Detecting and Treating Poor Night Vision
Helping patients who are experiencing decreased contrast sensitivity and night-vision problems.
BY STEVE SILVERSTEIN, M.D., F.A.C.S.
A 48-year-old cross-country truck driver presents to clinic with a history of declining vision, particularly while driving after dark. His examination reveals moderate posterior subcapsular cataracts, with a BCVA of 20/40 OD, and 20/60 OS. Cataract extraction is recommended, and discussion centers on the best choice in IOL technology, considering his age and his career/social activities.
While poor night vision is most notably associated with physiologic conditions, including, for example, retinitis pigmentosa, rod-cone dystrophy or cone-rod dystrophy and a variety of esoteric conditions, this article will focus on the natural effects of aging and iatrogenic causes of decreased contrast sensitivity and/or night vision.
Use of a brightness acuity tester (BAT) is one reliable measure of patient's subjective complaints. If the clinician has the equipment to perform this test, contrast sensitivity is an indicator that may further shed light on a patient's symptoms.
| Poor Night Vision is Widespread and Has Many Underlying Causes |
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Based on multiple FDA studies, difficulty with night driving in a younger population affects about one-third of that population, says Scott MacRae, M.D., professor of ophthalmology at the University of Rochester School of Medicine. "This is preoperative and is a fairly consistent problem," says Dr. MacRae. "Many people in the general population have this problem." Dr. MacRae says that until the advent of customized correction after refractive surgery, most refractive studies with conventional treatment showed that night vision was typically worse postoperatively. "With custom correction, you are more likely to get improved night vision," he says. "From the Zyoptics study,1 40% of the patients noted an improvement in night driving, 10% noted they were worse (but none of the 10% were dissatisfied with the surgery) and the remaining 50% noted no change. You were four times more likely to get better night vision than worse." Causes of Night Vision Problems Dr. MacRae sees a lot of interesting cases as an optics specialist. For patients with dysphotopsia, he normally performs wavefront measurements and will find a great deal of spherical aberration. "Some of these patients may benefit from customized spectacle correction which in now being offered by Ophthonix under the brand name iZon. In the United States, we don't have good customized topographic ablation available yet which could help these patients." He states that in post-cataract eyes, patients treated with monofocal or multifocal lenses typically have night-vision symptoms due to residual astigmatism or corneal high order aberrations (HOAs) that are confounding the multifocal optics. He recommends using a wavefront censor and corneal topography, as they can be helpful in identifying if the patient has a high level of spherical aberration or HOAs. Dr. MacRae says that surgeons need to become better informed about wavefront measurements — especially with premium IOLs. "These patients have underlying corneal HOAs, which most topographers don't really describe for surgeons very well, and those can cause or compound the multifocal aberration issue. Compounding the aberration structure causes the trouble with night driving." Dr. MacRae says that if a patient is experiencing light scatter, it can be caused by the tear film breaking up, which reduces image quality. Chronic meibomianitis or aqueous tear deficiency are common culprits. Another way that patients may experience poor night vision could be due to vitamin A deficiency. He says that while the vitamin A issue is rare, it is usually found in patients with malabsorption, extensive intestinal surgery or a history of liver disease and alcoholism. This deficiency may manifest as chronic dry eye or reduced ability to see at night. "This is why a good patient history is so important," he concludes. Taking Steps to Uncover the Cause Stephen E. Pascucci, M.D., of Bonita Springs, Fla., describes the steps he takes in order to uncover the cause of his patients' poor night vision. Dr. Pascucci says that night vision complaints are very common in his practice because he treats numerous "very social" retired people. "In our practice, we query every patient by having him/her fill out a questionnaire so that we can find out why they have come in," says Dr. Pascucci. "We then try to get into more specifics with our technicians. We try to pinpoint whether night vision is poor because of disease, cataracts or dry eye." At the next step, Dr. Pascucci confirms the patient's condition and asks more pointed questions. He then performs an exam. "I start with visual acuity testing and then have the patient refracted," says Dr. Pascucci. "I have a good look at their lens and evaluate their tear film. We evaluate everyone for dry eye and then look at other ideologies such as retinal and glaucoma." In the majority of Dr. Pascucci's patients, poor night vision is primarily due to cataracts or dry-eye related. "With dry eye, there is a slow deterioration over time. Patients come in with other complaints, not just night vision issues. If it is only an issue of night vision, it is usually due to a cataract," says Dr. Pascucci. A Device That Helps Detect Poor Night Vision Vision experts have learned that the pupil has a tremendous effect on the quality of the image that's focused on the retina. The Optical Path Difference map generated by Marco's 3-D Wave (Marco Ophthalmics, Jacksonville, Fla.) provides three refractions for patients. The first is in the center of the pupil, the second is at the 3-mm zone and the third is at the 5-mm zone. The 3-D Wave's Wavefront Total Map allows users to recalculate the zone to obtain a night prescription based on the patient's mesopic pupil size, out to 6 mm. For patients who need to function well in low light or very bright light, especially if they have significant prescription shift to pupil size, the illumination level is critical and should be varied accordingly.2 References
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The Aging Process
It has been well reported for decades that the aging process causes anatomic changes to the retinal pigment epithelium as well as changes to the cornea, including ocular surface and tear film abnormalities, changes in collagen matrices, changes to the natural crystalline lens, significant vitreous floaters, the potential for epiretinal membrane formation and/or macular pucker. Each of these occurs naturally, and has been shown to reduce contrast sensitivity and/or worsen patient symptoms of night vision performance.
The most common and obvious cause of these symptoms is cataracts. Nighttime driving issues or glare often precede changes in visual acuity. Oftentimes, it is the glare and decreased night driving that brings patients in for initial evaluation.
Front to Back
Practitioners should start with the front of the eye and work their way back as to the potential source of the complaint. Begin with the ocular surface. If the patient has tear insufficiency or ocular surface disease, artificial lubricants, treatment of meibomitis and blepharitis, as well as other causes of ocular surface disease must be addressed in order to maximize ocular surface health. You should look for corneal pathology including basement membrane dystrophy, scarring, punctuate keratitis or topographic irregularity. Then, examine the lens, which is the most frequent culprit. If a patient has a visually significant cataract, surgical options should be discussed.
Posteriorly, the vitreous may be a contributing factor, as some patients are plagued with a greater-than-average number of vitreous floaters, which interfere with their central acuity. These are caused by condensations forming in the vitreous gel, pigment that flecks off the retina or the sequelae of a posterior vitreous detachment. To a lesser degree, significant asteroid hyalosis can play a role, but usually the patient is unaware of this condition.
Glaucoma can cause night vision problems, particularly when peripheral vision is constricted. As a result, patients use less of the information presented to them, and images may appear darker. Retinal pathology in the form of epiretinal membrane, macular pucker, retinal drusen, scarring, macular edema (from any cause — diabetes, post-cataract surgery, etc), retinal pigment epithelial detachment and central serous maculopathy are some of the most common pathologies that may cause night vision abnormalities.
Iatrogenic Etiologies
Routine cataract surgery with a monofocal implant in either patients at greater risk, or in low-risk uncomplicated cataract patients, may develop increased macular thickening or clinical/subclinical macular edema, each of which may negatively impact night vision and/or contrast sensitivity.
The routine use of an NSAID medicine preoperatively and postoperatively is essential to lowering the risk of macular thickening and/or macular edema.
Finally, it is clear that premium IOLs, particularly multifocal IOLs, cause a decrease in contrast sensitivity and have a negative effect upon nighttime activities, such as driving. Multifocal lens implants, either refractive, diffractive or apodized, all impact contrast sensitivity. Usually the benefits of the lens far outweigh this mild decrease in contrast sensitivity, but it also suggests that it is particularly important to treat these patients with a steroid as well as a nonsteroidal to minimize the contribution caused by macular thickening at the time of surgery.
You need to know when you should avoid a multifocal lens implant. Patients who already have macular compromise, such as those with a previous history of retinal or epiretinal surgery, should not receive a multifocal IOL, but may be good candidates for a pseudo-accommodating lens implant because there is little to no decrease in contrast sensitivity with this technology.
A discussion with patients prior to surgery regarding these possible side effects is extremely important, as well as careful monitoring and reassurance postoperatively during the neuro-adaptation process. OM
Reference
1. Wittpenn J, Silverstein S, et al. A Randomized, Masked Comparison of Topical Ketorolac 0.4% Plus Steroid vs Steroid Alone in Low-Risk Cataract Surgery Patients. AJO, 146:(4):554-560.
| Steven M. Silverstein, M.D., F.A.C.S., is a partner in Silverstein Eye Centers, P.C., in Kansas City, Mo. He is also clinical professor of ophthalmology at the University of Missouri Kansas City Medical School and clinical professor of ophthalmology at the University of Health Sciences. He can be reached via e-mail at ssilverstein@silversteineyecenters.com |
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