Commentary: Relevance of orbital measurements for the orbit surgeon.

First of all, the authors should be congratulated for bringing out such a systematic study. They have very rightly reiterated its need especially for the Indian population.

We all agree that the usefulness of such a study will be its ultimate clinical application in the practicality and appropriate surgical planning. As orbital surgeons, we rely on imaging to a great extent especially in cases of Thyroid Eye Disease (TED) and Dysthyroid Optic Neuropathy where orbital decompression is warranted.[12]

One wonders whether the bone density could play a role because the dimensions in this study were higher compared to Dr Dhanwate's study on dry skulls.[3] It could be recommended to use thin slices preferably in the helical mode when selective CT orbit acquisition is done and enabling 3D reconstruction would mimic a dry bone study to an extent.

Alternatively, a few limited MRI sequences may be taken which would in addition to the morphology give information on the signal changes in the extra ocular muscles, orbital fat and so on. It could also clearly delineate between the optic nerve and its sheath which may prevent misinterpretation based only on optic nerve sheath complex noted on CT scan. For instance, optic atrophy may not be picked up on CT scan as it would be replaced by the CSF sleeve. The surgeon's confidence in diagnosing and planning an optic nerve sheath fenestration becomes manifold when one has the knowledge of the dimensions in the given patient versus normative data. We have noted that there can be significant muscle thickening and compression of the optic nerve even without increased proptosis as Asian Indian orbits tend to behave more tight in the TED process. This would be more in the South Indian population as the Orbital Indices are smaller when compared with Dr Dhanwate's study.[4] Normative indices would also help for surgical planning of slow growing orbital tumours and asking for these measurements in our radiological requisitions routinely would be worthwhile.[5]

Navigation-assisted orbital surgery and possible robotic orbital surgery in future could play a pivotal role and would certainly require these parameters. However, the ultimate importance of such data is to safe guard the vision with respect to the optic nerve function whatever the disease aetiology is.