Fig. 5.21  Psuedopapilledma. Buried drusen can give the appearance of disc edema

Ultrasound or high-definition CT may be useful in detecting drusen buried in the nerve head [166].

5.10  Hyperopia

Hyperopia may mimic subacute papilledema in moderately to severely hyperopic children and adults. The disc is elevated and its edges are indistinct. The physiological cup usually remains visible. The surface of the disc may have a grayish, opaque cast. The disc does not transilluminate. True papilledema or neuritis may be ruled out by the lack of venous congestion and by absence of dye leakage on fluorescein angiography. The elevated appearance of a hyperopic disc has been attributed to a narrowed scleral canal and also to hyperplasia of glial tissue.

5.11  Persistence of the Hyaloid System

This condition can occur unilaterally or bilaterally and can be associated with mild amblyopia. The physiologic cup may be obliterated, and there is often a dirty grayish cast to the surface of the disc. The glial hyperplasia may be associated with persistent hyaloid remnants. The retinal vessels may be tortuous and obscured

within the disc. This can be differentiated from papilledema by observing the consistent coloration of the veins as they course over the disc margin, in contrast to the alternately light and dark vessels seen on the truly edematous disc and retina. Venous and capillary dilatation, hemorrhages, and exudates are absent in this anomalous elevation of the optic disc.

5.12  Tilted Disc

5.12.1  Introduction

Tilted disc syndrome (TDS), also referred to as a segmental optic nerve hypoplasia, is a readily identified congenital nonhereditary bilateral defect of the optic disc with a variable ophthalmoscopic appearance and numerous associated visual deficits and complications.

5.12.2  Historical Context

In 1882, Fuchs was the first to explain this syndrome as being a form of typical coloboma with defective closure of the fissure in the involved regions.

5.12.3  Overview with Clinical Significance

TDS has varied appearance and ability to resemble closely acquired diseases of the optic nerve. It has frequently been misdiagnosed, and patients are needlessly subjected to unnecessary medical tests.

5.12.4  Genetics

The syndrome shows no hereditary patterns [76].

5.12.5  Pathophysiology

TDS is strongly suspected to result from incomplete closure of the fetal fissure at 6 weeks gestation with the formation of a typical coloboma of the disc, peripapillary

retina, RPE, and choroids [76, 167, 168]. In TDS, the colobomatous formation occurs exclusively at the inferior and the inferonasal aspect of the disc and peripapillary retina, RPE, and choroids. Chorioretinal and RPE changes are frequently found to a variable degree in TDS [169].

5.12.6  Incidence

The syndrome occurs equally in men and women in 1–2% of the population.

5.12.7  Natural History and Prognosis,

i.e., Signs, Symptoms, Timing, etc.

TDS has a highly varied appearance, which is dictated by the degree of colobomatous formation of the disc and peripapillary retina.

1.Rotated appearance of the optic nerve head: In TDS, the disc appears to be rotated about its axis (Fig. 5.22). However, there is no actual rotation of the disc. The appearance of rotation is due to the congenital absence of tissue. The nerve tissue is concentrated in the superior and superior temporal aspect of the disc,

whereas the inferior and inferior nasal aspect is deficient in axons. Instead of a vertically oriented disc, the nerve fibers appear shifted, so that the superior portion of the disc appears to be positioned in the superior nasal quadrant [76, 168]. This gives the disc in TDS a D-shaped appearance with the flat edge corresponding to the area of inferior conus.

2.Anomalous branching pattern of retinal vessels:

Situs inversus: oblique direction of the vessels often deviated toward inferior crescent (Fig. 5.23). In classic presentations, the major vessels will emerge from the disc temporally, immediately course nasally, then abruptly turn and course temporally in the typical distribution of these vessels. The abnormalities associated with the choriosclearl canal in TDS have been suggested as the cause of the anomalous vascular branching patterns. The vessels in the superior temporal aspect of the nerve must effect a sharp turn in order to pass through the chorioscleral canal, whereas the vessels in the inferior have a very gentle slope to accommodate in order to pass through the chorioscleral canal. Thus, the vessels have an oblique orientation exiting from the disc.

3.Hypoplasia of RPE, retina, and choroids: It has been shown that there is fewer ganglion cell fibers entering the disc in the inferior nasal aspect in TDS [168, 170]. There are also areas of thinning

Fig. 5.22  Tilted disc of the right eye. Disc appears to be rotated superior nasally. Can be associated with superior temporal visual field defect

Fig. 5.23  Tilted disc. Note straightening of the temporal vessels and peripapillary choroidal atrophy

choroid and RPE. These can be explained by the congenital coloboma, which extends beyond the optic disc [168, 170].

4.Conus of inferior or inferior nasal aspect of optic disc: this must be distinguished from the acquired crescent as in degenerative myopia, which typically is located temporally and enlarged over time.

5.Posterior ectasia and staphyloma (Fuch’s colo­ boma): inferior or inferior nasal aspect of disc and peripapillary area. The staphyloma may range from 6 to 9 D by retinoscopy [76] and correspond to the region of fundus pallor. The degree of posterior bulging can be demonstrable with B scan ultrasonography and neuroradiologic imaging. These eyes are usually mildly to moderately myopic. Astigmatism with an oblique axis is often present. In contrast to acquired pathologic high myopia, the myopia is not progressive.

6.Medullated nerve fibers

7.Lacquer crack: The staphyloma formation is theorized­ to be the etiology for the stretching of the tissues, with localized rents in Bruch’s mem­ brane.

8.Central retinal vein thrombosis

9.Peripapillary and macular subretinal hemor­ rhages and choroidal neovascularization: choroidal neovascularization has been seen in other conditions associated with faulty closure of the embryonic fetal fissure such as retinochoroidal coloboma [171] and optic nerve pit [172]. In TDS, the CNV typically develops in the area of fundus hypoplasia. They may also develop in the superior temporal peripapillary area and along the lacquer crack. Fortunately, the prognosis for retaining good visual function is quite good. Parafoveal photocoagulation has shown good result [173].

10.Colobomatous thinning of neuroretinal rim mim­ icking acquired glaucomatous notching

11.Segmental hypoplasia of the disc (Fig. 5.24)

12.Neural tissue concentration in superior and supe­ rior temporal aspect of the disc mimicking acquired disc edema

The most common visual deficit in TDS is visual field depression. The most commonly encountered defect is a superior temporal depression [76, 174–176]. Different from true quadrantanopsia seen in chiasmal compressive lesion, the field defect in TDS although

Fig. 5.24  Tilted disc appearance due to segmental temporal atrophy

occurs bilaterally, does not respect the midline. In select cases, the visual field defect has been seen to improve or even disappear with refractive correction. Other types of visual field defect reported include arcuate scotoma, blind spot enlargement, nasal contraction, and superior altitudinal defect. The etiology of the visual field depression in TDS may be a result of the chorioretinal hypoplasia. The presence of an inferior conus as well as phypopigmentation in the inferior and inferior nasal fundus should help to rule out chiasmal compressive lesion in patients presenting with bilateral superior temporal visual field defects, especially when the field changes are nonprogressive and do not respect midline.

5.12.8  Diagnosis and Diagnostic

Aids Treatment

Clinic appearance, visual field, refractive error. TDS typically exhibits electrofunctional deficits. Abnormal ERG and EOG indicate that TDS is a localized disease of the fundus [177]. This degree of abnormality is directly proportional to the degree of fundus hypoplasia. VEP is the most prevalent electrofunctional ­abnormality in TDS.