Preserving patients’ vision by monitoring glaucoma progression rate

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Glaucoma is a progressive optic neuropathy with characteristic damage of the optic nerve head that results in visual field loss. Changes such as loss of retinal ganglion cells, structural and functional alterations of the optic nerve happen in everyone with aging.

However, in patients with glaucoma these changes happen much more quickly and can lead to devastating complications, even to irreversible visual loss if left untreated. That’s why understanding the progression rate of glaucoma is crucial for timely intervention.

We have identified some risk factors for fast progression of the glaucomatous damage which help us recognize patients at higher risk of visual loss. These are the high intraocular pressure, the thin central corneal thickness, the presence of pseudoexfoliation as well as the presence of RNFL hemorrhages.^1,2

Moreover, advancing age, African ethnic origin, positive family history, overtreated high blood pressure and diabetes have been associated with glaucoma progression. Patients with advanced disease or rapid progression require more aggressive treatment strategies and frequent monitoring.

In order to detect progression of glaucomatous damage, we use clinical, structural and functional examination of the optic nerve.

1. Clinical examination

During clinical examination, the following findings are suggestive of progression:

• Increase of cup-to-disc ratio. This ratio compares the size of the cup (the central depression in the optic nerve head) to the size of the optic disc (the entire circular area of the optic nerve head)
• Changes in the course of blood vessels
• Hemorrhages in the nerve fiber layer
• Notches and thinning of the neuroretinal rim
• Extension of peripapillary atrophy
• Increase in size of retinal nerve fiber layer defects

Color and red-free photography of the optic nerve head can provide a baseline and help track changes over time and is more objective than drawings or notes. That’s why it is always useful to document clinical examination findings using fundus photography.

However, we have to consider the fact that the image quality depends on the transparency of the media, the co-operation of the patient and the pigmentation of the fundus and that the interpretation of the findings varies between different examiners.

2. Structural examination

Structural examination of optic nerve head is performed using spectral domain OCT (SD-OCT). OCT provides objective measurements for the thickness of the nerve fiber layer (RNFL), for optic nerve head parameters (C/D ratio, rim thickness, cup volume) and for the thickness of the ganglion cell layer (GCL).³ Of interest are changes that exceed the scatter of individual measurements and the loss due to physiological aging. OCT devices⁴ can provide progression analysis for all these measurements and can give plots that are easy to interpret.

Unfortunately, measurements from different SD-OCT devices are not comparable and also no useful information can be provided once a certain threshold value has been reached

3. Functional examination

Apart from clinical and structural examination of the optic nerve, visual field testing that measures optic nerve’s function is also crucial in detecting progression. Visual field testing, also known as perimetry, assesses the integrity of a patient’s visual field by measuring their ability to detect stimuli at various locations within their visual field. During testing, patients respond to visual stimuli presented at different intensities and locations, generating a map of their visual field sensitivity. Serial visual field examinations enable clinicians to track changes in visual sensitivity over time, identifying progressive visual field loss indicative of worsening glaucoma.⁵

Unfortunately, there is no consensus on the best method or threshold and on what amount of change is significant. The variability within a test and over several tests is considerable. Visual field machines have software which provide event-based and trend-based analysis. Event-based analysis can show if there is progression and trend-based analysis can demonstrate how fast the progression is happening. According to the recommendations of the European Glaucoma Society, newly diagnosed glaucoma patients should have three visual field tests per year during the first 2 years after diagnosis to determine rate of progression.

Monitoring the progression rate of glaucoma is integral to preserving visual function and quality of life in affected individuals. Combining structural and functional assessment modalities with trend analysis and patient-specific risk factors enables clinicians to tailor treatment strategies. Regular follow-up and timely intervention are essential in slowing disease progression and preventing irreversible vision loss.

References:

1. Heijl A, Leske MC, Bengtsson B, et al. Early Manifest Glaucoma Trial Group. Reduction of intraocular pressure and glaucoma progression: results from the Early Manifest Glaucoma Trial. Arch Ophthalmol. 2002;120(10):1268-1279.

2. Weinreb, R. N., & Khaw, P. T. (2004). Primary open-angle glaucoma. The Lancet, 363(9422), 1711-1720.

3. Medeiros FA, Zangwill LM, Bowd C, et al. Evaluation of retinal nerve fiber layer, optic nerve head, and macular thickness measurements for glaucoma detection using optical coherence tomography. Am J Ophthalmol. 2005;139(1):44-55.

4. Chen TC, Hoguet A, Junk AK, Nouri-Mahdavi K, Radhakrishnan S, Takusagawa HL, Chen PP. Spectral-Domain OCT: Helping the Clinician Diagnose Glaucoma: A Report by the American Academy of Ophthalmology. Ophthalmology. 2018 Nov;125(11):1817-1827.

5. Terminology and Guidelines for Glaucoma. European Glaucoma Society. 5th Edition.