Posterior microphthalmos with pigmentary retinopathy

Abstract

We report a case of 19-year-old man with gradual diminution of vision in both eyes since childhood. His best-corrected visual acuity was 20/160, N16 in the right eye and 20/200, N16 in the left eye. Slit-lamp biomicroscopic examination revealed normal cornea, anterior segment, intraocular pressure and lens. Fundus of both eyes showed crowded optic disc with pigmentary changes. Ancillary tests were performed to aid in the diagnosis. A-scan ultrasound revealed short axial lengths with normal corneal diameter, anterior chamber depth and lens thickness. Optical coherence tomography of both eyes showed inner retinal layer folds. Electroretinogram of both eyes showed extinguished photopic as well as scoptopic responses. A diagnosis of posterior microphthalmos with pigmentary retinopathy was made. The patient was counselled regarding nature of the disease and the condition was managed with low vision aids.

Background

Posterior microphthalmos is a rare subset of microphthalmia and nanophthalmos which is characterised by high hypermetropia due to reduced overall axial length of the eyeball with normal anterior segment dimensions which include corneal diameter, anterior chamber depth and anteroposterior length of the lens.^1–3 Various associations have been described with posterior microphthalmos.^4–6 Visual rehabilitation and counselling are the main aspects in the management of posterior microphthalmos. Our case highlights the association of pigmentary retinopathy with posterior microphthalmos. It also highlights the role of clinical examination and ancillary tests in differentiating posterior microphthalmos from microphthalmos and nanophthalmos.

Case presentation

A 19-year-old male presented with gradual painless diminution of vision in both eyes since childhood. His best-corrected visual acuity with cycloplegic refraction was 20/160 with +11.50 DS and N16 in the right eye and 20/200 with +12.50 DS and N16 in left eye. On slit-lamp biomicroscopy, his cornea, anterior segment, intraocular pressure and lens were within normal limits. Fundus of both eyes showed crowded disc and pigmentary changes, both nsal to disc and in periphery (figure 1A, B).

Figure 1.

Fundus images 1 (A) (right eye) and (B) (left eye) showing crowded optic disc (black arrow) with pigmentary changes (red arrow) nasal to disc and in the periphery. Fundus autofluorescent images (C) (right eye) and (D) (left eye) showing hyperautofluorescent ring in the posterior pole (yellow arrow) and hypoautofluorescent lesions (red arrow) nasal to disc and in the periphery.

INVESTIGATIONS

Fundus autofluorescence(FAF)

FAF in both eyes showed hyperautofluorescent ring in the posterior pole and hyperautofluorescent lesions nasal to disc and in the periphery correlating with the pigmentary changes in the fundus image (figure 1C, D).

FAF was performed in the utra-wide field colour fundus photograph (Optos camera, Optos, Dunfermline, UK).

Optical coherence tomography

Optical coherence tomography (OCT) of both eyes showed inner retinal layer folds with normal contour of outer retinal layers, retinal pigment epithelium and choroid (figure 2A, B). OCT was performed in swept-source Deep Range Imaging (DRI) OCT Triton.

Figure 2.

OCT images (A) (right eye) and (B) (left eye) showing inner retinal layer folds with normal contour of outer retinal layers, retinal pigment epithelium and choroid. A-scan ultrasound (C) (both eyes) showing short axial lengths with normal corneal diameter, normal anterior chamber depth and normal lens thickness. IOL, intra ocular lens; LS, lens status; LVC, laser vivion correction; OD, oculus dexter; OS, oculus sinister; VA, visual acuity; VS, vitreous status.

A -scan ultrasound

In view of high hypermetropia A-scan ultrasound was performed which revealed reduced axial lengths with normal corneal diameter, anterior chamber depth and lens thickness (figure 2)

Electroretinogram

In view of pigmentary changes and very low visual acuity, electroretinogram (ERG) of both eyes was performed which showed extinguished photopic as well as scoptopic responses in both eyes (figure 3).

Figure 3.

ERG of both eyes showing extinguished photopic as well as scotopic responses.

ERG was performed on Metrovision ERG system (Pe‘rerchies, France) as per International Society for Clinical Electrophysiology of Vision guidelines

Based on the above clinical findings and ancillary tests a diagnosis of posterior microphthalmos with pigmentary retinopathy was established.

TREATMENT

The patient was counselled about the nature of the condition and the prognosis. Visual rehabilitation was carried out with new hypermetropic glasses. The benefits of using magnifying devices for watching near objects and telescopes for distant objects was explained.

Outcome and follow-up

At the 3-month follow-up visit, the patient had a stable best corrected visual acuity (BCVA) of 20/160, N 12 in the right eye and 20/200, N16 in the left eye. The patient was comfortable with only hypermetropic glasses for distant vision whereas near vision was better with the use of magnifying devices.

DISCUSSION

Posterior microphthalmos is described as a rare subset of microphthalmia and nanophthalmos. It is characterized by high hypermetropia due to reduced overall axial length of the eyeball with normal anterior segment dimensions including corneal diameter, anterior chamber depth and anteroposterior length of the lens. It is also characterised by crowded optic disc and papillomacular retinal folds.^1–3 The Retinal Pigment Epithelium (RPE) and choroid remain structurally normal in these cases. Meire et al have attributed this fact to abnormally thickened sclera limiting the growth of RPE and the choroid, while allowing normal growth of the neurosensory retina leading to folding of the inner retinal layers.³ Our case presented with typical presentation with findings similar to previous reports of posterior microphthalmos. Posterior microphthalmos has been described to be having associated features like retinoschisis, dialysis, esotropia, optic nerve hypoplasia, chorioretinal folds, uveal effusion syndrome, pigmentary retinopathy, retinitis punctata albescens, Duane retraction syndrome and iridocorneal anomaly.^4–6 In our case pigmentary retinopathy was associated with features of high hypermetropia, crowded optic disc and retina folds. Our case adds to the existing pool of association which has pigmentary retinopathy with posterior microphthalmos. Our case also highlights the use of A-scan ultrasound to distinguish posterior microphthalmos from microphthalmos and nanophthalmos. Microphthalmos is characterised by reduced axial length due to global eye reduction with or without other ocular malformations. Nanophthalmos is characterised by reduced axial length due to small anterior and posterior segments with thickened choroid and sclera and normal lens volume. Posterior microphthalmos is characterised by reduced axial length due to reduced posterior segment dimension with normal anterior segment dimensions.⁷ The profound vision loss in our patient is explained by involvement of neurosensory retina and pigmentary retinopathy with extinguished responses in ERG. Visual rehabilitation and counselling are the main aspects in management of posterior microphthalmos.

Patient’s perspective.

I had visited many doctors before where in, the condition of my eyes was not diagnosed completely. Everywhere I was advised to wear glasses and I was reluctant to use them as they were very thick and heavy. With the use of glasses I was having a problem with my near vision, watching mobiles and reading. But I did not understand the cause of my low vision. This made me even more worried about my future and I thought I will go blind. I got a clear perspective of my disease after all the tests and explanation. I understood that the cause of my decreased vision is due to shortness of the back of my eye. I am willing to try the new glasses and rehabilitation aids suggested. I am looking forward to a change for the better in my lifestyle and day-to-day activities.

LEARNING POINTS/TAKE HOME MESSAGES:

• Usefulness of ancillary tests (optical coherence tomography, A-scan ultrasound, B-scan ultrasound and electroretinogram) in the diagnosis of posterior microphthalmos, microphthalmos, nanophthalmos and its associations.

• Pigmentary retinopathy should be kept in mind in a case of posterior microphthalmos with profound loss of vision.

• Visual rehabilitation and counselling of a patient with posterior microphthalmos and pigmentary retinopathy plays a vital role in improving day-to-day activity.