Raised intraocular pressure (IOP) without glaucoma

• the normal range for intraocular pressure (IOP) is 10-21mmHg
  • it has a diurnal variation with the highest value seen in the morning (1)
    
    
• ocular hypertension usually refers to any situation in which the IOP is higher than normal. Ocular hypertension is an eye pressure of greater than 21 mm Hg
  • ocular hypertension is commonly defined as a condition with the following criteria:
    • IOP of greater than 21 mm Hg measured in one or both eyes on 2 or more occasions
    • optic nerve appears normal
    • no signs of glaucoma are evident on visual field testing, which is a test to assess your peripheral (or side) vision
    • gonioscopically open angles
  • ocular hypertension in fact has been recognized as the most important risk factor for the development of primary open-angle glaucoma (POAG)
  • 2 per cent of adults have a pressure over 21mmHg with no evidence of glaucoma
    • lowering IOP below 24mmHg will prevent five-year conversion to glaucoma in this group, but the the number of people needed to treat in order to prevent one case of POAG is 15 (1)
      
      
• if glaucomatous damage is present then withholding IOP-lowering treatment results in progressive retinal ganglion cell damage when compared with treated controls
  
  
• progression with IOPs under 30mmHg may take several years; however if there is an IOP higher than 40mmHg then this will result rapid cupping of the disc and loss of visual field
  • a high IOP may also be associated with retinovascular occlusion and sudden loss of sight
    
    
• treatment of intraocular hypertension (2)
  • more recent evidence regarding the possible treatment of intraocular hypertension comes from a study of more than 1,800 patients
  • the European Glaucoma Prevention study investigated the use of dorzolamide versus placebo in patients with intraocular hypertension
    • dorzolamide reduced IOP by 15% to 22% throughout the 5 years of the trial
    • however, the EGPS failed to detect a statistically significant difference between medical therapy and placebo in reducing the incidence of POAG among a large population of OHT patients at moderate risk for developing POAG, because placebo also significantly and consistently lowered IOP
  • knowledge of corneal thickness is no longer needed to decide whether or not to treat OHT and a single threshold of 24 mmHg is now recommended for both onward referral and treatment (4)

Reference:

• (1) Kotecha A, Spratt A. Profiling glaucoma. Optometry today 2009
• (2) GP magazine (August 2nd 2004):33-4.
• (3) The European Glaucoma Prevention Study (EGPS). Group Results of the European Glaucoma Prevention Study. Ophthalmology 2005; 112(3): 366-375.
• (4) NICE (September 2017). Glaucoma: diagnosis and management of chronic open angle glaucoma and ocular hypertension