Cataracts

A cataract is an opacification of the ocular lens. Cataracts are painless but can lead to blindness if not treated. In fact, cataracts are the number one preventable cause of blindness worldwide, especially in areas with poor access to cataract surgery. The crystalline lens is made up of crystallin proteins, which accrue defects over time via age-related changes (eg, oxidation, post-translational modifications, accumulation of fluorescent chromophores, etc…). These defects produce opacities, which disturb the passage of light detection to the retina. Whereas in a healthy eye, the lens helps to focus light on the retina, cataracts interrupt this process and scatter light, causing a myriad of potential visual complications. And although the lens has physiological means to remove injured crystallin proteins, this waste system deteriorates with time, allowing the crystallin defects (and thus the opacities) to accumulate. In addition to opacification, lens protein defects lead to rigidity (decreased elasticity) and compaction in the central (nuclear) region of the lens, called nuclear sclerosis. This loss of flexibility results in a failure to accommodate, and thus presbyopia (impairment in far vision). There are numerous additional causes beyond age-related changes that produce cataracts. They include, but are not limited to:

• Trauma
• Toxic causes: tobacco, alcohol, sunlight exposure (UV-B exposure),
• Genetic factors in general and specific genetic disorders (eg, myotonic dystrophy, Wilson’s disease, galactosemia)
• Diabetes mellitus and metabolic syndrome
• Opportunistic infections
• Iatrogenic causes: steroids, phenothiazines, topical anticholinesterases, post ocular-radiation therapy.

Painless, progressive visual disturbance with a variable symptom progression involving issues such as:

• Inability to focus on close-up objects (inability to read fine print), called presbyopia
• Glare of oncoming headlights
• Trouble reading road signs

• Lens opacity is the most obvious sign.
• Red reflex test (the fundus reflex). You should stand 1.5 to 3 feet (~ 0.5 to 1.0 meter) from the patient and, using a direct ophthalmoscope, shines light at the retina. The reddish-orange hue of the retina should be illuminated and visible through the pupil, making the pupil appear red/orange. Cataracts and a variety of other conditions can impair this reflex.
• Note that although it’s called the “red” reflex, various pigmentations can alter the normal projection of the retina, so it’s helpful to compare the eyes and look for similarities/differences. We can see this red reflex in flash photography if the pupil doesn’t close fast enough and the bright light reaches the retina and bounces back to the pupil.
• Also, note that if you are illuminating the cornea (which does have some coloration), you will not be actually assessing the fundus reflex, so pay attention that you are doing the evaluation correctly.

The primary classifications of cataract are nuclear sclerotic, cortical, and posterior subcapsular. We illustrate the location of these cataracts in the accompanying diagram (to help with visual organization) but for details about their etiology and differing presenting symptoms, refer to the American Academy of Ophthalmology article on cataracts. Cataract surgery is common and effective. Phacoemulsification is an ultrasound technique that breaks the cataract into small particles that can be aspirated out. Other techniques exist including manual extracapsular cataract extraction (ECCE). Beyond removing the cataract, intraocular lens (IOL) placement is also performed during the cataract surgery to improve the ultimate visual outcome.

• “Cataract - EyeWiki.” Accessed July 10, 2024. https://eyewiki.org/Cataract#Management.

Lee, Cameron M., and Natalie A. Afshari. “The Global State of Cataract Blindness.” Current Opinion in Ophthalmology 28, no. 1 (January 2017): 98–103. https://doi.org/10.1097/ICU.0000000000000340.

• Michael, R., and A. J. Bron. “The Ageing Lens and Cataract: A Model of Normal and Pathological Ageing.” Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1568 (April 27, 2011): 1278–92. https://doi.org/10.1098/rstb.2010.0300.

• Nye, Christina. “A Child’s Vision.” Pediatric Clinics of North America, Pediatric Ophthalmology, 61, no. 3 (June 1, 2014): 495–503. https://doi.org/10.1016/j.pcl.2014.03.001.

• “Red Reflex - an Overview | ScienceDirect Topics.” Accessed July 10, 2024. https://www.sciencedirect.com/topics/medicine-and-dentistry/red-reflex.

• ResearchGate. “Fig. 1 Schematic Cross Section of the Lens Demonstrating Various Zones...” Accessed July 10, 2024. https://www.researchgate.net/figure/Schematic-cross-section-of-the-lens-demonstrating-various-zones-and-forms-of-age-related_fig1_10835261.

• Ruan, Xiaoting, Zhenzhen Liu, Lixia Luo, and Yizhi Liu. “Structure of the Lens and Its Associations with the Visual Quality.” BMJ Open Ophthalmology 5, no. 1 (September 1, 2020): e000459. https://doi.org/10.1136/bmjophth-2020-000459.

• Sharma, K. Krishna, and Puttur Santhoshkumar. “Lens Aging: Effects of Crystallins.” Biochimica et Biophysica Acta 1790, no. 10 (October 2009): 1095–1108. https://doi.org/10.1016/j.bbagen.2009.05.008.

Mature Cataract