The visual fields were re-assessed using Goldmann perimetry (Figure 8.16). Note that the parafoveal scotomas are fairly dense but the midperipheral and peripheral isopters are intact and do not demonstrate a superotemporal vertical step. The scotomas encroach on the smallest isopter in each eye but do not align along the vertical meridian. With this testing technique it is apparent that the defects are actually ceco-central scotomas that just happen to abut close to the vertical meridian. In light of this new interpretation of the visual field pattern, and in conjunction with the other clinical features, a diagnosis of dominant (Kjer’s) optic atrophy was considered. Records regarding other family members were obtained and were found to be consistent with this diagnosis.

Discussion: Dominant optic atrophy is a form of progressive optic neuropathy inherited in an autosomal dominant fashion but with variable penetrance. The responsible mutation has been localized

to the OP1 A gene, but the nature of the mutation varies among affected families. Onset of symptoms typically begins by age 10 and progresses very slowly over a lifetime. Central vision is predominantly affected, including loss of color vision with a characteristic tritanopic (blue-yellow) axis pattern. The optic discs show temporal pallor, which is sometimes accompanied by focal excavation. The degree of visual loss exhibits marked inter-individual variability, even among members of the same family. At the mild end of the spectrum some affected individuals retain 20/20 visual acuity and may therefore be unaware of their diagnosis. In suspected cases it may be helpful to actually examine relatives rather than relying on the patient’s report of a negative family history.

Diagnosis: Dominant optic atrophy

Tip: Bilateral ceco-central scotomas that abut the vertical meridian may mimic a chiasmal pattern of field loss, particularly on automated perimetry.

Abnormal field and photopsias

Case: A 64-year-old homemaker was referred because of a five-year history of persistent photopsias. She had also noted some difficulty seeing in dim illumination, such as finding her way in a darkened movie theater. She was generally healthy and family history was negative for similar visual loss. Examination showed normal visual acuity, color vision and pupillary responses. Goldmann perimetry demonstrated a dense scotoma in the temporal field of each eye (Figure 8.17). An MR scan was obtained, specifically looking for chiasmal compression, but was completely normal.

What aspect of this patient’s visual field defect is atypical for chiasmal compression and suggests instead an ocular disorder?

Her bitemporal defect involves the periphery and mid-periphery of the visual field, sparing the centralmost area. This pattern of field loss suggests a disorder of photoreceptors rather than an

optic nerve or chiasmal lesion. In addition, while the defects are indeed confined to the temporal hemifield of each eye, they do not respect the vertical meridian. This patient had a fullfield ERG that demonstrated marked loss of scotopic waveforms with mild reduction of photopic responses, consistent with a rod-cone dystrophy (Figure 8.18).

Discussion: About 90% of axons in the optic nerves and chiasm subserve the central 10 degrees of the visual field. Therefore, the earliest visual field change in chiasmal compression involves macular vision, usually appearing as a small, shallow defect just temporal (often superotemporal) to fixation in each eye. With continued compression, the central hemianopic defect grows in size and density, eventually breaking out to the periphery. This predilection for central field loss in chiasmal compression is in marked contrast to the pattern of loss seen in the above patient whose bitemporal defect was most marked in the mid-periphery. This pattern should suggest, instead, a retinal disorder, specifically one involving photoreceptors. The diagnosis of retinal