Peripapillary gamma zone pit as dehiscence between Elschnig´s border tissue and Bruch´s membrane with herniation and defect of the retinal nerve fiber layer

Background The parapapillary gamma zone has recently been defined as the parapapillary region free of Bruch’s membrane. Although it has been reported the presence of defects in peripapillary gamma zone, hitherto undescribed is the herniation of the retinal nerve fiver layer tissue into the peripapillary gamma zone defect with the resulting localized defects in the retinal nerve fiber layer. Case presentation Ophthalmoscopy in a 36-year-old man revealed a localized defect of the retinal nerve fiber layer associated with a yellowish-gray lesion at the inferior temporal outer margin of a peripapillary gamma zone. Enhanced depth imaging of spectral-domain optical coherence tomography (OCT) showed a dehiscence at the connecting point between the central end of Bruch’s membrane and the peripheral end of the border tissue of Elschnig and Jacoby. Retinal nerve fiber layer tissue was herniated through this defect into a cavitation located in the suprachoroidal space and the space above the cerebrospinal fluid space. At a 2-year follow-up examination, the defect and retinal nerve fiber layer defect appeared unchanged. Conclusion We present a peripapillary gamma zone pit originating as a dehiscence between Elschnig’s border tissue and Bruch’s membrane and associated with a herniation and defect of the retinal nerve fiber layer and with a suprachoroidal cavitation.


Background
Previous studies have shown that the peripapillary region can be divided into a peripheral alpha zone, characterized by Bruch's membrane covered with an irregularly structured retinal pigment epithelium; a beta zone showing Bruch's membrane denuded of retinal pigment epithelium; and a gamma zone free of Bruch's membrane [1]. Recent reports by Ohno-Matsui and our group showed the presence of defects in peripapillary gamma zone [2,3]. Here we describe a patient who showed a peripapillary gamma zone defect with herniation and defect of the retinal nerve fiber layer.

Case presentation
A 36-year-old, highly myopic man (refractive error, OD:−6.00 = −1.00/180°; OS: −5.50 = −0.75/180°) with best corrected visual acuity of 20/20 OU, axial length of 27.5 mm (OD) and 27.11 mm (OS), and normal intraocular pressure, showed upon ophthalmoscopy in his left eye a localized defect of the retinal nerve fiber layer in the inferior temporal  , showing a defect between the central end of Bruch's membrane (vertical green arrow with red border) and the peripheral end of the border tissue of Elschnig and Jacoby (horizontal blue arrows with red border), which normally separates the choroid from the intrapapillary region and connects between the central end of Bruch's membrane and the pia mater of the optic nerve (horizontal yellow arrow with blue borders); retinal nerve fiber layer tissue is herniated (white arrows) into the suprachoroidal / supra-cerebrospinal fluid space cavitation; the cavitation is bordered by an elongated and thinned posterior sclera (green arrows) which connects with the peripapillary scleral flange (between both yellow arrows) at the merging point of optic nerve dura mater (horizontal blue arrow with yellow borders) with the sclera; the peripapillary scleral flange forms the roof of the cerebrospinal fluid space (yellow star) between the pia mater of the optic nerve (horizontal yellow arrow with blue borders) and the presumed dura mater (horizontal blue arrow with yellow borders); between vertical green arrow with red borders and the vertical red arrow: peripapillary alpha zone with presence of Bruch's membrane and presence of irregularly structured retinal pigment epithelium; there is no peripapillary beta zone since Bruch's membrane (vertical black arrow with white borders) is covered with retinal pigment epithelium (normal or irregularly structured) all along its course  (Fig. 1). The localized retinal nerve fiber layer was spatially associated with a yellowish-gray lesion at the inferior temporal outer margin of a peripapillary gamma zone (Fig. 1). Enhanced depth imaging of spectral-domain optical coherence tomography (OCT) revealed a dehiscence at the connecting point between the central end of Bruch's membrane and the peripheral end of the border tissue of Elschnig and Jacoby. The latter normally separates the choroid from the intrapapillary region and extends from the central end of Bruch's membrane to the pia mater of the optic nerve (Fig. 2). Retinal nerve fiber layer tissue was herniated through this defect into a cavitation located in the suprachoroidal space and the space above the cerebrospinal fluid space (Figs. 2, 3 and 4). The cavitation was bordered by an elongated and thinned posterior sclera connecting with the peripapillary scleral flange at the merging point of the optic nerve dura mater with the sclera (Fig. 2 and 3). At a 2-year follow-up examination, the defect and retinal nerve fiber layer defect appeared unchanged.

Conclusions
Hitherto undescribed is the herniation of the retinal nerve fiver layer tissue into the peripapillary gamma zone defect with the resulting localized defects in the retinal nerve fiber layer. It has remained unclear whether a partial blockade of the axoplasmic flow in the nerve fibers by the herniation caused the drop-out of the fibers. Also, in contrast to the patients with peripapillary pits described by Ohno-Matsui et al., who were more myopic (−9.5D to −22.0D) and had longer axial lengths (29.5 mm to 32.8 mm), our patient was not that highly myopic [2]. The finding in our patient may suggest a peripapillary gamma zone pit can develop by a dehiscence between the border tissue of Elschnig and Bruch's membrane at their connecting point. In our patient, peripapillary gamma zone defect may not have been caused by a schisis in the sclera or in spatial correlation with an opening of a short posterior ciliary artery as described previously [1,3].
In conclusion, a peripapillary gamma zone pit was presented originating as a dehiscence between Elschnig's border tissue and Bruch's membrane and associated with a herniation and defect of the retinal nerve fiber layer and with a suprachoroidal cavitation.
Abbreviations OCT, optical coherence tomography