Role of Optometrist in Glaucoma Assessment and Management

The optometrist is a critical member of the glaucoma patient management team. His responsibilities in the care of patients with glaucoma include:

– Identifying factors that may indicate glaucoma (anamnesis)

– Performing key tests to characterize the glaucoma patient’s status

– Aiding in glaucoma patients’ treatment by explaining their condition, demonstrating treatment techniques, monitoring their compliance and treatment efficacy in preventing progression

– Assisting in pre-op preparation and post-op care of glaucoma surgical patients

What is Glaucoma?

According to a WHO survey, glaucoma is emerging as the second leading cause of blindness worldwide (Khanna & Ichhpujani, 2012). Usually, it is asymptomatic until a relatively late stage. The understanding of the disease is essential and may assist physicians and optometrists in referring high-risk patients for comprehensive ophthalmologic examination. It is important to enable physicians and optometrists to actively participate in the care of patients affected by this condition.

Glaucoma is a nonspecific term used to describe a group of progressive optic neuropathies characterized by degeneration of retinal ganglion cells (RGCs) and resultant changes in the optic nerve head (ONH). Ganglion cell loss is related to the level of intraocular pressure (IOP), but other risk factors may also play a role. Increased IOP can cause mechanical stress and strain on the posterior structures of the eye, most notably on the ONH and its accompanying tissues, such as the lamina cribrosa and neuroretinal rim (Quigley, 1981). Increases of fluctuations of IOP may result in compression and deformation of the ONH structures with following mechanical damage of axons. This mechanical damage may lead to rupture of axonal transport of molecules that are required for the survival of RGCs.

Glaucoma can be classified into two main categories: open-angle glaucoma and angle-closure glaucoma. Secondary glaucoma can result from tumours, trauma, inflammation, etc. Reduction of IOP is currently the only proven modifiable risk factor to treat the disease.

Glaucoma assessment

 

There are few  diagnostic tests, that should be taken in every glaucoma suspect:

Intraocular pressure: tonometry

Applanation tonometry is based on the Imbert-Fick principle, which asserts that the pressure (P) inside a sphere equals the force (F) necessary to flatten its surface divided by the area (A) of flattening, P=F/A (Townsend & McSoley, 2015). In practice, numerous methods use this concept to measure intraocular pressure. However, few examples of the physical properties of the ocular surface that have influence on applanation measurements can be given: corneal resistance, surface tension of the tears or central cornea thickness. Various methods of IOP measurement employ applanation tonometry, including Goldmann applanation tonometry, a Perkins tonometer, non-contact tonometers, Rebound tonometry, or the newest hand-held tonometer in category – iCare.

Gonioscopy

Gonioscopy is a clinical technique used to examine the structures of the anterior chamber angle (Berlin, et al., 2018). With this technique one can differentiate between the two major types of glaucoma: open-angle and angle-closure glaucoma, using a two major types of lenses: a “direct” goniolens and an “indirect”, mirrored lens.

Central cornea thickness

The role of corneal thickness is being assessed today. In understanding the patient’s actual IOP, thin corneas may place patients under grater risks. Corneal thickness is measured by pachymeter, shows results in micrometers. Newer generations uses ultrasound or OCT to evaluate the corneal thickness.

Structural: Optic nerve

– stereo disc photography

– nerve fiber layer thickness (optical coherence tomography [OCT])

– ultrasound biomicroscopy (UBM)

– confocal scanning ophthalmoscopy (Heidelberg retina tomograph)

– retinal nerve fiber layer assessment (GDx VCC)

Inspection of the optic disc is key to diagnose glaucoma. Because of an abnormal IOP, the cumulative effect of pressure results in atrophy of the RGCs and of the ONH at its exit from the eye, called the optic disc. Optometrists specialiazed on glaucoma follow the changes in the optic disc at regular events by photographing the disc and noticing changes over time. In my practice, we use Heidelberg retina tomograph (HRT) and OCT Spectralis with Glaucoma premium module (GMPE) to examine and evaluate changes on the optic disc over time. HRT has been considered as the gold standard for glaucoma specialists, however, GMPE now offers scan patterns based on unique anatomical landmarks with focus on multiple analysis options and accuracy. Moreover, GMPE compares patients’ eye to a normative database of healthy eyes, and can also monitoring eye status and structural changes from visit to visit.

Functional: Visual fields

– Standard automated perimetry ([SAP] white on white)

– Short-wave automated perimetry ([SWAP] blue on yellow)

– Frequency doubling technology (FDT) (Berlin, et al., 2018)

Although deep examination of the ONH can reveal signs of RGC axonal loss, we can find wide variability of its appearance in the healthy population. For this reason, importance of perimetry must not be neglected. Visual field (VF) defects characteristic of glaucoma are usually used to confirm the diagnosis. However, up to 50% or RGCs may be lost before defects are detectable by standard VF testing (Harwerth, et al., 2010). Evaluation and documentation of structural damage to the optic nerve over time must be essential in the diagnosis of the disease.

Optometrist’s role

“All optometrists are expected to at least recognize that a problem exists and refer the patient to another practitioner.”

The situation with optometrists vary continent to continent, country to country. Each optometrist have different training, experience and allowance. In some countries, optometrists are allowed to perform refractions, give glasses prescriptions, offer contact lens fitting, and in some cases preoperative evaluation before refraction surgery. In others, they are allowed to prescribe low vision aids for partially sighted, or detect ocular pathology and inform medical doctor of patients’ pathology, for example about glaucoma. If an optometrist is trained in glaucoma, he/she can offer a lot of important information about the patients’ pathology to medical doctor. Optometrists in UK, or some US states are allowed to use therapeutic drops or even use SLT for anterior segment procedures, so for glaucoma, too. However, there is a limit to what most optometrists are comfortable with, because they recognize that glaucoma can be a blinding disease. All optometrists, no matter their level of licensure, are expected to at least recognize that a problem exists and refer the patient to another practitioner.

In my opinion,  glaucoma is a widespread disease and every optometrist, no matter what country he works in, should be trained to recognize, basically evaluate and reffer to medical doctor or specialized glaucoma clinic, where the patient should be properly treated. There is no doubt, that optometrist with additional qualification should be allowed to use and prescribe therapeutic drops, that could be considered as a drops of first choice, to glaucoma patients. The patient continues to be a part of the optometrist’s practice but has access to needed expertise of glaucoma specialist. Close relationship between optometrist and medical doctor should be taken as essential.

Berlin, M. S., Stein, H. A., Lent-Schochet, D., Quach, C., & Cai, Z. (2018). Glaucoma. In Ophthalmic assistant: a text for allied and associated ophthalmic personnel (Tenth, pp. 436–474). New York: Elsevier.

Bryn Mawr Communications. (n.d.). The Optometrist’s Role in Glaucoma Care. Retrieved March 31, 2020, from http://glaucomatoday.com/2014/06/the-optometrists-role-in-glaucoma-care/

Burgoyne, C. F., Downs, J. C., Bellezza, A. J., Suh, J.-K. F., & Hart, R. T. (2005). The optic nerve head as a biomechanical structure: a new paradigm for understanding the role of IOP-related stress and strain in the pathophysiology of glaucomatous optic nerve head damage. Progress in Retinal and Eye Research24(1), 39–73. doi: 10.1016/j.preteyeres.2004.06.001

Diniz-Filho, A., Abe, R. Y., Zangwill, L. M., Gracitelli, C. P., Weinreb, R. N., Girkin, C. A., … Medeiros, F. A. (2016). Association between Intraocular Pressure and Rates of Retinal Nerve Fiber Layer Loss Measured by Optical Coherence Tomography. Ophthalmology123(10), 2058–2065. doi: 10.1016/j.ophtha.2016.07.006

Fechtner, R. D., & Weinreb, R. N. (1994). Mechanisms of optic nerve damage in primary open angle glaucoma. Survey of Ophthalmology39(1), 23–42. doi: 10.1016/s0039-6257(05)80042-6

Harwerth, R., Wheat, J., Fredette, M., & Anderson, D. (2010). Linking structure and function in glaucoma. Progress in Retinal and Eye Research29(4), 249–271. doi: 10.1016/j.preteyeres.2010.02.001

Jampel, H. D., Friedman, D., Quigley, H., Vitale, S., Miller, R., Knezevich, F., & Ding, Y. (2009). Agreement Among Glaucoma Specialists in Assessing Progressive Disc Changes From

Photographs in Open-Angle Glaucoma Patients. American Journal of Ophthalmology147(1). doi: 10.1016/j.ajo.2008.07.023

Khanna, A., & Ichhpujani, P. (2012). Low Vision Aids in Glaucoma. Journal of Current Glaucoma Practice6(1), 20–24. doi: 10.5005/jp-journals-10008-1104

Medeiros, F. A. (2009). Prediction of Functional Loss in Glaucoma From Progressive Optic Disc Damage. Archives of Ophthalmology127(10), 1250. doi: 10.1001/archophthalmol.2009.276

Quigley, H. A. (1981). Optic Nerve Damage in Human Glaucoma. Archives of Ophthalmology99(4), 635. doi: 10.1001/archopht.1981.03930010635009

Stein, H. A., Stein, R. M., & Freeman, M. I. (2018). Ophthalmic assistant: a text for allied and associated ophthalmic personnel (Tenth). New York: Elsevier.

Townsend, N. A. (2015, May 15). The Do’s and Don’ts of Measuring IOP. Retrieved March 31, 2020, from https://www.reviewofoptometry.com/article/the-dos-and-donts-of-measuring-iop

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