INTRODUCTION: of these aberrations are given in spherical
June 5, 2019
Eyes are the most important organ of our
human body as they provide vision to our brain for the understanding and
formation of the objects and things around us. Every organ in the body tends to
deteriorate, so does the eye. The difficulty that arises is the poorer visual
acuity of the eye, whether it is said to be nearsightedness or farsightedness.
The patients suffering from myopia (nearsightedness) can see distant objects
clearly but face difficulty in viewing the nearer objects. The patients
suffering from hyperopia (farsightedness) can see near objects clearly, but the
distant ones are not clear. The basic device used for the correction of these
aberrations is a phoropter device, that has a series of multiple lenses that
are switched before the patient eye, the lens that provides better vision is
prescribed by the optician. The values of these aberrations are given in
spherical and cylindrical lens power. Nearsighted has minus in their value,
while farsighted has positive in their value.
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Keeping in mind the following eye
problems, the first device made was a manual phoropter it has a huge structure
that was not mobile. It was created by Henry De Zeng in 1921. The common name
used for the ophthalmic device is Refractor. It is a medical device used by eye
care professionals. The procedure starts as the person sits behind the
phoropter and looks through it at an eye chart known as Snellen’s chart that is
placed at a fixed distance (6m or 20ft). The optician changes the power of
lenses according to the subject’s feedback. When the person’s vision has been
corrected then the optician prescribed the number of the lenses.
The main idea of our project is to make a
device which can go into remotely visited areas. Our device is Automated
Phoropter Device which works on the principle of bifocal lenses. The idea of
miniaturizing this device is to make it portable and accessible to unprivileged
people. The design made is very simple and comparatively precise and
constructed using basic optical and engineering techniques. The main component
of the device are bifocal lenses which has a range of -6 to +3 diopters. The
driving mechanism is controlled by micro controller Arduino with two multiturn
potentiometers connected to its respective lenses. On each side of the frame
design two knobs are attached for the movement of lenses. The lenses slide over
as the knob is rotated. Each user accommodates their vision according to their
acuity and the reading in diopters is shown on the LCD.
During the 17th century, lenses were the
main source to determine the optical correction and relied upon subjective
feedback. Since the 1800’s, practitioners of clinical refraction have been
trial lenses with
objective or subjective techniques to arrive at a final refractive
The scope of optometry expanded, but the subjective
refraction remained a major part of the vision examination.
In 1915, Baush and Lomb started to make
trial cases (known as the precision trial case) and trial frames. The precision
trial case lenses had a diameter of only 15 mm.
The first phoropter that in any way
resembled today’s phoropters was developed by De Zeng.
Most modern refracting units contain
the sphere and cylindrical lenses on three discs. The wheel closest
to the patient’s eye usually contains the high-power spheres, the second disc
contains the low power sphere and the third disc contains the cylindrical lenses.
Initially, the phoropters made consisted
of many parts and were complexed. The main idea behind this invention was to
correct the eye problems that prevailed among the population. It still serves
the same purpose. But the components
have been short down to few. But the structure remains the same.
Being a perishable organ, eye, has the
tendency in itself to deteriorate due to various biological , environmental and
physiological hazards. The most common problems that arises due to any external
factors or aging are farsightedness(hyperopia) and nearsightedness(myopia).
Common symptoms of myopia include:
Headaches from eyestrain
Trouble seeing at night
Difficulty driving or navigating
Myopia is treated with improvement in
vision. Common types of myopia treatment include:
Refractive Eye Surgery
Intraocular lens implants (IOLs)
Hyperopia is an eye defect due
to which patients cannot see the near objects clearly.
Farsighted typically have symptoms such
Farsightedness is a common eye-health
problem in the world. The treatment options that are available are as follows:
Our automated phoropter device is based on
dual power lenses technique. The two lenses are attached and overlaps each
other. Each lens is divided into half concave and half convex part that when
slides over each other changes the power. The power ranges from -6 to +3
diopters (Diopter being the unit of optical power). This technique was first developed by a Nobel
prize holder Alvarez, the technology so named Alvarez technique. After many
years from the invention of this technology it was finally adopted by
optometrist and ophthalmologist to be used as a tool for treating eye aberrations.
the reason that this technology was theoretical, and the practical
implementation of this technology was impossible due to the fact that these
lenses were very complex and cannot be fabricated. Variable-power spherical lens is composed of two thin lens
elements arranged in tandem, one behind the other along the optical axis of the
lens system, the optical axis being substantially normal to the lens surfaces
and passing substantially through their centers. At least one of these lens
elements is movable in a direction transverse to the optical axis, and
preferably both lens. Even if both lens elements move, non-variable lenses can
frequently be added to either one or both of the variable lens elements by
variation of their optional terms, if it is desired to do so 2.
The Alvarez technology has been adopted in various optical systems as well.
they are frequently used in optical lenses of digital cameras such as DSLR etc.
Figure 1. Principle of Alvarez Lens
A typical phoropter is a
large device consisting of variable power lenses that provides cylindrical and
spherical powers. The procedure starts as the optometrist placed the device in
front of the patient, who is compelled to respond the optometrist as the
letters on the chart (placed at a specified distance) start to get clearer as
the lenses in the phoropter are adjusted i.e. it is an iterative procedure. The trial
frame containing several lenses can become painfully heavy, especially for
older patients. According to the lens value and
readings, eye prescription is given.
Our automated phoropter
device design is smaller in size, and the procedure can be performed by the
individual himself. It consists of a pair of bifocal lenses that ranges from -6
to +3 diopters. The bifocal lenses work on the slide over mechanism. The
rotatory knobs present at each side of the device helps the user to change the
power of the lenses according to their vision acuity.
The rotatory motion is
controlled by a potentiometer which is further connected with gears that
corresponds to the power of lenses in accordance with the number of rotation.
One rotation is equal to 0.1 diopter value. The rotations are controlled by the
user with the help of the rotor regulators placed on each side of the frame. Each
regulator is responsible for the power changes in the lens of its respective
As the desired acuity is
reached the values in both the lenses are displayed on the lcd.
This section provides the
technical design specifications of our device. It contains details for all
major functional parts of the device.
Lens power (sphero-cylindrical range)
-6 to +3 diopters
2 mm each
Vision test type
Distant and near
6/6 meter, 20/20 feet
Set up time
COMPONENTS OF THE PROJECT:
1. MULTITURN POTENTIOMETER:
potentiometers are controlled by shaft which is rotating, but by several turns
rather than less than a full turn. We are using a multiturn potentiometer
having a rotation of 10 turns.
potentiometers are designed for control applications where accuracy and
high-reliability is important. These devices are available in conductive
plastic, wire wound or Hybritron element types, and in various sizes. Both
single-turn and multiturn models are available. Typical applications include
measuring linear distance, angles or rotations in production equipment,
industrial test and measurement equipment, and medical equipment. 3
A toothed machine part,
such as a wheel or cylinder, that meshes with another toothed part to transmit
motion or to change speed or direction. 4
Gears change the
direction and speed of rotation. it is used for transmitting power from one
part of a machine to another. The main purpose of using gear is
to change the
rotational speed of the output shaft with respect to the input shaft.
The 16×LCD is a very
basic show module. The 16×2 Lcd gives a display of 16 characters each line in 2
such lines. In this LCD each character is displayed in 5×7 pixel matrix. This
LCD has two registers, namely, Command and Data.
The command register
stores the command instructions given to the LCD. A command is an instruction
given to LCD to do a predefined task like initializing it, clearing its screen,
setting the cursor position, controlling display etc. The data register stores
the data to be displayed on the LCD. 5
4. ARDUINO UNO:
The Arduino Uno is a
microcontroller board based on the AT mega 328 . This microcontroller is what
executes the instructions in your program. The ATmega328 microcontroller is the
MCU used in Arduino UNO R3 as a main controller. ATmega328 is an MCU from the
AVR family; it is an 8-bit device, which means that its data-bus architecture
and internal registers are designed to handle 8 parallel data signals. 6
5. POLY ACRYLIC PLASTIC BODY:
The plastic body can
simply be formed into desired shape.
These are used for
turning the power on and off.
It is used for
controlling the device operation. Control knobs are used for the control or
adjustment of electronic or electrical devices. They are often referred to as
instrument knobs, electronic knobs, or electrical knobs. Control knobs provide
machines or instruments with precise position adjustments and controlled levels
of circular motion. They may be marked with graduations in the form of lines or
numbers to provide reference points for adjustments. Control knobs are usually
made of metal, plastic, or rubber
· It has a distinctive and ultra-portable design.
· It is easily affordable and easily transportable due to its
light weight and compact design to the under privileged areas of the country.
· It is extremely user friendly, the design omits the need of a
· The control buttons present on each side of the phoropter
allows the user to navigate according to their visual acuity.
· It delivers highest level of accuracy, the head mounted
design fits efficiently over the head of the user, thus, gives correct eye
positioning and reduces the odds of error.
· It doesn’t require substantial training or a specialized wide
space for the placement.
· It offers adaptable technology for eye aberrations
measurement and calculation.
· It has a corrosion-resistant material.
The person has to sit at a distance of 6m
or 20 ft from snellen’s chart or any object that is at a required distance.
The individual positions the phoropter and
mounds over his head. The phoropter is adjusted in such a way that his head
should be kept straight.
After adjusting the phoropter, the shutter
present at the front must be moved to one extremity whether right or left such
that it blacks out one eye means the other eye is ready to be tested.
The individual starts rotating the knob
and the lenses starts to slide over each other. As the vision gets cleared the
lens power is displayed on the LCD.
Since the 1800,
many different kinds of phoropters are being invented that are driven by
different principles to enhance its use and to provide better welfare for human
beings. The major drawbacks with the earliest
inventions are their huge mechanical structures that requires space and proper
fixations, be it any device. Initially, the phoropters made were very space
consuming and had a lot of parts in them.
From an article we found one more invention of
compact fluidically controlled phoropter. It has adjustable astigmatic and
defocus lenses. Contrary to our device, the lenses of this device have no
mechanical movement, they are controlled by using different fluids and
experimented upon an artificial eye with induced aberrations.
Incorporation of fluidic lenses into the
phoropter will allow a continuously varying optical wavefront that results in
reduction of the time required for the examination, since the process could be
computer controlled. The physical size and complexity of the standard phoropter
is problematic from a manufacturing and deployment perspective, and the
development of a fluidic lens system offers the potential to simplify and
greatly reduce the size of the instrument. Fluidic lenses that are
based on a flexible membrane use fluidic pressure to control the curvature of
the flexible membrane. This control allows alteration of the optical wavefront
in a continuous and consistent manner 7.
The phoropter is composed of one defocus lens and
two astigmatic fluidic lenses that work in unison to provide arbitrary
sphero-cylinder refraction. Each of the lenses is composed of an elastic
membrane that is secured with a metallic retaining ring and contains a 12.5 mm
glass rear surface, which is the clear aperture of the lens. A separate fluid
reservoir is present for each lens that is 1.65 mm thick and allows independent
control of the lenses. Adding or removing fluid from the chamber allows the
defocus lens to provide both positive and negative optical power. The defocus
lens has a circular restraining aperture of 23 mm in diameter, which is used to
secure the elastic membrane. The astigmatic lenses have a rectangular retaining
ring that results in a restraining aperture of 30.0 mm×16.0 mm, which is used
to secure the elastic membrane. The axes of the two astigmatic fluidic lenses
are oriented at 45° to each other. 8
The most important aspect of the result is
sampling. Carrying out trials to examine the accuracy and precision is an
essential part of any medical device as it is directly implemented on human
beings. Even the minor probability of any flaw can cause life altering threats
to the patient. To minimize these threats and to gain accuracy we arranged
screening for over 20 persons suffering from eye defects. Most of them which
were nearsighted that is they have myopia. Screening as a medical term is a way
of identifying the chances of an undiagnosed disease. The results are shown
below the table.
making and arrangements of minute details and components has made possible this
device. The core idea behind its invention was the welfare of human beings.
Every medical institution and facility strives for the betterment and providing
the best of their services to benefit the suffering ones. Uncorrected eye
vision is one of the main cause for blindness. Neglection and lack of medical
facilities result in improper or sometimes, no treatment.
According to GLOBAL INITIATIVE FOR THE
ELIMINATION OF AVOIDABLE BLINDNESS by world health organization ‘Of the
estimated 45 million cases of blindness by 1996, approximately 60% were due to
either cataract (16 million people) or refractive errors’. 9
The miniature and compact size of this
device make it portable and mobile to be transported in every corner of the
globe, benefitting the human race. Refractive errors, during the initial period
are not a life-changing threat, but as it remains undiagnosed and untreated, it
becomes perilous for that person.
errors (myopia, hypermetropia, astigmatism, presbyopia) result in an unfocussed
image falling on the retina. Uncorrected refractive errors, which affect
persons of all ages and ethnic groups, are the main cause of visual impairment.
There are estimated to be 153 million people with visual impairment due to
uncorrected refractive errors, i.e. presenting visual acuity