PMC6083636_01
Two pictures of the external part of the eyes of our case. The physical exam excluded albinism. The top image shows near normal position of the corneal reflexes captured with a camera-flash with relatively good alignment. With the ophthalmoscope, the reflexes showed generally good alignment and often exotropia was not observable when wearing glasses. However, without glasses, as seen in the bottom image, a large angle exotropia becomes visible.
CRIOPM2018-2146826.001.jpg
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fig1
Cover-test at near showed an intermittent exotropia that is shown in Figure 1; horizontal nystagmus was manifest only at extreme positions of gaze, likely representing end-gaze physiologic saccades.
PMC6083636_02
Images of both eyes of the case (top) and a control subject (bottom) obtained with spectral domain optical coherence tomography (OCT). The grayscale images are complemented with a colour-coded slice of the foveal pit (control) or the presumed anatomical location of the fovea (case). The horizontal cross-section corresponds to a horizontal section of the retina that is marked in the red-free fundus image with number 1; the OCT section shows absence of normal foveal pit in the case. All inner retinal layers are seeing crossing the anatomic foveal centre. The images of the case (top images) show a slightly thicker photoreceptor outer nuclear layer at the centre, surrounded by a ganglion cell layer that is thicker than at more peripheral locations (central ring of the retinal image), confirming the centration of this scan on the location of the anatomical fovea. Outer photoreceptor structures, such as the inner-outer segment layer and the interdigitation between the photoreceptor outer segments and the apical retinal pigment epithelium, have a normal appearance. Maps of total retinal thickness (overlapped with retinal image) show a nasal-to-temporal gradient of retinal thickness but the relative thicker parafoveal region is missing (also visible when compared with the control subject, bottom images). Of notice, the fixation position in right eye (the central ring) seems to be shifted, below the level of the optic disc. Whilst this observation might be an effect of the picture, it might also be another functional sign of an "immature" fovea and a possible explanation to more reduced vision in the right eye than the left eye. The image at the top-left corner can be used as a "legend" to analyse the OCT findings. In that legend, (a) extrusion of plexiform layers; (b) foveal pit; (c) out-segment (OS) lengthening; and (d) out nuclear layer (ONL) widening; this legend has been adopted from.
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fig2
Of interest, there was a variation of thickness of the GCL and the ONL with a gradual increase in thickness from nasal-to-temporal macula and greatest thickness near the location of the anatomical fovea. Our patient showed a significantly thicker macula when compared with an age and gender matched control (Figure 2).
Picture of the left eye of the case (top) and the control (bottom) obtained with a fundus camera. Both foveal regions have been magnified and are shown at the right side of each retinal picture. The top image shows the absence of the foveal avascular zone in the macular area.
CRIOPM2018-2146826.003.jpg
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fig3
Topcon TRC 50DX fundus camera, are shown in Figure 3. The patient's images (Figure 3, top panel) show a poorly defined foveal zone in the left eye as well as vascular branches crossing the location of the anatomic fovea.
Multiple raster cuts through the suspected foveal centre of both retinas.
CRIOPM2018-2146826.004.jpg
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fig4
Four multiple raster cuts through the anatomical position of the foveal centre clearly show evidence of fovea plana (Figure 4).
PMC6083636_03
Two pictures of the external part of the eyes of our case. The physical exam excluded albinism. The top image shows near normal position of the corneal reflexes captured with a camera-flash with relatively good alignment. With the ophthalmoscope, the reflexes showed generally good alignment and often exotropia was not observable when wearing glasses. However, without glasses, as seen in the bottom image, a large angle exotropia becomes visible.
CRIOPM2018-2146826.001.jpg
PMC6083636_03_CRIOPM2018-2146826.001.jpg
fig1
Cover-test at near showed an intermittent exotropia that is shown in Figure 1; horizontal nystagmus was manifest only at extreme positions of gaze, likely representing end-gaze physiologic saccades.