Isolated foveal hypoplasia without nystagmus: Imaging findings: A Case Report

Abstract

Foveal hypoplasia (FH) is commonly associated with other ocular anomalies as well as rarely as isolated. In this study, we reported the clinical features and imaging findings of an isolated FH without nystagmus. A 24-year-old female referred to the outpatient clinic complaining on non-progressive, mild visual impairment since early childhood without nystagmus. Spectral domain-optical coherence tomography (SD-OCT) revealed the absence of foveal depression in both eyes with continuity of all inner retinal layers. No capillary-free zone was observed in fluorescein angiography. In suspected cases, SD-OCT is a quick and non-invasive method for diagnosis but other imaging modalities may also helpful.

Keywords

Introduction

Foveal hypoplasia (FH) is defined as the lack of foveal depression with continuity of all neurosensory retinal layers in the presumed foveal area.¹ Foveal hypoplasia has been described in association with several anatomical eye disorders, such as albinism, aniridia, achromatopsia, microphthalmia, retinopathy of prematurity and incontinentia pigmenti.^1,2 There is decreased visual acuity (VA) and an association with nystagmus in most cases of FH.However, only a few cases as an isolated anatomical finding without nystagmus have been reported.^2,5 Isolated FH is usually bilateral. However, unilateral cases have been reported in the literature.^5,6 In this study, we report a case of an isolated form of bilateral FH without nystagmus in which various imaging modalities were used to confirm the diagnosis.

Case Presentation

A 24-year-old female referred to the outpatient clinic complaining on non-progressive mild visual impairment in both eyes since early childhood. Her familial and medical history were unremarkable. Her best-corrected VA for the right eye was 6/10 and the left eye was 7/10. She was able to read all the plates in the Ishihara’s color vision test with each eye. Her extraocular movements were full, and she was orthophoric at distance and near. The intraocular pressures were 13 mmHg bilaterally and Humprey visual field testing was normal. The pupils were round, equal, reactive and anterior chamber angle was normal with gonioscopy without evidence of aniridia (Figure 1). There was no nystagmus and no iris transillumination defects suggestive of ocular albinism and the iris was brown. The fundus examination revealed absent foveal reflexes in both eyes (Figure 2). The vitreous, papilla and retinal periphery were normal. No capillary-free zone was observed in the fluorescein angiography (FA), with the perifoveal capillaries running abnormally close to the presumed fovea and some of them crossing the horizontal
meridian (Figure 3). Spectral Domain-Optical Coherence Tomography (SD-OCT) showed the absence of a foveal depression in both eyes with continuity of all inner retinal layers (Figure 4). Central foveal thickness was 266 μm for the right eye and 264 μm for the left eye.

Discussion

The fovea is the most important retinal area for high VA and color vision. Morphologically, there are three important events in fovea maturation. At the first event, foveal depression starts to develop at 24-26 weeks ofgestation with peripheral centrifugal migration of inner retinal layers. The foveal depression continues to deepen and is completed at 15 months after the birth. The other important events are centripetal migrations of cones and cone specialization. The outer nuclear layer widening occurs when centripetal migration of cone photoreceptors toward the location of the incipient fovea. Cone specialization begins at the same time in a concomitant process with cone migration: outer segment (OS) lengthening and thinning. Cone centripetal migration and OS lengthening lead to an increase in foveolar cone packing density.^7,8 Patients with FH can have a wide range of vision, from normal to severely impaired.⁹ Our patient has mild visual impairment in both eyes. Charbel Issa et al.¹⁰ suggested that VA in FH may be worse at low macular pigment density, therefore anatomical and functional integrity of macula correlates with pigment density. Marmor et al.⁹ reported that foveal avascular zone (FAZ) and foveal depression were not critical to the postnatal cone lengthening and packing, that cone specialization could be maintained both anatomically and functionally. Thus, they have explained why some patients, such as the patient presented herein, may have a relatively good VA despite the absence of a normal foveal depression. Optical coherence tomog raphy angiography (OCTA) in eyes with FH showed an absence or severely reduced FAZ in the superficial capillary plexi but a small or partial FAZ area in the deep capillary plexi.^5,11 Bazvand et al.⁵ have suggested that the size of the FAZ on OCTA could be correlated with visual potential. Pakzad-Vaezi et al.¹¹ reported that a small or partial FAZ in deep plexus permits no resistance to continued centripetal cone migration and specialization resulting in intact vision. Thomas et al.⁸ identified four grades of FH with using SD-OCT scans based on the extrusion of foveal plexiform layers, the presence of foveal depression, photoreceptor OS lengthening and widening of the outer nuclear layer. There was a significant relationship between VA and the grade of hypoplasia. Increasing grades of FH was correlated with worsening VA. They have suggested that the grading system is a prognostic indicator for VA. Furthermore, this grading system is important to show in which stage foveal development is arrested. Both eyes of our patient conform to FH properties of grade 3 according to this classification. Various imaging systems are available for assessing the foveal region. Fluorescein angiography is one of the imaging modalities that can be used in suspected FH cases. On the imaging findings of FH in FA there is absence of FAZ, capillaries running abnormally close to the presumed fovea and some of them crossing the horizontal meridian, variable choroidal fluorescence due to macular pigment density.^2,4,12 It is not one of the primary methods prefered in making diagnosis because of being invasive, having a time limitation of 5-10 minutes after contrast practices, evaluating only retinal superficial capillaries and practical difficulties on children.¹³ Nowadays, SD-OCT is used as a non-invasive and quick method to confirm the diagnosis of suspected FH. In addition, thanks to the high- resolution images, the arrested stage of foveal development can be demonstrated by evaluating the retinal layers and morphology. Another advantage is that it can be used not only in adults but also in pediatric age groups.¹³ In conclusion, we report on a 24-year-old female with isolated FH, who has bilateral mild visual impairment without nystagmus or any ocular anomaly. Isolated FH is rare, therefore, should be considered in the differential diagnosis of visual impairment when foveal reflex is not observed. In suspected cases, SD-OCT is a quick and non-invasive method for the diagnosis. It is extremely useful but other imaging modalities may also help to diagnose.

Declarations

References

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