Cataract

Etiology

Multiple factors responsible for developing cataracts include the following:

Congenital cataract: Congenital cataracts can be unilateral or bilateral. Studies have documented a close association between congenital cataract and maternal nutrition, infections (Rubella and Rubeola), and deficiency of oxygenation due to placental hemorrhage.[4]

Age-related (senile cataract): A most common type of cataract [5]

Subcapsular cataract: An anterior subcapsular cataract is seen below the anterior lens capsule and is associated with fibrous metaplasia of the lens epithelium. The posterior subcapsular cataract lies in front of the posterior capsule and has a granular appearance or plaque-like appearance on oblique slit lamp evaluation. Posterior subcapsular cataracts appear black and vacuolated on retroillumination. The vacuoles are swollen migratory epithelial cells (bladder or Wedl), which are the same as those seen in posterior capsular opacification. Since the posterior subcapsular opacity is located at the nodal point of the eye, it affects the vision profoundly. The patients usually complain of glare, halos, and photophobia.[6]

Nuclear sclerotic cataract: Nuclear sclerosis is usually an age-related phenomenon, and changes are caused due to aging. Nuclear sclerosis is associated with myopia and leads to a secondary increase in the refractive index, and as a result, some elderly patients are able to read again without spectacles (the second sight of the aged). In some eyes, there can be a hypermetropic shift. In nuclear sclerosis, there is a yellowish hue due to the deposition of the urochrome pigment, which is best seen on oblique slit lamp illumination. Retroillumination reveals a good red reflex, but only careful evaluation will reveal a subtle distinction between the nucleus and cortex area. In advanced cases, the nucleus appears brown and rarely black.[7]

Cortical cataract: Cortical cataracts may involve the anterior, posterior, or equatorial cortex. The cortical opacities are seen as clefts and vacuoles between the lenticular fibers leading to cortical hydration. The opacification of the lens results in typical cuneiform (wedge-shaped) or radial spoke-like opacity often seen initially in the inferonasal quadrant. Glare and photophobia are common phenomena with this type of opacity.[8]

Christmas tree cataract: Christmas tree cataract is uncommon and is seen as a polychromatic needle-like formation in the deeper cortex and nucleus.[9]

Maturity grading of cataract  

• Immature cataracts are where the lenticular fibers are partially opaque.[10]
• A mature cataract is where the lens is completely opaque.[11]
• Hypermature cataract gives shrunken and wrinkled due to leakage of fluid out of the lens.[12]
• Morgagnian cataract is a variant of hypermature cataract in which there is liquefaction of the cortex, and the nucleus sinks inferiorly[13]

 Traumatic injury[14][15]: A most common cause of unilateral cataracts in young adults

• Perforating trauma
• Blunt trauma: causing a characteristic flower-shaped opacity
• Electric shock: a rare cause of cataract, causing diffuse milky-white opacification and multiple snowflakes like opacities, sometimes in a stellate subcapsular distribution
• Ultraviolet radiation: if intense, may rarely cause true exfoliation of the anterior lens capsule and cataract
• Ionizing radiation: usage for ocular tumor treatment and in cardiological interventions may cause posterior subcapsular opacities
• Chemical injuries: naphthalene, thallium, lactose, galactose

Systemic diseases: These include myotonic dystrophy, atopic dermatitis, and neurofibromatosis type 2.

Endocrine Diseases [16]

• Diabetes mellitus: In a hyperglycaemic state, there is a high level of glucose in the anterior chamber aqueous, which causes glucose to diffuse in the lens. Hence, when glucose is metabolized to sorbitol, sorbitol accumulates inside the lens resulting in secondary osmotic overhydration. In a mild degree of hyperglycemia, there is a change in the refractive index of the lens with a change in refraction related to the plasma glucose levels. The consequent hyperglycemia results in myopia and vice versa. The cortical fluid vacuoles develop and later result in frank opacities. The diabetic cataract is classically described as snowflake cortical opacities occurring in young patients. It may mature within a few days or resolve spontaneously. Age-related cataracts also occur in diabetes mellitus. Nuclear opacities are common and can progress more rapidly than age-related nuclear sclerosis.[2]
• Myotonic dystrophy: About 90% of the patients with myotonic dystrophy develop fine iridescent cortical opacities in the third decade resembling Christmas tree cataracts. These evolve into visually significant wedge-shaped cortical and subcapsular opacities, often resulting in star-like conformation by the end of the fifth decade. In later stages, they become indistinguishable from typical cortical cataracts.[17]
• Atopic dermatitis: Approximately 10% of the patients with severe atopic dermatitis develop cataracts in the second to fourth decade. They usually involve both eyes and may mature rapidly. It also causes shield-like dense anterior subcapsular plaque, which wrinkles the anterior capsule, which is characteristic. They may be associated with posterior subcapsular cataracts.[18]
• Neurofibromatosis type 2: In neurofibromatosis type 2 patients, cataract is seen in approximately 60% of the patients. The capsular opacities can be posterior, capsular, cortical, or mixed variety and develop in early adulthood. [19]
• Hypoparathyroidism or Cretinism

Secondary cataract: Secondary complicated cataracts can result from primary ocular pathologies. These include[20]

• Chronic anterior uveitis: This is the most common cause of secondary cataracts, and the incidence is related to the increased duration and intensity of inflammation. Steroids, whether topical or systemic, are the main causative agents. The changes are seen as polychromatic luster at the posterior pole of the lens. If the profound inflammation persists, it can result in posterior and anterior opacities. Cataract progresses more rapidly in the presence of posterior synechiae.[21]
• Acute congestive angle closure: Acute angle closure glaucoma may result in small anterior grey-white subcapsular or capsular opacities, glaucomaflecken to form within the pupillary area.  These results are from focal infarcts of the lens epithelium and are pathognomonic of previous acute congestive angle closure.[22]
• High myopia: Pathological myopia has been known to be associated with posterior subcapsular lens opacities and early onset nuclear sclerosis, which adds up to the myopic refractive error.[23]
• Hereditary fundus dystrophies: Dystrophies such as retinitis pigmentosa, Leber congenital amaurosis, Stickler syndrome, and gyrate atrophy are commonly seen associated with posterior subcapsular cataracts. Rarely anterior subcapsular opacity can be seen as surgery undertaken as an earlier resort due to opacification at the posterior capsule. Visual acuity improvement is noted after cataract surgery, even in the presence of severe retinal changes.[24]
• Traumatic: Trauma is one of the most common causes of unilateral cataracts in young individuals. It can result from the following:
  • Penetrating trauma- Usually results in a breach in the anterior lens capsule.
  • Blunt trauma leads to rosette-shaped or flower-shaper cataracts
  • Electric shock also results in diffuse milky white opacification of the lens and the development of snowflake-like opacities, sometimes in a stellate subcapsular distribution.
  • Infrared radiations- Seen in glassblowers, may rarely result in true exfoliation of the anterior lens capsule.
  • Ionizing radiation in cases with ocular tumors may result in posterior subcapsular opacification. The cataract is usually seen after months to years.[25]
• Drugs: Topical and systemic corticosteroids and anticholinesterase inhibitors can cause both posterior and anterior subcapsular opacities, respectively. Chlorpromazine can lead to anterior star-shaped lens opacity.
• Poor nutrition: a diet deficient in antioxidants and vitamins [26]
• Alcohol Use Disorder and Smoking

Epidemiology

Prevalence and incidence: Many studies in 2010 reveal that cataracts are most common in the White American race, where prevalence ranges from 17 to 18% per 100 people. Blacks were the second-highest affected by cataracts, with a 13% prevalence rate, followed by Hispanics, with a prevalence rate of almost 12%.[27]

Age: Onset is gradual and progressive, commonly in the older age group, typically in the fifth and sixth decade, though cases have been reported in children and the elderly as well.[28]

Sex: Recent studies reveal that the disease is more common in women than men, with a male-to-female ratio of 1 to approximately 1.3.[29]

Pathophysiology

The lens is a transparent structure made up of fibers (modified epithelial cells) enclosed in a membranous structure called the lens capsule. Lens matter consists of two main parts:

• Cortex (superficial part) - containing younger fibers
• Nucleus (deeper part) - containing older fibers

Many degenerative processes denature and coagulate lens proteins present in lens fibers by different mechanisms, which result in loss of transparency and, ultimately, cataract formation.[30] The various mechanisms involved are as follows:

• Disturbances occurring at any level of lens growth (congenital cataract)
• Fibrous metaplasia of lens epithelium (subcapsular cataract)
• Cortical hydration between lens fibers (cortical cataract)
• Deposition of certain pigments, i.e., urochrome (nuclear cataract)[31]

All these processes ultimately lead to an opaque lens behind the pupil, making it extremely difficult for the patient to carry on with routine activities.

History and Physical

History

The patient may present with one of the following symptoms:

• Decrease or blurring in the vision: gradual and painless; unilateral or bilateral depending upon the eye being affected without and at mature stages even with glasses
• Diplopia or polyopia: mostly uniocular but can be binocular- this is due to multiple refractions through clear areas between the opacities
• Colored halos around the light: Rainbow halos, possibly due to the collection of water drops between layers of lens fibers acting as a prism splitting light into its seven colors
• Sensitivity to glare: especially headlights of automobiles and sunlight 
• Increased frequency of changing refractive glasses: as the cataract matures, a person may visit his ophthalmologist more often for refraction
• Disturbance in color vision: fading or yellowing of objects[32]

Physical Findings

The following findings can be noticed during a thorough ophthalmic examination depending on the part of the lens involved:

Visual Acuity

• Decreased unilaterally or bilaterally depending upon the affected eye[33]

Cortical Cataract

• Wedge-shaped opacity with clear areas of lens matter mostly present at the periphery (incipient cortical cataract)
• Well-developed wedge-shaped opacity (progressive cortical cataract)
• Advanced opacity with a greyish lens, clear cortex, and an iris shadow (immature cortical cataract)
• Findings of the immature stage but with a swollen lens due to the accumulation of fluid making the anterior chamber shallow (intumescent cortical cataract)
• The entire opaque cortex with the absence of iris shadow (mature cortical cataract)
• Milky fluid bag with lens nucleus present at the bottom due to liquefaction of the cortex without an iris shadow and a shallow anterior chamber (hypermature cortical cataract)[34]

Nuclear Cataract

• Dark brown or black lens with an iris shadow
• No fundal view due to dark opacity in the center against a red glow
• No fourth Purkinje image[35]

Systemic Diseases

• Diabetes mellitus: classic snowflake cortical opacities 
• Myotonic dystrophy: Christmas tree cortical cataract which later evolves into wedge-shaped cortical and subcapsular opacities resembling a star-like in conformation 
• Atopic dermatitis: characteristic shield-like dense anterior subcapsular plaques 
• Neurofibromatosis type 2: mixed opacities; can be subcapsular, capsular, or cortical[17]

Evaluation

Indications of Cataract Surgery

• Troublesome glare
• Halos
• Photophobia (Posterior subcapsular cataract)
• Difficulty doing daily activities
• Difficulty in reading fine prints
• Defective distant vision
• Difficulty in driving at night
• Presence of whitish opacity
• Phacolytic glaucoma
• Lens induced glaucoma
• Phacomorphic glaucoma
• Cataract surgery to improve visualization of ocular media to treat retinal pathology[36]

Drug History

A detailed history regarding drug intake should be noted. The medication history will help guide the general medical assessment. The medications associated with ocular side effects could be

• Systemic Alpha Blockers- Tamsulosin is commonly associated with intraoperative floppy iris syndrome (IFIS).
• Antiplatelets/ Anticoagulants- Some surgeons prefer to stop the anticoagulants or antiplatelet agents 3-5 days before the surgery in collaboration with a physician. Some surgeons do not stop the anticoagulants except for oculoplastic procedures and glaucoma surgery. The anticoagulant status is expressed as an international normalized ratio (INR) that should be within the therapeutic range appropriate for the individual indication. This is higher for patients with prosthetic heart valve thrombosis and deep vein thrombosis patients. It is important to check the INR within 24 hours prior to surgery in stable patients.[37]

Allergy

Any significant history of allergy should be ruled out. True allergy should be confirmed rather than intolerance.

Allergy to medications- Sulphonamides and antibiotics commonly used during cataract surgery.

Iodine or Shellfish allergy- If the patient is allergic to iodine, skin or antiseptics such as chlorhexidine should be used.

Other allergies- If the patient is allergic to latex, then a latex-free glove may be necessary, plaster allergy, commonly used local anesthetic, insect bite, and cross-reaction with hyaluronidase that is often used with a local anesthetic.

Methicillin-resistant Staphylococcus aureus (MRSA) carriage- National and local protocols for the identification, characterization, and management of patients at high risk for MRSA carriage should be followed.

Mobility- For movement within the hospital and operation theatre, special arrangements should be made for patients with poor mobility or morbidly obese. For patients with urgent care, the medical risks should be assessed individually and as per the circumstances.[38]

Ophthalmic Assessment of the Patient

Visual Acuity

In all patients, visual acuity should be assessed by using Snellen’s chart.[33]

Cover and Uncover Test

A heterotropia may indicate amblyopia, which will result in a guarded visual prognosis or result in diplopia if the vision is improved. A squint with divergence may result in one eye with poor vision due to a cataract, and cataract surgery may straighten the eye.[39]

Pupillary Response

Relative afferent pupillary defect in the presence of a cataract indicates posterior segment pathology.[40]

Ocular Adnexa

Blepharitis, meibomian gland dysfunction, dacryoadenitis, chronic conjunctivitis, lagophthalmos, ectropion, entropion, and dry eye with tear film abnormality can lead to endophthalmitis. All these adnexal pathologies should be ruled out before performing any intraocular surgery.[41]

Cornea

The endothelial cell count is important as decreased endothelial cell count with the presence of guttae increases the risk of corneal decompensation. Specular microscopy and pachymetry are mandatory in these cases to protect the endothelium. Dense arcus senilis, corneal opacity, and crocodile shagreen all are associated with decreased clarity and reduced visual acuity.[42]

Anterior Chamber

Anterior chamber depth assessment is important as shallow AC can render cataract surgery difficult.[43]

Pupil

It is important to recognize a poorly dilating pupil and plan mechanical dilatation prior to performing a capsulorhexis and intracameral injection of the mydriatic. If the red glow is compromised, the capsule should be stained with trypan blue to allow a meticulous capsulorhexis.[44]

Lens

Nuclear, brown, and mature cataracts are hard and may need more power for phacoemulsification, while cortical, anterior, and posterior subcapsular tend to be softer. Black cataracts are extremely dense, and manual SICS or ECCE are preferred options compared to phacoemulsification. The presence of pseudoexfoliation indicates weak zonules, and phacodonesis with lens wobble can be a present and fragile capsule with poor mydriasis.[31]

Fundus Evaluation

Fundus pathologies such as age-related macular degeneration, macular scar, etc., may affect the visual outcome. Ultrasound is required to rule out retinal detachment and posterior staphyloma in eyes with dense cataracts, which preclude fundus examination.[45]

Sclera

If a prominent explant/encircling band is placed during retinal detachment surgery or in cases with thin sclera or myopic eyes, peribulbar and retrobulbar anesthesia should be avoided or given with caution.[46]

Refractive Status

Preoperative refraction is important to guide correct power IOL implantation. The keratometry readings should be obtained, and astigmatism should be noted to address astigmatism by means of targeted wound placement for toric IOL placement or a specific adjunctive procedure. It is important to assess the postoperative refraction from an eye previously operated upon so that any refractive surprise should be noted.[47]

Informed Consent

It is important to take informed consent from the patient before going on to the cataract surgery. The risks and benefits should be conveyed to the patient in a language that he or she can understand, with an explanation of more common and potential problems.[48]

Biometry

The lens power is calculated by means of biometry for a desired postoperative outcome. For biometry, the two important parameters to be calculated are keratometry and axial length (anterioposterior length).[49]

Keratometry

Is basically obtaining the value of corneal curvature denoted as K1 and K2 by means of Javal–Schiøtz keratometer or corneal topographer.[50]

Optical Coherence Biometry

It helps to obtain keratometry, anterior chamber depth, and white-to-white diameter and also helps to calculate IOL power by using a range of formulae. These measurements have high reproducibility and require less skill to perform.[51]

A-Scan Ultrasound

It’s less accurate but can be obtained by direct contact or, more accurately, using a water bath over the eye. The reflecting surfaces are represented by spikes on the oscilloscope display monitor.[52]

IOL Power Formulae

The various formulae available to calculate IOL power are SRK-T, Haigis, Hoffer Q, and Holladay 1 and 2, which are commonly available. Some formulae use additional parameters, such as anterior chamber depth and lens thickness, to obtain more accuracy.[53]

Previous Refractive Surgery

The standard IOL power calculation formulae don’t apply to eyes that have undergone previous refractive surgery. Any kind of refractive surgery leads to a change in the relation of the anterior and posterior corneal surface, and this makes a significant difference in the IOL power required, as standard IOL power calculations are unsuitable. The various methods used are the refractive history method, contact lens method, and insertion of values into Hoffer Q or Masket formula or ASCRS calculator or the Haigis-L regression formula to facilitate calculation on posy refractive surgery eyes using standard inputs. The patient should also be warned of over or under-correction, which may follow the surgery.[54]

Contact Lenses

In patients who wear contact lenses, the contact lenses should be discontinued for at least a week prior to allow for corneal stabilization. Hard or rigid gas-permeable lenses may need to be left out for at least 2 weeks.[55]

Personalized A-Constant

If some amount of constant refractive deviation is found in an individual surgeon's cases, it means some aspect of the surgical procedure may be constantly influencing the outcome. A personalized A constant can be programmed into the biometry apparatus and can be taken into account.[56]

Intraocular Lens

Position- Should be in the bag. In cases with posterior capsular rent, the IOL should be placed in the sulcus.[57]

Designs of IOL

• Flexible IOL
• Rigid IOL
• Sharp/ Square edged optics
• Blue light filters
• Aspheric Optics
• Heparin Coating
• Toric IOL
• Bifocal IOL
• Adjustable IOL[58]

Treatment / Management

The treatment choice depends upon the degree of opacity sufficient enough to cause difficulty in performing essential daily activities. The following treatment modalities are available:

Medical: If visual acuity is 6/24 or better, pupillary dilatation with 2.5% phenylephrine or refractive glasses is enough to carry on routine activities, and surgery is not required. Cyclopentolate and atropine can also be useful. Recently, there are also cataract drops under trial, which can dissolve cataracts.

Surgery: If visual acuity is worse than 6/24 or there is a medical indication (phacolytic glaucoma, phacomorphic glaucoma, retinal detachment) in which a cataract is adversely affecting the health of the eye, surgery is always needed.[59](A1)

• Congenital Cataract: No treatment is necessary if visual acuity is more than 6/24, and a patient can carry out their normal routine activities. Refractive glasses can be advised for the blurring of vision or diplopia. If visual acuity falls below 6/24, surgery is needed, and the surgeon can opt for one of the following surgical procedures depending upon the patient's complaints and the severity of the disease.[60]
• Irrigation and aspiration of the lens
• Irrigation and aspiration of the lens with intraocular lens (IOL) implantation
• Irrigation aspiration of the lens with IOL, anterior vitrectomy, and primary posterior capsulotomy
• Senile Cataract: Treatment options are the following[61][62]:
• Medical: No medical treatment is effective once the cataract has become mature.
• Surgical: Mature cataract has a very hard nucleus, and one of the following methods is used to extract the lens:
• Extracapsular cataract extraction: a procedure of choice
• Intracapsular cataract extraction: an old technique not used frequently due to complications 
• Phaco-emulsification: a modification of extracapsular cataract extraction (ECCE) with less astigmatism and early visual recovery
• Laser phacolysis: a recent advancement under trial
• Management of general conditions before surgery: Many general health conditions require optimization before surgery for better results.
• Diabetes mellitus
• Hypertension
• Myocardial Infarction
• Angina
• Respiratory Infection
• Stroke
• Leg ulcer
• Viral hepatitis
• AIDS
• Epilepsy
• Parkinson disease
• Rheumatoid arthritis

Steps of Manual Small Incision Cataract Surgery

• Conjunctival peritomy
• Conjunctival cautery
• Scleral incision
• Sclerocorneal tunnel
• Anterior chamber entry
• Continuous curvilinear capsulorhexis
• Hydro dissection
• Nucleus prolapse
• Nucleus delivery
• Cortex removal
• IOL implantation
• Viscoelastic wash
• Anterior chamber reformation [58]

 Steps of Phacoemulsification

• Side port creation
• Clear corneal entry
• Anterior capsular staining
• Viscoelastic injection
• Continuous curvilinear capsulorhexis
• Hydrodissection
• Nucleus rotation
• Nucleus trenching
• Subdivision of nucleus
• Nucleus emulsification
• Bimanual irrigation and aspiration
• IOL implantation
• Viscoelastic wash
• Side port hydration
• Anterior chamber reformation
• Moxifloxacin injection [63]

Differential Diagnosis

The differential diagnosis of cataracts includes many disorders, such as:

• Glaucoma
• Refractive errors
• Macular degeneration
• Diabetic retinopathy
• Corneal dystrophies and degenerations
• Optic atrophy
• Retinitis pigmentosa[64]

Staging

The Lens Opacity Classification System (LOCS II)[65]

The Lens Opacity Classification System (LOCS III)[66] 

Age-Related Eye Disease Study Clinical Lens Standards[67]

Nuclear Standard

Nuclear standard 1

Nuclear standard 2

Nuclear standard 3

Posterior Subcapsular Cataract (PSC)[68]

PSC standard 1

PSC standard 2

PSC standard 3

Cortical Standard

Cortical standard 1

Cortical standard 2

Cortical standard 3

Burrato Grading of Cataract[69]

NO, N1, N2, N3, N4, N5, N6, N7, N8, N9, N10

Grading of Nuclear Hardness

Grade 1- Whitish/ Greenish yellow

Grade 2- Yellow

Grade 3- Amber

Grade 4- Brown

Grade 5- Black[70]

Prognosis

Prognosis of cataract depends upon multiple factors such as:

• The degree of visual impairment
• Type of cataract
• Timing of intervention
• Mode of intervention
• Quality of life
• Unilateral or bilateral involvement of the eye
• Presence of another systemic disease

In most cases, surgery restores vision very effectively. The presence of another systemic disease, time of intervention, and mode of surgery can be instrumental in determining the visual outcome. Recent studies reveal that in most of the cases, the prognosis is excellent after surgery, almost 70 to 80%. Most patients show excellent results after surgery if they strictly follow postoperative instructions and medication regimens advised by their ophthalmologist.[71] A routine eye examination is advisable, which will detect any cataract development in the other eye. Many patients with a monofocal IOL may require refractive glasses to achieve their best visual acuity after surgical cataract removal.[72] Gradual opacification of the posterior capsule can develop in a large number of patients, which can affect the patient's vision (secondary cataract).

Complications

Cataracts cause multiple complications discussed as follows:

Congenital cataracts: These can be disease-related or surgery-related [73]:

• Disease-related complications: corneal ulcer, corneal perforation (acquired anterior capsular cataract), blindness
• Surgery-related complications: uveitis, posterior capsular thickening, aphakia, after cataract, growth-related refractive changes, glaucoma, retinal detachment

Acquired cataracts: These can be disease-related or surgery related:

• Disease-related complications: acute congestive glaucoma (Intumescent stage), phacolytic glaucoma, iritis, subluxation of the lens, secondary glaucoma(hypermature stage), blindness
• Surgery-related complications: these are classified as follows:
  • During surgery: posterior capsular rupture, hyphaema, expulsive hemorrhage, corneal burn, nucleus drop in vitreous
  • Post-surgery: iris prolapse, delayed anterior chamber formation, infections like endophthalmitis or panophthalmitis, striate keratitis, malpositioning of IOL, pseudophakic glaucoma, cystoid macular edema, dysphotopsia, ptosis, retinal detachment, posterior capsular thickening, and opacifications [74][75]