It occurs most often around 1.5 years after treatment and results in irreversible and severe vision loss, which may also be associated with damage to the retina (radiation retinopathy). This is thought to be due to damage to dividing glial and vascular endothelial cells. RON can present with transient visual loss followed by acute painless visual loss in one or both eyes several weeks later. The risk of RON is significantly increased with radiation doses over 50 Gy. Optic neuritis
Optic neuritis is inflammation of the optic nerve, which is associated with swelling and destruction of the myelin sheath covering the optic nerve. Young adults, usually females, are most commonly affected. Symptoms of optic neuritis in the affected eye include pain on eye movement, sudden loss of vision, and decrease in color vision (especially reds). Optic neuritis, when combined with the presence of multiple demyelinating white matter brain lesions on MRI, is suspicious for multiple sclerosis. Several causes and clinical courses are possible for the optic neuritis. It can be classified in: 

Single isolated optic neuritis (SION)
relapsing isolated optic neuritis (RION)
chronic relapsing inflammatory optic neuropathy (CRION)
the neuromyelitis optica (NMO) spectrum disorder
multiple sclerosis associated optic neuritis (MSON)
unclassified optic neuritis (UCON) forms.Medical examination of the optic nerve with an ophthalmoscope may reveal a swollen optic nerve, but the nerve may also appear normal. Presence of an afferent pupillary defect, decreased color vision, and visual field loss (often central) are suggestive of optic neuritis. Recovery of visual function is expected within 10 weeks.
The resection of the ileum leads to a malabsorption of vitamin B12, bile acids and the fat soluble vitamins A, D, E and K. Loss of the distal ileum also leads to loss of inhibitory hormones; leading to gastric hypersecretion, intestinal hypermotility (decreases in the intestinal transit time) leading to secretory diarrhea and macronutrient, micronutrient, vitamin and mineral deficiencies. Loss of the ileocecal valve leads to small intestinal bacterial overgrowth(SIBO) as bacterial flora normally found in the large intestines migrate proximally and colonize the small intestines leading to further malabsorption. SIBO leads to malabsorption as the bacteria colonizing the small intestine metabolize nutrients, directly competing with the intestinal absorption of nutrients. The bacteria colonizing the small intestines in SIBO may also cause bile acid deconjugation leading to malabsorption of lipids.In a process called intestinal adaptation, physiological changes to the remaining portion of the small intestine occur to increase its absorptive capacity. These changes usually take place over 1-2 years. These changes include:

Enlargement (increased diameter) and lengthening of the villi found in the lining
Increase in the diameter of the small intestine
Slow down in peristalsis or movement of food through the small intestine (an increase in the transit time) to increase the time available for nutrient absorptionOsteoporosis is a very common comorbidity in people with short bowel syndrome who are on parenteral nutrition, with an estimated prevalence of 57-67%. The contributing factors to the osteoporosis include malnutrition, vitamin D deficiency due to malabsorption and vitamin D deficiency due to scarce sunlight exposure due to chronic disability.