Early glaucoma detection and treatment
Several studies highlight the role of PERG testing in the detection of maculopathies before clinical evidence is apparent.1,2 These studies validate that objective functional testing of the retina provides important diagnostic and prognostic information to the clinician.
PERG testing has also been shown to demonstrate response to treatment, with improvements in PERG signal correlating with disease improvement. Oner et al showed that PERG signals improved after combined photodynamic therapy and anti-VEGF injections for the treatment of age-related macular degeneration, yet there was no change after photodynamic therapy alone.3
Moreover, the changes seen in the combined treatment group correlated with improvements in visual acuity that were not observed in the monotherapy group. The ability to detect response to treatment using PERG has been corroborated in other studies.4-6
PERG testing is also a reliable means to detect early indicators of glaucoma in eyes with ocular hypertension.7-9 Moreover, the use of PERG has been shown to predict pattern loss on visual field10 and anticipate an equivalent loss of structure on OCT by several years.11
Whilst early detection of glaucoma is important for prognostic purposes, there were, previously, few treatment options. Topical therapy has traditionally only been considered for individuals with clinically apparent glaucoma, or who already have visual deficits, yet there is an emerging belief that procedural treatments might pose less risk of unwanted outcomes even in mild to moderate glaucoma.
Nevertheless, the tolerance for risk among individuals with ocular hypertension and/or the absence of obvious signs of optic nerve damage is understandably lower. It is important to consider that any early-stage treatment undertaken should only expose patients to minimal risk of complications.
Selective laser trabeculoplasty (SLT) is an alternative, procedure-based approach to treatment that avoids risks associated with topical therapy. In recent years, compelling evidence has emerged that suggests a role for SLT in newly diagnosed and treatment-naïve glaucomas.
Due to the fact that SLT selectively ablates pigmented cells, it yields minimal damage to the trabecular meshwork, making it a safe and repeatable treatment for various types of glaucoma, including primary open-angle, pigmentary and exfoliative glaucomas, as well as ocular hypertension. In the context of patients without signs of damage on OCT and/or visual field progression, the application of SLT to improve aqueous outflow would reduce the potential for a relevant risk factor (i.e., compromised outflow) to have an injurious effect.
Theoretically, therefore, the combined use of PERG and SLT would represent a mechanism to detect early pattern irregularities indicative and predictive of glaucoma, to apply treatment, and then to monitor for effect – all at a time during the natural course of glaucoma when the disease has not yet ravaged important ocular structures.
1. Neubauer AS, et al. The multifocal pattern electroretinogram in chloroquine retinopathy. Ophthalmic Res. 2004;36:106-113.
2. Ventura LM, et al. The PERG in diabetic glaucoma suspects with no evidence of retinopathy. J Glaucoma. 2010;19:243-247.
3. Oner A, et al. Pattern electroretinographic results after photodynamic therapy alone and photodynamic therapy in combination with intravitreal bevacizumab for choroidal neovascularization in age-related macular degeneration. Doc Ophthalmol. 2009;;119:37-42.
4. Neveu MM, Tufail A, Dowler JG, Holder GE. A comparison of pattern and multifocal electroretinography in the evaluation of age-related macular degeneration and its treatment with photodynamic therapy. Doc Ophthalmol. 2006;113:71-81.
5. Varano M, et al. Macular function after PDT in myopic maculopathy: psychophysical and electrophysiological evaluation. Invest Ophthalmol Vis Sci. 2005;46:1453-1462.
6. OzkiriÅŸ A. Pattern electroretinogram changes after intravitreal bevacizumab injection for diabetic macular edema. Doc Ophthalmol. 2010;120:243-250.
7. Bach M, et al. Pattern ERG as an early glaucoma indicator in ocular hypertension: a long-term, prospective study. Invest Ophthalmol Vis Sci. 2006;47:4881-4887.
8. Parisi V, et al. Clinical ability of pattern electroretinograms and visual evoked potentials in detecting visual dysfunction in ocular hypertension and glaucoma. Ophthalmology. 2006;113:216-228.
9. Bode SF, Jehle T, Bach M. Pattern electroretinogram in glaucoma suspects: new findings from a longitudinal study. Invest Ophthalmol Vis Sci. 2011;52:4300-4306..
10. Bayer AU, Erb C. Short wavelength automated perimetry, frequency doubling technology perimetry, and pattern electroretinography for prediction of progressive glaucomatous standard visual field defects. Ophthalmology. 2002;109:1009-1017.
11. Banitt MR, et al. Progressive loss of retinal ganglion cell function precedes structural loss by several years in glaucoma suspects. Invest Ophthalmol Vis Sci. 2013;54:2346-2352.