Enhanced S-cone syndrome: Clinical spectrum in Indian population

Abstract

Purpose: Enhanced S-cone syndrome (ESCS), a rare disorder, is often misdiagnosed as other forms of retinal degenerations, which have a poorer prognosis than ESCS. The aim of this study is to report the varied clinical features of ESCS and distinguish it from other similar disorders.

Methods: We retrospectively scrutinized the records of patients with confirmed diagnosis of ESCS and analyzed the findings.

Results: We included 14 patients (age range 4-39 years) who were confirmed to have ESCS according to pathognomonic electroretinography (ERG) showing reduced photopic, combined responses, and 30 Hz flicker with reduced L, M cone responses and supernormal S cone responses. The disease presented in the 1^st decade with night blindness and was almost stationary or minimally progressive. Mid-peripheral fundus changes in form of nummular pigmentary alterations, yellow punctate lesions, and macular schisis were noted. The vision ranged from 6/6 to 6/36 with follow-up ranging from 1month to 22 years.

Conclusion: ESCS shows varied clinical features ranging from unremarkable fundus to pigment clumping and atrophic lesions. It has good prognosis with patients mostly maintaining their vision. ERG is diagnostic. More awareness and knowledge about this entity can help to differentiate it from other forms of night blindness.

Keywords: Electroretinography; enhanced S-cone syndrome; night blindness; retinal degeneration; stationary night blindness.

Figure 1

Fundus features of enhanced S-cone syndrome. Montage images of the right (a) and left (b) eye of patient no. 11 at the age of 19 years. Note the RPE alterations with atrophy in the mid-peripheral fundus. The optic nerve head and vessels are within normal limits. The insets show macular schisis with corresponding optical coherence tomography (OCT) images

Figure 2

Nummular patches of retinal pigment epithelium (RPE) clumping in enhanced S-cone syndrome. Clinical picture in a 27-year-old girl who was presented with nyctalopia at 4 years of age (patient no. 12). (a and b) note the nummular patches of RPE atrophy (blue arrowheads) with surrounding punctate atrophic lesions in the mid-peripheral fundus. (c and d) Corresponding optical coherence tomography images showing minimal schitic spaces in the foveal region. This patient tested positive for NRL gene mutation

Figure 3

Intraretinal punctate yellow dots in enhanced S-cone syndrome. 7-year-old male (patient no. 1) was presented with intra-retinal yellow dots in the mid-peripheral fundus (a and b), seen more prominently in the enlarged images. Note the minimal foveal schisis on optical coherence tomography (OCT) in right eye (c) and left eye (d). Genetic testing in the patient revealed mutation in NR2E3 gene

Figure 4

Torpedo-like lesions in enhanced S-cone syndrome. Torpedo-like lesions in the mid-peripheral fundus (a and b; enlarged in insets) of a 26-year-old male patient (patient no. 4). Note the large macular schisis in both eyes in the corresponding optical coherence tomography images (c and d)

Figure 5

Circumferential subretinal fibrosis in enhanced S-cone syndrome. Intraretinal yellow dots, punctate atrophic lesions, and circumferential subretinal fibrosis (blue arrowheads) in the right eye (a) and left eye (b) of an 18-year-old female (patient no. 13). The macula was within normal limits

Figure 6

Vitreous hemorrhage in enhanced S-cone syndrome. 18-year-old female (patient no. 3) presenting with vitreous hemorrhage in the left eye (c).The right eye showed the typical mid-peripheral patches of RPE alterations (a), better appreciated in (b). Optical coherence tomography in the right eye revealed macular schisis (d). Fluorescein angiography corresponded to the fundus picture in both eyes (e-h), with no obvious neovascularization in the left eye (g, h)

Figure 7

Typical electroretinogram in enhanced S-cone syndrome. The top row shows the ERG in a normal individual. Second and third rows show ERG of right and left eyes of a 7-year-old male (patient no. 11). The simplified scotopic 3.0 waveform [1^st column] is similar to the photopic 3.0 waveform [2^nd column] as both are dominated by the short-wavelength-sensitive mechanisms. Specific chromatic stimulation shows nearly non-detectable L- and M- cone responses [4^th column] and supernormal S-cone responses [5^th column]. Other features include delayed and reduced 30 Hz flicker[3^rd column]