Bitemporal visual field defects mimicking chiasmal compression in eyes with tilted disc syndrome

Transcription

1 Optometry (2009) 80, Bitemporal visual field defects mimicking chiasmal compression in eyes with tilted disc syndrome Joseph W. Sowka, O.D., a and Vincent V. Luong, B. Optom. b a Nova Southeastern University College of Optometry, Ft. Lauderdale, Florida, and b Eyes in Style Pty. Ltd., Vincent Luong Optometrists, Miller, New South Wales, Australia. KEYWORDS Tilted disc syndrome; Visual field defect; Bitemporal visual field defect; Coloboma; Chiasmal compression; Pituitary adenoma; Craniopharyngioma; Frequency doubling threshold perimetry Abstract BACKGROUND: Tilted disc syndrome (TDS) is a congenital optic nerve coloboma occurring from embryonic dysgenesis. Several features characterize TDS, including an inferiorly located conus, situs inversus of the major retinal vessels, and an anomalous disc shape. Commensurate with axonal dysgenesis, visual field defects may often occur from TDS, the most common of which involve the temporal and superior temporal visual field. These visual field defects can mimic those seen in chiasmal compression from a mass lesion. CASES: Five patients from New South Wales, Australia, with distinct TDS and bitemporal visual field defects on frequency doubling threshold perimetry seemingly respecting the vertical hemianopic line are presented. Neuroimaging and medical evaluation of each failed to show intracranial chiasmal pathology in any patient. CONCLUSIONS: TDS can present with visual field loss resembling that seen in chiasmal disease. Although most cases of temporal visual field loss from TDS do not respect the vertical hemianopic line and are not true quadrantanopsias, there are instances in which this does occur, likely caused by the testing modality used. It is essential that patients with suspected intracranial pathology undergo immediate neuroimaging, even in the face of TDS. Optometry 2009;80: Tilted disc syndrome (TDS) is a congenital defect of the optic nerve. Although the appearance may vary among patients, there are some distinct common ophthalmoscopic characteristics. The optic discs in eyes with TDS have a seemingly tilted appearance of the optic disc where a normally vertically oval disc has its long axis horizontally. There often is an associated hypoplasia of the retina, retinal pigment epithelium (RPE) and choroid, which presents as distinct pale areas of the fundus often seen more nasally and Corresponding author: Joseph W. Sowka, O.D., Nova Southeastern University College of Optometry, 3200 South University Drive, Ft. Lauderdale, Florida jsowka@nova.edu inferior nasally where the choroidal vessels are more readily visible. Frequently, there is situs inversus of the major retinal blood vessels, where most of the retinal vessels emerge out of the optic nerve into the retina nasally and then suddenly turn temporally in their course. However, the most characteristic finding is Fuchs coloboma, which is an ectatic conus of the inferior and inferior nasal aspect of the disc. 1-5 Although typically benign, rare complications can occur in TDS. Choroidal neovascularization has been reported to develop in eyes with TDS, specifically in the area of the inferiorly located conus, presumably caused by congenital ectasia predisposing the area to rents in Bruch s membrane. 6,7 However, the main difficulties arising from TDS are its ability to mimic serious neurologic diseases. This occurs /09/$ -see front matter Ó 2009 American Optometric Association. All rights reserved. doi: /j.optm

2 Sowka and Luong Clinical Care 233 because eyes with TDS have unusual-shaped discs often with unusual cupping that may be mistaken for glaucoma, elevation of superior segments that may be mistaken for disc edema, and scleral crescents that may be mistaken for optic atrophy. Although visual acuity in eyes with TDS typically is excellent, measurable visual field deficits can occur. Specifically, eyes with TDS can have temporal and superior temporal perimetric visual field defects. In that TDS is bilateral in 60% to 80% of cases, the possibility exists of patients manifesting bitemporal visual field defects mimicking that seen from compression of the optic chiasm by a mass lesion, such as a pituitary adenoma or craniopharyngioma. 8,9 However, the association between TDS and bitemporal visual field loss seems not especially well known. This report describes 5 patients with bilateral TDS and normal chiasmal neuroimaging with bitemporal visual field loss on frequency doubling threshold perimetry seemingly respecting the vertical hemianopic line, thereby mimicking chiasmal compression. Case 1 A 38-year-old Hispanic man presented for a comprehensive eye examination without complaints. Best-corrected visual acuity was 20/20 in each eye with a myopic correction (22.00 diopter sphere [DS] in the right eye [O.D.] and DS in the left eye [O.S.]). An evaluation for glaucoma was initiated because of abnormalities found on screening visual fields. Intraocular pressure (IOP) was 17 mmhg in both eyes (OU), and central corneal thickness (CCT) was 490 mm O.D. and 502 mm O.S. Dilated fundus examination showed TDS OU with situs inversus of the major retinal vessels and inferiorly located conus in each eye (see Figure 1). The appearance of the left eye was more characteristic for TDS. Threshold perimetry (Matrix FDT) showed a bitemporal visual field defect, which was densest O.S. and seemingly respecting the vertical hemianopic line in each eye, suggesting chiasmal compression (see Figure 2). There was no evidence or report of gynecomastia or galactorrhea, and the patient reported no headaches. Subsequent magnetic resonance imaging (MRI) failed to reveal any mass lesions affecting the optic nerves or chiasm. The visual field loss was subsequently ascribed to TDS, and the patient is being monitored. Case 2 A 37-year-old white woman presented for a comprehensive eye examination with no complaints. Biomicroscopic examination was unremarkable, and IOP was 16 mmhg OU. The patient manifested TDS OU with D-shaped optic discs, situs inversus of the major retinal vessels, and inferior conus and fundus hypoplasia OU (see Figure 3). Because the patient was on long-term prednisone use for Figure 1 Tilted disc syndrome seen in case 1 patient with prominent inferior conus and situs inversus OU. medullary cystic kidney disease, baseline perimetry was performed in case IOP increased from steroid use. A dense bitemporal visual field defect was obtained on threshold perimetry (see Figure 4). The patient denied amenorrhea and galactorrhea (though 5 months after initial presentation, she reported that her menstrual cycle had become irregular). The patient was immediately referred for both computed tomography (CT) and magnetic resonance imaging, both of which found no evidence of chiasmal compression. Adrenocorticotropic hormone, serum prolactin levels, follicle stimulating hormone, and thyroid stimulating hormones were all normal. The visual field loss was therefore attributed to TDS, and the patient remains under periodic observation.

3 234 Optometry, Vol 80, No 5, May 2009 Figure 2 Bitemporal threshold perimetric defect seemingly respecting vertical hemianopic line in case 1 patient.

4 Sowka and Luong Clinical Care 235 Figure 6). Subsequent contrast-enhanced CT scan of the orbits and chiasm found no mass lesion in the sellar and parasellar areas and no evidence of chiasmal compression. In the face of normal neuroimaging, the visual field loss was ascribed to TDS. The patient has since been lost to follow-up. Case 4 A 16-year-old white girl presented with complaints of blurred distance vision. Subsequent refraction improved acuity to 20/20 in each eye with a moderate myopic prescription. Biomicroscopic examination was unremarkable, and IOP was 19 mmhg OU. Dilated fundus examination found a D-shaped optic disc with inferior conus, situs inversus of the major retinal vessels, and fundus hypoplasia OU (see Figure 7). Because of the anomalous disc appearance and borderline IOP, baseline perimetry was performed, which found a bitemporal defect seemingly respecting the vertical hemianopic line (see Figure 8). The patient denied dizziness, headache, galactorrhea, and menstrual irregularity. The patient was referred for a contrastenhanced CT of the orbits, chiasm, sellar, and parasellar areas, which was normal. In the absence of intracranial pathology, the visual field loss was ascribed to TDS, and the patient continues to be monitored periodically. Case 5 Figure 3 D-shaped optic disc with inferior conus, situs inversus, and fundus hypoplasia OU in case 2 patient. Case 3 A 49-year-old Vietnamese man presented for a comprehensive eye examination with complaints of blur while reading. The patient s chief complaint was adequately addressed by refraction and appropriate spectacle add power. Biomicroscopic examination found a moderate cataract O.D., and IOP was 18 mmhg OU. CCT was 607 mm O.D. and 596 mm O.S. Dilated fundus examination found large anomalous nerves with inferior conus and situs inversus of the major retinal vessels (see Figure 5). Although both discs showed typical characteristics for TDS, there were additionally thin neuroretinal rims. For this reason, threshold perimetry was performed, which subsequently revealed a bitemporal defect seemingly respecting the vertical hemianopic line (see A 43-year-old white woman presented with vision complaints at distance and near. Her chief complaints were adequately rectified by subsequent refraction. The patient s history was significant for myocardial infarction 2 years earlier. She reported that her mother had glaucoma. Biomicroscopic examination was unremarkable, and IOP was 24 mmhg OU. CCT was 632 mm O.D. and 620 mm O.S. Dilated fundus examination found D-shaped optic discs with inferior conus, situs inversus of the major retinal vessels, and fundus hypoplasia OU (see Figure 9). Because of the family history of glaucoma and elevated IOP, threshold perimetry was performed, which found superior nasal and superior temporal defects in each eye. The nasal and temporal defects were considered to be separate scotomas because they were not contiguous. However, the densest area of defect was bitemporal (see Figure 10). Based on the visual field appearance, the patient was referred to her primary care physician who facilitated CT scanning. The CT scan showed no evidence of intracranial pathology. The patient is being monitored periodically. Discussion TDS is a congenital anomaly in which the optic disc appears to be rotated about its axis. However, it must be understood that there is no actual rotation, but only the

5 236 Optometry, Vol 80, No 5, May 2009 Figure 4 Bitemporal visual field defect seemingly respecting vertical hemianopic line in case 2 patient.

6 Sowka and Luong Clinical Care 237 Figure 5 Marked tilted disc syndrome with inferior conus and situs inversus in case 3 patient. appearance of rotation because the colobomatous formation inferiorly results in an absence of tissue. Thus, the remaining tissue is concentrated in the superior and superior temporal aspect of the disc. The inferior and inferior nasal aspect of the disc is deficient in axons. 1 Instead of a vertically oriented disc, the nerve fibers are shifted, giving many TDS discs a D-shaped appearance. 1,5,10 TDS is theorized to result from incomplete closure of the embryonic fetal fissure at 6 weeks gestation. This forms a typical coloboma, which may include the optic disc, parapapillary retina, retinal pigment epithelium (RPE), and choroid. This colobomatous formation occurs exclusively at the inferior and inferior nasal aspect of the disc. 1,4,5 The major retinal vessels often may be anomalous in TDS. Vessels often are obliquely deviated toward the inferior conus. These major vascular arcades will emerge from the disc, immediately course nasally, and then abruptly turn temporally. This anomalous branching pattern is termed situs inversus. 1,3-5 The most common visual abnormality occurring from TDS is visual field defect. 9,11-14 A number of visual field defect patterns have been identified, including temporal defects, upper altitudinal field defects, and enlarged blind spots. 9 However, the most commonly encountered visual field defect is located superior temporally. 3,9,11-14 Because of the inferior and inferior nasal absence of axons, superior and superior temporal visual field deficits can be anticipated. In cases of bilateral TDS, bitemporal field deficits can present, suggesting chiasmal compression. However, these visual field defects are not considered true quadrantanopsias because they are not restricted to the superior temporal quadrant and typically do not respect the vertical hemianopic line as would a chiasmally related quadrantanopsia. 1,9 However, in cases in which the visual field defect seemingly respects the vertical hemianopic line, differentiating the cause between TDS and true chiasmal compression can be tenuous. In such cases, neuroimaging of the chiasm is mandatory. In this case series, 5 patients with TDS and normal chiasmal neuroimaging were seen to have bitemporal field defects that seemingly respected the vertical hemianopic line on frequency doubling threshold perimetry. There are several possible explanations for this observation. Because of the anatomic arrangement of the fibers in the colobomatous disc, there could be, by chance, a field defect that stopped at the vertical hemianopic line. However, more likely, the appearance of bitemporal field defects that seemingly respect the vertical hemianopic line is a factor of the test modality used to measure the patients visual fields in concert with the congenital absence of nerve fibers. FDT threshold perimetry is designed primarily to assess for glaucoma. It is not especially well suited to test for neurologic conditions of the chiasm or retrochiasmal area because it does not test in great detail on either side of the vertical hemianopic line. An alternate perimetric device and test strategy such as a Humphrey Field Analyzer 30-1 or 24-1 or Goldmann Bowl perimeter could quite possibly identify field defects crossing the vertical hemianopic line. Unfortunately, alternate perimetric testing was not available for any of these patients. Conclusions TDS is a congenital coloboma involving the inferior and inferior nasal disc, retina, RPE, and choroid. This congenital absence of axons caused by embryonic dysgenesis often manifests in visual field defects, the majority of which are located superior temporally. When TDS occurs bilaterally, the resultant visual field defect may be described as bitemporal and can even mimic those deficits seen to occur from mass compression on the optic chiasm. Although the visual field defect occurring because of TDS is not limited by the

7 238 Optometry, Vol 80, No 5, May 2009 Figure 6 Bitemporal visual field defect seemingly respecting vertical hemianopic line in case 3 patient.

8 Sowka and Luong Clinical Care 239 Figure 7 D-shaped optic disc with inferior conus, situs inversus, and fundus hypoplasia OU in case 4 patient. vertical hemianopic line, it is not inconceivable that some of these visual field defects may seemingly respect the temporal quadrant only, as seen in the 5 cases presented here. Quite likely, the appearance that the field defects respecting the vertical hemianopic line may well be a factor of the type of threshold testing used. However, in that FDT threshold perimetry with the Matrix perimeter is commonly used in clinical practice, it is important for those who use this device Figure 8 Bitemporal visual field defect in case 4 patient.

9 240 Optometry, Vol 80, No 5, May 2009 Figure 8 (Continued). to be aware that patients with TDS may have bitemporal field defects seemingly respecting the vertical hemianopic line when tested on this device. In such situations, alternate field strategies may be considered before neuroimaging. However, regardless of the presence of TDS, any patient with bitemporal visual field defects suggestive of chiasmal compression should undergo neuroimaging in the event that a patient has both TDS and an underlying chiasmal mass lesion. However, Figure 9 D-shaped optic disc with inferior conus, situs inversus, and fundus hypoplasia OU in case 5 patient.

10 Sowka and Luong Clinical Care 241 Figure 10 Visual field defect in case 5 patient. Although there is nasal field loss additionally, the densest part of the scotoma is bitemporal. Also, the nasal and temporal defects are not contiguous and can be considered separate scotomas.

11 242 Optometry, Vol 80, No 5, May 2009 if neuroimaging fails to reveal intracranial pathology, the genesis of the visual field defect can be ascribed to TDS. References 1. Sowka J, Aoun P. Tilted disc syndrome. Optom Vis Sci 1999;76(9): Apple DJ, Rabb MF, Walsh PM. Congenital anomalies of the optic disc. Surv Ophthalmol 1982;27(1): Prost M. Clinical studies of the tilted disc syndrome. Klin Oczna 1991; 93(4-5): Young SE, Walsh FB, Knox DL. The tilted disk syndrome. Am J Ophthalmol 1976;82: Dorrell D. The tilted disc. Br J Ophthalmol 1978;62: Khairallah M, Chatti T, Messaoud R, et al. Peripapillary suretinal neovascularization associated with tilted disc syndrome. Retina 1996;16: Stur M. Congenital tilted disk syndrome associated with parafoveal subretinal neovasculatrization. Am J Ophthalmol 1988;105: Pyhtinen J, Lindholm EL. Imaging in optic nerve coloboma. Neuroradiology 1996;38: Manfrè L, Vero S, Focarelli-Barone C, et al. Bitemporal pseudohemianopia related to the tilted disk syndrome: CT, MR, and funduscopic findings. AJNR Am J Neuroradiol 1999;20: Giuffre G. Hypothesis on the pathogenesis of the papillary diversion syndrome. J Fr Ophthalmol 1985;8: Manor RS. Temporal field defects due to nasal tilting of discs. Ophthalmologica 1974;168: Berry H. Bitemporal depression of the visual fields due to an ocular cause. Br J Ophthalmol 1963;47: Brazitikos PD, Safran AB, Simona F, et al. Threshold perimetry in tilted disc syndrome. Arch Ophthalmol 1990;108: Vuori ML, Mäntyjärvi M. Tilted disc syndrome may mimic false visual field deterioration. Acta Ophthalmol 2008;86(6):622-5.