Fig. 23.1
Colour photograph of optic disc pit
23.2 Aetiology
Optic disc pits are congenital anomalies that most likely occur during the first trimester of pregnancy. They are known as ‘atypical colobomas’ due to incomplete closure of the embryonic fissure that would normally have surrounded the disc (Apple and Rabb 1998; Sugar 1962). Some argue, however, that optic disc pits are separate entities in that they are usually unilateral and rarely associated with systemic anomalies. Gass has suggested that optic disc pits are due to abnormal development of primordial optic nerve papillae and failure of complete resolution of peripapillary neuroectodermal folds, rather than being true colobomata from incomplete fissure closure (Gass 1969). Optic disc pit and other anomalies have been described in renal coloboma syndrome, with variable inheritance patterns (predominantly autosomal dominant) (Dureau et al. 2001). Mutations of the PAX2 gene, involved in the development of the optic and otic vesicles, genitourinary tracts and central nervous system, have been previously described (Eccles and Schimmenti 1999; Samimi et al. 2008).
23.3 Clinical Features
Optic disc pits may vary in size, occupying up to half the disc diameter. The morphology of the pit may also vary from localized distinct pit-like invaginations to excavated cuplike structures (Choi et al. 2014; Gregory Roberts et al. 2013; Kritzinger and Beaumont 1986; Waldstein et al. 2015). The pit may appear grey and white or sometimes be mistaken for cupping in glaucomatous optic neuropathy. The depression is frequently situated in the temporal or infra-temporal region of the optic disc. There have been reports of up to two to three depressions, although in the majority there is only one pit per optic disc (Kritzinger and Beaumont 1986). Peripapillary chorioretinal atrophy with pigmentary change is seen in almost all cases where the pit is situated near the optic disc margin. In 60 % of cases, a cilioretinal artery can be identified arising from the periphery of the pit (Krivoy et al. 1996).
Visual acuity may remain normal unless associated maculopathy develops. As many as 75 % of optic disc pits are associated with serous macula detachments (Brown et al. 1980; Gass 1969; Kritzinger and Beaumont 1986; Kranenberg 1960; Spencer 1986). These are usually related to larger pits located temporally in the disc and may present during childhood: however, these are more commonly present between the second and fourth decade of life (Krivoy et al. 1996). With the advent of ocular imaging (particularly optical coherence tomography), maculopathy can consist of intraretinal fluid and/or retinoschisis and/or macula serous detachment (Lincoff et al. 1988). Lamellar macular holes are usually in the outer retinal layers. Resolution of macular detachment without inducing full-thickness macular hole can result in good visual acuity; however, redetachment and delayed resolution are typical of optic disc pit maculopathies.
23.4 Clinical Investigations
23.4.1 Optical Coherence Tomography (OCT)
The use of optical coherence tomography (OCT) has indeed expanded our understanding of optic disc pit-associated maculopathy and corroborated with earlier histopathological findings and hypotheses (Jain and Johnson 2014). This non-invasive tool has helped demonstrate ultrastructural characteristics of optic disc pit-associated maculopathy and in the evaluation of outcome following intervention (Gregory Roberts et al. 2013; Ehlers et al. 2011).
Various papers in the recent years investigate the use of spectral-domain OCT(SD-OCT) (OCT 4000 Cirrus Carl Zeiss Meditec, Dublin, CA, USA; Spectralis OCT, Heidelberg Engineering, Heidelberg, Germany) with enhanced depth imaging (EDI SD-OCT) and the newer swept-source OCT (SS-OCT) (SS-OCT; DRI OCT-1; Topcon, Tokyo, Japan) in this condition, including intraoperative use (Bioptigen, Research Triangle Park, North Carolina). SD-OCT and SS-OCT have similar signal depth penetration. However, while the SD-OCT shows superior contrast of choroidal vasculature, SS-OCT has a much faster scanning speed (up to 100-fold), with less sensitivity roll-off (Waldstein et al. 2015). These developments in technology allow for faster scanning speeds compared with previous OCT, higher resolution and the ability for three-dimensional reconstruction (Fig. 23.2). These high-resolution OCTs are invaluable in the characterization of optic disc pit morphology (Gregory Roberts et al. 2013) and its contents and membranes that cover and line the optic disc pit in order to better understand this rare condition and guide its management.
Fig. 23.2
(a) SD-OCT showing the membrane overlying the optic disc region. Details of the base of the optic disc pit cannot be seen. (b, c) Comparison of (b) SD-OCT (EDI) and (c) SS-OCT of the same patient showing similar cuts through the fovea of optic disc and vitreous matter entering the optic disc pit
Morphology of the pit varies from localized distinct pit-like invaginations to deep excavated cuplike structures (Choi et al. 2014; Ehlers et al. 2011; Gregory Roberts et al. 2013). Small case series examined with EDI SD-OCT and SS-OCT were able to image choroidal and post-laminar structures with sufficient resolution to demonstrate defects in the lamina cribrosa and/or sclera and the track of fluid between perineural space and intraretinal/subretinal spaces, confirming previous histopathological findings (Ferry 1963; Gowdar et al. 2015; Irvine et al. 1986; Ohno-Matsui et al. 2013).
Herniation of dysplastic retina tissue into the optic disc pit can also be demonstrated (Aggio et al. 2007). Vitreous strands and glial tissue can sometimes be seen on SD-OCT or SS-OCT within the content of the pits, again correlating with histopathological understanding of this condition (Chang et al. 2012; Gregory Roberts et al. 2013; Ohno-Matsui et al. 2013; Theodossiadis et al. 2007). A hyperreflective diaphanous membrane is often demonstrated overlying the excavated disc anomaly (Fig. 23.3) (Chang et al. 2012; Gregory Roberts et al. 2013; Ohno-Matsui et al. 2013). Doyle suggested this was a protective barrier against vitreous entry to the pit, intraretinal space and thus maculopathy (Doyle et al. 2009). With advancements in SD-OCT and SS-OCT resolution and ability to visualize this membrane in slices several microns thin, this membrane is now seen to be porous and unlikely to serve this function. Similarly, a membrane lining the base of the optic disc pit does not seem to have prognostic value. This appears to represent pia mater (Ohno-Matsui et al. 2013), although histopathologically it has been reported as the continuation of the internal limiting membrane over the disc representing rudimentary retinal tissue (Ferry 1963). The fluid in the perineural space posterior to this can also now be visualized (Michalewski et al. 2014).
Fig. 23.3
SD-OCT showing the membrane overlying optic disc pit temporally (arrow), minimal intraretinal fluid and posterior vitreous detachment over macula region
Although aetiology of the retinal fluid associated with this rare condition is still under debate, SD-OCT and SS-OCT allow better visualization of the fluid, the level of the retina it is predominantly affecting and associations in each case with perineural and vitreous space. Fluid has been noted in various permutations with involvement of outer and/or inner plexiform layer and subretinal macula, with and without tracks emanating from the disc anomaly demonstrated (Fig. 23.4) (Krivoy et al. 1996; Michalewski et al. 2014; Hotta et al. 1999; Rutledge et al. 1996). SD-OCT and SS-OCT have also negated the importance of posterior hyaloid on the pathogenesis of optic disc pit maculopathy. Vitreomacular traction was not demonstrated in many cases with maculopathy contrary to previous beliefs (Chang et al. 2012; Hirakata et al. 2005; Imamura et al. 2010; Pham et al. 2007). In addition, maculopathy can recur following surgical development of posterior vitreous detachment (Jain and Johnson 2014).
Fig. 23.4
(a) Fundus photograph of patient with optic disc pit. Lamellar hole and lipofuscin associated with chronic fluid can be seen. Macula elevation (correlating with intraretinal fluid) with an area of taut swelling centrally (subretinal fluid) can be seen. (b) SS-OCT of the macula showing outer retinal lamellar hole and intraretinal and subretinal fluid. (c, d) SD-OCT (EDI) two cuts in the same patient. (c) Through the optic pit and (d) at the inferior edge of the optic disc pit showing fluid track in continuity with intraretinal fluid. Note there is intraretinal fluid in both outer and inner retina, in addition to subretinal fluid. (e) SS-OCT similar cut to 4c showing optic disc pit, intraretinal fluid (inner and outer retina) and subretinal fluid. Incomplete posterior vitreous detachment can be noted
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