CHAPTER 4

The Patient With Decreased Vision: Classification

and Management

The initial goal in the assessment of reduced vision is to localize the disorder. Decreased vision may arise from abnormalities in the ocular media, retina, optic nerve, optic tracts, visual radiations, and occipital cortex. Evaluation of the patient with vision loss requires consideration of the clinical history together with results of the examination and ancillary testing, as outlined in Chapter 3, to determine causation and management.

Ocular Media Abnormality

Irregularities or opacities of the ocular media tend to reduce visual acuity, but they do not affect pupils, color vision, or the appearance of the posterior pole. They may cause generalized reduction of sensitivity on automated perimetry testing. Such conditions should be sought on slit-lamp examination and by direct ophthalmoscopic examination. These conditions may be obvious or subtle. Keratometry readings or corneal topography evaluation can help identify irregular astigmatism or early cone formation in keratoconus. The identification of early tear breakup time and subepithelial corneal dystrophies requires careful slit-lamp examination. Lenticular irregularities include central nuclear darkening, irregularity of lenticular tissue, “oil droplet” formation, and posterior lenticonus.

Retinopathy

Diseases of the macula can sometimes mimic an optic neuropathy (Table 4-1). They can produce decreased visual acuity and central visual field loss with variable color vision loss. Generally speaking, however, a relative afferent pupillary defect (RAPD) is absent. Maculopathy tends to cause parallel losses in color discrimination and visual acuity, unlike optic nerve disease, which often causes a disproportionately greater loss in color vision than that in visual acuity. Visual field deficits in maculopathy tend to be focal and central, whereas deficits in optic neuropathies are larger, often cecocentral, and part of a generalized depression of visual field sensitivity. Metamorphopsia almost

always occurs in macular disease and almost never in optic neuropathy. In general, maculopathies produce visible fundus abnormalities that allow for correct diagnosis, but when subtle, evanescent, or absent, can be mistaken for optic neuropathy. Optical coherence tomography (OCT), fluorescein angiography, and multifocal electroretinography (mfERG) may help detect an abnormality of retinal structure or function. (see Chapter 3 and BCSC Section 12, Retina and Vitreous, for further discussion of these imaging techniques.)

Table 4-1

Common maculopathies and retinopathies that are often mistaken for optic nerve disease include acute idiopathic blind-spot enlargement, which overlaps with multiple evanescent white dot syndrome, and cone dystrophy. Patients with these entities may have normal funduscopic findings at presentation. Rarer entities include cancer-associated retinopathy (CAR) and melanoma-associated retinopathy (MAR). Other retinal disorders sometimes mistaken for optic neuropathies, such as central serous retinopathy, cystoid macular edema, and acute zonal occult outer retinopathy (AZOOR), are discussed in detail in BCSC Section 12, Retina and Vitreous.

Acute Idiopathic Blind-Spot Enlargement and Multiple Evanescent White Dot

Syndrome

Traditionally, enlargement of the blind spot (Fig 4-1) on visual field testing is associated with changes of the optic disc such as edema or tilting However, the term acute idiopathic blind-spot enlargement (AIBSE) describes a clinical syndrome in which the prominent visual symptom is a monocular scotoma, often temporal in location and associated with photopsias. The main finding is an enlarged blind spot. The fundus may appear normal or show evidence of disc edema, peripapillary retinal lesions, choroiditis, retinal pigment epithelium (RPE) changes, or uveitis. This variability has led to controversy over whether these entities are separate or a spectrum of 1 disorder. Multiple evanescent white dot syndrome (MEWDS) represents one such controversy. Fundus examination may reveal characteristic small, deep retinal white spots in the posterior retina usually lasting weeks and resolving spontaneously. The transient nature of the lesions could explain the normal retinal appearance at first examination. Any demonstrable retinal lesions show early wreathlike hyperfluorescence and late staining in fluorescein angiographic studies. Indocyanine green angiography produces a very striking pattern of hypofluorescent lesions concentrated in a peripapillary distribution corresponding to the enlargement of the physiologic blind spot.

Figure 4-1 Enlargement of the blind spot. A 32-year-old woman presented with a 6-month history of continuously flashing lights to the left side in the left eye. Visual acuity was 20/15 bilaterally with a less than 0.3 log10 unit right afferent pupillary

defect. Results of automated quantitative perimetry show enlargement of the physiologic blind spot. This temporal defect does not respect the vertical midline. (Courtesy of Michael S. Lee, MD.)

Photopsias are a prominent symptom thought to reflect disease of the outer retina. Results of mfERG show depression in the peripapillary region, whereas full-field ERG response may demonstrate depressed a-waves or substantial intereye asymmetry. Spectral domain OCT line scans of the peripapillary retina reveal attenuation of the outer layers. Although AIBSE and MEWDS represent outer retinal disorders, patients with these conditions can have an RAPD. In general, patients with these disorders have a good visual prognosis. (See BCSC Section 9, Intraocular Inflammation and Uveitis, and Section 12, Retina and Vitreous, for further discussion.)

Gross NE, Yannuzzi LA, Freund KB, Spaide RF, Amato GP, Sigal R. Multiple evanescent white dot syndrome. Arch Ophthalmol. 2006;124(4):493–500.

Quillen DA, Davis JB, Gottlieb JL, et al. The white dot syndromes. Am J Ophthalmol. 2004;137(3):538–550.

Volpe NJ, Rizzo JF III, Lessell S. Acute idiopathic blind spot enlargement syndrome. a review of 27 new cases. Arch Ophthalmol. 2001;119(1):59–63.

Vitamin A Deficiency

Factors that contribute to vitamin A deficiency include malnutrition, malabsorption, liver disease, and zinc deficiency (zinc is a cofactor in the conversion of retinol to 11-cis-retinal). Manifestations of vitamin A deficiency include xerosis, conjunctival Bitôt spots, keratomalacia, nyctalopia, peripheral visual field loss, and sometimes central vision loss. Ancillary testing reveals marked rod dysfunction on ERG. Patients often show dramatic recovery with treatment, which includes vitamin A supplementation and treatment of any underlying systemic disorder.

Hydroxychloroquine and Chloroquine Retinopathy

Antimalarial drugs such as chloroquine and hydroxychloroquine can, in rare cases, cause outer retinal damage in the parafoveal macula. Hydroxychloroquine is often used in the treatment of various rheumatologic disorders. Risk factors include duration of use greater than 5 years, cumulative dose of >1000 g (hydroxychloroquine) or >460 g (chloroquine), daily dose >400 mg (hydroxychloroquine) or >250 mg (chloroquine), older age (>60 years), kidney or liver dysfunction, and preexisting macular disease. Revised screening recommendations published in 2011 by the American Academy of Ophthalmology recommend a baseline evaluation within 1 year of beginning treatment and then annual examinations after 5 years of treatment. Screening procedures include dilated fundus examination (to detect RPE changes); automated, white 10-2 threshold perimetry (to detect paracentral field loss); and 1 or more of the following 3 objective tests, which may detect toxicity before fundus abnormalities become visible:

1.spectral domain OCT (to detect parafoveal outer retinal attenuation)

2.multifocal ERG (to detect parafoveal depressed amplitudes)

3.fundus autofluorescence (to detect parafoveal increased autofluorescence)

Contrary to previous recommendations, the use of fundus photography, Amsler grid testing, and color vision testing in screening evaluations is no longer recommended.

Marmor MF, Kellner U, Lai TY, Lyons JS, Mieler WF. Revised recommendations on screening for chloroquine and hydroxychloroquine retinopathy. Ophthalmology. 2011;118(2):415–422.

Semmer AE, Lee MS, Harrison AR, Olsen TW. Hydroxychloroquine retinopathy screening. Br J Ophthalmol. 2008;92(12):1653–1655.

Cone Dystrophy

Cone dystrophy is a rare disorder characterized by unexplained vision loss that may be mistaken for a bilateral optic neuropathy. Patients of any age can present with a gradually progressive decline in visual acuity and color vision. Photophobia and hemeralopia (“day blindness”) are common. In the early stages, the fundus can appear normal or show a slightly blunted foveal reflex with granular