mNetra: A Fundoscopy based Optometer

Vijay Kumar

and Kolin Paul

Amarnath Khosla School of Information Technology, Indian Institute of Technology Delhi, New Delhi, India

Department of Computer Science and Engineering, Indian Institute of Technology Delhi, New Delhi, India

Keywords:

Mobile Phone, Ophthalmoscope, Funduscopy, Refractometer, Optometer, Visual Acuity, Refractive Error,

Fundus Image, Mobile Phone, Android.

Abstract:

Untreated refractive error in the eye is one of the leading causes of preventable blindness. The devices nec-

essary for this is expensive and often requires skilled technicians to operate. In this paper, a common off the

shelf ophthalmoscope has been modiﬁed and integrated with a smart phone to build an affordable optometer.

The device has been tested on a statistically signiﬁcant population with refractive error range from −8.00D to

+3.50D. We found a reasonably good correlation with other prevalent methods of measuring refractive error

in the eye.

1 INTRODUCTION

Worldwide more than 285 million people suffer from

some form of visual impairment (WHO.int, 2014).

Out of this 90% person live in developing countries.

The WHO has published a report in 2010 that, the

leading causes of visual impairment throughout the

world are the untreated refractive error (43%), unop-

erated cataract (33%) and glaucoma (2%)(WHO.int,

2014). There are an estimated 19 million children are

visually impaired and out of these, 12 million chil-

dren are suffering from refractive errors, a condition

that could be easily diagnosed and corrected (Pascol-

ini and Mariotti, 2011). Worldwide myopia is lead-

ing cause of low vision in young children, especially

school going children (Resnikoff et al., 2008; Sax-

ena et al., 2015). That can hinder education, produc-

tivity, personality development and career opportuni-

ties. The impact of blindness due to refractive error

(myopia) in young age is very high as compared to

cataracts or glaucoma in old age because it affects the

person for a longer span of time starting from child-

hood. It also places a greater socioeconomic burden

for developing countries like India.

The human eye is a sophisticated and complex

imaging system which is capable of dynamically

adjusting its focal power for wide ranges of dis-

tance. The eye’s refractive power is maintained by the

air-cornea interface (corneal shape dependent ﬁxed

power) and crystalline lens (provides an adjustable

extra power to the eye). Common refractive errors

found in the eye (in Fig.1) are due to imperfections

in eyeball shape, lens and cornea. The Myopic eye

shown in Fig.1(b), has an enlarged axial length (the

length from the posterior corneal surface to the retina)

or an increase in the refractive power of the eye lens

and focuses parallel rays to a point in front of the

retina rather than on it. In contrast, the Hyperopic

shown in Fig.1(c), has a short eye or insufﬁciently

curved cornea and focuses parallel rays at a point be-

hind the retina. A Healthy eye (In Fig.1(a)) on the

other hand, can focus parallel rays to a single point on

the retina.

The refractive disorder is commonly treated us-

ing appropriate corrective lenses such as eyeglasses

or contact lens. For this to be possible a periodic but

comprehensive examination of the eye is mandated

especially in school and primary health care centers.

To do this, three diagnostic methods are primarily

used to evaluate the refractive error.

• Subjective Methods: Its screening result relies

upon the response and reaction of a patient, e.g.

patient’s judgment of sharpness or blurriness of a

test object (Snellen eye chart).

• Objective Methods: This method doesn’t depend

on the feedback from the patient. The optical in-

strument that can ﬁnd out the refractive error au-

tomatically, e.g. refractometer and optometer.

• Hybrid Methods: Currently, this is the most

common way to determine refractive error to pre-

scribe corrective lens. It consists of two steps. An

objective method is used in the ﬁrst step followed

by the subjective method to determine the accu-

Kumar, V. and Paul, K.

mNetra: A Fundoscopy based Optometer.

DOI: 10.5220/0005698500830092

In Proceedings of the 9th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2016) - Volume 5: HEALTHINF, pages 83-92

ISBN: 978-989-758-170-0

(a) Healthy eye (b) Myopia (c) Hyperopia

Figure 1: Common retinal refractive error in the human eye.

rate corrective lens.

For the above have a method of refractive error

screening ophthalmologists used optical technology

based diagnostic instruments such as auto refractome-

ter, focometer, retinoscopy, and wavefront analyzer

can be used for measuring the refractive power of the

human eye (Ko and Lee, 2006; Berger et al., 1993;

Dave, 2004) is bulky, expensive, sophisticated, highly

application speciﬁc and needs a trained technician to

operate these devices.

Recently, portable devices (smartphones and

tablets) have emerged as a versatile mobile computing

platform with high resolution display, which provides

us a new opportunity for mobile health (mHealth).

Paul et al. (Paul and Kumar, 2015) use the oph-

thalmoscope and mobile phone to develop an afford-

able fundus imaging based eye care device for glau-

coma screening. Peek Vision provides high qual-

ity tools for professional eye exams using a mobile

phone (PeekVision, 2015). It can be used to diagnose

cataracts, visual acuity and eyesight, colour and con-

trast of the eye. In (Pamplona et al., 2010; Cameracul-

ture.media.mit.edu, 2015), NETRA and CATRA pro-

vide affordable cell phone attachment that measure

the eye refractive power and cataracts information. It

creates an inverse Shack-Hartmann sensor based on

a ”high resolution programmable display and com-

bines inexpensive optical elements, interactive GUI,

and computational reconstruction”. Currently, Smart

Vision Labs have developed a smartphone based af-

fordable auto refraction technology based on Wave-

front aberrometry (Shack Hartmann) to measure the

refractive error of the eye (Zhou and Kassalow, 2010).

In this paper, we introduce a novel low cost, hand

held, portable, reliable, accurate and interactive in-

strument mNetra, based on view dependent display

to determine the refractive error in the human eye for

fast and accurate screening. The ophthalmoscope and

smart phone based device tries to get the best im-

age/video frame of the retinal scan after proper adjust-

ment of ophthalmoscope lens focusing wheel. This

paper presents,

• A methodology to do refraction of the eye for

screening using a mobile phone an ophthalmo-

scope.

• An Android based application has been devel-

oped, which allows collection of patient details

and perform the computation for refraction. A

generic Regression (R) model to demonstrate that

an off the shelf ophthalmoscope can be attached

to the mobile phone is also described in the paper.

We believe that our funduscopy based optometry

increase the usability and application of ophthalmo-

scope and mobile phone. It provides a suitable solu-

tion for affordable eye care in developing countries.

And this is particularly useful in prescribing correc-

tive lenses for patients who are unable to undergo a

subjective refraction that requires a judgment and re-

sponse from the patient (e.g. a person with communi-

cation problems or severe intellectual disabilities).

2 mNetra

The mNetra is a monocular, funduscopy based hand-

held optometry which uses the principle of ophthal-

moscopy to measure refractive error. The optician

uses the manual rotary wheel to focus the image on

the retina. This concept has been explored to do same

automated refraction in the mNetra. We describe the

methodology in the following subsection.

The Mobile ophthalmoscope is an optoelectron-

ics handheld, an affordable lightweight instrument for

screening the interior structure of the eye, especially

the back part of the eye (fundus: which includes

the retina, optical disk, optical cup, blood vessel and

fovea etc.). This also supports computation and com-

munication needs for processing and sharing of med-

ical data. This optoelectronic device has been made

possible by integrating the smartphone and an oph-

thalmoscope.

The total optical power of a multiple lens system

is equal to the linear summation of individual lens

power. In Fig. 4(b), ophthalmoscopy based screening

system’s optical unit consist of the ophthalmoscope,

subject (patient) eye and a camera rather than ophthal-

moscope, subject eye and observer eye (in Fig. 4(a)).

This new multiple lens optical system is in equilib-

HEALTHINF 2016 - 9th International Conference on Health Informatics

Figure 2: Basic concept of retinoscopic refractometer :In this ﬁgure, fundus image quality is detonated with increment or

decrement of focusing lens focus.

rium condition (total power is zero) for the healthy

eye with no refractive error. A small change in the

power (δP) of any lens in this system will disturb the

equilibrium of the whole optical system.To overcome

and nullify this problem, we should use the other lens

of opposite power (−δP) so it will again maintain the

equilibrium.

We use this concept to develop a funduscopy

based optometer using an ophthalmoscope and mo-

bile phone. This has been made possible by making

some changes in the basic ophthalmoscope and em-

bedding mobile phone. In Fig. 4(b) of the new opti-

cal system, the observer’s eye is replaced by CMOS

camera module (Mobile phone) and focusing lens can

be used to correct the ocular error i.e. due to sub-

ject/patient eye refractive alignment. The focusing

lens position is controlled by the ophthalmoscope fo-

cusing lens wheel (in Fig. 5(c)). In Fig. 2, we show

how the quality of the image frame depends on the

focal length of the focusing lens set with the focusing

wheel of the ophthalmoscope.

Mathematically, refractive error corrective power

(P) is the function of focusing lens position (x).

Where, x is the function of focusing wheel angle θ.

So that,

P = F(x) = F(g(θ)) = F(r × θ) (1)

Where, r is the radius of the focusing wheel. and in

another way it can be written as P =

and from the

equation 23, P ≡ P

2.1 Functional and Architectural

Overview

In this section, we outline the design of a mobile oph-

thalmoscope based optometer subjected to the con-

straints of Cost, Bulkiness, Portability and Adopt-

ability.The device is based on the Smartphone. This

has been made possible by embedding the Optical

(Ophthalmoscope and CMOS camera), Computing

Figure 3: Working diagram of ophthalmoscope based hand

held refractometer.

(Mobile phone and Microcontroller), Sensor (poten-

tiometer based position sensor) functionality in a sin-

gle device. As illustrated in Fig. 3, the device consists

of different functional block which are described be-

low:

• Optical System: This block capture the magni-

ﬁed fundus image with a CMOS camera –typical

CMOS in nature. The key innovation in the solu-

tion is to replace the eye of ophthalmologist by of

a smartphone camera based CMOS sensor to cap-

ture the image of patient’s fundus. We use a smart

phone of a high resolution (≥5MP) camera for the

same. We have also designed and build a custom

mobile phone holder Rapid Prototype (RP) model

to attach the Smartphone camera to the ophthal-

moscope.

• Computing Unit: This functional unit consists of

a smart phone processor and the microcontroller

for processing the mobile phone data (CMOS cap-

ture video/image) and controlling and processing

of focusing lens sensor output respectively. Mo-

bile phone centralized processing and control unit

is able to satisfy high compute power required

for image processing, result visualization and data

sharing that are part of the application software.

mNetra: A Fundoscopy based Optometer

• Sensory System: To measure the ophthalmo-

scope focusing lens position we used a sensor

module that will measure the current position of

focusing wheel. In Fig. 3, it consists of Position

sensor, Microcontroller and Bluetooth module

to share the current status of focusing wheel to the

mobile phone for further processing and represen-

tation.

2.2 The Mathematical Basis

Ophthalmoscopy based optometer’s optical setup and

working rays diagram are shown in Fig. 4. It consists

of the ophthalmoscope, subject eye and CMOS sen-

sor (mobile phone camera). In this optical setup, we

should consider the position of all lenses, i.e. magni-

fying lens (M

= {M

}), subject eye (E

) and

CMOS sensor (O

) are ﬁxed except focusing lens

). The focusing lens is used to overcome and nul-

lify the refractive error of the subject eye lens so that

image properly focused on CMOS sensor. In this

section, we explain the mathematical relationship be-

tween focusing lens (F

) position (x) and subjective

eye power (P = 1/ f

For subject lens E

, f

(2)

from the lens maker formula.

Similarly for lens M

, f

(3)

where, x

= x

+ q

. Hence 3 becomes

+ q

(4)

Similarly for lens F

, f

⇔

(5)

where, x

= X −x + q

. Hence 5 becomes,

(X − x + q

)

(6)

Similarly for lens O

, f

⇔

(7)

where, x

= (x = x

) + q

. Hence 7 becomes,

x + q

(8)

Rearranging 2 we get

− f

(9)

which implies q

is a function of f

= F( f

) (10)

Similarly

− f

+ q

)

+ q

) − f

(11)

⇒ q

= F(q

) = F(F( f

)) ⇒ q

= G( f

) (12)

where,

G = F(F) (13)

From 5 and 6

− f

(X − x + q

)

(X − x + q

) − f

(14)

= H(G) =

(X − x + G)

(X − x + G) − f

(15)

Also from 7 and 8 :

− f

(x + q

)

x + q

− f

(16)

Similarly

(x + H(G))

x + H(G) − f

(17)

= I(H,x) (18)

and q

is constant. and from 17

x =

H(G)− q

H(G)+ f

− f

)

(19)

Assuming the position and focal length of all the

lenses are ﬁxed except for the focussing lens F

. We

obtain from 9 and 11

− f

)

− f

) − f

⇒ q

− f

) + f

)

− f

) + f

) − f

− f

)

(20)

Using equations 14 and 16

⇒ q

(x + q

)

x + q

− f

(x + (

(X−x+q

)

(X−x+q

)− f

))

x + (

(X−x+q

)

(X−x+q

)− f

) − f

HEALTHINF 2016 - 9th International Conference on Health Informatics

(a) Optical system of ophthalmoscope used for funduscopy

(b) Optical system of mNetra

Figure 4: Optical rays diagram for (a) ophthalmoscope and (b) mNetra : Retinal image formation on observer eye/CMOS

sensor in ophthalmoscope from the rays coming from the subject eye.

⇒ q

(Xx − x

− 2 f

x + f

x) + q

( f

X − f

− f

) − f

X − X x f

+ f

− 2 f

(−q

x − q

( f

− f

) − f

x + f

)

(21)

Combining equation 12 and 20,

⇒

− f

) + f

)

− f

) + f

) − f

− f

)

(Xx − x

− 2 f

x + f

x) + q

( f

X − f

− f

) − f

X − X x f

+ f

− 2 f

(−q

x − q

( f

− f

) − f

x + f

)

Rearranging the above expression and we get,

(−q

x − q

( f

− f

) − f

x + f

)( f

+ f

)

−(q

(Xx − x

− 2 f

x + f

x) + q

( f

X − f

)

− f

X − Xx f

+ f

− 2 f

x)(x

+ f

)

(−q

x − q

( f

− f

) − f

x + f

) − (q

(Xx

−x

− 2 f

x f

) + f

x) + q

( f

X − f

)

− f

X − Xx f

+ f

− 2 f

x)(x

− x

+ f

)

(22)

We can write, 22 as a

N(x)

D(x)

+ N

x + N

+ D

x + D

(23)

where,

= (q

− f

)(x

+ f

)

= (−q

− f

)( f

+ f

) − (x

+ f

)

X − 2q

+ q

− X f

− 2 f

)

= ( f

− q

( f

− f

))( f

+ f

) + ( f

−q

( f

X − f

))(x

+ f

)

= (q

− f

)(x

− x

+ f

) f

= −q

− f

− q

X + (2q

− q

+X f

+ 2 f

)(x

− x

+ f

)

= −q

( f

− f

) + f

+ ( f

−q

( f

X − f

))(x

− x

+ f

)

Now from the 22 the lens power P

is ,

= 1/ f

D(x)

N(x)

+ D

x + D

+ N

x + N

(24)

From the above mathematical expression, we see

that the patient eye refractive power (P

is function

of x. and P

. We used this concept and mathe-

matical relation to develop a mobile ophthalmoscope

mNetra: A Fundoscopy based Optometer

(a) (b) (c) (d) (e) (f)

Figure 5: Ophthalmoscope based funduscope: (a) Mobile phone holder attached with ophthalmoscope (b) Mobile phone is

attached with ophthalmoscope using this holder and (c) Focusing wheel of ophthalmoscope: Its is used to focussing the image

onto the mobile phone camera. In funduscopy based refractometer used this wheel’s rotation to ﬁnd out refractive error of the

eye/lens. Position Sensor module (d)to (f):Position sensor interfaced with ophthalmoscopy based refractive error screening

device for communication with Android application using blue tooth.

based affordable handheld refractive error screening

device.

We describe the functional aspects of the design

in the next section.

3 DETAIL DESIGN

In this section, we outline the design of funduscopy

based optometer using the handheld ophthalmoscope,

mobile phone and its application software. This has

been made possible by integrating the optical (imag-

ing unit: ophthalmoscope and mobile phone camera),

computing (micro-controller and mobile phone) and

sensor (position sensor) unit in a single device shown

in Fig. 5. The three major components are described

below.

3.1 Ophthalmoscope

The ophthalmoscope is an optical instrument for ex-

amining the interior structure of the eye, especially

the back part of the eye (fundus), which includes

the retina, optical disk, optical cup, blood vessel and

fovea etc. An Ophthalmoscope is of two kinds, direct

and indirect. We use the PanOptic ophthalmoscope

(Fig. 6(a)) which is very similar to the traditional oph-

thalmoscope (Welchallyn.com, 2015).

3.2 Mobile Phone

For image capturing, image processing and data shar-

ing, we need a system that has the capability to per-

form all these jobs. We use a Smart-phone, which

has these features along with communication and data

sharing capability. It full ﬁlls the requirement of (a)

High resolution CMOS camera (b) Centralised Con-

trol System to synchronise and control all process (c)

High computation capability to perform image pro-

cessing (d) high resolution display and (e) sharing re-

(a) (b)

Figure 6: (a) Pan-Optic Ophthalmoscope and (b) Mobile

phone holder rapid prototype model.

sult and data with remote users. We have used an An-

droid based Samsung Galaxy S-3 smartphone.

Mobile Phone Holder

The smartphone camera is able to capture fundus im-

age only when if it is properly interfaced with a hand-

held portable ophthalmoscope. In this device, the

physician’s eye (Fig. 4(b)) is replaced by Smartphone

Camera. For that a special phone holder as shown in

Fig. 6(b) has been designed. The design of this was

done so that the functionality of the basic phone was

not impaired.

The material used in RP for building the case of

SLS. The mobile case, when integrated with the Oph-

thalmoscope, is shown in Fig. 5(b).

3.3 Rotary Detail or Sensor Module

In the Fig. 7, ophthalmoscope’s rotary wheel is used

to focus the retinal image on CMOS sensor camera.

This rotary wheel is connected to the focusing lens

such that it controls its position (x). It follows the re-

lation: x = r × θ where, r and θ are the radius and

rotational angle of the focusing wheel of an ophthal-

moscope.

To measure the precise position of the rotary

HEALTHINF 2016 - 9th International Conference on Health Informatics

Figure 7: Housing of the position sensor inside the oph-

thalmoscope to measure the lens position. The sensor will

measure the rotational movement (θ) of the focusing wheel.

wheel we have used a high precision position sensor

module. In Fig. 5 & Fig. 7, this module consists

of a potentiometer, a micro-controller (Arduino or

Intel Galileo Gen 2) board and a Bluetooth module

(RN42N) is used. This senses the current status of fo-

cusing lens position (x) as a function focusing wheel’s

angle (θ) and sends the processed data to the mobile

phone via Bluetooth. The sensor module uses embed-

ded software to control and communicate the wheels

rotational information and focusing lens data to the

mobile phone.

An Android application has been developed to

provide an interactive testing environment to the de-

vice. It consists of two sections, one is to display the

fundus scan (retinal scan ) and another one is to dis-

play the current status of focusing lens (refractive er-

ror value of the eye).

4 RESULTS

This section discusses the experiments conducted in

the laboratory and a hospital for the validation of our

new ophthalmoscope based funduscopy type optome-

ter. This has been done in two stages. In the ﬁrst

stage, we have performed a lab based primary con-

cept validation (Fig. 8). Here we put different lenses

in front of mobile phone based fundus imaging de-

vice and then focus the image on the CMOS sensor

using the focusing wheel. This enables us to closely

relate the mNetra refractive power (P(x)) expression

24 with potentiometer reading. For this, experimen-

tal data and the result are shown in Table. 1. It is

clear that the ophthalmoscope focusing wheel read-

ing depends on the power of the lens in the test. In

the second stage, we have performed the testing and

validation with real (subjective) data (Patients) in the

(a) (b)

Figure 8: mNetra Concept validation test: (a) Optical setup

of the laboratory and (b) the optical lens.

hospital. For this experiment, we chose volunteers in

the age group 20-45 year. The volunteers were se-

lected randomly to cover a range of refractive error

power.

4.1 Test Methodology

For the above two scenarios, we followed a standard

predeﬁned test procedure. In the ﬁrst stage, we used

an optical eye model (Fig. 8(a)) in which variable lens

(+3.5D to -6.0D) (Fig. 8(b)) and the object was placed

at a distance of 1 meter. And for device validation,

we estimate it’s lens power (shown in Table. 1) using

our funduscopy based method. With the second stage

of subjects, we compared our result with the hybrid

method of refractive error screening. The data were

collected using this protocol.

1. The lighting in the room is dim/dark: This ensures

that person pupil’s is dilated to the maximum.

2. The person is sitting in the rest condition.

3. To minimize the eye lens power measurement er-

ror, observer asks the patient to focus his/her eye

on distinct object and inﬁnity. This helps in accu-

rately performing the refraction.

4. The observer/technician measuring the blur in the

image using the focusing wheel.

5. Take the reading of focusing wheel when the fun-

dus image quality is best as compared to previous

Table 1: Experimental results: Lens power measurement

using mNetra.

S.No Lens Power (D) mNetra reading

01. +3.5 2.0

02. +2.0 1.25

03. +1.0 0.75

04. 0.0 0.25

05. -1.0 0.0

06. -2.50 -0.25

07. -3.5 -1.0

08. -4.0 -1.75

09. -5.25 -2.25

10. -6.0 -2.75

mNetra: A Fundoscopy based Optometer

Figure 9: Regression and Curve ﬁtting plot of the actual

lens power vs mNetra measured power. R value for mNetra

readout is (0.98634).

Table 2: Curve ﬁtting parameter: Lens power P(x) mea-

surement using mNetra.

General model

Rational model :

P(x)or f (x) = (p1 ∗ x

+ p2 ∗

x + p3)/(x

+ q1 ∗ x +q2)

Coefﬁcients

(with

p1 = −9.967(−54.24, 34.3)

95% conﬁdence p2 = 42.38(−11.15, 95.91)

bounds) p3 = −16.33(−40.82, 8.148)

q1 = −5.104(−27.09, 16.88)

q2 = 14.44(−9.752, 38.64)

Goodness of ﬁt SSE: 1.276, R-square: 0.9861,

Adjusted R-square: 0.9749,

RMSE: 0.5052

all images shown on mobile screen.

6. Repeat 3-5 again to take a retinal scan of another

eye also.

4.2 Data Analysis

The data that is collected is analyzed for accuracy and

efﬁciency in use for practical settings. The ﬁrst set of

trials gives the test data for obtaining the correlation

between the potentiometer based readout and the ac-

tual power of the subject lens.

Experiments for the lens of power range +3.5D to

-6.0 were performed and the data are shown in Table

1. The data is subject to a curve ﬁt as shown in Fig. 9.

For this regression analysis, we get the regression

coefﬁcient 0.98634 and curve ﬁtting result is shown

in table 2. This shows that the potentiometer readout

is able to track closely the actual power of the subject

lens.

Table 3: Subjective trial of device: Refractive power of eye

estimated using hybrid method and using funduscopy based

device.

Sex Age left

eye

power

(D)

left

eye

mNe-

tra

read-

ing

right

eye

power

(D)

right

eye

mNe-

tra

read-

ing

1 F 35 -1.5 -1.33 -0.75 -1.17

2 F 36 -0.25 -0.42 -0.25 -1.33

3 M 24 -2.25 NA -1.25 NA

4 M 26 -0.5 -1.125 -0.5 -1.75

5 M 25 -1.25 -1.875 -2.25 -6.25*

6 M 24 -2.25 -2.25 -2.0 -1.25

7 M 23 -0.25 0.0 +3.5 +1.75

8 M 24 -4.0 -3.5 -4.0 -4.0

9 M 23 -8.0 -6.0 -8.0 -6.25

10 F 24 -6.5 -5.25 -6.5 NA

11 M 23 -2.25 -1.75 -2.75 -2.125

13 F 27 -4.25 - 3.0 -4.50 NA

14 M 20 -2.75 -2.75 -2.50 -2.125

*/NA Data sets are not considered for analysis

Figure 10: Regression analysis of eye lens power using an

ophthalmoscope and Regression coefﬁcient R = 0.9749.

Subjective

In the second stage, data are collected from volunteers

using our device and hybrid method for refractive er-

ror estimation (shown in table.3) is used.

Validation

For the validation, we compared mNetra reading (D

)

with eye refractive power (i.e. true power D

) shown

in table 5. For this, we compute the estimated power

using the mNetra power Equation 24 and then ﬁnd out

the error power (D

= D

−D

). We got the Standard

HEALTHINF 2016 - 9th International Conference on Health Informatics

Figure 11: In this graph refractive power (D) vs mNetra

potentiometer reading’s relation ﬁtted with rational function

f (x) = P(x).

Table 4: Curve ﬁtting parameter’s value for a rational model

of expression 24 with subjective trial.

General

model

Rational

model

P(x)or f (x) = (p1 ∗ x

+ p2 ∗ x +

p3)/(x

+ q1 ∗ x +q2)

Coefﬁcients p1 = −2.393e + 04(−9.676e +

07,9.672e + 07)

(with 95% p2 = 5.816e + 04(−1.291e +

08,1.292e + 08)

conﬁdence p3 = −3.215e + 04(−4.932e +

07,4.925e + 07)

bounds) q1 = −3.472e + 04(−1.404e +

08,1.403e + 08)

q2 = 5.469e + 04(−8.377e +

07,8.388e + 07)

Goodness

of ﬁt

SSE: 3.697, R-square: 0.9505, Ad-

justed R-square: 0.9381, RMSE:

0.4807

Deviation, Mean, and RMS value for refractive error

power (D

) is 0.4019, 0.4344 and 0.5686.

Table 5: Subjective refarctive data for the validation and

performance (error power) analysis of mNetra.

mNetra

Read-

ing

True

power

Estimated

power

Error power

) (D

) D

= P(D

) D

= D

− D

-0.625 -0.75 -1.0191 0.2691

-0.25 -0.50 -0.7604 0.2604

-0.67 0.0 -1.0501 1.0501

-0.25 0.0 -0.7604 0.7604

-2.90 -2.25 -2.5875 0.3375

-2.67 -2.50 -2.4290 -0.0710

5 CONCLUSION AND FUTURE

WORK

This paper discusses the design and use of an Oph-

thalmoscope based Optometer/ refractometer which

can be used for affordable eye care. It has been shown

that the application of this mobile phone based fundus

imaging device can be used to determine retina im-

pairment and ametropias. Primary experimental data

also suggest its usability and easy handling capabil-

ity. It can be used in primary health care center, OPD

and Healthcare camp where fast screening is neces-

sary. On the basis of stage one result, the device also

can be used to measure the optical power of the lens.

Some of the features like image/video stabiliza-

tion available in the modern phone can be integrated

in the application in the future. This basic infrastruc-

ture can be used for screening of other ocular dis-

eases.

REFERENCES

Berger, I. B., Spitzberg, L. A., Nnadozie, J., Bailey, N.,

Feaster, J., Kuether, C., Tran, M., and Swann, S.

(1993). Testing the focometer-a new refractometer.

Optometry & Vision Science, 70(4):332–338.

Cameraculture.media.mit.edu (2015). Netra/catra,

camera culture; http: //cameraculture.media.mit.

edu/cubeportfolio/netracatra/.

Dave, T. (2004). Automated refraction: design and applica-

tions. Optom Today, 48:28–32.

Ko, D.-S. and Lee, B.-H. (2006). Optics of refractometers

for refractive power measurement of the human eye.

Journal of the Optical Society of Korea, 10(4):145–

156.

Pamplona, V. F., Mohan, A., Oliveira, M. M., and Raskar,

R. (2010). Netra: interactive display for estimating

refractive errors and focal range. In ACM Transactions

on Graphics (TOG), volume 29, page 77. ACM.

Pascolini, D. and Mariotti, S. P. (2011). Global estimates of

visual impairment: 2010. British Journal of Ophthal-

mology, pages bjophthalmol–2011.

Paul, K. and Kumar, V. (2015). Fundus imaging based af-

fordable eye care. In Proceedings of the International

Conference on Health Informatics, pages 634–641.

PeekVision (2015). Professional eye exams from a

phone.http://www.peekvision.org/.

Resnikoff, S., Pascolini, D., Mariotti, S. P., and Pokharel,

G. P. (2008). Global magnitude of visual impairment

caused by uncorrected refractive errors in 2004. Bul-

letin of the World Health Organization, 86(1):63–70.

Saxena, R., Vashist, P., Tandon, R., Pandey, R., Bhardawaj,

A., Menon, V., and Mani, K. (2015). Prevalence of

myopia and its risk factors in urban school children in

delhi: The north india myopia study (nim study). PloS

one, 10(2).

mNetra: A Fundoscopy based Optometer

Welchallyn.com (2015). Welch allyn panoptic oph-

thalmoscope: A difference you can see. http://

www.welchallyn.com/promotions/panoptic/def

ault.htm.

WHO.int (2014). Who—visual impairment and blindness,

fact sheet no 282; http://www.who.int/mediacentre/

factsheets/fs282/en/.

Zhou, Y. and Kassalow, J. (2010). Preliminary evaluation

of svone autorefractor for low order refractive errors.

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