Black cataract (Cataracta Nigra) is the most severe form of cataract, in which the lens nucleus becomes extremely hardened and blackened. It represents the final stage of nuclear sclerosis, beyond the stage also called brunescent cataract.
The lens nucleus discolors and hardens with age. This discoloration process is called brunescence, progressing gradually from yellow to orange to brown. Black cataract is the extreme end of this brunescence, showing such advanced opacification and hardening that it cannot be evaluated by standard cataract grading systems such as LOCS III.
Visual acuity decreases to hand motion or light perception, resulting in legal blindness. Cataract classification systems used worldwide are primarily designed for moderate opacification and are not intended for extreme cases like black cataract.
In India, there is a custom of mistakenly calling optic atrophy and irreversible blindness due to glaucoma “black cataract,” but this is a completely different concept from the original definition.
QWhat is the difference between brown cataract and black cataract?
A
Brown cataract refers to a condition where the nucleus turns yellow to brown along with hardening, and is a broad concept indicating the degree of sclerosis. Black cataract is the most severe type within this category, where the nucleus is maximally hardened and blackened, and vision is reduced to the level of hand motion or light perception.
Slit-lamp examination reveals marked opacification of the lens nucleus, appearing black to dark brown. The cortex often remains relatively clear. The red reflex is significantly diminished or absent.
Appearance Findings
Blackening of the nucleus: The lens nucleus turns black to dark brown. The cortex is often relatively transparent.
Loss of red reflex: The red reflex is almost absent on fundus examination or under the surgical microscope.
Anterior chamber depth: The anterior chamber may be shallow due to age-related changes.
Visual Dysfunction
Visual acuity: Hand motion or light perception only.
Incorrectable: Due to the extreme degree of opacity, visual acuity cannot be improved with glasses.
Legal blindness: Severe visual impairment causing significant difficulty in daily life.
QWill vision return after developing black cataract?
A
Vision recovery can be expected with appropriate surgery. However, if secondary damage to the retina and optic nerve has occurred due to prolonged severe vision loss, sufficient vision may not be obtained even after surgery. It is important to evaluate the condition of the retina and optic nerve before surgery.
Black cataract occurs as a result of long-term neglect of age-related nuclear cataract. The hardening and discoloration of the lens nucleus are based on the following biochemical changes.
Protein denaturation and aggregation: With aging, reduced glutathione (GSH) decreases, and aggregation of oxidized crystallins progresses.
Decreased water content: In nuclear cataracts, the water content of the lens nucleus decreases, leading to hardening.
Pigmentation: Insoluble fluorescent pigments such as kynurenine derivatives, which are oxidative metabolites of tryptophan, accumulate, causing discoloration from yellow to brown to black.
Accumulation of oxidative stress: Antioxidant capacity, such as superoxide dismutase (SOD), declines with age.
The main risk factors are as follows.
Advanced age: Long-term accumulation of nuclear sclerosis makes it common in people in their 80s and 90s.
Lack of cataract treatment or neglect: More common in environments with poor access to medical care.
Smoking: Promotes lens protein denaturation by cyanide, increasing the risk of nuclear cataract.
Strong UV exposure: Accelerates nuclear sclerosis through photooxidation.
Diabetes: May accelerate the progression of cataracts.
Slit-lamp microscopy: Evaluates nuclear blackening, degree of opacity, cortical status, and anterior chamber depth. Loss of red reflex is a characteristic finding.
Electrophysiological tests (ERG, VEP): Preoperative assessment of retinal and optic nerve function. Useful for predicting postoperative visual prognosis.
Corneal endothelial cell density measurement (specular microscopy): It is important to predict prolonged ultrasound energy exposure and record preoperative endothelial cell density.
Axial length measurement and IOL power calculation: If optical measurement is difficult due to severe opacity, measure axial length using A-scan ultrasound.
The Emery-Little classification assesses nuclear hardness on a 5-grade scale from 1 to 5, with black cataract corresponding to grade 5 (hardest). At this grade, extracapsular cataract extraction may be indicated.
QCan the likelihood of visual recovery be known before surgery?
A
Electrophysiological tests (ERG, VEP) and B-scan ultrasound can evaluate retinal and optic nerve function preoperatively. However, in eyes with long-term blindness, disuse changes may occur, making complete prediction of prognosis difficult even with these tests.
The choice of surgical technique depends on nuclear hardness, surgeon experience, and facility equipment.
Phacoemulsification (PEA/Phaco): This is the mainstream cataract surgery, used in over 99% of cases. With appropriate technique and equipment, it can be the first choice for black cataract. However, longer ultrasound time and higher power are required than usual.
Extracapsular Cataract Extraction (ECCE): For extremely hard nuclei such as Emery-Little grade 5, ECCE may be chosen. It may avoid complications better than small-incision PEA.
Femtosecond laser pretreatment: In facilities with advanced equipment, pre-nuclear fragmentation (laser cracking) using a femtosecond laser may be recommended to reduce the ultrasonic energy required during PEA.
The ESCRS guidelines state that PEA for brown or black cataracts (dense brown lens) increases the risk of posterior capsule rupture, endothelial damage, and zonular instability, potentially requiring additional surgical procedures, and adequate patient explanation is necessary1).
Additionally, the AAO Preferred Practice Pattern from the Cataract and Anterior Segment Committee indicates that PEA has lower rates of intraoperative complications such as iris prolapse and posterior capsule rupture, and achieves better postoperative visual acuity compared to manual extracapsular cataract extraction or manual small-incision cataract surgery (MSICS)2).
PEA for black cataracts requires the following technical considerations.
Appropriate size of continuous curvilinear capsulorhexis (CCC): Because the nucleus is very hard, the size and shape of the CCC should be properly designed. The use of a highly cohesive OVD reduces the risk of capsulorhexis tear-out1).
Sufficient hydrodissection: Perform until the nucleus can be easily rotated.
Deep grooving and nuclear division: Conventional chopping methods often do not work; deep grooving and division (groove-and-crack technique) are required. For very hard nuclei, dividing into 6 or 8 smaller pieces is advantageous.
Generous use of dispersive OVD: Use dispersive ophthalmic viscosurgical devices (OVD) liberally to protect the corneal endothelium from prolonged ultrasound exposure.
Utilization of bimanual technique: For hard nuclei, bimanual PEA using the US tip and a hook (sustainer) inserted through a side port is effective. The hook allows manipulation of the nucleus and enables nuclear division using the wound as a fulcrum.
Management of ultrasound power: Since prolonged, high-power ultrasound is often required, always be mindful of the risk of endothelial cell damage during the procedure.
Postoperatively, in addition to standard cataract postoperative management (antibiotic and steroid eye drops, etc.), the following points should be noted.
Monitor postoperative changes in corneal endothelial cells.
If intraoperative complications (such as posterior capsule rupture) occur, subsequent management (including conversion to vitrectomy) should be performed.
QHow is black cataract surgery different from ordinary cataract surgery?
A
Since the nucleus is much harder than in ordinary cataracts, the ultrasonic oscillation time is longer, placing a greater burden on the endothelial cells. Additionally, the risk of complications such as posterior capsule rupture and zonular dialysis is high, and conversion to extracapsular cataract extraction may be necessary. Management by an experienced surgeon is recommended.
The lens has a precise biochemical mechanism to maintain transparency, but these functions gradually decline with age.
Process of protein denaturation:
The transparency of the lens is maintained by the orderly arrangement of crystallins (α, β, γ). With aging, the following changes occur.
Decreased reduced glutathione (GSH) increases aggregation of oxidized crystallins.
Superoxide dismutase (SOD) activity declines with age (to about one-third of normal), increasing oxidative damage from reactive oxygen species.
Decreased Na⁺-K⁺ ATPase and Ca²⁺ ATPase activity leads to intracellular accumulation of Na⁺ and Ca²⁺, and reduction of K⁺.
In nuclear cataract, water content decreases and hardening of the lens nucleus progresses.
Mechanism of blackening:
Brunescence is caused by accumulation of insoluble fluorescent pigments (kynurenine derivatives: 3-OHKG, DHKN-Glc, etc.), which are oxidative metabolites of tryptophan. These pigments accumulate in the lens nucleus, causing a gradual color change from yellow to orange to brown to black. Exposure to near-ultraviolet light accelerates this process.
Changes according to category:
According to the ESCRS guidelines, nuclear cataract is characterized by deposition of pigments in the lens nucleus, and is classified as NO (nuclear opalescence) and NC (nuclear color) using the LOCS III system 1). Black cataract corresponds to a state exceeding the highest value of this NC classification.
Pathophysiological Background of Intraoperative Difficulty
Extreme hardening of the nucleus increases surgical difficulty through the following mechanisms:
Increased ultrasound energy: Emulsifying a hard nucleus requires longer oscillation time and higher power than usual, exposing corneal endothelial cells to excessive ultrasound energy.
Increased mechanical stress: During nucleus chopping and division maneuvers, mechanical load on the zonules and posterior capsule increases.
Anterior chamber instability: Instability of the anterior chamber due to prolonged surgical manipulation increases the risk of posterior capsule rupture and nuclear drop.
7. Latest Research and Future Perspectives (Research-stage Reports)
Preoperative nuclear fragmentation using a femtosecond laser (laser cracking) is a technique that has attracted attention for reducing the ultrasonic energy required for PEA in extremely hard nuclei, from the perspective of protecting the corneal endothelium. The ESCRS guidelines report that increasing the post-to-pre capsular distance and decreasing the pre-to-pre capsular distance in femtosecond laser capsulotomy may reduce the incidence of incomplete capsulotomy 1).
However, in black cataracts where the red reflex is lost, laser docking and focusing may be difficult, and this technique cannot be applied to all cases.
The ESCRS guidelines state that highly cohesive OVD is effective in reducing the risk of tear-out during capsulorhexis (CCC) 1). The soft-shell technique (combination of dispersive and cohesive OVD) is being used to achieve both endothelial protection and anterior chamber maintenance.
With improvements in surgical techniques and equipment, PEA is increasingly applicable to cases with extremely hard nuclei that were previously indicated for extracapsular cataract extraction. Minimizing intraoperative ultrasonic energy and improving endothelial protection techniques remain future challenges 2).
American Academy of Ophthalmology Cataract and Anterior Segment Committee. Cataract in the Adult Eye Preferred Practice Pattern. Ophthalmology. 2021;128(11):P1-P54.
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