Anterior segment examination: A new contact lens patient typically has a complete eye exam before contact lenses are fit.  The ophthalmologist or optometrist will pay particular attention to the following details of the examination:

Health of the lids, conjunctiva, and cornea - patients with corneal diseases or chronic blepharitis are not good contact lens candidates.  A pterygium or pinguecula may be irritated by contact lens wear. 

Tear production -  poor tear production alone may cause a patient to discontinue contact lens wear.  A Schirmer tear test and tear break-up time (BUT) may be performed.

 

Lids - the lids must be elastic and fit closely to the globe.  This picture would obviously be an exaggeration of a loose lid. 

The lid aperture must be wide enough for the patient to be able to insert the contact lens.

 

Giant papillary conjunctivitis may be in the history of a former contact lens wearer wanting to wear lenses again.  This is characterized by large bumps, or "papillae", which cover the upper tarsal conjunctiva.  It is usually caused by wearing contact lenses that are covered with deposits.  The lid must be "everted" to view the extent of the condition.  The patient must usually discontinue wear for the condition to subside.  Some patients can resume contact lens wear with a frequent replacement schedule.

Soft Contact Lenses: 

         

 

Indications for Contact Lens Wear Most contact lens fittings are performed for one or more of the following reasons: 

 

Cosmetics: The patient may not like her appearance in glasses.  The patient may want to change his eye color or wear one of the contact lenses that has a symbol on the surface (popular at Halloween time).

Better vision:  Some patients see better with contact lenses than they do with glasses.  Peripheral vision is better with contact lenses.  Image size is larger with contact lenses for the high myope.  Vision may be less distorted for the astigmat wearing contact lenses.

Artificial iris:  An eye that is missing a significant portion of the iris due to trauma or other reasons may be less light sensitive when wearing a contact lens with a colored, opaque "iris".  An artificial pupil in the contact lens may also improve the vision.

Bandage lens:  Soft contact lenses are sometimes used as a "bandage" to protect the cornea as the cornea heals from trauma, surgery, or disease.

 

History Taking  History taking, of course, is an important component of any medical examination.  Good history taking is especially important for the contact lens patient.  For the vast majority of patients, contact lens wear is optional, and motivation plays a big role in determining success or failure.  For the contact lens fitter, "chair time" plays a big role in determining the financial feasibility of a particular contact lens fitting.  Good history taking goes a long way toward ensuring reasonable expectations on the part of patient and the practitioner. Keep in mind that the simplest, most successful contact lens fits are generally on young patients with spherical myopia who do not want to wear glasses.  The least successful patients include the presbyope with significant astigmatism who wants to "try" contact lenses.  The following list of history taking queries is not all inclusive, but it will give you a good idea of what you should be thinking about in the contact lens history taking process. 

Why?:  Ask the patient why she wants to wear contact lenses.  You want a sense of the patient's level of motivation.  The teenaged girl who does not want to be seen wearing glasses will be highly motivated.  The teenaged boy who wants to wear contact lenses for sports will be highly motivated.  During the history taking process, the patient with low motivation can be steered to arrive at his own conclusion that he is not a good

 

Pupil size - if the diameter of the pupil approaches or exceeds the optical zone diameter of the contact lens, then annoying distortion and flare occur.  If the patient has unusually wide pupils in a well lit room, she may not be a good contact lens candidate.

   

 

Hygiene - take a look at the patient's appearance during the exam.  Dirty fingernails are a good indicator of a contact lens problem child.

   

 

Lens type:  Before the actual contact lens evaluation begins, a lens manufacturer and a particular lens model must be selected.  Some practitioners have a favorite lens that they fit the majority of patients with.  The choice may depend upon patient preference for daily, flexible, or extended wear, frequency of replacement, power limitations, cosmetics (color), and other factors.  Commonly, a daily wear lens with a light blue (visibility) tint is a good choice, with replacement every 1 to 3 months.  The spherical soft contact lens has three variable parameters: diameter, power, and base curve. Diameter:  Most manufacturers have a standard diameter for a particular lens model (e.g. 14.0mm, or 14.5mm).  A larger or smaller diameter may be available for special situations. Base curve:  As discussed earlier, for a given diameter, the fit of the lens is adjusted by changing the base curve.  There are usually three base curves available: steep, medium, and flat.  Most manufacturers identify the base curve by radius of curvature.  Examples would be 8.9 (flat), 8.6 (medium), and 8.3 (steep).  Some use the Vault system: Vault I (flat), Vault II (medium), and Vault III (steep). 

 

The starting point for choosing a base curve is keratometry.  The manufacturer gives guidelines regarding which base curve should be used for a given K reading.  An average K reading of 43.50 might call for a base curve of 8.6 in our 14.0 diameter trial contact lens.  

 

     Power:  Since we are fitting a spherical soft contact lens, the eye should

not have more than .75 D of astigmatism.  If it does have more astigmatism than that, a toric soft lens or a hard gas permeable (HGP) lens is indicated for optimum vision. Thicker spherical soft contact lenses are thought to be able to "mask" a low amount of astigmatism.  A thin lens however will drape over the curves of the cornea and the residual astigmatism will limit the visual acuity obtained with the spherical lens.  If only one eye has significant astigmatism, it is sometimes acceptable to the patient to wear spherical lenses in both eyes, especially if the better seeing eye is the dominant eye.

   

 

If the eye being fit has astigmatism, the refraction is converted to minus cylinder, and the spherical equivalent power is used. For example: OD MR = -6.00+1.00x180Minus cyl. = -5.00-1.00x90Spherical equivalent = -5.50

   

 

The spherical equivalent power must then be adjusted for vertex distance.  This is because the refractive power is measured at approximately 12 to 13 mm away from the cornea.  The contact lens, of course, will be on the corneal surface.  For powers 4 diopters or less, this calculation makes little difference.  The greater the lens power is, the more difference this calculation makes in the contact lens power.  Most contact lens publications have a table for figuring this adjustment.  You will need to remember that, for minus lenses, power is taken away from the refractive lens power to arrive at the contact lens power.  For plus lenses, power is added to the refractive power to arrive at the contact lens power.  

       

 

Pictured to the right is a hyperope corrected with a glasses lens.  VD is the vertex distance, which is measured from the back of the glasses lens to the cornea.  FD is the focal length of the compound lens system (the glasses lens plus the cornea and the natural lens.

 

Pictured here is the same hyperopic eye corrected with a contact lens.  The VD is zero and the focal length is shorter.  Because the focal length is shorter, the plus powered contact lens will need to be proportional stronger than the glasses lens to focus light on the retina.  Thus the vertex power adjustment increases the power of the plus powered contact lens compared to the power of the glasses lens.

 

Picture to the left is a myopic eye corrected with a glasses lens.  The vertex distance (VD) and the focal distance (FD) are marked.  Remember that a minus lens diverges light so that the focus is lengthened for the nearsighted eye.

 

Pictured here is the same myopic eye corrected with a contact lens.  The VD is zero and the focal distance is shorter.  Since the focal distance is shorter, the minus lens will need to be less powerful to achieve the same focus.  Thus the vertex power adjustment decreases the power of a minus powered contact lens compared to the power of the glasses lens.

 

The clinical optics calculator that we give away free on this website has a vertex distance calculator.  We would enter -5.00-1.00x90 into the calculator, along with a "present vertex distance" of 13 and a "new vertex distance" of zero.  The calculator gives us a spherical equivalent, vertex adjusted contact lens power of -5.10, which we would round off to -5.00. This would be the power that we would choose for our trial lens.  If a -5.00 D lens is not available in the fitting inventory, choose the closest power available. Fit evaluation:  If the patient has no contact lens experience, you will need to insert the lenses for the evaluation.  After insertion, wait at least 10 minutes before you evaluate the lens.  This allows time for patient acclimation and time for the water content of the lens to stabilize.  The lens will loose water after insertion, and it will fit tighter as a result.  During this time, if the patient complains of a foreign body sensation, remove, rinse, and reinsert the lens. Start the 10 minute wait again after reinsertion.

     Evaluate the fit of the trial lens with the slit-lamp microscope, keeping

the following points in mind:1. Coverage - the lens should cover the entire surface of the cornea

in all meridians and should go slightly beyond the limbus.  A very loose lens may ride low, exposing an upper portion of the cornea.  A solution may be a tighter lens.  A lens that is loose may be too small.  A larger diameter may solve the problem.  Remember that a larger diameter lens will fit tighter if the base curve is kept the same.

2. Centering - the lens should center well on the cornea.  A very loose lens may ride low.  A high plus lens, particularly an aphakic lens, may ride low.  A larger diameter lens may solve the problem.

3. Drape - the lens should fit closely to the cornea without any pockets between the lens and the cornea.  This is rarely a problem unless the contact lens parameters are not close to what

they should be. 4. Movement - the lens should show some movement.  A thin lens

will usually show less movement than a standard thickness lens.  The standard for movement will depend upon the practitioner.  Some doctors like to see .5 to 1 mm of movement with a complete blink.  To evaluate this, watch an edge of the lens with the slit-lamp as the patient blinks. Other doctors think that a lens that does not move with a blink is not necessarily too tight.  

However, every lens should show movement if it is mechanically pushed. To evaluate this at the slit-lamp, have the patient look slightly upward.  With your finder, push on the patient's lower lid so that the lid pushes against the lower edge of the lens.  The lens should move, if not, the lens is too tight.  The fit can be loosened by going to a flatter base curve and/or a smaller diameter. A lens that is really tight will actually indent the conjunctiva at the edge of the lens.  This degree of tightness usually only shows up on extended wear patients at the end of the wear period. A lens can also demonstrate too much movement.  Excessive movement may give the patient a foreign body sensation, and the vision will be disturbed as the lens moves on the cornea.  The fit can be tightened by going to a steep base curve and/or a larger diameter.  The fit could also be tightened by using a thinner lens.  Before deciding that a lens is too loose, be sure to allow enough time for stabilization, perhaps longer than the minimum 10 minute period.

 

Evaluate the power of the trial lens - your power calculation should have you close to the optimum power, if not dead on.  Evaluate the power by performing an over-refraction with the phoroptor or loose lenses.

   

 

Most of the time, a spherical over-refraction will be sufficient.  The exception might be the patient with significant astigmatism (>.5D) who is being fit with a spherical soft lens.  Any spherical error found during the over-refraction is simply added or subtracted from the trial lens power when finalizing the contact lens prescription. Ordering the contact lenses - if the lenses are being fit from an inventory, and the patient's optimum prescription is on hand, then the patient can leave the office wearing the lenses.  Even if the optimum Rx is not on hand, if there are lenses in inventory close to the optimum prescription, then the patient can leave with those lenses and the correct Rx can be ordered.  This always makes the patient happy, and we do like to make the patient happy.

     Insertion and Removal (I&R) -  This routine is usually only for the new

contact lens wearer, although some experienced patients can use the review.  This duty can be drudgery, because it is always the same thing, over, and over, and over again.  To minimize the drudgery, have the patient watch a videotape of I&R procedures.  This procedure mainly

has to do with the patient getting over the fear of sticking her finger in her eye.  Once that is overcome, it is usually smooth sailing.

Soft contact lenses can be flipped inside-out. They are usually most comfortable, and vision is usually the best, when the lens is inserted correct-side out.  Although with thin lenses, it doesn't seem to make much difference.  The "taco test" is used to determine which way is the correct way.

   

 

The lens is slightly pinched between the thumb and forefinder, to make it look like a taco. It helps if the lens is slightly dry. The edge of the lens is observed.  If the edges slope inward, then the lens is in the correct position.

   

 

If the lens edges reverse and curve outward, then the lens is inside-out. This phenomenon can usually be observed without pinching the lens.

   

 Some manufacturers print initials near the edge of their lenses.  A keen observer (or someone using a slit-lamp) can then tell if the lens is inside-out.

   

 

The soft lens is inserted by positioning the lens on the index finger of the dominant hand.  The lids are opened and held by the remaining fingers of both hands.  The lens is guided to the cornea until contact is made.

   

 

It is helpful if all parts of the lens edge make contact with the eye at the same time.  The lids are not released until the lens has adhered to the cornea.  The lens can usually be centered with a few blinks, if not, the lens can be pushed toward center with a finger.  It is helpful for most patients to look at themselves in the mirror during the procedure.  Alternatively, the contact lens can be placed on the conjunctiva below the cornea as the eye looks upward.  The lens is then moved onto the cornea with a finger.

   

 

The soft lens is removed by pinching the lens between the thumb and index finger of one hand.  As with insertion, the lids are held open with the remaining fingers.  It is helpful to look slightly upward, and pinch the lower edge of the lens.  Some find it helpful to first slide the lens downward from the cornea before pinching the lens.

   

 

Most contact lens patients eventually become very adept at insertion and removal.  Many are able to use a one handed technique that simply pulls the lower lid down for insertion and removal.  It is best to teach the two handed technique and let them improvise on their own.

     The patient should be taught what to do if the contact lens becomes de-

centered.  Knowing ocular anatomy, we know that the lens will not become "lost behind the eye", but the patient may not know this.  Finding a de-centered lens is just a matter of searching the conjunctival area after the lids have been pulled away from the globe.  The lens is then pinched, removed, and then re-inserted. Even though your I&R video may cover these next points, be sure they are part of a printed handout for the patient. You may want to add to or modify this list as your experience may suggest:

Always wash your hands before handling a contact lens. Short fingernails are better than long nails.  Care must be taken

so that long nails do not tear the lens. Hand lotions and creams should not be used prior to contact lens

handling. It is best to use hair spray before contact lenses are inserted. It is best to apply makeup after contact lenses are inserted and

remove the contact lenses before makeup is removed. Only use appropriate care products for cleaning, wetting, and

rinsing contact lenses. Saliva and tap water should not be used as wetting or rinsing agents.  

Eye redness, discomfort, or blurry vision should be reported to your doctor immediately.

If the contact lens becomes de-centered from the cornea, it cannot travel behind the eye.  Using a mirror, try to locate the lens on the white part of the eye, or under the upper or lower lid.   Move the lens with your finger if necessary.  Remove the lens by pinching it with your fingers.  Re-insert the lens in the usual manner. If you cannot find the lens, it may have fallen out. 

It is not a good idea to wear contact lenses while swimming.  The lenses can easily become dislodged and/or soft lenses may soak up some chlorine and irritate your eyes.

Do not use eye drops with contact lenses, except for lubricating drops approved for your lenses.

Do not sleep with your contact lenses unless they are approved for overnight wear.

Wear safety glasses over the contact lenses in appropriate situations.

 

Initial wearing time:  This varies with the practitioner.  Many patients tolerate soft contact lenses right away.  Some practitioners like to start the patient with 4 hours the first day and add 2 hours each day until the lenses are worn for all waking hours if desired.

   

 

Soft contact lens care  It is the goal of every contact lens care system to remove foreign matter and microorganisms from the surface of the lens, and to neutralize or kill any remaining microorganisms on the lens.  This is usually called "cleaning" and "disinfection".  Care systems use various combinations of daily cleaners, rinsing agents, and disinfectants.

     Daily cleaners work well only if combined with mechanically cleaning

the lens.  This is accomplished by putting a drop of cleaner on the lens and rubbing the lens gently with a finger in the cupped palm of the other hand.  The lens can be flipped inside out so that the other surface can be cleaned. A rinsing agent is used to wash the daily cleaner and other matter from the surface of the lens.  A rinsing agent should be used whether or not a daily cleaner is used.  Rinsing the lens will obviously be much more effective if a daily cleaner is used. Disinfection can be accomplished by storing the contact lenses overnight in a disinfecting solution. Enzymatic cleaners are used to remove tear protein deposits from the surface of the contact lens.  These are deposits that may not be removed with a daily cleaner.  These cleaners are for the patients who are more susceptible to these deposits than other patients.  Excessive protein deposits can block oxygen transmission through the lens and they may trigger a hypersensitivity reaction under the eyelids.  More frequent replacement of the lenses also reduces this problem. All-purpose soft contact lens care systems are currently popular for contact lens care.  One solution is used for cleaning, rinsing, and for disinfection (storage in the case).  The idea is to encourage better compliance with a more simple system.  Unfortunately, many patients think all they have to do is remove the lenses and place them in the solution overnight.  Be sure to encourage the patient to rub and rinse the lenses as described above.   The all-purpose solutions are expensive.  The cost for the patient can be reduced if the all-purpose solution is only used as the cleaning agent

and the disinfecting agent (storage).  A much less expensive contact lens saline solution can be purchased to rinse the lens during cleaning and to rinse the lens before insertion. Some patients may become hypersensitive to the preservatives in chemical care systems.  Symptoms may include soreness, stinging, foreign body sensation, redness of the conjunctiva, redness of lids. swelling of the conjunctiva and/or lids, and punctate staining of the cornea.  A major offender has been the preservative thimerosal.  It is best to avoid care systems with this preservative.  Switching the patient to a chemical care system with a different preservative may solve the problem. Alternatives to chemical care systems are daily disposables or a hydrogen peroxide care system as discussed below. A hydrogen peroxide based care system requires more steps for the patient, but it may be the only choice for the patient who is hypersensitive to the preservatives in other care systems.  The peroxide is an efficient antimicrobial and it has some protein cleaning activity as well.  The system requires an exposure step of about 10 minutes and a neutralization step that lasts from 20 minutes to a few hours, depending on the system. General instructions to the patient should include:

Only use products that are compatible with your lenses.  Check with your doctor's office.

Do not mix care product brands unless recommended by the doctor's office.

Wash hands before handling lenses. Do not skip steps in your lens care routine, as instructed by the

doctor's office. Keep the lens care environment clean (case, counter, storage

bag, etc.). Keep care product bottle tops from touching any surface. Work over a clean surface.  Use paper towels if in a public

restroom. If you drop your lens prior to insertion, rinse the lens well before

insertion.  Notify your doctor's office if you experience eye or lid redness

and/or irritation.

         Soft Lenses for the astigmatic patient

 Does the patient really need astigmatic correction? Not all low astigmats (<1.25 D) require astigmatic correction.  Not all of them want astigmatic correction, particularly if the dominant eye does not have significant astigmatism.  If in doubt, trial fit with spherical soft lenses and over-refract.  Show the patient the difference between astigmatic correction and correction with the spherical equivalent.  Toric lenses are more expensive to replace, although the cost differential has come down significantly in recent years. Toric lenses generally are not as comfortable as spherical lenses.  The difference in vision may not outweigh these other factors.  The trial contact lens that you use may make a difference in this determination.  Thicker, lower water content soft lenses tend to "mask" low amounts of astigmatism better than thin lenses. Toric soft lenses vs. hard gas permeable lenses To be able to offer the astigmatic patient the best lens for his/her eyes, we need an understanding of the options in terms of lens design and the advantages and disadvantages of each type. The patient with significant astigmatism (generally > .5D) can be fit with toric soft contact lenses or hard gas permeable (HGP) contact lenses. Although HGP lenses can efficiently fit almost any degree of astigmatism, many astigmats less than 2.50 D are fit with toric soft lenses because of the initial comfort factor.   Toric soft contact lenses correct astigmatism by providing a cylinder correction in the lens itself.  The correction is similar to a glasses correction.  For this to work, the lens must not rotate significantly on the cornea.

     Rotational stability

is accomplished with a variety of lens designs, including weighting the bottom of the lens (prism ballast, top image) and/or flattening the bottom edge of the lens so that it rests against the lower lid (truncation, bottom image).      

    

 

The conventional HGP lens corrects astigmatism with a "tear lens".  This rigid, spherical lens is fit to one curve of the cornea (picture on the left).  Because of astigmatism, the lens does not fit the other curve perfectly, but the space between the lens and cornea is filled in with tear fluid (picture on the right), which acts as a refracting surface to correct the astigmatic error.  The tear lens is represented by the black area in the picture on the right.

     For the conventional HGP design, lens rotation does not affect

the astigmatic correction.  The conventional HGP lens works well only for low to moderate amounts of astigmatism.  HGP lenses can also be designed to fit the cornea exactly for higher amounts of astigmatism (bitoric design).  A  bitoric HGP design is more complicated and more costly. The toric soft contact lens must maintain little or no lens rotation on the eye for maximum acuity.  The regular HGP lens does not have this problem.  For this reason, it is best to determine the patient's cylinder power and axis "sensitivity" before a lens type is recommended.  If the patient notices a decrease in vision with a small axis rotation, she may be better off with an HGP lens fitting. Cylinder Sensitivity testing At the completion of the manifest refraction, have the patient view a line on the chart one line above the line of best corrected visual acuity (BCVA).  Ask the patient to let you know when she notices the letters blurring.  Slowly rotate the cylinder axis away from the refracted axis.  Stop when the patient notices blurring.  The axis sensitivity is the degree of rotation from the refracted axis.  For example: suppose the refracted axis is 90 and the patient reports blurring at axis 100, then the axis sensitivity would be 10 degrees.  Usually, the greater the cylinder power is, the more sensitive the patient is to axis rotation.

 If the patient has an axis sensitivity of 5 degrees, and the best fitting soft toric lens frequently rotates 10 degrees off axis, then the patient may be better off wearing HGP lenses. How much astigmatic correction does the patient need? A similar procedure can be followed for cylinder power.  The cylinder power is reduced by .50 D while simultaneously changing the sphere .25 D to keep the spherical equivalent.  For example: change a +1.50 D cylinder power to +1.00 D, and at the same time change the sphere power .25 D in the plus direction.  Again, the patient reports when blurring occurs.  The distance traveled on the cylinder power wheel is the measure of cylinder power sensitivity.  For example: suppose the refracted cylinder power is 1.5 D.  The patient reports blurring at 1.00 D.  The cylinder power sensitivity is thus .5 D. Most patients do well with an automatic .5 D reduction in cylinder power in the SCL prescription.  Depending upon the cylinder power sensitivity, a greater reduction may be possible. Using a trial toric soft lens A diagnostic or "trial" set of soft toric contact lenses (torics) should be used.  Some practitioners have one or two favorite lens designs, and they fit these from inventory.  Evaluating a lens with the exact parameters needed decreases the "chair time" needed to fit torics.  However, many manufacturers have liberal return policies that allow you to fit from a limited trial set and return an ordered lens that may not be optimum when worn by the patient. Toric lens parameters vary from brand to brand.  Variables include the following:

base curve diameter range of sphere powers range of cylinder powers range of axis alignments flexible wear, planned replacement, or daily wear

As you can imagine, fitting torics form inventory requires a lot of lenses.  To help you sort things out, there are publications that organize all this information for you (e.g. Tyler's Quarterly).  Obviously, you will be spared some frustration by beginning your fitting with a brand that includes the parameters that you need for a particular patient. Choosing a trial lens To begin your toric lens fitting, you will need the manifest refraction and the keratometry readings.  Toric lenses usually have a large diameter to aid stability, so measuring the patients cornea is usually not necessary. Just as with spherical soft lenses, the glasses lens power (or

manifest refraction) will need to be adjusted for vertex power.  Toric vertex adjustment is a little tricky because you may have to adjust both the sphere power and the cylinder power.  Let's look at an example: MR = -8.00+2.00X180 First of all, we convert to contact lens language (minus cyl.). MR = -6.00-2.00X90 From the optics modules, you may (hopefully) remember that we are really dealing with two different lenses.  On an axis cross, the powers convert to:  -6.00 D at 180 degrees-8.00 D at 90 degrees If we look up each of these powers on a vertex conversion chart, -6.00 D at a vertex distance of 12mm converts to -5.62 D at zero vertex distance, and -8.00 D converts to -7.25 D.  Therefore, our CL Rx will be -5.62-1.63X90.  You can also use the optics calculator to arrive a the same answer.  Our ideal toric trial lens power would be -5.50-1.50X90.  Remember that you want to start with a cylinder power that is less than the refracted power. Many manufacturers offer -1.25 and -1.75 cylinder powers and do not offer a -1.50 cylinder power.  If this is the case, you would want to start with the -1.25 cylinder power. Just as with a spherical contact lens fitting, you will follow the manufacturers recommendation for the starting base curve.  Most lenses come in "medium", "steep", and "flat" base curves.   Example: Av. K reading      Base Curve < 43.00               9.1  (flat)43.00 - 45.00       8.7  (medium)> 45.00                8.4  (steep)  Evaluating the fit The same basic evaluation criteria used with spherical soft lenses also applies to toric lenses. For best vision, the axis of the contact lens cylinder correction should line up with the axis as determined by the manifest refraction.  All is well if the contact lens rotates to the correct position after insertion, and it should stay in the correct orientation throughout the day.  This, of course, is not always the case. All toric soft lenses have some type of markings that assist in the evaluation of lens rotation.  It might be a single mark at the 6

o'clock position, marks at 3 and 9 o'clock, three marks at 5, 6 and 7 o'clock, or some other marking scheme.  The marks are viewed with a slit lamp to determine the degree of rotation of the lens.  The rotation of the lens should not be evaluated until the lens has had time to stabilize on the eye.  Ten to 15 minutes after insertion is usually sufficient time for stabilization. If a toric lens consistently rotates to the same position on the eye, then the prescription can be adjusted to accommodate the rotation.  For this adjustment, the "LARS" system is used.  LARS stands for "left-add, right-subtract".  If the lens is rotating to the right, then the degree of rotation is subtracted from the refractive axis.  If the lens is rotating to the left, then the degree of rotation is added to the refractive axis. Let's look at an example: This patient is wearing a toric soft lens (light blue color over a blue iris) with a 6 o'clock rotational marker and two marks 15 degrees to either side.  Ideally, after the lens has stabilized, the center marker should be at the 6 o'clock position as you look at the lens with a slit lamp. 

 Let's suppose that our lens stabilizes to a position with the lens rotated somewhat counterclockwise, like this: 

 The arrow marks the 6 o'clock position, so our lens has not rotated enough for the left 15 degree marker to align with the 6 o'clock position.  So, we will have to estimate the degree of rotation.  It looks like it has rotated about 2/3 of the way toward the marker.  We estimate that it has rotated 10 degrees. Let us say that the patient's glasses prescription is -2.00-1.25x170, and this is the power of the lens that we have inserted.  Our lens has rotated to our right.  The LARS rule is: left add, right subtract.  Therefore, we will subtract 10 degrees from 170 to get a contact lens axis of 160.  This means that we will order the patient a new lens with the axis at 160.  Theoretically, the new

lens should behave the same way, rotating 10 degrees to the right after stabilization.  If so, the cylinder axis will be in the correct position for good vision, at axis 170. As with a spherical soft lens, the toric lens should center well and exhibit some movement, at least when pushed with the lower lid. A loose fitting toric lens will generally not be a successful fit, as the excessive movement contributes to lens rotation and blurry vision. Once an acceptable fit has been achieved, with minimal rotation after being allowed enough time to stabilize, an over-refraction should be performed.  Perform the refraction as you would with an eye not wearing a contact lens.  In other words, perform the normal refractometry routine, checking sphere, cylinder axis, and cylinder power.  Record the results.  To arrive at the final contact lens prescription, place the trial contact lens power specifications (adjusted for rotation) into a trial frame.  Then place the over-refraction results into the same trial frame along with the other lenses.  Now place the over-loaded trial frame onto a lensometer and read the final contact lens power Rx.  This is the contact lens power that you will order, along with the other specifications of the particular trial lens that was used.  If the results of the over-refraction were minimal, you can dispense with this final exercise and simply order the specifications of the trial lens as adjusted, if necessary, for lens rotation. The insertion, care, and handling of toric soft lenses are very similar to that of standard soft lenses.  The patient need not pay particular attention to the orientation of the insertion, as the lenses should rotate to the proper position in a short period of time.  The patient should, however, pay particular attention to inserting the lenses so that they are not inside-out. This is usually not a problem as most toric lenses give an obvious "taco test". The patient should be seen back in a week or two for a review of the fit.  Many soft toric contact lens vision and comfort complaints originate from toric lens dehydration.  This may become apparent in the return visit, but may not show up until much latter.  If the symptoms are relieved by regular use of re-wetting drops, then the patient will need to make this a part of his routine. If the patient complains of intermittent blurring, then the lens may be too loose, allowing for excessive rotation upon blinking.  A steeper base curve may be necessary. If the patient complains of constant blurring, the lens may be constantly misaligned, or the prescription may be wrong.  If the fit seems adequate (not too steep or flat), a predictable axis misalignment can be again adjusted with the LARS principle. The prescription can be rechecked with over-refraction if necessary.  When evaluating vision complaints, always keep in mind that the patient may have switched the lenses.  If all else fails, the fit can be started from scratch before soft lenses are abandoned for RGP lenses.  Some would argue, why put up with this non-

sense?  Simply fit RGP lenses in the first place!  To be fair, many patients are successfully fit with soft toric lenses the first time. z Presbyopia is the term for difficulty focusing at near due to the aging lens of the eye.  Symptoms usually first occur between the ages of 40 and 50, with most patients needing some degree of near compensation by age 45.  Near compensation means more plus power, which brings the near point closer Soft lenses plus readers  There is no ideal contact lens correction for presbyopia.  The presbyopic contact lens wearer must compromise, therefore, motivation is a key factor in successfully fitting the presbyope with contact lenses.  Before modifying the contact lenses for near vision, be sure that your patient understands that readers can be worn over distance powered contact lenses.  This is not always obvious to them, and it is the most simple solution.  Of course, not everyone wants "simple", some do not want glasses, even for near vision. Over-plusing the contact lens power Helping the new presbyope who already wears contact lenses may be as simple as over-plusing the correction in both eyes.  Over-plusing means changing a +1.50 correction to +2.00 or changing a -3.00 correction to -2.50.  Hyperopes usually tolerate this better than myopes.  The idea is to over-refract binocularly in the plus direction until the distance vision is unacceptable, and then back off a little until it is acceptable.  If overplusing is not acceptable, then monovision may be tried.   Monovision Monovision is a technique that corrects only one eye for near vision, while leaving the other eye for distance vision.  Not everyone can tolerate having one eye blurry all the time.  The success rate is enhanced by keeping the dominant eye the distance eye, and by minimizing the power difference between the two eyes. There have been many methods described for determining the dominant eye, and some of them don't work very well.  Try first asking the patient which eye is dominant,  Many patients already know what you are talking about and can give you the information.  My personal experience has been that the vast majority of right handed people are also right eye dominant.  My experience has also been that many left handed people are also right eye dominant.  There are some people who seems not to have a dominant eye. If the patient is not aware of eye dominance, there are two methods that may work to determine dominance: 

The camera method: Keep an old camera handy and have the patient take a picture.  Whichever eye is used to look through the viewfinder is the dominant eye. Look through the hole method:  The patient extends both arms and holds the hands together so that a hole is formed through which the patient views a distant object.  You cover one eye at a time and ask if the object can be seen.  Whichever eye it is that can see the object is the dominant eye. Keep in mind that most people are right eye dominant, including almost everyone who is right handed.  But, this is not always the case.  That's why we check. When adjusting the contact lens power for monovision, the distance eye is given as much plus power (or as little minus power) as the patient will tolerate before complaining about blurry distance vision.  This narrows the power difference between the two eyes and improves the intermediate and near vision.  The near eye is given the minimum additional plus power to do the job.  Keep in mind that, because of the vertex distance change, less plus power will be needed than what is given in the glasses bifocal correction.  In other words, a +0.75 add with contact lenses is equivalent to a +1.00 add power in a glasses bifocal.  When in doubt, give less power and have the patient try it for a few days. 

Examples: A 45 year old right eye dominant presbyope with a distance contact lens correction of -3.00 OD and -3.00 OS might end up with a monovision contact lens correction of: OD -2.75OS -2.25 Our patient tolerates a .25 reduction in the minus correction for the right eye, which focuses at distance.  He can read well enough with a +0.75 D "add" for his left eye, which is the reading eye. A 60 year old right eye dominant presbyope with a distance contact lens correction of +1.50 OD and +1.50 OS might end up with a monovision contact lens correction of: OD +2.00OS +3.25

 This hyperope can tolerate a .5 D increase in the correction for the right eye, which is the distance eye.  He can read well enough with a +1.75 D "add" for his left eye, which is the reading eye. From the above you might surmise that the 45 year old will have the greater chance of success because there is less power difference between the two eyes.  If your patient does not tolerate monovision, bifocal contact lenses may be considered. Bifocal soft lenses  Bifocal contact lenses offer the possibility of success (compromised) for some of your contact lens patients who do not want to wear glasses for anything.  The downside for the fitter is increased "chair time".  The downside for the patient is increased expense. The are several design types of bifocal contact lenses.  The simultaneous view bifocal design uses concentric circles of different powers that project focused light from two different distances simultaneously on the retina.  The aspheric bifocal design is a type of progressive power design.  The translating or alternating bifocal design is similar to the bifocal in a pair of glasses.  The optics of these designs are complex and are beyond the scope of this module.  They are mentioned in order to familiarize you with the vocabulary. The fitting techniques and characteristics of bifocal contact lenses are very specific to the brand.  Proper alignment on the cornea is usually critical, and pupil size plays a role.  Many practitioners prefer to begin with a "modified monovision", meaning one eye is fit with a conventional contact lens and the other eye is fit with a bifocal contact lens