Understanding Vision Loss from Pathological Myopia
Richard L. Windsor, O.D., F.A.A.O.
Laura K. Windsor, O.D.
(Published in Vision Enhancement Magazine)
Pathological or Degenerative Myopia is quite different from the simple refractive myopia or nearsightedness that affects so many people around the world. Pathological myopia is an extremely high amount of nearsightedness that causes a major alteration of the shape or globe of the eye, which may lead to profound vision loss. In the United States, it occurs in about 2% of the population and is the seventh leading cause of legal blindness. It occurs most often in those of Chinese, Japanese, Middle Eastern, or Jewish descent.
Thirty percent of all cases of pathological myopia occur at birth. Sixty percent of patients are diagnosed with the condition between the ages 6 and 13, and it continues to progress throughout life. Early examinations of children at risk are crucial, for the failure to detect high myopia in young children may lead to further vision loss from amblyopia.
Associations with Other Conditions
Pathological myopia has been associated with other ocular and systemic diseases. These conditions include Down’s Syndrome, Ocular Albinism, Infantile Glaucoma, Marfan’s Syndrome, Retinopathy of Prematurity, Ehler’s-Danlos Syndrome, low birth weight, and maternal alcoholism. Patients with these diseases or conditions should be considered “at risk” for pathological myopia and carefully monitored.
Pathological myopia causes the eye to elongate, which in turn stretches and thins the retina and the sclera of the eye. This leads to a bulging of the posterior portion of the eyeball. This condition is called a staphyloma. By the age of sixty, 50% of patients with staphylomas in both eyes will be legally blind.
Myopic Macular Degeneration
As the eyeball grows and stretches, it may also cause an area of atrophy and/or cracks in the layers under the retina. These cracks can serve as conduits for abnormal blood vessels to grow under the retina. These vessels can hemorrhage and scar which is similar to what happens in wet macular degeneration. The onset of the nets of abnormal blood vessels, called Fuch’s spots, often occur in the 4th to 6th decades of life. Approximately 5% of pathological myopia patients develop Fuch’s spots, which lead to damage in the macular region of the eye and a subsequent loss of central vision.
The thinning of the layers of the eye may lead to degenerative changes in the peripheral retina including retinal holes and lattice degeneration which puts one at high risk for a retinal detachment. If retinal breaks develop, fluid may leak behind the retina causing it to detach. The risk of a retinal detachment increases significantly as the amount of myopia increases. It is crucial for all highly myopic patients to undergo dilated retinal examinations every year.
The incidence of glaucoma may increase due to alterations of the drainage angle of the eye causing which causes an increase in the fluid pressure of the eye. Detection of glaucoma may be more difficult since highly myopic patients have thicker, more rigid corneas, which can be interpreted as higher eye pressures even when the pressure is not really elevated. The thickness of the patient’s eyeglass lenses may impair visual fields testing, which is imperative in monitoring glaucoma. If the patient wears contact lenses, more accurate visual fields can be obtained.
High Refractive Error
Pathological myopia patients may present with prescriptions from –6 diopters to in excess of -40 diopters. This creates problems in correcting the patient’s refractive error. The lenses may be extremely thick and heavy. Fortunately, we are able to use small eyeglass frames combined with high index lenses to make the lenses thinner, lighter and more cosmetic.
Contact lenses have been a good option for high myopes for many years. It eliminates the weight and thickness of the lenses in eyewear. It also eliminates the side vision difficulties inherent in these thick lenses. Myopic patients usually report having better vision when wearing contact lenses, because of eliminating the problems that the eyewear causes.
Refractive Surgery / LASIK
LASIK or laser refractive surgery has not been as effective in the highly myopic corrections, as it has in the lower ranges of myopia. An alternative for the profoundly myopic patients is a “Bear Claw” intraocular lens implant. It is affixed in the anterior chamber through a simple incision and can correct extreme amounts of myopia. In some cases, a clear lens extraction may be performed. The procedure is identical to a cataract extraction. The patient’s lens is removed, but an intraocular lens in not inserted. By removing the lens, about fifteen diopters of myopia is automatically corrected.
Low Vision Considerations
Pathological myopia patients who wear eyeglasses may remove them to read. By removing their eyeglasses, it makes them automatically in focus at a few inches from their face, creating a significant amount of magnification. Most patients respond well to low vision care and low vision aids including magnifiers and CCTVs. These patients often present with mild photophobia and benefit from sunglasses. Patients with retinal detachments, myopic macular degeneration and staphylomas may have a poorer prognosis depending upon the location of the problem.
Safety Issues – Physical Education
Patients with pathological myopia have thinned retinas that can easily develop tears, holes and retinal detachments. Patients should not participate in any physical activities that can lead to jostling or trauma to the eye. Contact sports and ball sports are too dangerous. Even activities like jumping rope or volleyball can lead to a retinal detachment. Children should not participate in physical education or competitive sports without the prior review and approval of their eye doctor.
Knowing the Signs of Retinal Detachment
Every patient with pathological myopia must know the signs of a retinal detachment. These include the sudden appearance of flashes of lights, like lighting flashes. Also floaters, little shadowy dots, and/or cobwebs, shadowy strands could be the first sign of an impending retinal detachment or a tear of the retina. If you experience the sudden onset of both flashes and floaters at the same time, the risk of detachment is extremely high. In a retinal detachment, you may notice impairment in one area of your vision described like a curtain coming down. This can occur from any direction including the right or left side or from the top or bottom of the vision. You should seek an immediate retinal examination if any of these symptoms occur.
Regular Retinal Monitoring
The best way to reduce the risk of vision loss is to have regular dilated retinal examinations, and to seek immediate eye care if you have any flashes, floaters or decrease in your vision.