Musgrove Park Hospital said the cause of the "technical issues" in the hired facility was being investigated.
Surgery was carried out on 62 patients with just under half reporting complications while some 15 people had "more significant" corneal issues.
The use of the mobile facility was ceased when the issues were discovered.
All affected patients have been spoken to and care plans are now in place for their ongoing treatment, a hospital spokesperson said.
Vanguard Healthcare had been hired to provide the theatre to help clear a backlog for some ophthalmic services.
The unit, which consists of an anaesthetic room, operating theatre and two-bed recovery, is at the hospital until the end of the year.
Vanguard said it was "co-operating fully" with the hospital for the investigation which would focus on the drugs, equipment, sterilisation and protocols used.
"The majority of operations were successful, however a number experienced an unusual level of discomfort after surgery," added a spokesperson.
"We have, with the hospital, conveyed to the patients our concern and sympathy for the discomfort or distress they have experienced."
The hospital's chief executive, Jo Cubbon, said the issues meant many patients who had already waited longer than they should have, will now have to wait again for their operation.
"We are very sorry this has happened and are working to put a solution in place so that these patients will receive their treatment as soon as possible," Ms Cubbon said.
About 30 patients in Somerset who had cataract surgery inside a mobile hospital theatre have been left with blurred vision or other complications.