According to the Global Burden of Disease Study, cataracts were the leading cause of moderate-to-severe vision loss and blindness in 2020. Over 15 million people aged 50 years and older are blind due to cataracts, with the global prevalence of cataracts estimated at 17.2%.
Glaucoma was the second leading cause of blindness in 2020 and the fourth leading cause of moderate-to-severe vision impairment. The worldwide prevalence of glaucoma is 3.54% for patients aged 40-80, accounting for 64.3 million cases in 2020. The number of patients with glaucoma is forecasted to increase to 111.8 million by 2040.
Cataracts and glaucoma are two of the most common ocular conditions affecting millions globally. This article explains cataracts and glaucoma, describes the differences between the two diseases, and focuses on their diagnostic testing methods and available treatment options.
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What is Glaucoma and What Are Cataracts?
The role of the crystalline lens in the eye is to focus light on the retina. A cataract is an opacification of the lens that causes a deterioration of the image quality in one or both eyes.
Cataracts are classified based on the location of the opacity and can be further divided into subgroups depending on pathology, such as age, trauma, and systemic conditions.
The most prevalent type of cataract is caused by aging of the lens. As one ages, lens opacification causes changes in refraction, blur, decreased contrast sensitivity, and color perception.
Glaucoma describes a diverse and multifactorial group of diseases that cause optic neuropathy, which is the injury and loss of optic nerve neurons. Additional subtyping considers factors such as the anterior chamber angle, acute and chronic duration, and pathophysiology.
This progressive degeneration causes visual field defects, starting in the periphery and extending to the central visual field. As glaucoma advances, the central visual acuity is affected, eventually leading to irreversible blindness.
What Are the Risk Factors for Developing These Conditions?
Cataract and glaucoma development share many common risk factors.
Non-modifiable Risk Factors
Systemic Disease and Medication Risk Factors
- Diabetes
- Hypertension
- Systemic, topical, and inhaled corticosteroid use
Ocular Disease Risk Factors
- Previous ocular trauma and retinal surgery
- Retinitis pigmentosa and uveitis
Other Risk Factors
- Smoking and ultraviolet B exposure are documented risk factors related to cataracts.
- Elevated intraocular pressure (IOP) is a risk factor in developing glaucoma rather than a disease characteristic. This is because not all types of glaucoma have increased IOP. For example, in low-tension glaucoma, there is optic nerve damage without elevated IOP.
How to Diagnose Glaucoma and Cataracts
Screening and Early Detection of Glaucoma
Most glaucoma patients feel little discomfort because elevated IOP rarely causes any sensation of pain or pressure. Also, most patients have little awareness of peripheral visual field loss, especially if central visual acuity remains unaffected in the early stages of the disease.
One-third of glaucoma patients fail to seek treatment until they are legally blind. This late presentation is the most significant factor in the progression of glaucoma, highlighting that undiagnosed glaucoma patients are at the greatest risk of blindness.
This highlights the importance of screening, early detection, regular eye examinations, and patient education, especially for high-risk patients.
- Diagnostic Tests for Glaucoma: Tests used to diagnose glaucoma include tonometry (to measure eye pressure), ophthalmoscopy (to examine the optic nerve), and visual field tests.
- Diagnostic Tests for Cataracts: Describe how cataracts are diagnosed primarily through a comprehensive eye exam that includes a visual acuity test, slit lamp examination, and retinal exam.
Comprehensive Eye Examination
A comprehensive eye examination is indicated for all patients regardless of the suspicion of cataracts, glaucoma, or other ocular disease. The examination protocol reveals ocular abnormalities and findings that guide additional testing. The routine protocol and order of diagnostic tests include the following:
- A complete history
- Gross external observation of eyelids, lashes, and lacrimal system
- Evaluation of pupil sizes and responses in normal, bright, and low lighting conditions
- Ocular motor testing to rule out misalignment of the eyes and other disorders caused by abnormalities of the muscles responsible for eye movement
- Confrontation visual field testing to assess gross peripheral vision
- Documentation of uncorrected and corrected visual acuities at distance and near
- Refraction and documentation of best corrected visual acuities at distance and near
- Measurement of IOP
- Slit-lamp biomicroscopy for detailed assessment of eyelid margins, lashes, tear film, sclera, conjunctiva, cornea, anterior chamber, iris, lens, and anterior vitreous
- Dilated fundus examination to evaluate the vitreous, retina, and optic nerve
Additional Diagnostic Tests for Cataracts
Glare and Contrast Sensitivity Testing
Glare testing involves introducing light scatter and glare to determine visual impairment, while contrast sensitivity measures the ability to distinguish different shades of light and dark. Although glare and contrast sensitivity testing are not diagnostic for cataracts, they can help determine the cause and impact on the patient's visual symptoms.
Corneal Evaluation
Additional corneal testing is not diagnostic for cataracts but gives supplemental information to determine if corneal factors contribute to visual impairment, evaluate complex anterior segment anatomy, and identify appropriate candidates for cataract surgery.
Anterior Segment Optical Coherence Tomography (AS-OCT)
Anterior segment optical coherence tomography (AS-OCT) evaluates the anterior structures and pathologies that impact cataract management.
Additional Diagnostic Testing for Glaucoma
Serial Intraocular Pressure (IOP) Measurements
IOP is not static; it has been well documented that IOP fluctuates diurnally from 3 to 5 or more mmHg throughout a 24-hour period. Often, peak IOPs occur outside of in-office testing. Serial measurements can help establish a patient's usual range of IOP.
Gonioscopy
Gonioscopy is a procedure used to visualize the anterior chamber angle and structures. Interpretation of the gonioscopic findings is fundamental for diagnosing and monitoring glaucoma.
Corneal Pachymetry
Corneal pachymetry, or the central corneal thickness (CCT) measurement, is a major component in the diagnostic workup for glaucoma. CCT has been shown to be associated with different types of glaucoma and a possible predictor of glaucoma development.
Optical Coherence Tomography (OCT)
Visualization of the anterior chamber structures with AS-OCT is valuable not only in lens appraisal but also for anterior chamber angle assessment for laser procedures. AS-OCT is also helpful for directly observing anterior segment structures after glaucoma surgery.
Spectral-domain optical coherence tomography (SD-OCT) is a non-invasive imaging technique that uses light waves to take high-resolution cross-sectional scans of the retina. SD-OCT gives quantitative measurements of the most significant parameters in detecting glaucomatous loss: retinal nerve fiber layer thickness, optic nerve head measurements, and ganglion cell thickness.
Automated Perimetry
Automated perimetry testing detects glaucoma and evaluates the amount of functional visual field impairment. Additional sequential automated perimetry with trend analysis is useful in managing the progression of glaucoma.
How to Treat Glaucoma
Topical Medications
Topical glaucoma medications work by lowering intraocular pressure (IOP), reducing aqueous fluid production, and increasing aqueous fluid outflow of the eye. Each class of medications differs in their mechanism of action, effectiveness, dosing, and side effects.
- Carbonic anhydrase inhibitors (CAIs), one of the oldest classes of glaucoma medications, are now primarily prescribed as adjunctive therapies due to side effects.
- Cholinergic agonists, such as pilocarpine and carbachol, are used as second or third-line therapies in treating glaucoma.
- Alpha 2-adrenergic agonists, like brimonidine, are typically prescribed in combination with other glaucoma medications.
- Beta-adrenoceptor (β) blockers, either cardioselective (betaxolol) or non-cardioselective (timolol), are highly effective in decreasing IOP. With convenient dosing and minimal ocular side effects, topical β-blockers had been the most prescribed class of glaucoma drugs until the emergence of the prostaglandin analogs.
- Prostaglandin analogs (PGAs), like bimatoprost, latanoprost, and travoprost, outperform all other classes of glaucoma medications in reducing IOP. This advantage, combined with convenient once-a-day dosing and a low side effect profile, makes PGAs the first-line medication for glaucoma.
- The newest class of glaucoma medications, Rho-associated protein kinase (ROCK) inhibitors, target the Rho GTPase/Rho kinase pathway to regulate aqueous humor outflow. Latanoprostene bunod and netarsudil, examples of ROCK inhibitors, are used as second-line adjunctive therapy due to increased conjunctival hyperemia.
Laser Therapy
Neodymium: Yttrium-Aluminum-Garnet (Nd:YAG) Laser Peripheral Iridotomy (LPI)
Neodymium: yttrium-aluminum-garnet (Nd:YAG) laser peripheral iridotomy (LPI) is the most widely used procedure for angle closure glaucoma. LPI creates an opening in the iris, which allows aqueous fluid to travel from the posterior to the anterior chamber, relieving pupillary block in angle closure.
Laser Trabeculoplasty (LT)
Laser trabeculoplasty (LT) employs argon, diode infrared, or frequency-doubled Q-switched Nd:YAG lasers. These laser wavelengths target the trabecular meshwork, the spongy tissue responsible for draining aqueous fluid, to increase outflow out of the eye.
LT can be used as first-line treatment or adjunctive therapy for patients with primary open-angle glaucoma and ocular hypertension.
Selective Laser Trabeculoplasty (SLT)
Selective laser trabeculoplasty (SLT) is similar to LT except that specific pigmented trabecular meshwork cells are selectively targeted by a Q-switched, frequency-doubled Nd:YAG laser. The SLT technique preserves the trabecular meshwork and causes less thermal damage.
Surgical Glaucoma Procedures
In advanced glaucoma cases that have been unsuccessfully treated by first-line therapies, more invasive surgical procedures are considered. Additionally, mild to moderate glaucoma patients can benefit from adjunctive glaucoma procedures combined with another ocular procedure.
Laser Cyclophotocoagulation
Laser cyclophotocoagulation reduces the IOP by damaging the ciliary body, thereby decreasing aqueous fluid production. The procedure uses a diode or Nd:YAG laser and can be conducted using alternate surgical approaches.
Endoscopic cyclophotocoagulation (ECP) offers direct visualization of the ciliary tissue. In contrast, transscleral techniques, such as micropulse diode laser transscleral cyclophotocoagulation (micropulse TSCPC), are recommended for cases where incisional surgery is contraindicated.
Trabeculectomy
Trabeculectomy is considered the gold standard for glaucoma patients who have had unsuccessful treatments and require maximum IOP control. It is an invasive surgery that creates a passage for aqueous fluid to flow out of the eye.
Trabeculectomies can be performed using different dissection techniques with options for adjunctive therapies, such as wound-healing substances and add-on filtration devices.
Minimally Invasive Glaucoma Surgery (MIGS)
Minimally invasive glaucoma surgeries (MIGS) address the need for treatment options for mild to moderate glaucoma patients who require an IOP reduction of at least 20%. MIGS are less invasive than traditional glaucoma surgeries. They are safe, the ocular structure is minimally altered, and there are fewer postoperative side effects.
One of the significant advantages of certain MIGS is that they can be used in combination with other MIGS and cataract surgery. The addition of MIGS can be beneficial for glaucoma patients with coexisting cataracts. Studies have demonstrated that IOP is lower when MIGS are coupled with cataract surgery than cataract surgery alone.
How to Treat Cataracts
Early Non-Surgical Cataract Management
Patients with early cataracts may have symptoms of blur, especially while reading, and glare from the sun or oncoming headlights while driving.
Management for early cataracts includes providing the most accurate and up-to-date spectacle lens prescription possible. Extra magnification at specific focal lengths may benefit patients with special workstation needs.
Strategic lighting can be recommended depending on the type and location of the cataract. Extra lighting aimed from behind the patient, focused on the reading material, is helpful for resolution and reducing glare.
For cataract patients having difficulty driving due to glare, suggestions include avoiding driving during twilight or setting sun conditions and refraining from night driving if possible.
Cataract Surgery
Cataract surgery is one of today's safest, most effective, and most common procedures. The most widely used technique is sutureless, small-incision phacoemulsification with foldable intraocular (IOL) implantation.
Extracapsular Cataract Surgery
All modern techniques are variations of extracapsular cataract surgery, in which the lens is removed and the surrounding clear lens capsule is left intact to hold a replacement lens.
In phacoemulsification, an ultrasonic probe tip is used to break up the lens into smaller particles that can be removed either by the ultrasonic tip or a separate aspiration tip. The aspirated chunks are simultaneously replaced with a balanced salt solution that maintains the volume and pressure of the anterior chamber.
Femtosecond Laser-Assisted Cataract Surgery
Femtosecond lasers can assist in creating corneal incisions, making the anterior capsular opening, and fragmenting or softening the lens nucleus.
Artificial Intraocular Lens (IOL) Replacement
Artificial intraocular lenses (IOLs) are made of various materials, such as silicone and acrylic, each with unique characteristics that can be tailored to patients' needs. Most IOLs are foldable, allowing the implant to pass through a small incision and then unfold, expanding to full size after being placed in position.
- Monofocal IOLs have one focal point and can be used to correct vision at a distance or near.
- Toric IOLs are monofocal IOLs with the added correction for astigmatism, a refractive error caused by ocular curvature.
- Multifocal IOLs have two or more focal points, correcting vision at far, intermediate, and near ranges. Differences in designs provide multiple focal points, either by accommodation, pupil/light adjustment, or regional differences in strength within the lens.
With so many IOLs available, surgeons can choose an IOL based on ocular measurements, preexisting ocular factors, and the desired level of dependency on spectacles after cataract surgery.
Comparing Treatments and Outcomes
Effectiveness and Prognosis
While cataract surgery is one of the oldest and most successful procedures in medicine, treatment success in glaucoma has been a more significant challenge.
Cataract surgery can restore vision, with success rates of over 95% of patients achieving 20/40 best-corrected visual acuity. In fact, stable vision is expected as soon as 4 weeks after small-incision cataract surgery, when a reliable prescription for eyeglasses can be released.
Because glaucomatous damage is irreversible, glaucoma treatments aim to maintain and prevent future vision loss. Treatment success varies with particular procedures, but for trabeculectomy in advanced glaucoma, for example, favorable outcomes based on IOP control range from 77% to 88.6%.
Postoperative Care
The postoperative care after glaucoma surgery varies depending on the procedure. However, it is much more intensive than the postoperative care for cataract surgery. This glaucoma postoperative protocol reflects the increased risk of complications inherent in glaucoma surgery compared to cataract surgery.
Postoperative Medication Regimen
The postoperative cocktail of topical medications tends to be longer after glaucoma surgery. For example, topical antibiotics are used for approximately 2 weeks after a typical trabeculectomy.
Topical corticosteroids are prescribed postoperatively and continued for 8-12 weeks or longer, depending on the level of inflammation. However, after cataract surgery, topical antibiotics and steroids are usually discontinued after 2 weeks.
Follow-Up Examinations
Glaucoma surgery requires a higher frequency of follow-up examinations compared to cataract surgery. High-risk patients are evaluated several hours after trabeculectomy surgery, with all other glaucoma patients seen the next day and then every week, possibly for months, depending on inflammation, IOP control, and complications.
High-risk cataract patients are examined within the first 24 hours after surgery or earlier if experiencing complications. Otherwise, low-risk patients are usually seen within 48 hours after surgery. Uncomplicated surgical follow-up examinations are generally at one week, one month, and then as needed since complications are unusual and are usually addressed immediately.
Complications
The most common early complication after trabeculectomy is wound leakage, which causes hypotony, a potentially vision-threatening condition when the IOP is too low or nonexistent. A retinal detachment, globe perforation, or excessive filtration can also cause postoperative hypotony.
A rare complication after cataract surgery is endophthalmitis, an ocular infection considered a medical emergency. Patients with endophthalmitis usually present 1-2 days postoperatively with decreased vision, redness, and severe eye pain.
Preventative Measures and Lifestyle Adjustments
Nutrition and Cataracts
Research suggests that a higher dietary intake of certain nutrients may decrease the risk of cataracts, specifically:
Nutrition and Glaucoma
Although there is less evidence-based research on nutrition and glaucoma compared to cataracts, several observational studies have identified some associations:
- Patients with open-angle glaucoma tend to have diets lower in vitamin A activity (retinol equivalence) and vitamin B1.
- Higher dietary nitrate intake, green leafy vegetable consumption, and lower ultra-processed food (UPF) consumption are all linked with a lower risk of developing open-angle glaucoma.
Exercise and Ultraviolet Radiation (UVR)
A 2024 review found that exercise may have an antioxidant effect, suppressing inflammation and potentially reducing the development and progression of both cataracts and glaucoma.
Ultraviolet radiation (UVR) exposure is strongly linked to eyelid skin cancers, and there is growing evidence that medium-wave ultraviolet B (UVB) light contributes to cortical cataracts.
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Key Takeaways
- Cataracts and glaucoma are the two most common ocular diseases responsible for vision loss worldwide.
- Preventative health care through patient education and regular eye examinations are vital for managing cataracts and glaucoma, especially for older patients and those with risk factors.
- Early detection of glaucoma is critical because the lack of early signs or symptoms can lead to delays in treatment and vision loss.
- Preventative measures can delay the onset of cataracts and manage glaucomatous progression.
- Healthcare professionals can encourage a healthy diet rich in antioxidants, participation in regular exercise, wearing protective eyewear, and having regular eye examinations to maintain optimal eye health and vision.
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