Factors Influencing Pseudo-Accommodation-The Difference between Subjectively Reported Range of Clear Focus and Objectively Measured Accommodation Range.

Dhallu Dhallu,Sheppard Sheppard,Mihashi Mihashi,Wolffsohn Wolffsohn,Zapata-Díaz Zapata-Díaz,Drew Drew,Radhakrishnan Radhakrishnan,Iskander Iskander

doi:10.3390/vision3030034

Abstract

The key determinants of the range of clear focus in pre-presbyopes and their relative contributions to the difference between subjective range of focus and objective accommodation assessments have not been previously quantified. Fifty participants (aged 33.0 ± 6.4 years) underwent simultaneous monocular subjective (visual acuity measured with an electronic test-chart) and objective (dynamic accommodation measured with an Aston open-field aberrometer) defocus curve testing for lenses between +2.00 to −10.00 DS in +0.50 DS steps in a randomized order. Pupil diameter and ocular aberrations (converted to visual metrics normalized for pupil size) at each level of blur were measured. The difference between objective range over which the power of the crystalline lens changes and the subjective range of clear focus was quantified and the results modelled using pupil size, refractive error, tolerance to blur, and ocular aberrations. The subjective range of clear focus was principally accounted for by age (46.4%) and pupil size (19.3%). The objectively assessed accommodative range was also principally accounted for by age (27.6%) and pupil size (15.4%). Over one-quarter (26.0%) of the difference between objective accommodation and subjective range of clear focus was accounted for by age (14.0%) and spherical aberration at maximum accommodation (12.0%). There was no significant change in the objective accommodative response (F = 1.426, p = 0.229) or pupil size (F = 0.799, p = 0.554) of participants for levels of defocus above their amplitude of accommodation. Pre-presbyopes benefit from an increased subjective range of clear vision beyond their objective accommodation due in part to neural factors, resulting in a measured depth-of-focus of, on average, 1.0 D.

Highlights

The subjectively experienced range of clear focus during accommodation is greater than the objectively measured increase in ocular power due to the depth of focus [1,2,3,4]
Pseudophakic patients implanted with monofocal intraocular lenses (IOLs) are sometimes able to demonstrate relatively good near ability through non-accommodative means, attributed to the change in pupil size, anterior IOL movement, higher order aberrations (HOAs), and tolerance to blur [3,8,10,11,12,13]
Blur thresholds increase with a smaller pupil size [19] and with greater retinal eccentricity [20,21], the latter thought to occur due to a combination of anatomical, physiological, optical and perceptual factors such as sharpness overconstancy [21,22]

Summary

Introduction

The subjectively experienced range of clear focus during accommodation is greater than the objectively measured increase in ocular power due to the depth of focus [1,2,3,4]. Pseudophakic patients implanted with monofocal intraocular lenses (IOLs) are sometimes able to demonstrate relatively good near ability through non-accommodative means, attributed to the change in pupil size, anterior IOL movement, higher order aberrations (HOAs), and tolerance to blur [3,8,10,11,12,13]. Blur tolerance is known to increase with age [16,17] as a result of age-related optical factors, pupil miosis, as well as experience-mediated neural compensation [18]. Blur thresholds increase with a smaller pupil size [19] and with greater retinal eccentricity [20,21], the latter thought to occur due to a combination of anatomical, physiological, optical and perceptual factors such as sharpness overconstancy [21,22]

Methods

Discussion

Conclusion