June 2021
Volume 62, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2021
Emmetropic, but not myopic human eyes distinguish positive defocus from calculated blur
Author Affiliations & Notes
  • Barbara Swiatczak
    Institute of Molecular and Clinical Ophthalmology Basel (IOB), Basel, Switzerland
  • Frank Schaeffel
    Institute of Molecular and Clinical Ophthalmology Basel (IOB), Basel, Switzerland
    Eberhard Karls Universitat Tubingen, Tubingen, Baden-Württemberg, Germany
  • Footnotes
    Commercial Relationships   Barbara Swiatczak, None; Frank Schaeffel, None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science June 2021, Vol.62, 1337. doi:
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      Barbara Swiatczak, Frank Schaeffel; Emmetropic, but not myopic human eyes distinguish positive defocus from calculated blur. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1337.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : It is well established that defocus blur imposed by positive lenses induces hyperopia development while blur imposed by diffusers induces deprivation myopia. While it is known that such ocular growth changes are controlled by the retina, it is unclear whether the retina can distinguish between both conditions when the magnitude of blur is matched. We have studied this question in young human subjects.

Methods : Ten emmetropic (average refractions 0.0±0.3D) and ten myopic (-2.7±0.9D) young subjects (average age: 24±4 years) watched a movie on a large screen (65”) at 2 m distance. The movie was presented either unfiltered (“control”), or with calculated low-pass filtering equivalent to a defocus of 2.5 D, or with real optical defocus of +2.5D that was imposed by +3D spectacle lenses in both eyes. Before and after 30 minutes of movie watching, axial length was measured using low coherence interferometry (Lenstar LS-900 with autopositioning system). Spatial filtering movies was done in real-time by software written in Visual C++. Defocus was simulated by convolving each pixel with a blur circle that was calculated for 2.5D of defocus, using the average pupil size of the subjects (6.5+0.7 mm).

Results : Watching unfiltered movies (“control”) caused no changes in axial length. In emmetropes, watching movies with calculated defocus caused axial eye elongation (+9.8±7.6µm) while watching movies with real positive defocus caused shorter eyes (-8.8±9.2 µm; difference between both p<0.0001). Also in myopes, calculated defocus caused longer eyes (+8.4±9.0µm) compared to control (-3.0±8.3µm, p=0.001). Strikingly, myopic eyes responded differently to positive defocus since they became also longer (+9.1±11.2µm, p=0.02, compared to control). The difference in responses to positive defocus between emmetropic and myopic subjects was highly significant (p=0.001).

Conclusions : Two conclusions emerge: (1) in emmetropic human subjects, the retina appears to be able to distinguish between real positive defocus and calculated defocus even when the modulation transfer function was matched, (2) in myopic eyes, the retina apparently no longer distinguishes between both conditions since the eyes became longer in both cases. These results suggest that the retina in a myopic eye has reduced ability to detect positive defocus and restrain axial growth.

This is a 2021 ARVO Annual Meeting abstract.

 

Effect of positive defocus on axial length in emmetropic and myopic subjects.

Effect of positive defocus on axial length in emmetropic and myopic subjects.

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