Glaucoma is a group of eye diseases that damage the optic nerve and can result in vision loss and blindness. However, with proper treatment, it is possible to slow down the progression of glaucoma and preserve vision for many years. In this article, we will look at how fast glaucoma can progress after treatment is started.
What is glaucoma and how is it treated?
Glaucoma occurs when there is increased pressure inside the eye (intraocular pressure or IOP). This increased pressure damages the optic nerve which transmits visual information from the eye to the brain. The most common form of glaucoma is open-angle glaucoma where the exit point for aqueous humor (fluid inside the eye) is slowly blocked over time. Other types of glaucoma can occur from blunt trauma, inflammation, or blockage in the iris.
Treatment for glaucoma aims to lower and control eye pressure through medications, laser procedures, or surgery. Common glaucoma medications are eye drops that either decrease fluid production or increase fluid outflow. Laser procedures like selective laser trabeculoplasty help open the drainage canals. Surgery like trabeculectomy can create new channels for fluid to drain. Lowering eye pressure prevents ongoing damage to the optic nerve.
How is glaucoma progression measured?
There are several ways ophthalmologists measure the progression of glaucoma to assess if treatment is working effectively:
- Visual field testing – This tracks changes to peripheral and central vision over time. Constriction of visual fields indicates glaucoma progression.
- Optical coherence tomography (OCT) – OCT can measure thinning of retinal nerve fiber tissue which detects worsening damage to the optic nerve.
- Disc photography – Comparing disc photos over many years can reveal progressive optic nerve damage.
- Eye pressure – Although not a perfect indicator, repeatedly high eye pressure indicates treatment may need to be modified.
What is the usual rate of glaucoma progression with treatment?
Most studies show that the average rate of glaucoma progression significantly slows down with treatment to lower intraocular pressure. However, there is some continued optic nerve damage and visual field loss in most patients.
In the Collaborative Initial Glaucoma Treatment Study, patients were randomized to medication or initial surgery. After 5 years, both groups showed stability and minimal glaucoma progression:
- Medication group – Average visual field loss progression was -0.39 dB per year.
- Surgery group – Average visual field loss progression was -0.35 dB per year.
In the Early Manifest Glaucoma Trial, patients had progression slowed from -1.90 dB/year before treatment to -0.53 dB/year in the first 6 years after starting treatment. After 11 years, average rate of progression was -0.65 dB/year.
In the Canadian Glaucoma Study, the average rate of visual field loss before treatment was -2.12 dB/year. After 5 years of treatment, this was slowed to -0.28 dB/year.
Based on these major studies, the average rate of visual field loss progression with treatment is between -0.3 to -0.65 dB per year. This means that most patients continue to lose some vision, but only at around 1/3 to 1/2 the rate compared to their likely progression without treatment.
Factors affecting rate of progression on treatment
Although most patients respond to treatment, some progress faster than others even on glaucoma medications or surgery. Factors linked to faster progression include:
- Older age
- Higher eye pressure or poor IOP control
- Thinner corneas
- Severe optic nerve damage at diagnosis
- Presence of optic disc hemorrhages
- Loss of more vision in first few years after diagnosis
- Mild glaucoma at diagnosis (early loss seems faster)
- Exfoliation glaucoma or pigmentary glaucoma
- Impaired blood flow to the optic nerve
- Migraines
- Sleep apnea
- Diabetes
- Genetic factors
Patients with these risk factors may need closer monitoring, lower target eye pressure, more medications or surgery to slow their progression as much as possible.
Is it possible for treated glaucoma to get worse quickly?
While most treated glaucoma patients progress slowly, it is possible for some people to experience rapid vision loss even with medications and surgery lowering eye pressure. This accelerated damage is more likely in high risk patients with very high eye pressure or very thin corneas.
In one study of treated open angle glaucoma patients who suffered rapid progression, defined as loss of 2 dB per year, the following statistics were noted:
- Average rate of visual field loss was -3.93 dB/year before treatment and -2.70 dB/year after treatment started
- 35% of these fast progressors went blind within 5 years
- Progression was faster in older patients
- 40% of fast progressors had very thin corneas (less than 555 microns)
Very thin corneas seem to be a particular risk factor for faster progression in glaucoma patients. In another study looking at progression in treated glaucoma patients with thin corneas:
- Average visual field loss was -1.01 dB/year
- 41% experienced rapid progression averaging -2.12 dB/year
Rapidly progressing glaucoma is challenging to manage but switching medications, laser or surgery can sometimes stabilize vision loss if caught early. Many ophthalmologists monitor high risk patients every 3-4 months to immediately address any acceleration.
Can glaucoma ever progress with normal eye pressure?
Typically, glaucoma progression is linked to higher eye pressure. However, normal tension glaucoma (NTG) is a subtype where optic nerve damage occurs even with normal IOP in the 10 to 21 mm Hg range. Patients require treatment to lower their eye pressure below this normal level.
In studies of NTG progression on treatment, results included:
- Progression rate averaged between -0.36 to -0.47 dB/year on medication
- Every 1 mm Hg higher eye pressure increased risk of progression by 10-13%
- Some patients continued to progress at very low normal pressures
This indicates that although important to treat, lower IOP alone does not fully control progression in some normal tension glaucoma cases. Other factors like unstable ocular blood flow likely contribute.
Does glaucoma ever progress after surgery like trabeculectomy?
Trabeculectomy surgery is often very effective at slowing glaucoma progression by lowering intraocular pressure. However, some continued optic nerve damage can still occur years after surgery in many patients.
In one study looking at trabeculectomy results after 10 years:
- Average IOP was lowered from 26.2 to 12.5 mm Hg
- Average visual field loss progression was -1.09 dB/year before surgery and -0.73 dB/year after surgery
- 33% of patients had vision loss progression despite very low postoperative IOP
This indicates that even with very successful surgeries producing very low pressures, glaucoma can continue to progress in some patients. Regular monitoring of the optic nerve and visual fields is important to detect any ongoing damage.
Does medication always slow glaucoma progression long term?
Glaucoma medications like eye drops are effective at lowering IOP and slowing disease progression, especially early after diagnosis. However, their effectiveness can diminish over time.
In one long term study, visual field progression on glaucoma medication after diagnosis was:
- -0.4 dB/year (0 to 6 years on treatment)
- -0.8 dB/year (6 to 12 years on treatment)
- -1.4 dB/year (12 to 18 years on treatment)
These results show that medications were able to slow progression significantly in the first 6 years. However, the protective effect decreased over time with faster average vision loss by 18 years after diagnosis. This illustrates the importance of monitoring glaucoma patients on medications long term to ensure adequate control of progression.
Does progression ever stabilize over time?
For most glaucoma patients on treatment, progression continues but at a much slower rate than without medication or surgery. However, some studies have found IOP lowering treatment can sometimes stabilize damage in a subset of patients.
In the Collaborative Initial Glaucoma Study, around 13% of treated patients showed very minimal progression averaging -0.1 dB/year (essentially stable). Similar stabilization rates of 10-15% have been seen in other studies once IOP is well controlled.
Stabilization is more likely in patients with mild glaucoma who start treatment early. Early detection and treatment are key to slowing and potentially stopping glaucoma damage.
Conclusion
In summary, most glaucoma patients progress at substantially slowed rates averaging between -0.3 to -0.65 dB/year visual field loss after IOP lowering treatment is started. Although progression continues in most cases, it is significantly reduced compared to estimated pre-treatment speed. Monitoring for rapid progression is important, especially in high risk patients, to optimize glaucoma management and preservation of vision.