I) retina then it is called myopia or short

I)                  
Abstract

 

The main idea of this project is to overcome the acuity error. Human
acuity error occurs because of unexpected focal points in the human eye. Human
eyesight varies based upon the focal points. 
These are usually corrected by using contact lens or spectacles. Doctor
uses retinoscopic mirror to detect the eye sight. Earlier, they use to keep
charts at a distance from patient and keep on asking the objects on the charts.
Now a days monitor displaying different sized images and patient have to
describe it..  But patient may loose
his/her interaction with the chart/monitor for moving it or showing different
slides, which occurs acute errors in the measure. Even through changing the
lens also interaction may loose.To test the eye sight of the patient in the
present system, we have manual testing and computerized eye testing. To make
sure that the error is accurate, after the doctor determines the eye sight of
the patient using the trial lens, he is given a tablet PC device which displays
the Snellen chart (blurred images), then the patient selects the blurred image
that looks similar to that when he have seen the image in the projector. Based
on the image selected the accurate acuity error of the patient is determined by
the doctor. The main objective of this project is to design application for
handheld device which calculates the human eye sight. This project is done by
Digital Image processing techniques in a practical approach, that would help us
to compute the accurate readings.

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II)               
Introduction

Actually there are many methods in measuring sight of
an eye. And also these methods are having
some acute problems. So, to overcome those problems, we are creating a user
interface. Human acuity error occurs
because of unexpected focal point(s) in the human eye. If the focal point falls
before retina then it is called myopia or short sight and if the focal point
falls beyond retina, then it is called Hyperopia or long sight. These are
usually corrected by using contact lens or spectacles. Doctor uses retinoscopic
mirror to detect the type of disease. Earlier, they use to keep the snellen
charts at a distance from patient and keep on asking the contents of the
charts.Patient’s interaction is found to be less which may result in errors while
assigning power to the spectacles-leveled equations, graphics, and
tables are not prescribed, although the various table text styles are provided.
The formatter will need to create these components, incorporating the
applicable criteria that follow.

III)              
Overview

      Doctor uses mirror to detect the type of
disease. Earlier, they use to keep the Snellen charts at a distance from
patiend and keep on asking contents of the charts. Patients interaction is
found to be less which may result in errors while assigning power to the
spectacles.

 

IV)              
Literature
survey

Anatomy of
Eye:

a) 
Section of Human Eye:

The eye is a slightly asymmetrical globe, about an inch in
diameter. The front part of the eye (the part you see in the mirror) includes:

·        
The Iris (the pigmented part)

·        
The Cornea (a clear dome over the iris)

·        
The Pupil (the black circular opening that lets light in)

·        
The Sclera (the white part)

·        
The conjunctiva (an invisible, clear layer of tissue the
front of the eye,except the cornea) Abbreviations and Acronyms

 

Description of Parts of Eye:

a) Cornea: The cornea is a clear,
dome-shaped surface that
covers the front of the eye. It is the first and most powerful lens
in the eye’s optical system. To keep it transparent the cornea contains no
blood vessels. Tears that flow over it and aqueous humor in the chamber behind
it keep it nourished.

 

b) Eye Ball: The
eye is like a little video camera  If
someone’s eyeball is larger then this, they will be nearsighted (myopic); if it
is smaller then this, they will be farsighted (hyperopic).

 

c)
Fovea: The fovea is an indentation in the center of the macula. Its diameter
is only 1.5 mm or about 1/16 inch. This small part of our retina is responsible
for our highest visual acuity. It is the center of our central vision.

 

d) Retina: The retina is the film of the eye. It converts light

rays into electrical signals
and sends them to the brain through

the
optic nerve. The sides of the retina are responsible for our peripheral vision.
The center area, called the macula, is used

for our fine central vision
and color vision. The retina is where

most
the problems leading to vision loss Occur.

 

Defects of Eye. :

 

Myopia(nearsightedness) :

 

This is a defect of vision in which far objects appear
blurred but near objects are seen clearly. The image is focused in front of the
retina rather than on it usually because the eyeball is too long or the
refractive power of the eye’s lens too strong. Myopia can be corrected by
wearing glasses/contacts with concave lenses these help to focus the image on the
retina.

Hyperopia
(farsightedness)

This is a defect of vision in which there
is difficulty with near vision but far objects can be seen easily. The image is
focused behind the retina rather than upon it. This occurs when the eyeball is
too short or the refractive power of the lens is too weak. Hyperopia can be
corrected by wearing glasses/contacts that contain convex lenses.

Astigmatism

 

This defect is when the light rays do not all
come to a single focal point on the retina, instead some focus on the retina
and some focus in front of or behind it. This is usually caused by a
non-uniform curvature of the cornea. A typical symptom of astigmatism is if you
are looking at a pattern of lines placed at various angles and the lines
running in one direction

Eye testing

Visual Acuity Test

            The
visual acuity test measures distance vision. If a patient already wears
glasses, the test would be performed while wearing the glasses or contact
lenses. The patient covers one eye and reads rows of letters aloud from a
chart, known as the Snellen chart, 20 feet away and then switches eyes. The

 smallest row that can be read is recorded as
the vision in that eye.

Using auto refractometer

At present doctors are using auto refractometer. This
instrument sends light into the patient’s eye and has ability to calculate the
readings of sphere, cylinder, axis of the eye.

Snellen Chart:

A Snellen chart is an eyechart used by eye
care professionals and others to measure visual acuity.Visual acuity = Distance at which test is made /
distance at which the smallest optotype identified subtends an angle of 5 arcminutes. The chart is at a distance of 20 ft, but a person with
normal acuity could be expected to read these letters at a distance of 40 ft.
This line is designated by the ratio 20/40. If this is the smallest line a
person can read, the person’s acuity is “20/40,” meaning in a very rough kind of way that this person needs to approach to
a distance of 20 ft to read letters that a person with normal acuity could read
at 40 ft.  

 

Lens Theory

1. Sphere: The sphere (Sph)
specifies the strength of lens required to correct your focus – a plus sphere
to correct long-sightedness (hyperopic – difficulty focusing on close objects)
and a minus to correct short sightedness (myopia – difficulty focusing on
distant objects.) The sphere is measured in Dioptre’s, your prescription
may have the word Plano or Pl or an infinity sign, this means that you are
neither long nor short sighted but zero power for the Sphere, however you may
have astigmatism – a CYL and AXIS on your prescription.

2. Cylinder: The CYL and AXIS compensate
for astigmatism. So what’s an astigmatism? An astigmatism is where the eye is
shaped slightly like a rugby ball or referred to as ‘toric’, not a perfect
sphere like a football. This just means the eye has difficulty focusing at
certain angles. This box maybe empty or have a plus or a minus value in
it. The measurement is the Dioptre. Most values range from +/- 0.25 to +/- 4.00
and will go up in steps of 0.25.

3. Axis: The AXIS is
only present if there is a value in the CYL box, the AXIS tells us where the
astigmatism is on your eye. The measurement is in Degrees. The values range
between 0 and 180 and may go up in steps of ½, 1, 5 or 10 degrees, we only show
the AXIS to a whole number but if you have a ½ degree on your prescription you
can list this in the additional information box when ordering.

 

Eyeglass Prescription:

An eyeglass prescription is an order written by an eyewear
prescriber, such as an optometrist or ophthalmologist, that
specifies the value of all parameters the prescriber has deemed necessary to
construct and/or dispense corrective lenses appropriate for a patient.

 

 

Proposed
system:

To
test the eye sight of the patient in the present system, we have manual testing
and computerized eye testing. To make sure that the error is accurate, after the
doctor determines the eye sight of the patient using the trial lens, he is
given a tablet PC device which displays the blurred images, then the patient
selects the blurred image that looks similar to that when he have seen the
image in the projector. Based on the image selected the accurate acuity error
of the patient is determined by the doctor. In this project we are using
SNELLEN CHART to determine the eye sight. This chart is the common and standard
chart which is used for testing of human acuity. The snellen chart contains
English letters at different sizes, where the patient should be able to
recognize them at different level of size.

 

      

 

References

·       http://journals.lww.com/optvissci/Abstract/1976/11000/New_Design_Principles_for_Visual_Acuity_Letter.6.aspx

·        
http://journals.lww.com/retinajournal/Abstract/2010/07000/Novel_Method_for_Analyzing_Snellen_Visual_Acuity.8.aspx

·       https://www.osapublishing.org/ao/abstract.cfm?uri=ao-49-20-3980

·        
https://link.springer.com/article/10.3758%2FBF03201553?LI=true