Low-cost cell-phone attachments that measure the eye-glass prescription and cataract information from the eye.
Project Description
Vitor F. Pamplona*        Ankit Mohan        Manuel M. Oliveira*      Ramesh Raskar
David Schafran           Erick Passos      Everett LawsonCamera Culture Group – MIT Media Lab
* Visiting from Instituto de Informática – UFRGSSee our latest works on Cataract Mapping and tailored displays
NETRA Concept
OneSight’s Mission Trip – Nairoby, Kenya                   LVPEI’s Clinical Trials – Hyderabad, India
Figure 1: Netra is a $2 clip-on eyepiece that goes on top of a cell phone. The user looks through this eye piece and interactively aligns the displayed patterns by clicking the buttons. The number of clicks required to bring the patterns into alignment indicates the refractive error. Our optometry solution combines inexpensive optical elements and interactive software components to create a new portable and inexpensive device that mimics (and replaces) the expensive laser-based Shack-Hartmann wavefront aberrometers. Ilustration: Tiago Allen


We introduce a portable and inexpensive solution for estimating refractive errors in the human eye. While expensive optical devices for automatic estimation of refractive correction exist, our goal is to greatly simplify the mechanism by putting the human subject in the loop. A traditional Shack-Hartmann wavefront sensor uses lasers and highly sensitive digital sensor which makes those solutions expensive, bulky and requires trained professionals.

Our solution creates an inverse Shack-Hartmann sensor. It is based on a high-resolution programmable display and combines inexpensive optical elements, interactive GUI, and computational reconstruction. The key idea is to interface a lenticular view-dependent display with the human eye at close range – a few millimeters apart. Via this platform, we create a new range of interactivity that is extremely sensitive to parameters of the human eye, such as the refractive errors, focal range, focusing speed, lens opacity, etc. We propose several simple optical setups, verify their accuracy, precision, and validate them in a user study.


Ignition Grant

Innovation Grant

Research Papers

    1. Vitor F. Pamplona
      Interactive Measurements and Tailored Displays for Optical Aberrations of the Human Eye 
      PhD Thesis
      Draft Version.
    2. Vitor F. Pamplona, Ankit Mohan, Manuel M. Oliveira, Ramesh Raskar.
      NETRA: Interactive Display for Estimating Refractive Errors and Focal Range. 
      Proc. of SIGGRAPH 2010
       (ACM Transactions on Graphics 29, 4), 2010. 
    3. Vitor F. Pamplona, Ankit Mohan, Manuel M. Oliveira, Ramesh Raskar.
      Dual of Shack-Hartmann Optometry Using Mobile Phones. 
      Proc. of Frontiers in Optics, Optical Society of America. Oct. 24, Rochester, New York. 2010. 
    4. Vitor F. Pamplona, Ankit Mohan, Manuel M. Oliveira, Ramesh Raskar.
      Low-cost and Portable tool for Measuring Eye Refractive Disorders using Active Participation. 
      Proc. of 88th Annual Meeting of the American Academy of Optometry
      , San Francisco.
    5. Veerendranath Pesala, Sangeetha Srinivasan, Ethan Solomon, Vitor F. Pamplona, Manuel M. Oliviera, Ramesh Raskar, Shrikant Bharadwaj.
      Comparison of a Novel Cell Phone-Based Refraction Technique (NETRA) With Objective Clinical Retinoscopy.
      ARVO 2011
    6. Vitor F. Pamplona, Ankit Mohan, Manuel M. Oliveira, Ramesh Raskar.
      NETRA: A Novel Clip-on Eye-piece for Mobile Phone based Optometry Solution and Low Cost Eye Tests. 
      mHealth Summit 2010
  1. Martha P. Lang, Helena M. Pakter, Lisia B. Ferreira, Ankit Mohan, Ramesh Raskar, Vitor F. Pamplona, Manoel M. Oliveira
    Comparison of a Cell Phone-Based Refraction Technique (NETRA) With Auto-Refraction.
    ARVO 2012
  2. Bruce D. Moore, Nadine Solaka, Vitor F. Pamplona, David Schafran, Amy Canham, Ramesh Raskar, Hilary Gaiser.
    Comparison of a Novel Cell Phone-based Refraction Technique (NETRA-G) with Subjective Refraction. AAO 2012, Chicago, IL.
    Abstract Suplement

Worldwide Impact

 29 research teams in 14 countries already have our prototypes.

NETRA worldwide
Collaboration opportunities and clinical studies, please introduce yourself at our google group.
Please look at FAQ for more information. Press package, pictures and illustrations here.


TEDxBoston: EyeExams: there is an app for that.

MIT Media Lab LabCast: Credit, Paula Aguilera and Jonathan Williams

NETRA at NASA Launch

Ramesh Raskar @ NASA Launch

1st Prize: Vodafone Wireless Innovation Project 2011

More videos here.

Slide Set

Brief Technical Description

The NETRA system uses the dual of a Shack-Hartman sensor, and replaces the laser with simple user interaction. Todayś methods using the Shack-Hartmann sensor shine a laser into the eye of the patient, and measure the reflected light with a wavefront sensor. Hence they are quite expensive, and require a trained professional operator.  A cell phone based solution significantly reduces the cost of the device and makes it appropriate for self-evaluation, while still providing comparable data.

The subject looks into this display at a very close range and aligns (overlaps) displayed patterns (Figure 1). Since the light rays from these patterns pass through different regions of the visual system, the alignment task gives a measure of the optical distortions of those regions. The subject repeats this procedure for a few meridians with appropriate variation in the patterns. The system computes the corresponding refractive error for myopia, hyperopia and astigmatism.

Prototype Nexus One Prototype
Figure 2: Current prototypes using the Samsung Behold II and the Nexus One. We place an optical phase plate to create virtual images and achieve 0.6 and 0.4 diopter resolution respectively.

Evaluation: We tested accuracy and precision of the technique in two experiments: (i) using lenses and a SLR camera and (ii) comparing our device against actual prescriptions in a user study. The resolution is 0.4 diopters using the Nexus One device (focal length 30mm). The Apple iPhone 4G, with the new Retina Display should achieve a resolution of approximately 0.28 diopters (focal length 30mm). For measuring eye correction, the average absolute errors from the known prescriptions were under 0.5 diopter (σ = 0.2) for both cylindrical and spherical powers. The average absolute error of our estimates of the cylindrical axis was under 6 degrees. Optometrists typically prescribe in multiples of 0.25 diopter, and 10 degrees axis.

In controlled user experiments with 16 subjects, the average absolute errors from the known prescriptions were under 0.5 diopter, with a standard deviation of 0.2 diopter for both cylindrical (astigmatism) and spherical powers (myopia and hyperopia). The average absolute error of the cylindrical axis is less than 6 degrees. We are able to achieve this without the use of cycloplegic eye drops for relaxing accommodation.

Limitations: Since our solution relies on subjective feedback, it cannot be used by individuals who cannot reliably perform the user-required tasks, such as very young children.

Existing Techniques

Existing systems to diagnose refractive eye conditions include Snellen charts (with a set of trial lenses), auto-refractometers, and wavefront aberrometers.  The NETRA solution offers some unique benefits over these existing techniques, which make it specially suited for deployment in developing countries:

  • Cost: NETRA relies on innovative use of existing hardware (a cell-phone), and custom software. We augment an existing cell-phone display with a device that costs as little as $2. This is significantly cheaper than sophisticated techniques such as aberrometers, and even a set of trial lenses which costs $100 or more.
  • Safety: Since our device does not use lasers, has no need for cycloplegic drugs, and includes no moving parts, there are reduced concerns about danger in improper use, specialized training, or damage in transit.
  • Speed: Conventional methods of diagnosis usually require two steps (step 1 objectively measures the refraction error, and step 2 verifies it based on patient feedback). Our hybrid approach combines these in a single user-driven step to obtain a measurement in less than 3 minutes.
  • Accuracy: Unlike the Snellen chart, the NETRA system relies on a simple alignment task rather than the patient’s ability to discern blur. This gives comparable accuracy, and a simpler user interaction task.
  • Mobility: Based on a cell-phone, the NETRA system easily fits in a backpack for remote deployment.
  • Self-evaluation: The ease of use, cheap cost, and the inherent safety of the NETRA system allows for (possibly at-home) self-evaluation.
Current solutions for analyzing refractive errors.
Figure 3: Current solutions for analyzing refractive errors. Subjective Methods (far left and center) rely upon the user’s judgment of sharpness or blurriness of a test object. Objective Methods (far right) require a mechanically moving lens, a camera, a trained technician, and a large investment.

Refraction Services Requirement on Developing Countries [Vision 2020 Report]: The following table provides a comprehensive list of techniques and equipment for assessing refractive conditions of an eye.

Technique Objectivity Speed Accuracy/ Reliability Electricity Requirements Mobility Training
Equipment Requirements (Cost bracket)*
Cost Efficiency rank Suitability for Children
Retinoscopy (Slit Lamp)
Objective = does not rely on patient responses Fast +/- 0.50D unless affected by media opacities or accommodation Batteries Good High Retinoscope, plus trial lens set and trial frame ($2000), OR phoropter($1600), OR variable focus specs ($1600)
Economical – low up-front cost, high durability, low maintenance Sometimes
Subjective refraction (Eye Charts)
Subjective = does rely on patient responses Slow +/- 0.25D but dependent on patient reliability None Good High Trial lens set and trial frame($1400), OR phoropter ($1000), OR variable focus specs ($600)
Economical Sometimes (only with experienced practitioners)
Auto Refraction Objective Fast Relies on both equipment and patient factors Mains Low Basic Auto-refractor ($15K)
Expensive No
Portable Auto Refraction Objective Fast Relies on both equipment and patient factors Mains or batteries Good Basic Portable auto-refractor ($20K)
Expensive No
NETRA Subjective Fast Relies on both equipment and patient factors

< 0.50D unless affected by accommodationCell phone batteriesExcellentBasicPlastic Piece ($2) and a cell phone ($300).

* Costs were extracted from the Vision2020 report. Some cheaper options may exist – for example, we were able to acquire a set of trial lenses for $300. Note that simple reading charts can be expensive because they must be used under optimal lighting conditions and need a set of trial lenses.

Potential Impact

More than two billion people worldwide have refractive error. Very few have access to quality eye-care because existing solutions require a trained optometrist or expensive equipment [VISION2020 ReportHolden2007]. This impacts the developing world in a significant way:

  • 517 million have uncorrected near-vision impairment affecting daily livelihood.
  • 153 million have uncorrected far-vision impairment (affecting 2% of the world population).
  • Uncorrected Refractive Errors are the 2nd leading cause of blindness* globally. 87% of those affected live in the developing world.
  • For many children, hyperopia may remain undiagnosed, leading to undue stress and headaches.
  • Access to a trained optometrist and equipment is extremely limited.

* WHO definition for blindness: vision worse that 3/60 in the better eye.

Uncorrected refractive problems may lead to a significant loss in productivity, with estimates ranging from USD 88.74 to USD 133 billion. To put things in perspective, this productivity loss exceeds the annual GDP of 46 of the 52 African countries. Our technology can address all types of refractive errors.

Acknowledgments: Thanks to the volunteers who tested our device, Xiaoxi Wang and Andrew Song for prototype construction, Tiago Allen Oliveira for illustrations, Tyler Hutchison for the video voiceover, Taya Leary for her relentless support, the entire Camera Culture group for all the useful discussions; and the reviewers for their valuable feedback. Dr. James Kobler (Mass. General Hospital), Dr.  Dr. Joseph Ciolino (Mass. Eye and Ear Infirmary), and Dr. Fuensanta Vera Diaz (Schepens Eye Research Institute) provided valuable resources and insightful discussions about optometry and ophthalmology. We thank Dick Lyon and Google’s open source office for Google Nexus One mobile phone, and Samsung Electronics for Samsung Behold II mobile phone. Vitor and Manuel acknowledge CNPq-Brazil fellowships 142563/2008-0, 200763/2009-1, 200284/2009-6, 476954/2008-8. Ramesh Raskar is supported by an Alfred P. Sloan Research Fellowship.

Media Coverage


    • Group Picture
Group Picture
NETRA team: Ankit Mohan, Manuel M. Oliveira Neto, Vitor Pamplona and Ramesh Raskar at the MIT Media Lab.
Photo: Jonathan Williams
  • NETRA at NASA 
Astronaut Ron using NETRA
Astronaut Ron Garan testing NETRA at the Kennedy Space Center

© Mike Ritter /

© Mike Ritter /

© Mike Ritter /

© Mike Ritter /

© Mike Ritter /

© Mike Ritter /
  • NETRA at Conceição Hospital – Brazil
    • Teresina – PI – Brazil
    • NETRA at UFRGS Open House
Testing NETRA
Picture Credit: Anderson Maciel
Testing NETRA
Picture Credit: Anderson Maciel
Testing NETRA
Picture Credit: Anderson Maciel
UFRGS Vice Reitor Rui Oppermann checking NETRA out
Picture Credit: Anderson Maciel
    • NETRA at the American Academy of Optometry
Image Credit:Dominick M Maino

NETRA Poster at AAO

    • NETRA at L.V. Prasad Eye Institute, India.

(Credit: Ethan Solomon)

(Credit: Ethan Solomon)

(Credit: Ethan Solomon)

(Credit: Ethan Solomon)

(Credit: Ethan Solomon)
    • NETRA at the International Centre for Eye Health – London School of Hygine & Tropical Medicine

Andrew Bastawrous

Matthew Burton

Hannah Kuper
    • NETRA with the OneSight Group at Kenya
  • NETRA at UNIFESP in Brazil (Photos by Caio Regatieri) 
NETRA in Brazil NETRA in Brazil NETRA in Brazil
    • NETRA at Tufts and New England Optometry School

Dr. Vicki Chen at Tufts
    • Author’s Individual Pictures
Vitor Pamplona demonstrates NETRA

Vitor Pamplona demonstrates NETRA
Vitor Pamplona demonstrates NETRA.

Vitor Pamplona demonstrates NETRA
Manuel Oliveira demosntrates NETRA

Manuel M. Oliveira demonstrates NETRA
Manuel M. Oliveira and Vitor Pamplona

Manuel and Vitor
Ramesh Raskar demosntrates NETRA

Ramesh Raskar demonstrates NETRA
Ramesh Raskar and Ankit Mohan

Ramesh and Ankit
Ankit Mohan

Ankit Mohan demonstrates NETRA
Ankit Mohan demonstrates NETRA

Ankit Mohan demonstrates NETRA
    • IDEAS Competition

Vitor Pamplona, Margaret McKenna, Ankit Mohan and Chika Ekeji.
Photo by Xun (Helen) Hou

Vitor Pamplona, Margaret McKenna, Ankit Mohan and Chika Ekeji.
Photo by Xun (Helen) Hou

Margaret McKenna, Chika Ekeji, Ankit Mohan and Vitor Pamplona.
Photo by Xun (Helen) Hou

Photo by Xun (Helen) Hou
    • First prototypes
People using the Samsung Behold setup

Photo: Michal Massey
PerfectSight: Prototypes ready for Siggraph
PerfectSight: Viewmaster Prototype
PerfectSight: Final Behold protytpe
    • First user study and experimental validation
PerfectSight: Using the Evaluation Setup PerfectSight: Camera Evaluation
    • First visit to an Optometrist
    • Initial Exploration
PerfectSight: Initial Tests PerfectSight: Initial Tests

Please visit the Camera Culture group page to see more projects.

Project Details