As the eye is accommodating, the crystalline lens makes up to 33 diopters (D) of its optical power. In a relaxed state, the lens usually has 20 D of power while the other majority of the eye's 60 D of total optical power is from the cornea. The iris and vitreous humour do not refract light.

Giant papillary conjunctivitis is commonly associated with poor cleaning of contact lenses. This causes irritation of the palpebrae conjunctiva of the upper lid. The resulting inflammation leads to very large papillae (or bumps). Pterygium is a growth in the conjunctiva and a subconjunctival hemorrhage is when a blood vessel in the conjunctiva breaks. Atopic keratoconjunctivitis is characterized by chronic inflammation of the conjunctiva.

In myopia (nearsightedness) light focuses in front of the retina, whereas with hyperopia (farsightedness) light focuses behind the retina. An emmetropic eye requires no correction because light already focuses on the retina.

A convex (plus) lens is used to correct hyperopia. A concave (minus) lens is used to correct myopia. A cylindrical lens corrects astigmatism.

A pupilometer is used for fitting a patient for glasses. A phoropter is a machine which assists the prescriber in refracting the eye while a keratometer measures the patient's cornea. Corneal topography can also be used when a patient requires rigid gas permeable or hybrid lens.

Tear Break-Up Time (BUT) is a test where fluorescein dye is used to track how long it takes dry spots to form after a patient blinks. Visual acuity (or the patient's ability to see) and refraction (the process of determining a patient's refractive error) are normal parts of an eye exam. Knowing which eye is dominant is essential for fitting monovision and some multifocal lenses.

Since there is a 2 diopter (D) difference between the corneal measurements of the eye and also the amount of cylindrical power listed in the refraction, the patient has corneal astigmatism. The patient's astigmatism is not caused by the difference in curvature of the crystalline lens (lenticular astigmatism). The astigmatism at 130 degrees is also known as oblique astigmatism. Against-the-rule astigmatism is described as an axis located approximately between 0 degrees to 30 degrees or 150 degrees to 180 degrees. With-the-rule astigmatism is described as an axis located approximately between 60 degrees to 120 degrees.

A spectacle prescription is transposed by adding the cylinder power to the sphere, switching the cylinder's sign and changing the axis by 90 degrees. The transposed prescription will read +6.00 -2.50 x 165. Since the sphere is higher than +4.00, the next step is to adjust for the vertex effect. The corresponding contact lens prescription will then be +6.50 -2.50 x 165.

The corneal measurement (K) of 41.00/41.25 x 90 is considerably steep and matches up best with the 8.2 base curve (BC). Usually the higher the BC, the flatter the contact lens will appear.

Keratoconus is a thinning of the cornea which leads to a steep coning of the front of the eye. Hybrid lenses (Rigid Gas Permeable lenses with a soft lens skirt) therapy can be used to improve vision. When either the front surface of the eye, the cornea, or the lens inside the eye have mismatched or misshapen curves, astigmatism occurs causing blurred vision at all distances. Presbyopic patients require additional plus power in certain zones of the contact lens in order to help accommodate for lost near vision. A cataract is a clouding of the crystalline lens.

Presbyopic patients require additional plus power in certain zones of the contact lens in order to help accommodate for lost near vision. Another option is monovision where one eye is corrected for far vision and the other eye is corrected for near vision. A toric (or cylindrical) lens corrects astigmatism.

The patient's daily activities and age range are important factors to consider for a successful contact lens fitting (including what modality of lenses should be chosen). Unless a contact lens is custom made, a fitter will have to select a brand with parameters that match the patient's contact lens prescription.

Soft lenses can be inserted by placing them anywhere on the sclera. Unlike soft lenses, Rigid Gas Permeable (RGP) lenses must be placed on the cornea for proper insertion. RGP lenses can also be removed by blinking while your hand is placed in the outer corner of the eye or with use of a contact lens plunger.

A flat fit is not an ideal RGP fit. A fluorescein pattern resembling a bullseye with apical clearance is optimal. The fitter also will check that the lens is not too tight allowing for slight dynamic movement.

The over-rotation of the toric lens is causing the effective contact lens prescription to be 1.75 -1.25 x 080. In order to get the desired effective contact lens prescription, 10 degrees must be added to the original prescription. If the over-rotation had been to the right, 10 degrees would need to be subtracted instead.

Temporary blurriness after blinking is caused by excessive contact lens movement. The patient should be refitted in toric lenses with either a different ballast system or decreased base curve to decrease unwanted movement. If the blurriness was resolved by blinking, this is an indication of dry eyes, dictating the use of rewetting drops. Masking of the astigmatism with spherical lenses will provide less movement but will not improve visual acuity.

A monthly contact lens should only be used for a 30-day period, regardless of how many days the contact lens is worn during the 30 days. Patients should not sleep in contact lenses.

In fitting RGPs, also known as hard lenses, it is recommended that the patient builds up wear time by adding an hour each day. Soft lenses are made from silicone hydrogel or hydrogel material.

All of these solutions can be used with contact lenses however, since the hydrogen peroxide solution contains hydrogen peroxide to disinfect the lenses, the patient must use the provided case which includes a neutralizing disc. The active ingredient will be completely neutralized by the time listed in the instructions, usually 6 to 8 hours (or overnight). This type of solution may be recommended for patients with allergies to preservatives found in other types of contact lens solution.

Saline solution does not disinfect contact lenses. It is only a combination of sodium chloride and sterilized water. Multipurpose contact lens solution is a disinfectant used to clean lenses and usually contains preservatives.

Topping off old contact lens solution and swimming in contact lenses increases a patient's risk of eye infection. In fact, any normal use of contact lenses can increase risk of infection. This is why it is important to wash hands before/after handling, not sleep in the lenses and clean them properly.

Using any type of water to clean contact lenses will increase the risk of eye infection. One corneal infection associated with distilled or tap water is Acanthamoeba Keratitis.

The comfort level of the contact lens is a subjective finding given by the patient. Over-refraction, visual acuity and over-rotation are measured objective findings.

The measured visual acuity of the contact lens is an objective finding. Subjective findings include the patient's feelings and opinions about the contact lenses.

Visual acuity test, over-refractions and refitting are common parts of a contact lens follow-up to fine-tune the prescription, while refraction usually occurs at the initial exam. For this reason sometimes the prescriber will not provide a finalized contact lens prescription until the patient returns for the follow-up.

A patient should contact the prescriber in any of the above situations. Sudden changes in vision or trouble handling the lenses should be addressed as soon as possible. Once a contact lens prescription expires, a patient will be unable to receive any lenses until they have a new exam.

The Food and Drug Administration regulates contact lenses because they are a medical device. Contact lenses require a valid prescription which includes the contact lens brand for purchase.

As long as a patient has paid their eye exam/contact lens fitting fees and the prescriber has finalized their contact lens prescription, a copy of this prescription must be given to the patient as mandated by the Fairness to Contact Lens Consumers Act.

According to the Health Insurance Portability and Accountability Act of 1996 (HIPAA), for patients 18 years and older, patient consent is needed to share medical information. However, this medical information must be shared through secure methods. Sending the contact lens prescription through the person's patient portal which is encrypted, is a more secure option then using non-encrypted e-mail.

According to the Federal Trade Commission's Fairness to Contact Lens Consumers Act, a contact lens prescription must be verified and unexpired in order for the patient to legally purchase contact lenses from a seller other than the prescriber.