Continuing Education Activity

Cataracts are the world’s leading cause of remediable blindness. While some cataracts, may be congenital, secondary to trauma, or drug-induced, most cataracts are age-related. Cataract surgery is the most effective, and currently, the only approved intervention for cataracts regardless of etiology. This activity presents the pathology of cataracts as well as the most common surgical technique, complications, and outcomes of cataract surgery.

Objectives:

• Review the pathogenesis of cataracts.
• Describe the various cataract surgery techniques as well as their advantages and disadvantages.
• Identify the most common and the most serious complications of cataract surgery.
• Outline the indications and contraindications of cataract surgery

Introduction

Cataracts are the world’s leading cause of remediable blindness. While some cataracts, may be congenital, secondary to trauma, or drug-induced, most cataracts are age-related. Age-related cataracts are due to the opacification of the lens. The crystalline lens is a biconvex structure that focuses light on the retina. It is transparent with a diameter of 10 mm and an axial length of around 4 mm. The lens consists of fibers that are derived from lens epithelium, a thin surrounding capsule, and zonular fibers that allow for accommodation in conjunction with the ciliary body. With age, the lens stiffens, leading to farsightedness known as presbyopia. While one of the main functions of the lens is to focus light, it is not a passive optical element. In order to maintain transparency, the lens has a microcirculation pathway driven by sodium channels that deliver nutrients to deeper fibers through extracellular inward flow. Intracellular outward flow is maintained through gap junctions and is used to remove waste. The lens also serves as a UV filter that protects the retina. Finally, the lens acts as an oxygen sink with some of the highest concentrations of the antioxidant glutathione (GSH) in the body. Glutathione scavenges reactive oxygen species, is a co-factor for repair enzymes, and is thought to be released into the aqueous humor to be used by the avascular tissues such as the cornea and trabecular network. With age, oxidative damage can accumulate, causing an opacification of the lens.[1][2]

Regardless of the etiology, the treatment is cataract surgery when the visual function is affected. Cataract has secondary complications such as glaucoma and uveitis when it is allowed to progress on its natural course. With newer and well-developed techniques, cataract surgery is one of the most successful clinical managements in medicine with direct improvements in visual acuity as well as large improvements in activities of daily living and decreased mortality. While as many as 95% of patients will have improved visual acuity, cataract surgery does have complications. The most common include posterior capsule opacification and cystoid macular edema. Rare but serious complications include endophthalmitis and retinal detachment.

Cataracts are one of the most common ophthalmic pathologies characterized by the opacification of the lens. In 2013, the United States had more than 22 million people who had cataracts.[3] In 2020, that number is expected to reach 30.1 million.[4] Incidence increases with age; 43-year-old to 54-year-old patients have an incidence of 8.3%, while patients over 75 have an incidence as high as 70.5%. Women are slightly more affected, with an average incidence of 26% and men 22.6%.[5] In 2015, 3.7 million cataract surgeries were performed in the United States[4] with data suggesting that the incidence of cataract surgery will continue to increase.[3]

Anatomy and Physiology

A majority of adult cataracts are age-related with other etiologies suspected to be due to ultra-violet (UV) light exposure, smoking, diabetes, corticosteroid exposure, and other oxidizing drugs. Pediatric cataracts can be hereditary, idiopathic, or part of multisystem syndromes, metabolic disorders, or maternal infection.[6] Age-related cataracts are thought to be due to oxidative damage to the lens[7] and are divided anatomically into nuclear, cortical, and posterior subcapsular. Nuclear cataracts are the most common, with an incidence of 13.1%.[5] With age, the lens adds new fibers that compress the nucleus, eventually leading to nuclear sclerosis.[6] While cortical cataracts are the second most common (incidence of 8.2%), they are the most likely to require surgical intervention.[5][8] Typically, they present on examination as opacities within the cortex known as cortical spokes.[6] Posterior lens opacity is the least common (incidence of 3.4%)[5] and is due to opacification in the posterior cortex. 

Around half of congenital cataracts are genetic, and most genes are involved in lens development, including a, b, and g crystallin as well as lens cytoskeletal protein. Other causes include metabolic disorders, maternal infection, trauma, and toxic effects. Corticosteroids are associated with posterior subcapsular cataracts. Other medications that can also cause cataracts include busulfan, amiodarone, and phenothiazine.[7] Cataracts caused by trauma require special attention as the damage is rarely limited to the lens alone, with nearly half of injuries damaging the posterior segment.[9]

Indications

The type of cataract determines the initial presentation. Nuclear cataracts can present with decreased distance visual acuity, decreased ability to recognize faces and discriminate colors. Patients with nuclear cataracts can have good levels of Snellen acuity. Cortical cataracts may cause glare, difficulty reading, and light sensitivity. Patients with posterior subcapsular cataracts can present paradoxically, with poor vision in good lighting and improved vision in dim lighting. They can also have difficulty with driving during the day and reading.[10] If left untreated, hyper-mature senile cataracts can develop. Complications include uveitis, glaucoma, dislocation of the lens, which may lead to severely impaired vision or even complete loss of visual acuity.[11] Signs and symptoms of congenital defects depend on the stage of presentation, but white cataracts can be recognized by parents and pediatricians can notice the asymmetry of the red reflex, as well as signs of poor vision, i.e., failure to look at light sources, no tracking, and failure to make eye contact.

According to the American Academy of Ophthalmology, the goal of diagnosis is to determine if visual complaints are due to the presence of cataracts, if a cataract is present, to understand the clinical significance, and to rule out other conditions that cause visual impairment.

The evaluation includes:

• A comprehensive history
• Visual acuity with correction
• Glare testing
• Assessing pupillary function
• Examining ocular alignment
• External examination
• Measuring intraocular pressure (IOP)
• Slit-lamp examination of the anterior segment, lens, vitreous humor
• Ophthalmoscopy of the macula, retina, and optic nerve
• Other tests that may be considered include, optical coherence tomography (OCT), to evaluate retinal or anterior segment disorder. B-scan ultrasound can be done if cataract density prevents visualization of the posterior segment.

Differential Diagnosis

1. Glaucoma
2. Diabetic Retinopathy
3. Age-related macular degeneration

Glaucoma is a group of conditions that are characterized by progressive damage to the optic nerve. Although it is often associated with increased ocular pressure, the optic disc can be damaged with normal IOP. Initially, the patient is asymptomatic but eventually begins to lose both peripheral and central vision. Vision loss is permanent. The incidence is highest among black Americans.[12]

Diabetic Retinopathy: Presents in patients with both type 1 and type 2 diabetes. Patients typically present complaining of fluctuating vision, floaters, photopsia, and visual loss. On exam, microaneurysms, intraretinal hemorrhages, and hard exudates in the non-proliferative type. In the proliferative type, fibrous proliferation, new blood vessels, and macular edema can be seen.[13]

Age-related Macular Degeneration (AMD): Dry AMD presents with worsening vision and more dependence on brighter lights or magnifying lenses. Scotomas, difficulty reading, or driving might be noticed.[14] Drusen can be seen on examination. Wet AMD will present with central visual disturbances that are clinically tested with line distortion known as an Amsler grid.[15]

Cataracts may occur in patients with glaucoma, diabetic retinopathy, or age-related macular degeneration. Comorbidities should be managed appropriately. 

Indications for surgery vary by country but generally include poor visual acuity, visual difficulties, or both due to cataracts.[16] Formal assessments that can be used to assess for cataract surgery include the Catquest-9Sf questionnaire or the Visual Functioning Index-14.[7]

Contraindications

Contraindications to surgery include cataracts without visual impairment or medical/ophthalmic conditions that do not allow for safe surgical outcomes.  

Equipment

Intraocular Lens (IOL): Before intraocular lenses were used, cataractous lenses were simply removed, and the patients would then need high-power spectacles or contact lenses to attain optimal visual acuity.[17] Originally, a clear lens of polymethyl methacrylate was placed in the posterior chamber.[18] The lens was rigid and worked well with the ECCE technique. However, the small incisions of newer techniques like phacoemulsification necessitated foldable lenses of acrylic and silicone, which are the materials used today.[19] Toric IOLs are used to correct astigmatism and also reduce the need for glasses.[7] Once in the capsular bag, IOLs must be fixed, which is accomplished by several haptic designs: plate-type, one-piece, and three-piece lenses. Plate-type is molded from the same material as the lens and appears as a rectangular shape. Plate-type haptics can be inserted by a small incision, but have an increased risk of dislocation.[20] One-piece designs are also made from the same material as the lens but have open-loop haptic arms. These are associated with more posterior capsular opacification but fewer dysphotopsias.[21] Three-piece designs consist of the lens and two open loops, which can be made out of PMMA, polypropylene, or polyamide. Three-piece IOLs are equal in visual outcomes to single-piece IOLs.[22][23][24]

Intraocular lenses (IOL) can be monofocal, multifocal, and toric. Monofocal aspheric IOLs correct for power lost by the removal of the natural lens. They are the most commonly implanted due to their low cost. Since the IOL corrects only one focal distance, glasses or contact lenses may be necessary for either distance or near vision. Note that the patient has an option to choose monovision as an outcome, where one eye has an IOL for distance vision while the other eye is for near vision. Multifocal IOLs are used to correct refractive vision errors to decrease the need for glasses. Of the multifocal lenses, bifocal diffractive lenses provide better near visual acuity than monofocal lenses. Trifocal diffractive lenses are intended to improve intermediate vision; although, current evidence of their effectiveness is inconclusive.[25] Another multifocal lens, extended depth of focus, was invented to focus light on a continuous plane which would eliminate halo effects and provide improved whole range vision.[26] Another type of lens, known as a light adjustable lens, when hit with UV light, will change shape and produce a different IOL power.[27] Accommodative IOLs are designed to move with contractions of the ciliary body.[28] Once a lens is in place, a new technique using a femtosecond laser is being developed as a way to adjust the power.[29]

Before surgery, ophthalmologists take into account patient anatomy and other factors to determine the needed power of the intraocular lens.[30] Several instruments are used to calculate IOL power. These include measuring corneal power with computerized videokeratography, axial length, A-constant, and gain.[31] Theoretical formulas are then used to calculate power. The largest contributor of error is the estimated lens position (ELP). Five generations of formulas have been developed to more accurately predict the lens position. The first generation formula, SRK, used a constant value for ELP; the second generation, Hoffer, formula used axial length to predict ELP; third-generation formulas (Holladay, SRK/T, and Hoffer Q) predict ELP using axial length and anterior corneal curvature; fourth and fifth-generation formulas use third-generation measurements and include anterior chamber depth.[32]

Preparation

The ophthalmologic evaluation includes a thorough ophthalmic history, with a focus on visual acuity as well as comorbidities, and slit-lamp examination. Several measurements of the eye are then taken, including the anterior chamber depth, to determine intraocular lens refraction.[33] While thorough medical history should be taken before surgery, routine systemic preoperative tests do not need to be ordered.[34] Some institutions may require clearance from the primary care physician when patients have underlying systemic diseases.[35] Due to the low risk of bleeding, antithrombotic drugs can be continued.[36] The use of alpha-1-antagonists should be noted due to the risk of intraoperative floppy iris syndrome.[37]

Technique or Treatment

Anesthesia: Historically, general anesthesia and retrobulbar blocks were used for intracapsular cataract surgery. However, with the advent of phacoemulsification and small incision surgeries, clinicians have since moved to local and topical anesthesia.[38][39]

Intracapsular Cataract Extraction (ICCE): A technique that was discovered in the 18th century that involves removing the entire lens and capsule through a single incision. Due to lower complication rates with improved surgical techniques, ICCE is rarely performed.[40]

Manual Extracapsular Cataract Extraction: In this technique, the lens is extracted through an incision, and the intraocular lens (IOL) is then inserted. The incision is large, usually 9 mm to 13 mm, to accommodate extraction, and sutures are necessary. However, there is an increased risk of posterior capsule opacity, age-related macular degeneration, and corneal edema when compared to phacoemulsification.[41] However, lower costs led to continued use of this technique throughout the world. Today, an adaptation of ECCE, manual small incision cataract surgery, has comparable outcomes to phacoemulsification.[42]

Manual Small-incision Cataract Surgery (MSICS): Instead of a large incision, MSICS uses a scleral tunnel that can self-seal. The much smaller external incision (6.5 mm to 7 mm) with a larger internal incision (9 mm to 11 mm) leads to a natural seal. The lens is then delivered through the V-shaped incision, and an IOL is inserted.[43] A Cochrane review published in 2013 found that while phacoemulsification may be superior in early postoperative uncorrected visual acuity, MSICS and phacoemulsification have comparable outcomes for long-term best-corrected visual acuity as well as postoperative complications. The reviewers did find that MSICS was significantly cheaper (70 vs. 15 USD).[44]

Phacoemulsification: This is a technique developed by Charles Kelman in 1967. It involves making a small incision of 2 mm to 3 mm and the insertion of an ultrasonic probe. The probe is then able to emulsify and aspirate the lens.[45] The smaller incision allowed for a self-sealing wound. Foldable lenses were developed to fit into the small incision.[19] Advantages over ECCE include improved visual acuity, decreased risk of astigmatism, and decreased postoperative inflammation. Suture-related complications are also avoided.[42][46](Videos 1 & 2)

Femtosecond Assisted Laser Cataract Surgery (FLACS): This technique, developed in 2008, uses a laser to microscopically dissect tissue, greatly reducing the risk of collateral damage.[47] The laser, originally used in LASIK, is used to create the corneal incision and perform the capsulotomy and initial lens fragmentation. This has decreased the need for manual incisions as well as reducing the time and energy of phacoemulsification.[48] However, due to increased cost over phacoemulsification, with marginal benefit, many clinicians question the current practicality of FLACS.[49]

Refractive Lens Exchange (RLE): RLE uses cataract surgery techniques to replace the lens of a patient with a high refractive error when laser ablative surgery is not possible or in patients with impending cataracts. In addition to cataract procedural risks, these patients are at a higher risk of retinal detachment due to cumulative risk over time. Patients with moderate to severe myopia are at even more of an increased risk for retinal detachment. Patients with severe hyperopia are more likely to develop choroidal edema. Additionally, patients are more likely to develop early age-related macular degeneration, which is thought to be due to the loss of free-radical scavenging properties with the removal of the lens.[27] Patients are also more likely to develop open-angle glaucoma believed to be due to damage to the trabecular network from increased oxygen levels.[2]

Postoperative Care: Typically, patients are prescribed topical antibiotics, corticosteroids, or non-steroidal anti-inflammatory drops for 1 to 4 weeks postoperatively. Patients are counseled to follow up the day after surgery, at 1 week, 1 month, and then 3 months postoperatively.[7]

Complications

Complications can be divided into three time periods, i.e., intraoperative, early postoperative, and late postoperative. 

Intraoperative Complications: The most common include posterior capsule rupture (0.5% to 5.2%), intraoperative iris floppy syndrome (0.5% to 2.0%), or iris or ciliary body injury (0.6%-1.2%).[7] Posterior capsule rupture can lead to retained lens fragments, corneal edema, and cystoid macular edema.[50] Posterior capsule rupture leads to a six-fold increased risk in endophthalmitis[51] and increases the risk of retinal detachment as high as 19 times.[52]

Early Postoperative Complications: Some of the more common complications include transient elevated intraocular pressure, cornea edema, toxic anterior segment syndrome, and endophthalmitis.[7] Even in glaucomatous eyes, after one year, all patients will have IOP control, with some even having a decreased need for medication.[53]

Endophthalmitis, while rare due to intracameral antibiotics, is one of the most severe complications post-cataract surgery. The increased risk of endophthalmitis is reported in patients with Diabetes mellitus, advanced age (over 80), vitreous communication, and large incision ECCE.[54] Patients typically present within two weeks after surgery with decreased visual acuity, red-eye, and pain.[55] Hypopyon is commonly present, around 80% of the time.[56] Common organisms include coagulase-negative staphylococci and Staphylococcus aureus, which account for 80% of infections.[55] Management includes vitreous humor tap and injection of broad-spectrum antibiotics. Typically, vancomycin 1 mg/0.1 mL with either amikacin 0.4 mg/0.1 mL or ceftazidime 2.25 mg/0.1 mL.[55] Even with treatment, outcomes can be severe, including permanent decreased visual acuity to no light perception, with the prognosis being highly dependent on the microbiologic etiology.[56]

Late Postoperative Complications: Common complications that present later include posterior capsule opacification (0.3% to 28.4%), clinical cystoid macular edema, and retinal detachment (0.1% to 1.3%).[7]

Posterior capsule opacification is the most common late complication. It can occur as many as 1 in 5 eyes in the three years following surgery with even higher rates in the following years.[57] Posterior capsule opacification is due to residual lens epithelial cells on the anterior capsule that then migrate to the posterior capsule after cataract surgery, decreasing visual acuity.[58] Patients can also present with blurred vision as well as complaints of glare. Treatment involves using a YAG laser to perform the capsulotomy. Complications from this treatment include damaging the IOL, transient pressure elevation, cystoid macular edema, and retinal detachment.[59]

Cystoid macular edema is due to leaky perifoveal capillaries secondary to the release of proinflammatory cytokines.[60] Common complaints include decreased vision, central loss of vision, or distorted vision.[61] Treatment includes topical corticosteroids and nonsteroidal anti-inflammatory drug (NSAID) eye drops.[62]

Increased risk of retinal detachment is reported in patients who are younger and male. Anatomical risk factors include axial length greater than 26 mm and posterior vitreous detachment.[63] Symptoms typically include flashing lights, floaters, as well as peripheral vision loss with progression to complete vision loss. Retinal detachments are usually diagnosed with direct or indirect ophthalmoscopy, where edematous retinal folds with a loss of transparency can be seen. On slit lamp, pigment cells present in the anterior vitreous are a sensitive finding. Depending on the presentation, treatment can include laser-pexy, pneumatic retinopexy, pars plana vitrectomy, or scleral buckle.[4]

Common complaints after surgery: even though cataract surgery greatly improves vision and quality of life, patients may continue to have subjective visual complaints. Commonly, they will include seeing shadows, halos, glare, starburst patterns around lights, and hazy vision. These symptoms are known as dysphotopsias and can be divided into positive and negative symptoms. Positive symptoms involve starbursts and haloes, while negative symptoms include shadows or dark areas. These symptoms can be caused by acrylic IOLs, and management for intolerable symptoms can include an exchange with a PMMA or silicone IOL. Risk factors for negative symptoms include small pupils, short distance to IOL, functional nasal retina, and an IOL with a high index of refraction. Treatments can include repositioning the IOL, secondary placement of IOL, and Nd:YAG laser anterior capsulotomy.[64]

Clinical Significance

Cataract surgery is a safe and highly effective treatment. As many as 95% of patients will have a best-corrected visual acuity of 20/40 after surgery.[65] Patients report improvement in mental and emotional well-being, improved social interactions, as well as improvements in reading, watching television, and recognizing people.[66] Patients who undergo cataract surgery are also less likely to be involved in traffic crashes.[67] There is an overall mortality benefit to patients who undergo cataract surgery.[68] Finally, there is an economic benefit to cataract surgery with an ROI of 833% due to high costs associated with poor vision such as depression, injury, hospital admissions, necessary caretakers, and decreased employment.[69]

Enhancing Healthcare Team Outcomes

Primary care physicians and providers (PCP) have an important role in identifying patients with decreased visual loss due to cataracts. With patient complaints of decline in visual functions such as difficulty reading, difficulty recognizing faces, or smaller objects such as golf balls, glare, or worsening vision at night, a PCP should suspect cataracts and do a thorough history and physical exam. If cataracts are visualized, or the PCP has a high degree of suspicion, they should refer to ophthalmology. Within surgery, ophthalmologists rely on anesthesiology, nurses, as well as scrub techs. While ophthalmology follows postoperatively for up to one year, some complications, like posterior capsule opacification, can present up to 3 years later. With these later complications, ophthalmologists rely on primary care teams to recognize these later-term complications as patients might present in their clinic.