Transcript 05_17_10 Project Demonstrationx

QD Imaging
A 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):1011.
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. Epithelium
2. Bowman’s layer
3. Stroma
4. Descemet’s membrane
5. 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
•
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
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.
Case Study #2
•
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
1. “New goggles take hassle out of eye test.” Indo-Asian News Service August 9, 2008.
Case Study #3
•
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.
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.
1. “Perfect Sight – Increasing global accessibility to diagnostic services for eye care.” MIT Media Lab
(2010).
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 Sodium
Protein fluorescent dye binds directly to the basal membrane of the
corneal epithelium. Often used to find dry eye patches, abrasions,
ulcers, etc.
Camera
1. 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.
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.
Design
Goal: 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
RT  (Vs  VL ) / IL
Vs = 9 volts
VL = 3.4 volts
RT = 360 ohms
IL = 15.5mA < 20
mA max.
Design
Step 3: Filter out light with wavelength greater than 500 nm to
prevent interference with the fluorescent signal expected at 540 nm.
LEDs were covered
with a plastic primary
blue filter from Rosco.
Transmission spectra
shown here.
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
Design
Step 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 Front View
Total Dimensions
3D Side View
Total Dimensions
Head Dimensions
Design
Step 6: Assemble together – troubleshoot.
Front View
Rear View
Results
Test 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
Results
Test 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
Results
Test 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
Safety
The 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