Читать книгу Fundamentals Of Glaucoma: A Guide For Ophthalmic Nurse Practitioners, Optometrists And Orthoptists - Группа авторов - Страница 19

Normal tension glaucoma is a variant of POAG where glaucomatous damage to the optic nerve occurs at ‘normal’ pressures. The central corneal thickness must be accounted for, which, if significantly below 520 μm, can mean that the Goldmann pressure measurement is significantly underestimated. Also consider that if the patient is on a systemic beta blocker there will be some IOP lowering effect of this medication, thereby taking a previously diagnosed NTG patient into a pressure range in keeping with POAG. Visual field defects close to fixation are more common in this cohort of patients.

The differential diagnosis of glaucoma must be considered before a final diagnosis of NTG is made, and the practitioner must be confident that the probability of alternative etiologies is as low as possible, by careful history taking and thorough clinical examination.

Differential diagnosis:

•Progressive structural neurological disease — can be effectively ruled out with MRI brain.

•Previous anterior ischaemic optic neuropathy.

•Previous neurological insult, such as severe head trauma or septicemic shock, which results in either compressive or ischaemic optic nerve damage.

•Previously raised IOP e.g. due to acute anterior uveitis, or steroid use (peri-ocularly or systemically at high dose).

Pressure lowering is of benefit for some patients, but significant progression of visual field loss can still occur with pressures in the mid-teens. If a 30% reduction in IOP from the baseline is achieved, 80% of patients achieve stability and no progression of their visual field defects.