QD ImagingA Rapid and Affordable Eye Diagnostic Camera

Project Demonstration May 17, 2010

By Shivam Shah

Outline

1. Introduction

2. Prior Art – Case Studies

3. Project Design

4. Preliminary Results

5. Cost

6. Future Work

7. Live Demonstration

Global Blindness

• 314 million people are visually impaired including 45 million that are blind.

• Over 87% of the visually impaired live in the developing world.

• Over 85% of visual impairment cases are preventable.

• On average there is less than 1 ophthalmologist per million of people living in Africa.

1. “The prevention of blindness: report of a WHO Study Group.” World Health

Organization (1973):10-11.2. Foster A, Johnson G. “Blindness in the developing world.” British Journal of

Ophthalmology 77 (1993):398-399.

Cornea

Corneal tissue is arranged in five layers which are (from outside in):1. Epithelium2. Bowman’s layer3. Stroma4. Descemet’s membrane5. Endothelium

Epithelial cells anchor to the basement membrane part of the epithelium.

1. “Facts about the Cornea and Corneal Disease.” National Eye Institute (2010).

Corneal Afflictions

• Second primary cause of blindness behind cataracts.

• Corneal infections arise from a foreign object in the eye or bacteria from a dirty contact lens. Reduce visual clarity and can lead to blindness.

• Dry eye is caused by the absence of proper lubrication by tears. Allergies and contact lens wear has increased number of dry eye cases.

• Corneal dystrophy occurs when one or more parts of the cornea lose transparency. Over 20 dystrophies exist.

1. “Facts about the Cornea and Corneal Disease.” National Eye Institute (2010).

Case Study #1

1. Keefe JE, et al. “A simplified screening test for identifying people with low vision in developing countries.” Bulletin of the World Health Organization 74(5) (1996):525-532.

• Screening kit includes visual acuity card, a pinhole mask, and two manuals.

• 85% sensitivity and 96% specificity when compared to Snellen test

• Expected to cost less than $1.

• Problem: No Ocular Disease

Case Study #2

1. “New goggles take hassle out of eye test.” Indo-Asian News Service August 9, 2008.

• Goggles determine quality of peripheral vision which can be used to diagnose glaucoma and optic nerve damage.

• Measure patient’s reflex to visual stimuli automatically.

• Can be used anywhere with a computer hook-up.

• Expected to cost more than $100.

• Problem: $$$, No Ocular Disease

Case Study #3

1. “Perfect Sight – Increasing global accessibility to diagnostic services for eye care.” MIT Media Lab (2010).

The optical piece is attached to the cell phone. Tasks on the cell phone are completed with audio feedback and controls. The prescription is determined by the cell phone application.

• Retrofitted cell phone with $1 optical piece provides prescription directly.

• Affordable, High Scalability, Safer as no lasers or eye drops needed.

• Problem: Absolute error is 0.5 diopters, No ocular disease information.

Major Problem

The primary issue is that solutions in case studies do not offer information to help diagnose ocular disease or identify the cause of visual impairment.

Fluorescein SodiumProtein fluorescent dye binds directly to the basal membrane of the corneal epithelium. Often used to find dry eye patches, abrasions, ulcers, etc.

1. Williams R. “The Sodium Fluorescein Technique.” Medical and Science Photography (2002).

2. Grossman J. “A simple technique for fluorescein photography.” Plastic and Reconstructive Surgery 67(2) (1981):257-258.

Camera1. A light source covered

with a blue filter excites the fluorophore.

2. Both blue light and yellow light are reflected towards the camera.

3. A yellow barrier filter passes only the fluorescent light to the camera.

DesignGoal: Adapt a web camera with a USB interface for eye diagnostic testing of the cornea with fluorescein sodium.

Step 1: Obtain a web camera with a USB interface. Step 2: Need a blue light source. 2 LEDs + 360 ohm resistor + 9 volts

LLsT IVVR /)(

Vs = 9 voltsVL = 3.4 voltsRT = 360 ohmsIL = 15.5mA < 20 mA max.

DesignStep 3: Filter out light with wavelength greater than 500 nm to prevent interference with the fluorescent signal expected at 540 nm.

1. Williams R. “The Sodium Fluorescein Technique.” Medical and Science Photography (2002).

2. Grossman J. “A simple technique for fluorescein photography.” Plastic and Reconstructive Surgery 67(2) (1981):257-258.

3. “Color filter technical data spreadsheet” access: http://www.rosco.com/us/filters/permacolor.asp

LEDs were covered with a plastic primary blue filter from Rosco.

Transmission spectra shown here.

DesignStep 4: Need to filter only fluorescence – light around 540 nm.

Used a yellow band-pass filter which passes light with wavelength 530-560 nm.

Step 5: Need housing for device.

Used Pro/ENGINEER and SolidWorks to make housing. Schematics with dimensions shown on next slide.

3D Side View

3D Front View

Total Dimensions

Head Dimensions

Total Dimensions

DesignStep 6: Assemble together – troubleshoot.

Front View Rear View

ResultsTest 1: A healthy eye was imaged with the diagnostic camera without any fluorescent staining or yellow light filter (left). The same healthy eye was imaged without any fluorescent staining but with the yellow filter (right). Darkness is good!

– Stain– Yellow Filter

– Stain+Yellow Filter

ResultsTest 2: A paper was stained with fluorescein sodium. The paper was imaged without the yellow filter (left) and the with the yellow filter (right). Brightness is good!

+ Stain– Yellow Filter

+ Stain+ Yellow Filter

ResultsTest 3: A healthy eye was stained with fluorescein sodium. The eye was imaged without the yellow filter (left) and with the yellow filter (right). No fluorescence confirms eye is healthy!

+ Stain– Yellow Filter

+ Stain+ Yellow Filter

SafetyThe maximum permissible exposure (MPE) to the eye was determined to be 2.92J/cm2

The power generated by one LED is the current multiplied by the voltage: 0.016 A*3.4 V= 0.0544 W.

The total power of both LEDs is 0.1088 W.

Assuming that the area of the eye is 2 cm2, the LEDs provide 0.0544 W/cm2.

Dividing the MPE of 2.92 J/cm2 by 0.0544 W/cm2 gives the maximum exposure time of the device – 53s.

1. Calkins JE. “Retinal light exposures from ophthalmoscopes, slit lamps and overhead surgical lamps.”

Cost Breakdown

The cost of the prototype was $9.24, but this included many free components.

The bulk manufacturing cost would be $11.88.

Pricing is affordable for developing world.

Future Steps 1. Manufacture 50 devices to assist in clinical testing and

determine the reproducibility of the design.

2. Clinical study (#1) to determine if the images provided by the eye diagnostic camera are comparable to images provided by more expensive adapted slit-lamp biomicroscopes. The study will help determine if this device can be used by eye specialists to diagnose ocular diseases.

3. Clinical study (#2) to determine which ocular diseases can be identified and the maximum speed of screening. The corneal

abrasion is visible due to staining and imaging with fluorescein sodium.

1. Sowka J, et al. Handbook of Ocular Disease Management Jobson. Publishing LLC. (2001).

Demonstration