The family of a little girl who lost an eye from a treatment injury are fighting ACC for the compensation they believe their daughter is due.

On top of the trauma of coming to terms with the fact their courageous three-and-a-half year old will only be able to view life through her right eye, the Taupo family is now battling ACC for an extra payment they say they were promised once her left eye was removed.

Alex and Maria Geisler have been left feeling frustrated and have lost confidence in ACC's process for determining impairment levels after receiving two separate - and contradictory - assessments of their daughter.

Annabelle Geisler was diagnosed with congenital glaucoma when she was just one week old.

Since then, the cheerful pre-schooler has undergone more than 25 surgeries and procedures as doctors attempt to try and control the pressure in her eyes.

In a bid to fix her more problematic left eye, a molteno tube was inserted to help drain it in January last year. But nine months later the tube eroded through the conjunctiva causing infection - and resulting in Annabelle going blind in that eye.

ACC accepted a claim lodged by Auckland District Health Board which, in its letter, labelled it a rare phenomenon.

A medical expert contracted by ACC met Annabelle when she still had her left eye that was shrinking, discoloured and slowly changing shape.

She assessed her to give an understanding of their treatment and rehabilitation needs and whole body impairment rating was issued.

Alex and Maria Geisler have been left feeling frustrated and have lost confidence in ACC's process for determining impairment levels. Photos / Alan Gibson

The Geislers then received what they view as a "pretty abysmal" payout, but were buoyed by the assessor's advice that they would be eligible for more money after she had the eye removed as the impairment would be greater.

But a different assessor, who conducted a second assessment in July this year, found the original calculation was incorrect and the impairment rating was not as bad as originally stated.

"He said to us if I would have done your original review you would have got a lesser payout," Alex said.

"He said we are not going to ask you for your money back, but said it was bit of a blessing for you guys that he didn't do the first one."

Annabelle, 3, and her parents Maria and Alex Geisler.

The Geislers are now challenging the inaccuracies in the second report which they say was riddled with mistakes and made conclusions based on out of date ophthalmology report.

The two assessors were also at odds about whether Annabelle's right eye should have been included in the assessment.

"This guy who knows nothing about eyes said she is going to be able to wear glasses and it's going to get better and commenting on all of this and we have a letter from the surgeon saying it's not going to get better even with glasses.

"He's a medical professional, he's a trained registered medical assessor and he hasn't really done his due diligence and lacking little bits of research," Alex said.

"You're kind of like, your both ACC registered assessors, surely you'd be on the same page. They are making a judgement call on someone's future."

The Geislers complained to ACC about the different assessments and minor corrections were made to the second report to correct the names of the surgeries. Alex had also incorrectly been called Steve.

But they feel ACC has still not addressed why there were two different impairment ratings in its "arrogant" response and have asked for a review hearing.

An ACC spokesperson said there could be variations in impairment assessments of complex injuries carried out by different medical experts. This was why ACC carried out a peer review process seeking advice from both assessors.

In response to why the Geislers had been promised a bigger payout as a result of Annabelle having to have her eye removed, the spokesperson said the family was advised a reassessment could result in a higher or lower impairment rating.

"The role of the review specialist is to consider the decision that has been made, review all information available and consider a way forward. If the review specialist deems the original decision was incorrect, they will take steps to amend it."

ACC acknowledged Annabelle's parents were frustrated with the outcome of the assessments.

"We continue to support Annabelle with her treatment and rehabilitation needs. We'll also remain in touch with Annabelle's parents as the review progresses," the spokesperson said.