CONTACT LENSES

 

There are Nearly 75 million contact lens wearers in the world. 

About half of them live in the United States.

If contact lenses are to replace glasses, then they need to be extremely comfortable as well as provide excellent vision with little or no adverse effects.  Otherwise, what would be the point?  Patient criteria must be met in order to have an ideal contact lens candidate.   Generally, the following considerations are taken into account when determining if someone is a good candidate for contact lenses.

            1.  Eyelids:   

                     - If lids are tight, they may cause rotational force on lens

                     - If lids are retracted, this may cause lid impact
                     - If the patient is experiencing Ptosis (drooping of the eyelid):
                       drooping lid may not move the lens sufficiently                                        
          2.  Blinking patterns:

                     -tear film must be good and general health of the eye and

                      cornea.  If the eyes are too dry, then wearing contact lenses
                      May become difficult unless you start to administer eye drops
                      frequently.

3.  Safety is very important in fitting contact lenses.  There are many occupations which will rule out the wearing of contact lenses such as:

           Welders, miners, construction workers, jobs that involve
            sandblasting  or drilling

4.  Infection--the cornea may be infected due to the environment emitting: radiation, dust, vapors, for fumes.  Profession such as plumbers, auto mechanics, furniture builder--cannot get their hands perfectly clean—this can contaminate lenses

5.  There is a saying in the opticianry profession --PATIENT SELECTION:  AVOID THE 5 D’S

           The dirty, drunk, diseased, disabled and the dumb

 GENERAL GUIDELINES FOR FITTING CONTACT LENSES

For Rigid Gas Permeable (RGP) lenses—usually fit either on K, flatter than K or steeper than K (Keratometry readings—we will get into this later)

For Soft lenses—ideally fit to obtain the three-point touch.  For the three-point touch, the contact lens must come in contact with the corneal apex and the periphery on both sides of the cornea.

Soft contact lenses are usually fit larger than the corneal diameter for centration and stability.  A well-fit contact lens should show:  good centration, adequate movement, stable vision, clear undistorted keratometry mires.

A contact lens fit may be too loose or too tight—may change the lens parameters for a better fit i.e.  change the diameter or radius of contact lens
(If you increase diameter, lens will be tighter)
(If you decrease radius, lens will be tighter)

ASTIGMATIC EYES

For Astigmatic eyes, they require special toric lenses. 

If an astigmatic eye is fit with normal soft lenses, the patient will experience fluctuating or blurred vision

WEARING SCHEDULE FOR SOFT

If new to wearing soft lenses, you must have a ‘break-in’ period in which your eyes need to adjust to the contact lens.  The first day of wear, it is recommended to keep them on for 4 hours.  The wearing time may be increased by 2 hours daily until all-day wearing schedule is achieved.  The patient should return to the office for follow-up in 1 week, then 2-week intervals for three visits.   During these visits, lenses should be evaluated and lens changes made if needed.

--keratometer:  follow-up keratometry—pay attention to mires and to changes to radius of curvature

COMPLIANCE

Deposit formation on lens surface is affected by:

          -lens material
          -the wearing time
          -lens care system used

A build up of protein, lipids, and minerals on the lens may result in the following:

       -decreased vision, red and irritated eye, a change in the fit of the lens, a decrease in oxygen transmission of the lens.  Studies have shown that surface deposits extend over 50% of a hydrogel lens within 5 minutes after the lens is worn and over 90% of the lens after 8 hours.

The protein build up on the lens may cause GPC (Giant Papillary Conjunctivitis)—corneal and bulbar conjunctival inflammation.  Methods of Cleaning:  Surfactant cleaners, Oxidative Agents, Enzyme cleaners, Ultrasound, disinfection

 

DISPOSABLE CONTACT LENSES

Disposable contact lenses are a good choice for the sake of health.  As they are being replaced daily, there is less chance of protein and bacteria build up.

A patient will save on lens cleaners and solutions as well since, contact lenses are discarded after use

 

ASTIGMATISM



ASTIGMATIC EYE

What is it?

 This is an error with the way light is focused on the retina.  Similar to nearsightedness or farsightedness, astigmatism is a refractive error.  In a normal eye, light rays come to a single point focus on the retina.   In an astigmatic eye, however, light rays do not come to a single point focus and thus a clear image is not produced.  There are many focus points in an astigmatic eye—some in front or behind the retina, or both.

The cornea of an eye is normally shaped like a ball, or sphere.  However, this need not always be the case.  An astigmatic eye is shaped like a football with one meridian being more curved than the one 90 degrees away from it.   To understand meridians, think of the directional North South East West cross sign.  The North-South is the 90 degree meridian and the East West is the 180 degree meridian. 

The meridians are measured in terms of their ‘steepness.’  One meridian is usually flatter than the other.

Astigmatism may also be caused by the shape of the lens within the eye.  This is referred to as lenticular astigmatism as opposed to corneal astigmatism. 

SYMPTOMS OF ASTIGMATISM

Vision appears to be blurry and distorted at various distances for a person experiencing uncorrected astigmatism.   Generally, after a period of time, a person may experience eye strain, headaches and will often find the need to be squinting.  Astigmatism may be classified as regular and irregular.

REGULAR ASTIGMATISM

Regular astigmatism can be broken down into five categories:

1.) SIMPLE MYOPIC ASTIGMATISM

 -One meridian is emmetropic—light rays focus on the retina(no correction is required—Rx Plano)

Example:  Plano -2.00 x 090

-Opposite meridian is myopic—light rays come to a point focus in front of the retina.  A minus lens is required for correction

2.) COMPOUND MYOPIC ASTIGMATISM

-Light rays in both meridians fall short of the retina

Example:  -1.00 -2.00 x 090

The first number (-1.00) is the sphere power (in diopters) for the correction of myopia in the flatter (less nearsighted) principal meridian of the eye.

          The second number (-2.00) is the cylinder power for the additional  myopia       correction in the more curved principal meridian.

The third number (90) is called the axis of astigmatism. This is the location (in degrees) of the flatter principal meridian, on a 180-degree rotary scale (in which 90 degrees designates the vertical meridian of the eye, and 180 degrees designates the horizontal meridian).

3.) SIMPLE HYPEROPIC ASTIGMATISM

-One meridian is emmetropic (light rays focus on the retina)

                     -One meridian is hyperopic (light rays focus behind the retina and a plus                lens is required for correction)
                     Example:  Plano +2.00 x 090

4.)  COMPOUND HYPEROPIC ASTIGMATISM 

-Both meridians are hyperopic

-Light rays in both meridians focus behind the retina.

Example:  +1.00+2.00 x 090

     5.)  MIXED COMPOUND ASTIGMATISM

                   -One meridian is farsighted and the other is       nearsighted

  IRREGULAR ASTIGMATISM

Irregular astigmatism results when the principal meridians are not 90 degrees apart.  This ends up happening as a result of an eye injury which may scar the cornea.  Eye surgery and a condition called Keratoconus (cone shaped cornea as a result of thinning) as well results in the principal meridians not being perpendicular to one another. 

Astigmatism is corrected by using contact lenses, glasses or by having refractive surgery.

 

 

THEORY OF COSMESIS

 

Did you know that there is an actual theory as to how to pick a pair of glasses that will suit your face shape?

It is called the theory of Cosmesis and it is essentially a method used to fit frames cosmetically. The goal, in accordance with this theory is to achieve the best possible appearance with the frames chosen taking into account the following considerations:

     1.)     classification of frames

 2.)     facial shape

 3.)     facial features

 4.)     color (skin tone)

 5.)     hair style

Frame selection is often a process of trial and error.  An optician can assist in choosing a frame, but a frame consultant or salesperson can offer helpful suggestions as well. 

CLASSIFICATION OF FRAMES BY WEIGHT

You will notice that frames can be physically heavy or light depending on the material used to make them and as well on the style of the frame.

Usually a heavy frame is recommended for people with large, broad features.  A medium frame is recommended for people with normal features or with large features and small stature.  A light frame is recommended for small delicate features, usually women with childlike features or for children.

 

CLASSIFICATION OF FRAMES BY COLOR

Eyeglass frames come in a variety of colors which can help to make a fashion statement or help to draw attention away from a problem area or towards an area of the face you may be trying to enhance. 

The following are frame colors that are available in an optical store.

1.)       Solid color—even color throughout

2.)       Vertically gradient—brow bar darker, lower eyewire light or clear

3.)       Horizontally gradient- darker temporally, lighter at bridge

4.)       Clear bridge (area at top of nose)

5.)       Multicolor

6.)       Yellow gold

7.)       White gold

FACIAL SHAPE

A Frame can influence the shape of a face either by its lines being similar to and accenting those of the face, or by its lines being dissimilar to and de-emphasizing those of the face.

i.e. a round frame shape de-emphasizes the squareness of a face or a square frame shape ( a frame having straight lines) de-emphasizes roundness in a face.

 THE WELL-PROPORTIONED FACE

 Being human means that we are all made uniquely and therefore we may not all have the ‘perfect well-proportioned’ face.  But we need not worry as this is where the Theory of Cosmesis can help with giving the illusion of having a well proportioned face.  Regardless of the shape of your face, the key in selecting a good frame is to keep the frame in proportion to your face.

  A face consists of 3 sections:  In a well-proportioned face, all sections are equal

1.)   top of the head to top of the eyes

2.)   eyes to bottom of nose

3.)   bottom of nose to chin

An individual with the following face shapes should choose the recommended frame styles to give them the best possible appearance.

      i.  Heart Shaped—The frame should cover the width of the      face.  Frames with       detail towards the temples draws attention away from the slimmer lower part       thus deemphasizing sharp features or problem areas.


 

     ii.     Square Shaped—Rectangular or oval shaped frames are well suited to a square face.  To deemphasize the ‘squareness,’ avoid picking frames with sharp corners or frames that are flat at the bottom.  Round frames generally are a good pick.
 

 iii.  Round Shaped—To deemphasize the ‘roundness,’ a good choice of frame would be one that’s rectangular or a narrow oval.  The frame should sit high on the face to give the illusion of more length from below the frame to the bottom of the chin.

 iv.  Oblong Shaped—Frames well suited to this face shape are those with a strong horizontal line or frames that are rounder.  A frame with detail at the bottom will draw attention away from the length of the face thus minimizing the length.   

 

v.     Oval Shaped—This is the IDEAL face shape in that an individual may wear most any shaped frame and they will be able to carry it off well.

 

   

 

 

 

THE CORNEA



LAYERS OF THE CORNEA

The cornea contains most of the eye’s power—precisely two thirds of it.  It is the transparent and is shaped much like a dome which covers the front of the eye including the iris, pupil and the anterior chamber.   The cornea is comparable to the face of a watch since it is the part you look through.   It is transparent primarily due to the fact that it lacks pigment and does not have any blood vessels.   It is extremely sensitive as the cornea contains many nerve endings.  The entire cornea is approximately 0.5mm in thickness and is comprised of 5 layers: Epithelium, Bowman’s Layer, Stroma, Descemet’s Membrane and the Endothelium

 The cornea contains layers of tissue called lamellae which are arranged in a ‘lattice’ pattern.  This pattern allows light to pass through thus giving the cornea its transparency.

5 layers of the Cornea:

i.                 Epithelium:  The  epithelium forms 10% of the corneal thickness.  It is a membranous, multicellular layer which is not waterproof and therefore absorbs some of the tear film.

The epithelium has the ability to regenerate itself within a week, if scratched, abraded or damaged.  However, if the injury is deeper than the epithelial layer, then an opaque  scar results which causes the cornea to appear cloudy.   It is comprised of three cell layers: 

a.       Bottom/Basal Layer:  Columnar shaped, single layer of cells that move to the top

b.      Middle/Wing Cell Layer:  Polyhedral (various shapes) cells that flatten near the top

c.       Top/Surface Cell Layer:  These are squamous or flat cells

ii.               Bowman’s Membrane:  This is the condensed outer layer of the stroma.  It is made up of layered protein fibres called collagen.   Although the Bowman’s membrane is very resistant to injury, if it does sustain injury, there appears an opaque scar which may result in vision loss.

iii.              Stroma:  The stroma makes up 90% of the corneal thickness and is mostly made up of water and collagen.   There are no blood vessels in the stroma.   Bands of collagen fibres called lamellae are embedded in a ‘ground substance.’  This keep s the collagen arranged in a pattern to maintain transparency.

iv.              Descemet’s Membrane:  Located under the stroma, is a thin sheet of tissue which helps protect against infection, trauma and injuries.  It is secreted by the endothelium and able to regenerate itself after an injury.

v.                Endothelium:  This is a single layer of flattened cells attached to the Descemet’s Mebrane.   It is a very thin, innermost layer of the cornea.  These cells do not regenerate themselves in case of injury.   If too many cells are destroyed, blindness may occur leaving the only available option to be a corneal transplant.    The remaining cells spread out to fill in the space.  This layer’s primary purpose is to pump extra fluid out of the stroma

When light enters the cornea, it is refracted or bends onto the lens in the eye.  The lens also further focuses the light rays onto the retina, a layer of light receptor cells in the back of the eye.  In order for a person to see a clear image, light rays must bend and be focused by the cornea to fall on the retina.  The retina has an important job of converting the light rays into impulses via the optic nerve to the brain.  The bran converts these impulses to images and we are able to translate light into vision.  The cornea also serves as a filter to block out the most damaging ultraviolet light.

 

LIGHT



LIGHT

What is it?

Light is a form of radiant energy.  It is electromagnetic in nature and it is comprised of wavelengths.   Not all of these wavelengths produce vision.  Visible light waves are the only electromagnetic waves we can see.

How is light measured?

To measure the wavelength of solar energy, a unit called the NANOMETER is used

Radiant Energy

What are three types of energy that the sun emits?

1. Ultraviolet
2. Visible Light
3. Infrared

How is light interpreted?

Light is interpreted as color according to the length of the light wave that hits the retina.  We see these waves as colors of the rainbow.  Each color has a different wavelength.  The human eye is blind to many wavelengths of light.

Which end of the spectrum has the shortest wavelength/ longest wavelength?

The blue-violet end has the shortest wavelength whereas the red end of the spectrum has the longest wavelength.

What happens when all of the waves are seen together?

         We see white light.

Seeing Using Visible Light

The cones, part of the external retina, are receivers for visible light. The receptor cells of the retina allow us to see in color.   The sun is a natural source for visible light waves.  Our eyes see the reflection of sunlight off the objects around us.  The color of objects we see, is the color of light reflected—all other colors are absorbed

What are the colors of a rainbow? (in order)

 ROYGBIV  red, orange, yellow, green, blue, indigo, violet

What type of instruments do we use to help us see beyond our world?

  Satellites and telescopes help us to see beyond our world.

 

Ultraviolet Radiation

Ultraviolet radiation is electromagnetic radiation with a wavelength shorter than 400nm.   It is the most dangerous part of the spectrum to the eye.  It contains the shortest wavelengths in the spectrum.  The shorter the wavelength, the more biologically harmful the radiation will be.  There are three categories of UV radiation:  UVA, B and C.  They are broken down by their wavelengths.

w  VA:  320-400nm—low doses over a long period of time can cause serious eye damage

w  UVB:  290-320nm—causes sunburns

w  UVC:  200-290nm—filtered out by the ozone layer