Objective Amplitude of Accommodation Computed from Optical Quality Metrics Applied to Wavefront Outcomes

Abstract

PURPOSE:We studied the accuracy and precision of 32 objective wavefront methods for finding the amplitude of accommodation obtained in 180 eyes. METHODS: Ocular accommodation was stimulated with 0.5 D steps in target vergence spanning the full range of accommodation for each subject. Subjective monocular amplitude of accommodation was measured using two clinical methods, using negative lenses and with a custom Badal optometer. RESULTS Both subjective methods gave similar results. Results obtained from the Badal optometer where used to test the accuracy of the objective methods. All objective methods showed lower amplitude of accommodation that the subjective ones by an amount that varied from 0.2 to 1.1 D depending on the method. The precision in this prediction also varied between subjects, with an average standard error of the mean of 0.1 D that decreased with age. CONCLUSIONS: Depth of field increases subjective of amplitude of accommodation overestimating the objective amplitude obtained with all the metrics used. The change in the negative direction of spherical aberration during accommodation increases the amplitude of accommodation by an amount that varies with age. KEY WORDS: image quality metrics; amplitude of accommodation; presbyopia; subjective methods; objective methods. RESUMEN OBJETIVO:Estudiamos la exactitud y la precisión de 32 métodos objetivos de calidad de imagen aplicados al frente de onda ocular y utilizados para calcular la amplitud de acomodación en 180 ojos. MÉTODOS: Se estimuló la acomodación ocular modificando la vergencia del estímulo a pasos de 0,5 D, de forma que se cubriese todo el rango de acomodación de cada sujeto. Se midió la amplitud de acomodación monocular subjetiva utilizando dos métodos habituales en la práctica clínica: uno basado en el uso de lentes negativas y otro basado en un optómetro de Badal adaptado. RESULTADOS: Con ambos métodos subjetivos se obtuvieron resultados parecidos. Los resultados obtenidos con el método basado en el optómetro de Badal se utilizaron para evaluar la exactitud de los métodos objetivos. En todos los casos, con todos los métodos objetivos se obtuvo una menor amplitud de acomodación que con los subjetivos; la diferencia entre ambos tipos osciló entre 0,2 D y 1,1 D, dependiendo de cada sujeto concreto. La precisión de esta estimación también varió entre un sujeto y otro: el error estándar de la media fue, en promedio, igual a 0,1 D, disminuyendo con la edad. CONCLUSIONES: La profundidad de campo aumenta la amplitud de acomodación subjetiva que sobrestima los valores objetivos encontrados por cualquiera de las métodos objetivos usados. Los resultados indican que la variación, hacia valores más negativos, de la aberración esférica durante el proceso de acomodación hace que aumente la amplitud de acomodación en una cantidad que varía con la edad. PALABRAS CLAVE: métricas de calidad de imagen; amplitud de acomodación; presbicia; métodos subjetivos; métodos objetivos.

Changes in the Objective Amplitude of Accommodation with Pupil Size

“…The effect of the change in SA on the AA produced by the light conditions could be very important; 18 however, because subjective refractions tend to be paraxially biased, 25 a relatively small change can be expected, as occurred in our experiment (0.21 D).…”

“…This makes AA RMSw lower than AA PARAX , in accordance with results reported previously. 4,18 Because accommodative pupil miosis will decrease negative SA in the accommodating eye, the minRMS refraction and AA RMSw will be more like the paraxial measures of AA. Similarly, at lower light levels where pupils are larger and SA is larger, the eye's minRMS refraction will be less myopic when accommodating and thus AA will appear reduced if evaluated with a minRMS refraction technique and large pupils.…”

“…For each lighting level and target vergence, three sets of aberrometry and pupillometry data were obtained, and the trial demonstrating the greatest accommodative response defined by the minimum RMS refraction 11,18,20 was used for further analysis. The intersubject mean and SD of AA, size of the relaxed and maximally constricted pupil, defocus, and fourth-order SA, C 4 0 , were calculated.…”

“…Initially, target vergence was set to +0.5 D beyond each subject's far point (predetermined by Zernike refraction 17,18 ) and increased to j1 D closer than the average age-specific near point given by the Hofstetter table. 19 From the start, accommodative demand (AD) was increased in steps of 0.5 D to the nearest position at which the subject was able to clear the test.…”

“…Further details of the wavefront measurements and the apparatus used are described elsewhere. 10,18 All measurements were performed under two light conditions, high and low, which generated two different pupil sizes for all the range of ADs. The two levels of light were achieved by changing the ambient light with the room light.…”