test solutions were Cellumed, with high viscosity, and Refresh Contacts, with low viscosity. Low contrast visual acuity, symptoms with analogue scales (symptom scoring), non-invasive tear break-up time, and tear evaporation were measured before (prestress) and 2 min after (poststress) application of TST. Two weeks of washout period was allowed after first test solution.

RESULTS

In unprotected test condition, there was no significant difference between pre- and poststress visual acuity (p = 0.102), tear evaporation (p = 0.530), and non-invasive tear break-up time (p = 0.878), however, poststress total symptom score was significantly higher than prestress (p = 0.002). No significant differences were seen between pre- and post-total symptom score at relief (p = 0.241 for Cellumed and 0.114 for Refresh Contacts) and immediate protection (p = 0.890 for Cellumed and 0.136 for Refresh Contacts) for both test solutions, whereas postsymptoms total score was significantly higher than prestress at chronic protection (p = 0.003 for both). No significant differences were seen in the effect of the two solutions in all test conditions.

CONCLUSIONS

There is an increase in dry eye symptomatology after ocular stress. The use of artificial tears just before or after ocular stress is helpful in relieving resultant symptoms in normals.

fMRI reveals a preference for near viewing in the human parieto-occipital cortex

Posterior parietal cortex in primates contains several functional areas associated with visual control of body effectors (e.g., arm, hand and head) which contain neurons tuned to specific depth ranges appropriate for the effector. For example, the macaque ventral intraparietal area (VIP) is involved in head movements and is selective for motion in near-space around the head. We used functional magnetic resonance imaging to examine activation in the putative human VIP homologue (pVIP), as well as parietal and occipital cortex, as a function of viewing distance when multiple cues to target depth were available (Expt 1) and when only oculomotor cues were available (Expt 2). In Experiment 1, subjects viewed stationary or moving disks presented at three distances (with equal retinal sizes). Although activation in pVIP showed no preference for any particular spatial range, the dorsal parieto-occipital sulcus (dPOS) demonstrated a near-space preference, with activation highest for near viewing, moderate for arm's length viewing, and lowest for far viewing. In Experiment 2, we investigated whether the near response alone (convergence of the eyes, accommodation of the lens and pupillary constriction) was sufficient to elicit this same activation pattern. Subjects fixated lights presented at three distances which were illuminated singly (with luminance and visual angle equated across distances). dPOS displayed the same gradient of activation (Near>Medium>Far) as that seen in Experiment 1, even with reduced cues to depth. dPOS seems to reflect the status of the near response (perhaps driven largely by vergence angle) and may provide areas in the dorsal visual stream with spatial information useful for guiding actions toward targets in depth.

Computer vision syndrome: a review

As computers become part of our everyday life, more and more people are experiencing a variety of ocular symptoms related to computer use. These include eyestrain, tired eyes, irritation, redness, blurred vision, and double vision, collectively referred to as computer vision syndrome. This article describes both the characteristics and treatment modalities that are available at this time. Computer vision syndrome symptoms may be the cause of ocular (ocular-surface abnormalities or accommodative spasms) and/or extraocular (ergonomic) etiologies. However, the major contributor to computer vision syndrome symptoms by far appears to be dry eye. The visual effects of various display characteristics such as lighting, glare, display quality, refresh rates, and radiation are also discussed. Treatment requires a multidirectional approach combining ocular therapy with adjustment of the workstation. Proper lighting, anti-glare filters, ergonomic positioning of computer monitor and regular work breaks may help improve visual comfort. Lubricating eye drops and special computer glasses help relieve ocular surface-related symptoms. More work needs to be done to specifically define the processes that cause computer vision syndrome and to develop and improve effective treatments that successfully address these causes.

Effects of viewing distance on accommodative and pupillary responses following a three-dimensional task

We have investigated accommodation and pupil responses after viewing stereoscopic images related to the resting position of accommodation. After a 10-min visual task viewing stereoscopic three-dimensional images, measurements of dynamic accommodation and pupil response were made using an infrared optometer and a pupil analyser. Four conditions were given for the viewing distance: 0.4 m (closer than the subjects' resting position), 1 m (approximating to their resting state), and 1.5 and 3 m (farther than the resting position). For the 0.4- and 1-m groups, a delay in the accommodation response for near-to-far movement was shown after the task, from 817 to 1120 ms and from 830 to 898 ms, respectively, but there was no change in the pupillary response. In the 1.5- and 3-m groups, on the other hand, a significant delay in the accommodation response for far-to-near movement was shown, from 827 to 912 ms and from 857 to 1150 ms, respectively, and greater miosis was found, from 7.2 to 9.2 mm2 and from 8.0 to 10.4 mm2. The data reveal that there are different after-effects on accommodation and pupillary functions when subjects perform the task within their accommodative resting position, than when the task is performed outside the resting position.

The proximity-fixation-disparity curve and the preferred viewing distance at a visual display as an indicator of near vision fatigue

PURPOSE

This laboratory study investigates the relation between measures of fixation disparity (FD) (and other optometric measures) and near vision fatigue at a computer workstation.

METHODS

Young adult subjects with normal binocular vision performed three blocks of a visual task of 30 min each. In Block A, the viewing distance was 100 cm, as a reference without near vision. In Block B, the viewing distance of 50 cm induced a defined near vision load. In Block C, subjects were free to choose a comfortable viewing distance. This preferred viewing distance was used as an indicator of near vision fatigue because subjects adopting longer viewing distances in Block C had more near vision fatigue at 50 cm in Block B.

RESULTS

Subjects with preferred viewing distances longer than average (63 cm) had steeper slopes of FD as a function of viewing distance (100-30 cm), as shown by discriminant analyses.

CONCLUSIONS

Thus, this steep proximity-FD curve indicates a weak disparity vergence system that may cause near vision fatigue. This may explain why some young adults prefer longer viewing distances at the computer workstation.

A procedure to determine the individually comfortable position of visual displays relative to the eyes

In an intervention phase, 38 operators used four different imposed screen positions (near versus distant, high versus low) for a full working day to experience the advantages and disadvantages. Screens at about 66 cm induced more reported strain than screens at about 98 cm. When operators later freely selected their individually most comfortable screen position, individually different changes due to the intervention were observed: some subjects changed to shorter, others to longer viewing distances, some operators adjusted the screen lower, others higher. These effects were confirmed in repeated tests. Thus, trying out different screen positions appears useful for arranging the VDU workstation to the individually most comfortable screen location relative to the eyes.

Preferred position of visual displays relative to the eyes: a field study of visual strain and individual differences

At office workplaces equipped with visual display units (VDU) that were adjustable to various positions relative to the eyes short and long viewing distances from the eyes to the screen were imposed (mean value of about 63 and 92 cm) at two levels of screen height so that the visual target was either at eye level or 18 cm below, on the average. The change from far to near viewing distance produced a larger increase in eyestrain when the VDUs were at eye level. High screens resulted in greater eyestrain than low screens, as shown by correlations over subjects. When operators were free to adjust the most comfortable screen position, the group of 22 participants preferred viewing distances between 60 and 100 cm and vertical inclination of gaze direction between horizontal and -16 degrees downwards. However, within most subjects the range of preferred screen positions was much smaller. Between 3 days during a 1-month period the test-retest correlations of the preferred screen positions were highly significant, both for viewing distance and vertical gaze inclination. When operators were forced to work at a shorter distance than their preferred viewing distance they reported more visual strain. Thus, operators appear to prefer an individual adjustment of the screen relative to the eyes in order to avoid visual strain and discomfort at VDU work.