The Diagnostic Potential of Iris Anterior Segment Optical Coherence Tomography in Albinism

Abstract

Purpose: : Albinism is associated with visible abnormalities of the iris such as transillumination which can assist in the diagnosis of albinism although transillumination can be difficult to quantify objectively. Recent innovations in Anterior Segment Optical Coherence Tomography (AS-OCT) now permit accurate imaging of iris anatomy. We have used AS-OCT to compare the thickness of layers within the iris in patients with albinism compared to healthy control subjects to evaluate the potential of this method diagnostically. We have also explored the relationship between iris layers (stroma and anterior border layer (SAB) and posterior epithelial layer (PEL)), iris transillumination and visual acuity in the albinism group.

Methods: : We imaged the irides of 55 patients with albinism (diagnosis confirmed by abnormal VEP crossing) using high resolution AS-OCT. These were compared to 45 healthy control subjects. All individuals were illuminated using a constant bright light source to constrict the pupils. Total iris thicknesses, SAB and PEL were measured in nasal and temporal cross sectional images along the horizontal meridian of both eyes using ImageJ software and thicknesses were averaged at 111µm intervals. These measures were compared to visual acuity and to the clinical iris transillumination severity using the Summers classification scheme.

Results: : Total thickness of the iris was thinner in individuals with albinism compared to healthy control volunteers (mean thickness±SD = 175.2±26.9µm in albinism and 194.0±22.5µm in controls) with the greatest differences towards the iris root. SAB thickness was only thinner in individuals with albinism compared to controls at the root end of the iris whereas PEL thickness was significantly thinner along the whole profile (mean thickness±SD = 22.8±7.1µm in albinism and 32.8±6.0µm in controls, P<0.001). Using PEL thickness as a diagnostic indicator for albinism yielded a sensitivity of 85% and specificity of 78%. There were no significant relationships between iris layers thickness and visual acuity or transillumination grading.

Conclusions: : This is the first time abnormalities of iris layers have been quantified in humans and we demonstrate that these measures have diagnostic potential clinically.

Keywords: nystagmus • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • iris