Ans. is 'c' i.e., Coico-cavernous fistula Proptosis Proptosis is bulging of the eyeball (forward bulging) beyond the orbital margins. Though the word exophthalmos is synonymous with proptosis; some source define xophthalmos as a protrusion of globe greater than 18mm and proptosis as a protrusion equal to or less than 18 mm. Proptosis may be classified as follows : ? Unilateral Proptosis Proptosis of one eye. Inflammatory lesions :- Orbital cellulitis, abscess, cavernous sinus thrombosis, etc. Vascular disturbances :- Haemorrhage, varicose orbital veins, haemangioma, etc. Cysts and tumour :- Dermoid cyst, osteoma, lymphoma, lymphosarcoma, glioma, meningioma of optic nerve, retinoblastoma and metastatic deposits in orbit Neuroblastoma, breast, prostate, lung, GIT, Kidney, Ewing's tumor, melanoma, wilms tumor (Nephroblastoma)]. Systemic diseases - Leukemias and endocrine disturbances such as Graves' disease and thyrotropic exophthalmos in initial stages. Paralysis of extraocular muscles as in complete ophthalmoplegia. Mucocele of PNS' - Frontal (most common), ethmoid, maxillary. Bilateral Proptosis Proptosis of both eyes. evelopmental anomalies of the skull- Oxycephaly (tower skull). Endocrine exophthalmos, both thyrotoxic and thyrotropic. Inflammatory lesions - Cavernous sinus thrombosis. Tumours - lymphosarcoma, lymphoma, pseudotumour, nephroblastoma, Ewing's sarcoma. Systemic disease - Histocytosis (Hand - schuller christon disease), amyloidosis, wegner's granulomatosis. Intermittent proptosis Proptosis developing intermittently and rapidly in one eye when venous stasis is induced by forward bending or lowering the head, turning the head forcibly, hyperextension of the neck, coughing, forced expiration with or without compression of the nostrils, or pressure on jugular veins. The most impoant casue is orbital varix (varicocele). Pulsatile proptosis : - Pulsatile proptosis is seen in caroticocovernous fistula; saccular aneurysm of ophthalmic aery; and due to transmitted cerebral pulsation as seen in meningocele, neurofibromatosis and traumatic or operative hiatus.