Praveen Kumar Bandela

PhD Candidate

PhD Candidate

Research Title: Utility of optical and non-optical cues by the accommodative system to decode the sign of defocus 

Supervisors: Dr. Ravi Bakaraju, Associate Professor Klaus Ehrmann, Mr Darrin Falk 

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The human visual system deals with multiple complex scenarios, differentiating the sign of defocus (myopic vs. hyperopic) is one such scenario. The underlying mechanism of precise and accurate identification of myopic and hyperopic defocus remains unclear. We propose to use ocular accommodation as a channel to address this lacuna.

Ocular accommodation enables the eye to focus objects at different distances to see clearly. Previous research suggests that retinal defocus is the primary stimulus for initiating the accommodative responses. To achieve a clear vision the accommodative system needs to respond differently for the myopic (disaccommodate) and hyperopic (accommodate) blur. However, an ambiguity arises in differentiating the defocus type in a diffraction limited optical system, which encounters similar image characteristics for both myopic and hyperopic defocus. Numerous optical and non-optical factors/cues abet the visual system to differentiate the type of blur. Optical factors include ocular wavefront aberrations (monochromatic/chromatic), accommodative microfluctuations, Stiles Crawford Effect, target size and color. Non-optical factors include the cognitive state of the subject, environmental cues, etc.

Although the individual contribution of these cues in providing the sign of defocus has been explored, the conclusions are still  unclear. Also, the combined effect of these cues in providing the sign of defocus and accommodative responses has not been studied in detail. Our study predominantly focuses on contributions of the optical factors to the accommodative responses and in guiding the sign of defocus. In order to address this, we will use computational optics to understand the effect of optical cues on accommodative responses and sign of defocus. We will also explore whether the cue management differs in various refractive errors. The latter part includes the accommodative response measurements using a binocular open-field autorefractor (Grand Seiko, WAM-5500).

Although the accommodative responses are due to short-term defocus exposure, the results of this study may provide insights into the understanding of long-term defocus exposure and its possible influence on myopia progression and emmetropization.


After completing his Bachelors of Optometry in the year 2012, Praveen worked as a consultant Optometrist at L V Prasad Eye Institute (LVPEI) India for a tenure of five years. Along with clinical care he was involved in research as well as teaching at the Bausch and Lomb School of Optometry. His past research focussed particularly on the effect of asymmetrical interocular optical quality on binocular vision has been presented in various international and national conferences and has also published in peer reviewed journals. With his past experience and his own research interest he is exploring ocular accommodation as a part of his PhD.  



2012, BSc Optometry: Bausch and Lomb School of Optometry, India 

2008, BSc General Science: Osmania University, India 



Journal Articles 

Bharadwaj SR, Bandela PK, Nilagiri VK. Lens magnification affects the estimates of refractive error obtained using eccentric infrared photorefraction. J Opt Soc Am A Opt Image Sci Vis. 2018 Jun 1; 35(6). 

Bandela PK, Satgunam P, Garg P, Bharadwaj SR, “Corneal Transplantation in Disease Affecting Only One Eye: Does It Make a Difference to Habitual Binocular Viewing?” PLoS One. 2016 Mar 3;11(3).  



2018, University International Post-Graduate Scholarship award (UIPA)

2012 Prof T. Navaneeth Rao Gold medal for best outgoing student award in Optometry 



Bandela PK, Preetam K, Bharadwaj SR :“Spatial and Depth Vision with Different Contact Lens Management Modalities in Keratoconus”: at E V Memorial Scientific Session, Elite School of Optometry, Chennai, India, March-2017  

Bandela PK, Preetam K, Bharadwaj SR :“A Qualitative and Quantitative Comparison of Binocular Visual Performance of Keratoconus Patients With Various Contact Lens Modalities” at Indian Eye Research Group, Hyderabad, India,July-2016  

Bandela PK, Satgunam P, Garg P, Bharadwaj SR: “Functional Utility of Corneal Transplantation In Unilateral Visual Impairment “at Elite School of Optometry International Vision Science and Optometry Conference (EIVOC), Chennai India, August-2015  



Optical Society of America