In refractive errors, vision becomes impaired because a shortened or elongated eyeball that prevents light rays from focusing sharply on the retina. This impairment may be corrected by eyeglasses or contact lenses.
- Ophthalmic refraction determines refractive errors of the eye for vision correction, and consists of placing various types of lenses in front of the patient’s eyes to determine which lens best improves the patient’s vision.
- Emmetropia: the image is focused on the retina; normal refractive condition with no optical defects.
- Myopia: the image is focused before it hits the retina (deep eyeball), resulting in nearsightedness.
- Hyperopia: the image is not focused when it hits the retina (shallow eyeball), resulting in farsightedness.
Vision impairment is defined as having central visual acuity of 20/40 or worse in the better eye with the best possible correction. Low vision describes visual impairment that requires the use of devices and strategies to perform visual tasks. Blindness is having a best corrected central visual acuity of 20/400 to no light perception (absolute blindness). Legal blindness only requires a best corrected central visual acuity of 20/200, or those whose widest visual field diameter is 20 degrees or less. This may range from inability to perceive light to having some vision remaining.
Diagnostic Examination
- Patient Interview: determine potential cause and duration of visual impairment. Customary ADLs, medication regimen, habits (e.g. smoking), acceptance of the physical limitations brought about by visual impairment, and realistic expectations of how low-vision aids are identified and included in the plan of care, as well as safety guidelines and referral to social services.
- Retinitis pigmentosa is featured in genetic abnormality.
- Diabetic macular edema typically feature fluctuating visual acuity.
- Macular degeneration features central acuity problems that result in difficulties in activities requiring finer vision.
- Peripheral field defects produce difficulty in mobility.
- Contrast-Sensitivity Testing measures visual acuity in different degrees of light and dark contrast to determine visual function. Glare testing measures visual acuity with glare, and also determines visual function.
- Loss of contrast and glare sensitivity produce difficulty in low light environments, such as driving at night or in foggy conditions.
Medical Management
- Magnification and Image Enhancement through Low-vision Aids and Strategies: optimize the patient’s remaining vision and assist the patient to perform customary activities. These aids include hand magnifiers, bifocals, spectacles, and lightweight handheld monoscopes or telescopes.
- Medications may manage conditions that result in visual impairment, such as glaucoma.
Elective procedures can be performed to correct refractive errors (myopia or hyperopia) and astigmatism by reshaping the cornea. Laser Vision Correction alters the major optical function of the eye and carries risks. Precise visual outcome cannot be guaranteed. Both the cornea and the error itself must be stable. Patients with conditions that are likely to adversely affect corneal wound healing are not good candidates for surgery. Any superficial eye disease must be diagnosed and treated before a refractive procedure.
- Laser Vision Correction Photorefractive Keratectomy: an excimer laser is applied directly to the cornea, which decreases relative curvature for myopia, or increases relative curvature with hyperopia. A bandage contact lens (like the one used in corneal abrasion) is used for promoting epithelial healing.
- Laser-Assisted In Situ Keratomileusis (LASIK) flattens the anterior curvature of the cornea by removing a stromal lamella or layer. Corneal tissue is cut (not completely) to access the stromal bad, where the laser acts. There are few adverse outcomes of this procedure. Effectivity of myopic correction compared to PRK has not been determined.
- Errors in LASIK may result in central islands and decentered ablations, resulting in monocular diplopia, halos, glare, and decreased visual acuity.
- Phakic Intraocular Lenses: increasingly being used for moderate to severe myopia as of 2019. Phakic IOLs may be used in either the anterior or posterior chamber. Because it leaves the natural lens and anatomy in place, this surgery is reversible, and produce more predictable results. It is safer, and has higher patient satisfaction scores. Complications include cataract, iritis/uveitis, endothelial cell loss, and increased IOP.
- Conductive Keratoplasty: correction of low to mild hyperopia using thermal keratoplasty, applying a radiofrequency current to the peripheral cornea with a thin, handheld probe. This does not involve the removal of corneal tissue.
Nursing Management
Sensitivity to challenges faced by patients with visual impairments is necessary. Emotional adjustment determines the success of the physical and social adjustments of the patient.
- Promote Coping: allow the patient to recognize the permanence of low vision or blindness. A newly visually impaired patient and family members can undergo various steps of grieving. Willingness to adapt to the changes influence successful rehabilitation of the patient with vision loss.
- Promote Spatial Orientation and Mobility: spatial concepts are required to perform some ADLs such as walking to a chair from a bed; their relative positions in the room should be known, and how to approach each area safely. Collaborative efforts between the patient and companions are required. Determine the degree of physical assistance required. Encourage independence and ensure safety.
- Promote Home, Community-Based, and Transitional Care: braille, service animals, print magnification technology, technology-assisted speech output, etc.