Cataract Grading Systems
Cataracts are primarily graded using standardized classification systems that assess the type, location, and severity of lens opacities, with the Lens Opacities Classification System III (LOCS III) being the most widely accepted method for clinical and research purposes. 1
Types of Cataracts
Cataracts are categorized based on their anatomical location within the lens:
Nuclear cataracts: Central opacification or discoloration of the lens that interferes with visual function, classified as either brunescent, opalescent, or both. These typically progress slowly and affect distance vision more than near vision. 2
Cortical cataracts: Can be central or peripheral, appearing as opaque spokes or oil droplets. Patients commonly complain of glare symptoms. When the entire cortex becomes white and opaque, it's referred to as a mature cortical cataract. 2
Posterior subcapsular cataracts (PSC): Located just inside the posterior lens capsule, causing substantial visual impairment when involving the axial region. Patients often experience glare and poor vision in bright light, with near vision typically more affected than distance due to miosis with near accommodation. PSCs are more common in younger patients and tend to progress more quickly than other types. 2
Less common types: Include anterior subcapsular, anterior polar, and posterior polar cataracts. 2
Lens Opacities Classification System III (LOCS III)
LOCS III is the most comprehensive and widely used grading system, consisting of:
- Nuclear opalescence (NO): Graded using 6 slit-lamp images on a decimal scale (0.1-6.9) 1, 3
- Nuclear color (NC): Graded using 6 slit-lamp images on a decimal scale (0.1-6.9) 1, 3
- Cortical cataract (C): Graded using 5 retroillumination images on a decimal scale (0.1-5.9) 1, 3
- Posterior subcapsular cataract (P): Graded using 5 retroillumination images on a decimal scale (0.1-5.9) 1, 3
LOCS III offers improved precision over previous systems with reduced 95% tolerance limits:
- 0.7 for nuclear opalescence
- 0.7 for nuclear color
- 0.5 for cortical cataract
- 1.0 for posterior subcapsular cataract 1
Clinical Relevance of Grading
Cataract grading serves several important clinical purposes:
Surgical planning: Higher grades of nuclear cataracts (NC and NO) correlate exponentially with greater phacoemulsification energy requirements during surgery. Preoperative LOCS III classification helps create a customized operative plan. 4
Disease progression monitoring: Grading allows for tracking cataract progression over time. PSCs typically progress more quickly than nuclear and cortical cataracts. 2
Visual function correlation: Different types of cataracts affect vision differently:
Alternative Grading Systems
Oxford Clinical Cataract Classification and Grading System (OCCCGS): Uses standard diagrams and Munsell color samples for grading. Studies show linear relationships between LOCS III and OCCCGS for nuclear and posterior subcapsular cataracts. 5
Japanese Cooperative Cataract Epidemiology Study Group System: Classifies cataracts into cortical, nuclear, and subcapsular types with three grades of advancement (I-early, II-moderate, III-advanced). Lens coloration is graded from I (pale yellow) to IV (brown). 6
Clinical Assessment Considerations
When evaluating cataracts, several testing modalities may help determine the impact on visual function:
Glare testing: Particularly useful for cortical and posterior subcapsular cataracts, which significantly impact vision in bright light conditions 2
Contrast sensitivity testing: May reveal functional vision loss not detected by standard visual acuity testing 2
Wavefront imaging: Can detect visual aberrations caused by even mild cataracts 2
Remember that while several grading systems exist, variations between them make it difficult to compare prevalence rates across studies. The choice of grading system should consider the clinical or research purpose and the need for standardization. 2