The effects of multifocal refractive lenses on occipital extension and forward head posture during a visual task

Influence of external fixation on the isomeric strength of the shoulder flexors in individuals with scapular elevation

BACKGROUND

Sufficient shoulder flexor strength is necessary for accurate movement of the shoulder joint because several factors can cause compensatory movements of the scapula.

OBJECTIVE

We investigated the influence of external fixation on the isometric shoulder flexors strength (ISFS) in individuals with and without scapular elevation (SE) during shoulder flexion.

METHODS

The healthy and SE groups included 29 individuals. The ISFS was measured using a tensiometer (kg) under conditions of with and without external fixation, in a random order. The change in the ISFS (the strength difference with and without external fixation) was compared between the healthy and SE groups using an independent t-test.

RESULTS

The change in the ISFS differed significantly between the healthy and SE groups (3.5% and 32.3%, respectively; p= 0.001).

CONCLUSION

These findings suggest that external fixation should be considered during shoulder flexion to determine the ISFS accurately in individuals with compensated SE.

Effect of unifocal versus multifocal lenses on cervical spine posture in patients with presbyopia

Significance. There are many environmental considerations which may or may not lead to the development of faulty cervical mechanics. The design of near-vision lenses could contribute to the development of such cervical dysfunction and consequently neck pain. Decision-making regarding the proper type of lens prescription seems important for presbyopic individuals. Purpose. To investigate the effect of unifocal and multifocal lenses on cervical posture. Methods. Thirty subjects (18 females and 12 males) participated in the study with an age range from 40 to 64 years. Each subject wore consequently both unifocal and multifocal lenses randomly while reading. Lateral cervical spine X-ray films were taken for each subject during each lens wearing. X-ray films were analyzed with digital software (AutoCAD 2D version 22) to measure segmental angles of the cervical vertebrae (occiput/C1, C1/C2, C2/C3, C3/C4, C4/C5, C5/C6, C6/C7, C3/C7, C0/C3, and occiput/C7). Results. Higher significant extension angles were observed in the segments C0/C7, C1/C2, C5/C6, C6/C7 and C3/C7 (p < 0.05) during multifocal lens wearing, in contrast to higher flexion angles between C3/C4 and C4/C5 (p < 0.05) when wearing unifocal lenses. Conclusion. Multifocal lens spectacles produce increased extension in the cervical vertebrae angles when compared with the use of unifocal lenses.

The impact of different lenses on visual and musculoskeletal complaints in VDU workers with work-related neck complaints: a randomized controlled trial

Objectives

The impact of wearing lenses on visual and musculoskeletal complaints in VDU workers is currently unknown. The goal of this study was 1) to evaluate the impact of wearing VDU lenses on visual fatigue and self-reported neck pain and disability, compared to progressive lenses, and 2) to measure the effect of both lenses on head inclination and pressure pain thresholds during the performance of a VDU task.

Methods

Thirty-five eligible subjects were randomly assigned to wear progressive VDU lenses (VDU group) (n = 18) or progressive lenses (P group) (n = 17). They were enquired about visual complaints (VFQ), self-perceived pain (NRS) and disability (NDI) at baseline (with old lenses), and 1 week, 3 months and 6 months after wearing their new lenses. In addition, Forward Head Angle (FHA) and PPTs were assessed during and after a VDU task before and 6 months after wearing the new lenses. A short questionnaire concerning the satisfaction about the study lenses was completed at the end of the study.

Results

In both groups, visual fatigue and neck pain was decreased at 3 and 6 months follow up, compared to baseline. All PPTs were higher during the second VDU task, independent of the type of lenses. The VDU group reported a significantly higher suitability of the lenses for VDU work.

Conclusion

It can be concluded that there is little difference in effect of the different lenses on visual and musculoskeletal comfort. Lenses should be adjusted to the task-specific needs and habits of the participant.

Experimental procedure for measuring and comparing head-neck-trunk posture and movements caused by different progressive addition lens designs

This study demonstrates that appropriate measurement procedures can detect differences in head movement in a near reading task when using three different progressive addition lenses (PALs). The movements were measured using an anatomical reference system with a biomechanical rationale. This reference system was capable of representing rotations for comparing head flexion relative to trunk, head flexion relative to neck, head rotation relative to trunk and trunk flexion. The subject sample comprised 31 volunteers and three PAL designs with different viewing zones were selected. Significant differences were found between the lenses for three of the seven movement parameters examined. The differences occurred for both vertical and horizontal head movements and could be attributed to aspects of the PAL design. The measurement of the complete kinematic trunk-neck-head chain improved the number of differences that were found over those in previous studies. STATEMENT OF RELEVANCE: The study proposes a methodology based on a biomechanical rationale able to differentiate head-neck-trunk posture and movements caused by different progressive addition lens designs with minimum invasiveness. This methodology could also be applied to analyse the ergonomics of other devices that restrict the user's field of view, such as helmets, personal protective equipment or helmet-mounted displays for pilots. This analysis will allow designers to optimise designs offering higher comfort and performance.