Differential visual acuity - A new approach to measuring visual acuity / Agudeza visual diferencial - Nuevo método para medir la agudeza visual

BACKGROUND: A novel type of acuity measurement, which we refer to as 'differential acuity', requires the observer to identify one unique target among three others which are identical. This is a proof of concept study aimed to determine if differential acuity is equivalent to standard measures of recognition acuity. METHODS: To create a range of visual acuity, vision was optically blurred in sixteen adults with normal visual acuity. Visual acuity was then measured with the differential acuity targets in both crowded and uncrowded format, and compared with standard ETDRS acuity or with singly presented letters and uncrowded letters were analysed separately. RESULTS: The visual acuity results for crowded and uncrowded letters were analysed separately. Repeated measures analysis of variance showed that when a crowded Sloan C had to be differentiated from three crowded Os (CvsO), the results were not significantly different from ETDRS acuity or from naming one of four letters presented centrally (Name4) (p < 0.05). Similar results were found for uncrowded letters - the C versus O and Name4 gave similar visual acuity. The 95% limits of agreement between the naming and C versus O differential acuity measures were between 0.17 and 0.27 logMAR. CONCLUSION: From this proof of concept study we conclude that differential acuity gives similar results to the ETDRS chart in adults. We infer that the comparable but cognitively simpler differential visual acuity task could be applied in clinical settings for young children or patients with developmental delay who cannot respond by naming or matching

ANTECEDENTES: Un nuevo tipo de medición de la agudeza, al que denominaremos 'agudeza diferencial, requiere que el observador identifique un único objetivo entre tres otros objetivos idénticos. Se trata de una prueba de estudio de concepto, que trata de determinar si la agudeza diferencial es equivalente a las mediciones estándar de agudeza de reconocimiento. MÉTODOS: Para crear un rango de agudeza visual, se degradó ópticamente la visión en dieciséis adultos con agudeza visual normal. A continuación se midió la agudeza visual con los objetivos de agudeza diferencial, tanto en formato aglomerado como no aglomerado, y comparándose con la agudeza ETDRS estándar, o con letras presentadas de manera única, analizándose las letras no aglomeradas separadamente. Los análisis de mediciones repetidas de varianza reflejaron que cuando una C Sloan aglomerada debía diferenciarse de tres O aglomeradas (CvsO), los resultados no eran significativamente diferentes de la agudeza ETDRS, o de nombrar una de las cuatro letras presentadas centralmente (Nombrar4) (p < 0,05). Se encontraron resultados similares para las letras no aglomeradas - C versus O - y Nombre4 arrojó una agudeza visual similar. Los límites de acuerdo del 95% de las mediciones de agudeza diferencial, entre nombrar y C versus O, se situaron entre 0,17 y 0,27 logMAR. CONCLUSIÓN: A partir de este estudio de prueba de concepto concluimos que la agudeza diferencial arroja resultados similares al cuadro ETDRS en adultos. Podemos inferir que podría aplicarse la tarea de agudeza visual diferencial, comparable pero cognitivamente más simple, al entorno clínico para jóvenes o pacientes con retraso del desarrollo cognitivo, y que no pueden responder mediante denominación o emparejamiento

Differential visual acuity - A new approach to measuring visual acuity.

BACKGROUND: A novel type of acuity measurement, which we refer to as 'differential acuity', requires the observer to identify one unique target among three others which are identical. This is a proof of concept study aimed to determine if differential acuity is equivalent to standard measures of recognition acuity. METHODS: To create a range of visual acuity, vision was optically blurred in sixteen adults with normal visual acuity. Visual acuity was then measured with the differential acuity targets in both crowded and uncrowded format, and compared with standard ETDRS acuity or with singly presented letters and uncrowded letters were analysed separately. RESULTS: The visual acuity results for crowded and uncrowded letters were analysed separately. Repeated measures analysis of variance showed that when a crowded Sloan C had to be differentiated from three crowded Os (CvsO), the results were not significantly different from ETDRS acuity or from naming one of four letters presented centrally (Name4) (p<0.05). Similar results were found for uncrowded letters - the C versus O and Name4 gave similar visual acuity. The 95% limits of agreement between the naming and C versus O differential acuity measures were between 0.17 and 0.27 logMAR. CONCLUSION: From this proof of concept study we conclude that differential acuity gives similar results to the ETDRS chart in adults. We infer that the comparable but cognitively simpler differential visual acuity task could be applied in clinical settings for young children or patients with developmental delay who cannot respond by naming or matching.

Myopia progression control lens reverses induced myopia in chicks.

PURPOSE: To determine whether lens induced myopia in chicks can be reversed or reduced by wearing myopia progression control lenses of the same nominal (central) power but different peripheral designs. METHODS: Newly hatched chicks wore -10D Conventional lenses unilaterally for 7 days. The myopic chicks were then randomly divided into three groups: one fitted with Type 1 myopia progression control lenses, the second with Type 2 myopia progression control lenses and the third continued to wear Conventional lenses for seven more days. All lenses had -10D central power, but Type 1 and Type 2 lenses had differing peripheral designs; +2.75D and +1.32D power rise at pupil edge, respectively. Axial length and refractive error were measured on Days 0, 7 and 14. Analyses were performed on the mean differences between treated and untreated eyes. RESULTS: Refractive error and axial length differences between treated and untreated eyes were insignificant on Day 0. On Day 7 treated eyes were longer (T1; 0.44 ± 0.07 mm, T2; 0.27 ± 0.06 mm, C; 0.40 ± 0.06 mm) and more myopic (T1; -9.61 ± 0.52D, T2; -9.57 ± 0.61D, C; -9.50 ± 0.58D) than untreated eyes with no significant differences between treatment groups. On Day 14 myopia was reversed (+2.91 ± 1.08D), reduced (-3.83 ± 0.94D) or insignificantly increased (-11.89 ± 0.79D) in treated eyes of Type 1, Type 2 and Conventional treated chicks respectively. Relative changes in axial lengths (T1; -0.13 ± 0.09 mm, T2; 0.36 ± 0.09 mm, C; 0.56 ± 0.05 mm) were consistent with changes in refraction. Refractive error differences were significant for all group comparisons (p < 0.001). Type 1 length differences were significantly different from Conventional and Type 2 groups (p < 0.001). CONCLUSIONS: Myopia progression control lens designs can reverse lens-induced myopia in chicks. The effect is primarily due to axial length changes. Different lens designs produce different effects indicating that lens design is important in modifying refractive error.