|Year : 2016 | Volume
| Issue : 1 | Page : 55-58
Structural and functional evaluation of macula in a 9-year-old boy with occult macular dystrophy and his affected elder sibling
Tapas Ranjan Padhi1, Chetan Videkar1, Subhadra Jalali1, Sujoy Mukherjee1, Krushna Gopal Panda1, Taraprasad Das2
1 Vitreoretinal Services, L. V. Prasad Eye Institute, Bhubaneswar, India
2 Srimati Kanuri Santhamma Centre for Vitreo Retinal Diseases, L. V. Prasad Eye Institute, Hyderabad, Telangana, India
|Date of Web Publication||10-Feb-2016|
Tapas Ranjan Padhi
L. V. Prasad Eye Institute, Patia, Bhubaneswar - 751 024, Odisha
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Two siblings aged 9 and 15 years with unexplained visual loss had normal pupillary reactions, unremarkable anterior and posterior segment, normal fluorescein angiography, visual evoked potential, and flash electroretinogram (ERG). Spectral domain optical coherence tomography (OCT) showed loss of normal inner segment-outer segment (IS-OS) junction line bump at fovea in one and absent IS-OS junction line at fovea in the other. Characteristic hypovoltaged responses from central macula in multifocal ERG (mfERG) confirmed the diagnosis of occult macular dystrophy (OMD) in both siblings. Marked difference in OCT findings despite same visual acuity indicate that structural changes in OCT might not always correlate with the extent of functional loss. Obvious mfERG changes and very subtle OCT defect in the younger one suggests that functional changes probably appear much earlier than the structural changes. OMD is often underdiagnosed because of lack of high index of suspicion and detailed work up. The patients presented here represent first OMD report from India, one of them being the second youngest reported so far (medline search).
Keywords: Inner and outer photoreceptor segment junction, multifocal electroretinogram, occult macular dystrophy, spectral domain optical coherence tomogram
|How to cite this article:|
Padhi TR, Videkar C, Jalali S, Mukherjee S, Panda KG, Das T. Structural and functional evaluation of macula in a 9-year-old boy with occult macular dystrophy and his affected elder sibling. Oman J Ophthalmol 2016;9:55-8
|How to cite this URL:|
Padhi TR, Videkar C, Jalali S, Mukherjee S, Panda KG, Das T. Structural and functional evaluation of macula in a 9-year-old boy with occult macular dystrophy and his affected elder sibling. Oman J Ophthalmol [serial online] 2016 [cited 2021 May 17];9:55-8. Available from: https://www.ojoonline.org/text.asp?2016/9/1/55/176103
| Introduction|| |
Occult macular dystrophy (OMD) is an unusual macular dystrophy characterized by a progressive decrease of visual acuity due to macular dysfunction despite a normal fundus appearance, fundus fluorescein angiogram (FFA), full field electroretinogram (ERG), and visual evoked potential (VEP). ,, The disease is under-reported because it usually gets missed or misdiagnosed as some other entity. Till date, 71 patients have been reported in the literature.  OMD is known for its broad range of age at disease onset, from 6 to 81 years.  Although inherited, OMD is a genetically heterogeneous disorder, mutations in the RP1L1 gene have been described in several patients. , Spectral domain optical coherence tomography (SD-OCT) may show reduced foveal thickness,  thinning of the outer nuclear layer, or sometimes very minimal to no changes despite foveal malfunction.  In general, fundus autofluorescence (FAF) in OMD is not severely abnormal and can show mild hyperautofluorescence in some and normal autofluorescence in the other.  The multifocal ERG (mfERG) is characteristic and show subnormal responses from the central macula.  The patients presented here show few interesting and novel features that not only add to the existing literature but also alert the physician to keep OMD as a possibility in a case of unexplained visual loss.
| Case Reports|| |
A 9-year-old boy presented with a nonprogressive reduction of vision in both eyes of 3 years duration. The past medical and ocular history was unremarkable. His elder brother had similar visual symptoms (patient 2). There was no history of parental consanguinity, and none of the other family members up to two generations had any significant ocular illness except refractive error. There was no history of photo-aversion. The best-corrected visual acuity (BCVA) was 20/100 (Plano), N18. Pupils were round, regular, and reacting briskly to light. Anterior segment examination by slit-lamp biomicroscopy was normal in both the eyes. The intraocular pressure by applanation tonometry was 16 mm Hg in both the eyes. Fundus examination of both the eyes showed normal optic disc (Bergmeisters' papilla in right eye) and bright foveal reflex [Figure 1]a and b. A severe red-green color vision deficiency was found on the Isihara pseudoisochromatic plates. The amplitude and latencies of full-field ERG were within normal range for both rod and cone components in the right [Figure 2]a and left eye [Figure 2]b. FFA [Figure 1]c and d and flash VEP [Figure 3] were unremarkable. The automated visual fields were unreliable due to high fixation loss in both eyes. The SD-OCT showed intact external limiting membrane, preserved but flat inner segment-outer segment (IS-OS) junction (absence of normal bowing effect/bump of IS-OS junction line in normal individuals) in both the eyes [Figure 1]e and f. The mfERG showed waveforms with decreased signal amplitudes and prolonged latency originating from the central macula [Figure 4]a and b, the central rings were affected more than the peripheral rings. Based on these investigations, he was diagnosed as a patient of OMD. All available immediate family members received comprehensive eye examination and were found to be normal except the elder brother (patient 2). The clinically unaffected and asymptomatic family members did not agree for further evaluation with SD-OCT and mfERG.
|Figure 1: Fundus fluorescein angiogram and spectral domain optical coherence tomogram (transfoveal line scan) of right (a, c, and e) and left (b, d, and f) eye of patient 1 show normal appearance except loss of normal inner segment-outer segment junction bump at fovea|
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|Figure 2: Full field electroretinogram of the right (a) and left (b) eye of patient 1 showing normal responses|
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|Figure 3: Flash visual evoked potential showing waveforms with normal amplitude and latency in patient 1|
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|Figure 4: Trace arrays and ring averages of multifocal electroretinogram of the right (a and c) and left eye (b and d) showing subnormal responses from the central macula, inner rings being affected more than the outer rings in patient 1|
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This 15-year-old elder brother of the proband had painless nonprogressive decline in the vision of 6 years duration and had been labeled as "cause unknown" at previous evaluations in different places. His BCVA was 20/100 (Plano) and N18 in both eyes. Anterior segment examination including pupillary reaction, lens, and intraocular pressures were unremarkable. Color vision on Ishihara pseudoisochromatic plates showed moderate red-green deficiency but lesser than his younger sibling. The fundus photo [Figure 5]a and b was normal in both eyes. FAF [Figure 5]c and d showed small elliptical area of hypoautofluorescence at fovea surrounded by patchy areas of hyperautofluorescence in both the eyes. FFA, full-field ERG, and flash VEP did not show any significant abnormality. SD-OCT [Figure 5]e and f horizontal transfoveal scans showed an intact external limiting membrane and absence of IS-OS junction line in both the eyes. The automated visual fields, though unreliable due to high fixation loss, showed central scotoma [Figure 6]a and b with reduced foveal threshold of 27 and 26 dB in left and right eyes, respectively. The mfERG [Figure 7]a-d showed waveforms with reduced amplitude and prolonged latency from macular area.
|Figure 5: Fundus and autofluorescence imaging of right (a and c) and left (b and d) eye of patient 2 appear normal. Spectral domain optical coherence tomogram (transfoveal line scan) show absence of inner segment-outer segment junction line in both eyes (e and f)|
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|Figure 6: Pattern deviation plot obtained through Humphrey visual field analyzer 24-2 of right (a) and left (b) eye show central scotoma in patient 2|
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|Figure 7: Trace arrays and ring averages of multifocal electroretinogram of the right (a and c) and left eye (b and d) showing subnormal responses from the central macula, inner rings being affected more than the outer rings in patient 2|
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| Discussion|| |
OMD possess diagnostic challenges and should be kept in mind as an important differential diagnosis of unexplained visual loss. We believe that ours is the first report of OMD from the Indian subcontinent (medline search) and one of the patients (patient 1) is the second youngest reported so far in the literature.  Careful interpretation of mfERG and SD-OCT helped us to sort out the diagnosis despite subnormal vision, normal fundus, normal fluorescein angiogram, unremarkable flash ERG, and VEP in these paired siblings. While many reports have described OMD as a progressive disease, , both the patients reported here had subnormal but stable vision at least for the period of observation. (Past consultation elsewhere at different places showed that the visual acuity was constant over last 4 years in the younger sibling and over last 6 years in the elder brother). Studies show that the degree of photoreceptor layer abnormality correlates with visual acuity and symptom duration.  However, interestingly the siblings presented here had similar visual acuity and similar mfERG despite markedly different SD-OCT morphology. Though the OCT changes were very subtle in patient 1, mfERG from central macula was significantly affected in both. This indicates that the extent of damage as seen in the SD-OCT might not always correspond with the loss of vision. The foveal malfunction in mfERG can appear earlier than the structural loss of photoreceptors as seen in patient 1 and similar to that reported by Brockhurst and Sandberg.  However, larger series of patients from diverse ethnic groups and at different ages are likely to improve our understandings on the structural and functional correlates of OMD and its ethnic and regional variations better.
Chhoton De, Administrator, L. V. Prasad Eye Institute, Bhubaneswar, India.
Financial support and sponsorship
Hyderabad Eye Institiute, India.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]