Myopia Vs Hypermetropia
Hypermetropia (also called hyperopia) and myopia are both words used to describe a person’s need for glasses to see better. When someone is hyperopic (has hypermetropia) it means that they are far-sighted and when someone is myopic it means they are nearsighted. Nearsighted people see clearly up close and have blurry vision at a distance, and for far-sighted people, the opposite is true. Patients with myopia will have a negative sign in front of their prescription, such as -4.00. Patients with hyperopia or hypermetropia have a plus sign in front of their prescription, such as +4.00.
These terms are related to how and where the light rays are focused when they enter the eye. This is called the focal point. The focal point of an eye is determined by how light is bent as it passes through the eye structures including the cornea, aqueous humor, lens and vitreous.
In hyperopia, without corrective lenses the light is focused posterior to the retina. This causes the focal point of the eye to be past infinity which will cause blurred vision at near greater than at distance. Correction for hyperopia uses plus power (or convex lens) glasses or contact lenses to correct the focal point to exactly infinity (also called emmetropia). Plus power lenses are thicker in the center of the lens and thinner on the outer rim of the lens.
In myopia, the light is focused anterior to the retina without corrective lenses. This causes the focal point of the eye without correction to be closer than infinity. The location of the focal point is based on the amount of myopia. Someone with low amounts of myopia will have a focal point 15 or 20 feet away whereas someone with high myopia may have a focal point just a few inches away from their eye. Correction for myopia involves minus power (or concave) glasses or contact lenses. Minus power lenses are thinner in the center of the lens and thicker on the outer rim of the lens.
An eye doctor can determine the level of hyperopia or myopia by performing a refraction. This involves a patient looking through a machine called a phoropter which holds a large number of different powered lenses. These lenses are shown to the patient one at a time to determine the lens which provides the best vision and, therefore, determines the lens power to put in that patient’s glasses. In nonverbal patients a glasses prescription can also be found through a technique called retinoscopy. This involves shining a thin beam of light into a patient’s eye while looking through a lens of a specific power. The reflection of light can be used to determine the correct lens power needed to provide the patient with emmetropia.
There are certain medical conditions that are more prevalent in patients with myopia versus hyperopia. The risk of these medical conditions is mostly related to the size of the eye. Hyperopes have shorter eyes on average and are at higher risk for conditions related to having a short eye including angle closure glaucoma and accommodative esotropia. Myopes have longer eyes on average and are at higher risk for conditions related to having a long eye including retinal detachment, posterior vitreous detachment, open angle glaucoma and cataracts.
Myopia Treatments Vs Hyperopia Treatments
Treatment for myopia and hyperopia is most commonly done with glasses, contacts or both. Before the advances of modern surgery, glasses and contacts were the only ways to treat myopia and hyperopia. However, there are now procedures available known as refractive surgery which can correct certain levels of myopia and hyperopia. These include procedures like laser-assisted in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and small incision lenticule extraction (SMILE). Eligibility for refractive surgery will depend on a number of factors including a patient’s prescription, corneal thickness and type of refractive surgery. A full evaluation should be performed by a refractive surgery specialist to determine an individuals refractive surgery options.
Related: Dry Eyes With Contacts
Myopia Vs Hyperopia (Hypermetropia): Take Home Points
When you can not see far, a person is usually has myopia. People with myopia usually have a negative prescription. The opposite is true for people who have hypermetropia, also called hyperopia. Patients with hyperopia have difficulty seeing up close and their prescriptions are positive, or have a plus sign in front of them. You can correct both of these eye problems with glasses, contacts, or refractive eye surgery.
Sources:
Moore BD, Augsburger AR, Ciner EB, Cockrell DA, Fern KD, Harb E. Optometric Clinical Practice Guideline: Care of the Patient with Hyperopia. St. Louis, MO: American Optometric Association; 1997:1-29
American Association of Pediatric Ophthalmology. Retinoscopy. http://www.aapos.org/terms_faqs/faq_list/retinoscopy. [May 2010]
American Association of Pediatric Ophthalmology. Refractive errors. http://www.aapos.org/faq_list/refractive_errors . [May 2010].
