Repeatability of ocular aberration measurements in patients with keratoconus

Purpose: To explore the repeatability of lower-order and higher-order ocular aberrations measured in patients with keratoconus. Methods: The IRX-3 (Imagine Eyes, Paris, France) aberrometer was used to record lower-order and higher-order aberrations in 31 eyes of 31 patients with keratoconus. Four monocular measurements were taken consecutively for each patient. The aberrometry data were analysed up to the 5th Zernike order for a 4-mm pupil diameter. The data were evaluated using repeated-measures anova and Friedman analyses. Repeatability was analysed using within-subject standard deviation (SW) and the repeatability limit (r) calculated as 1.96 ×√2×Sw. Results: Of the 11 aberration terms evaluated, the repeatability of Z (2,0) (mean= 1.36μm; SW=0.09μm; r=0.26μm); Z (2,±2) RMS (mean=1.05μm; SW= 0.09μm; r=0.24μm) and Z (4,0) aberrations (mean=0.34μm; SW=0.09 μm; r=0.24μm) showed the highest variability. In contrast, Z (3,±1) RMS aberrations (mean=0.85μm; SW=0.06μm; r=0.16μm) and Z (4,±2) RMS aberrations (mean=0.40μm; SW=0.07μm; r=0.18μm) showed comparatively better repeatability. Conclusions: The lower-order and higher-order aberrations measured in this group of keratoconic patients showed higher levels of variability compared to previous investigations of visually-normal subjects. These results may be of interest to eyecare practitioners involved in the design and fitting of aberration-controlling contact lenses for patients with keratoconus. © 2011 The College of Optometrists.

Oculo-visual changes and clinical considerations affecting older patients with dementia

Purpose: Dementia is associated with various alterations of the eye and visual function. Over 60% of cases are attributable to Alzheimer's disease, a significant proportion of the remainder to vascular dementia or dementia with Lewy bodies, while frontotemporal dementia, and Parkinson's disease dementia are less common. This review describes the oculo-visual problems of these five dementias and the pathological changes which may explain these symptoms. It further discusses clinical considerations to help the clinician care for older patients affected by dementia. Recent findings: Visual problems in dementia include loss of visual acuity, defects in colour vision and visual masking tests, changes in pupillary response to mydriatics, defects in fixation and smooth and saccadic eye movements, changes in contrast sensitivity function and visual evoked potentials, and disturbance of complex visual functions such as in reading ability, visuospatial function, and the naming and identification of objects. Pathological changes have also been reported affecting the crystalline lens, retina, optic nerve, and visual cortex. Clinically, issues such as cataract surgery, correcting the refractive error, quality of life, falls, visual impairment and eye care for dementia have been addressed. Summary: Many visual changes occur across dementias, are controversial, often based on limited patient numbers, and no single feature can be regarded as diagnostic of any specific dementia. Nevertheless, visual hallucinations may be more characteristic of dementia with Lewy bodies and Parkinson's disease dementia than Alzheimer's disease or frontotemporal dementia. Differences in saccadic eye movement dysfunction may also help to distinguish Alzheimer's disease from frontotemporal dementia and Parkinson's disease dementia from dementia with Lewy bodies. Eye care professionals need to keep informed of the growing literature in vision/dementia, be attentive to signs and symptoms suggestive of cognitive impairment, and be able to adapt their practice and clinical interventions to best serve patients with dementia.

A longitudinal study of accommodative changes in biometry during incipient presbyopia

PURPOSE: To profile accommodative biometric changes longitudinally and to determine the influence of age-related ocular structural changes on the accommodative response prior to the onset of presbyopia. METHODS: Twenty participants (aged 34-41 years) were reviewed at six-monthly intervals over two and a half years. At each visit, ocular biometry was measured with the LenStar biometer (www.Haag-Streit.com) in response to 0.00, 3.00 and 4.50 D stimuli. Accommodative responses were measured by the WAM 5500 Auto Ref/Keratometer (www.grandseiko.com). RESULTS: During accommodation, anterior chamber depth reduced (F = 29, p < 0.001), whereas crystalline lens thickness (F = 39, p < 0.001) and axial length (F = 5.4, p = 0.009) increased. The accommodative response (F = 5.5, p = 0.001) and the change in anterior chamber depth (F = 3.1, p = 0.039), crystalline lens thickness (F = 3.0, p = 0.042) and axial length (F = 2.5, p = 0.038) in response to the 4.50 D accommodative target reduced after 2.5 years. However, the change in anterior chamber depth (F = 2.2, p = 0.097), crystalline lens thickness (F = 1.7, p = 0.18) and axial length (F = 1.0, p = 0.40) per dioptre of accommodation exerted remained invariant after 2.5 years. The increase in disaccommodated crystalline lens thickness with age was not significantly associated with the reduction in accommodative response (R = 0.32, p = 0.17). CONCLUSION: Despite significant age-related structural changes in disaccommodated biometry, the change in biometry per dioptre of accommodation exerted remained invariant with age. The present study supports the Helmholtz theory of accommodation and suggests an increase in lenticular stiffness is primarily responsible for the onset of presbyopia.

Clinical evaluation of the Shin-Nippon SRW-5000 autorefractor in adults:an update

Purpose: The Shin-Nippon SRW-5000 is an open view autorefractor that superseded the Canon R-1 autorefractor in the mid-1990s and has been used widely in optometry and vision science laboratories. It has been used to measure refractive error, accommodation responses both statically and dynamically, off-axis refractive error, and adapted to measure pupil size. This paper presents an overview of the original 2001 clinical evaluation of the SRW-5000 in adults (Mallen et al., Ophthal Physiol Opt 2001; 21: 101) and provides an update on the use and modification of the instrument since the original publication. Recent findings: The SRW-5000 instrument, and the family of devices which followed, have shown excellent validity, repeatability, and utility in clinical and research settings. The instruments have also shown great potential for increased research functionality following a number of modifications. Summary: The SRW-5000 and its derivatives have been, and continue to be, of significant importance in our drive to understand myopia progression, myopia control techniques, and oculomotor function in human vision.

On the shoulders of a giant:his legacy will live on

Editorial

An introduction to Point-Counterpoint articles

Editorial

The value of tablets as reading aids for individuals with central visual field loss:an evaluation of eccentric reading with static and scrolling text

Purpose: Technological devices such as smartphones and tablets are widely available and increasingly used as visual aids. This study evaluated the use of a novel app for tablets (MD_evReader) developed as a reading aid for individuals with a central field loss resulting from macular degeneration. The MD_evReader app scrolls text as single lines (similar to a news ticker) and is intended to enhance reading performance using the eccentric viewing technique by both reducing the demands on the eye movement system and minimising the deleterious effects of perceptual crowding. Reading performance with scrolling text was compared with reading static sentences, also presented on a tablet computer. Methods: Twenty-six people with low vision (diagnosis of macular degeneration) read static or dynamic text (scrolled from right to left), presented as a single line at high contrast on a tablet device. Reading error rates and comprehension were recorded for both text formats, and the participant’s subjective experience of reading with the app was assessed using a simple questionnaire. Results: The average reading speed for static and dynamic text was not significantly different and equal to or greater than 85 words per minute. The comprehension scores for both text formats were also similar, equal to approximately 95% correct. However, reading error rates were significantly (p=0.02) less for dynamic text than for static text. The participants’ questionnaire ratings of their reading experience with the MD_evReader were highly positive and indicated a preference for reading with this app compared with their usual method. Conclusions: Our data show that reading performance with scrolling text is at least equal to that achieved with static text and in some respects (reading error rate) is better than static text. Bespoke apps informed by an understanding of the underlying sensorimotor processes involved in a cognitive task such as reading have excellent potential as aids for people with visual impairments.