Structure Function Correlation in Primary Open Angle Glaucoma
Condition: Primary Open Angle Glaucoma
MeSH terms: Glaucoma; Glaucoma, Open-Angle
Study type: Observational

Summary: 
      Glaucoma is an optic neuropathy characterised by progressive degeneration of retinal ganglion
      cells and axons that leads to nerve fibre loss, optic disc cupping, and consecutive
      glaucomatous visual field defects. It is considered to be one of the major causes of
      blindness worldwide.

      It is a well accepted fact least 25 - 40% of retinal ganglion cells need to be lost before
      statistically detectable visual field defects appear on automated visual field testing, which
      is also consistent with post-mortem histologic findings in glaucomatous eyes. Since the
      damage associated with glaucoma is irreversible, and retinal nerve fibre layer loss is
      considered as an early sign of glaucomatous damage, its early detection and prevention is
      warranted. Retinal nerve fibre layer studies can be undertaken through non - invasive,
      reproducible technologies such as optical coherence tomography, scanning laser polarimetry
      etc.

      The purpose of the study is to evaluate the relationship between visual fields and retinal
      nerve fibre layer thickness as measured by Cirrus spectral domain optical coherence
      tomography with visual fields by Humphrey Field Analyser (HFA) in early and moderate primary
      open - angle glaucoma.
    

Detailed description: 
      It is often said that the structural damage due to glaucoma precedes functional loss, it is
      not always clear in its interpretation. To define, which test shows up the earliest sign of
      glaucomatous damage would be difficult to predict, since the outcome can be influenced by
      many factors, such as the sensitivity of the test, inter - individual difference or the stage
      of the disease process itself. Studies on post-mortem retinal ganglion cells counts and SAP
      field loss in humans and monkeys lead to an observation that, on an average about 25% retinal
      ganglion cells loss leads to development of an afferent pupillary defect, 35% loss for visual
      field defects and 40% loss leads to worsening of visual acuity. It would be safe to state
      that a) the most important clinical challenge is early detection of glaucomatous damage and
      progression over a period of time; b) Both structural and functional tests are important in
      assessing early damage and progression; c) significant damage to the retinal ganglion cells
      can occur before standard tests detect a functional loss in vision. These have paved the way
      to the development of many studies on the structure - function correlation and stating linear
      models for the same. However these studies present a dilemma; is the structure - function
      relation on glaucoma, a statistical statement (a structural measure will reach significance
      before a functional test) or relational statement (statistical correlation between the
      structural and functional tests).

      We propose to evaluate the structure - function correlation in early and moderate open -
      angle glaucoma by assessing the retinal nerve fibre layer thickness by Spectral Domain
      Optical Coherence Tomography and areas of decreased visual field sensitivity given by
      Humphrey 24 - 2 Swedish Interactive Threshold Algorithm Standard protocol of automated
      perimetry and determine any representational or statistical significance, if any between the
      two tests.
    

Observational model: Case-Only
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Subjects presenting to the glaucoma clinic of a tertiary eye care hospital an diagnosed to
        have primary open angle glaucoma
      
Keywords: Structure function correlation; Optical coherence tomography; Retinal Nerve fibre layer thickness; Visual fields; Primary open angle glaucoma