Steven Dell: Eye Health

Ophthalmology and Eye Anatomy

• Ophthalmology: medical and surgical specialty dealing with the eye
• Ophthalmologists: eye surgeons who diagnose and treat eye diseases
• Optometrists: non-​​surgical eye care professionals who fit glasses, screen for eye diseases, and manage pre- and post-​​operative care

Ophthalmology Residency

• Four-​​year residency, including a transitional internship with exposure to various medical disciplines
• Bread and butter cases during training: cataract surgery and retinal disease treatment (often related to diabetes)

Eye Anatomy Basics

• Retina: located at the back of the eye, responsible for receiving light and converting it into electrical signals to be sent to the brain
• Cornea: clear, dome-​​shaped surface at the front of the eye that helps focus light entering the eye

Ophthalmology Procedures

• Cataract surgery: removal of the cloudy lens in the eye and replacement with an artificial lens
• Retinal disease treatment: various procedures to address retinal issues, often related to diabetes and its complications
  Explaining the Eye
• Eye is like a camera 
  • Front: cornea (covering, like a watch)
  • Pupil: hole in the iris
  • Lens: behind the pupil
  • Vitreous cavity
  • Retina: back of the eye, connects to the optic nerve
• Images come in, bent by cornea and lens, focus on retina 
  • Fovea: center of retina, where images fall
• Nearsighted: images come into focus not on retina
• Lens: size and shape of an M&M candy 
  • Elastic when young, less elastic and harder with age
  • Cataract: lens becomes stiff, hard, and opaque
• Lens is avascular, immune privileged 
  • Blood-​​retinal barrier protects retina from systemic disease
• Potential future treatment: soften lens to delay farsightedness and cataract onset

• Pupil: dark part of the eye, changes size due to iris movement (dilation and constriction)
  Pharmacological Solutions for Presbyopia

• Eye drops that shrink the pupil 
  • Increases depth of focus
  • Works in 15 minutes
  • Lasts 6–8 hours, possibly up to 10 hours
  • Commercial availability expected in early 2022
• Lipoic acid choline ester 
  • Softens the lens
  • Works in 15 months
  • Aimed at reducing the incidence or delaying the onset of cataract formation

Eye Color and Evolution

• Darker eye colors offer more protection from UV and visible light 
  • Darker eye colors are more common closer to the equator
  • Retinal pigment epithelium shields the vascular supply behind the retina from radiation

Rods and Cones

• Cones
  • Responsible for daytime vision
  • Clustered in the center of the retina (macula)
• Rods
  • Responsible for dim illumination vision (night vision)
  • Located in the periphery of the retina
  • Good at detecting motion
• Both rods and cones are single cells with photosensitive structures 
  • Photon hits the cell, causing a change in the membrane and ion flow, generating a signal

Visual Processing in the Brain

• Most visual processing occurs in the neocortex 
  • Autonomic functions, like pupil responses, occur in the midbrain
  • Left visual sphere sends information to the right side of the brain, and vice versa
• Optic chiasm
  • Point where optic nerves cross
  • If a visual deficit is in one eye only, the issue is in front of the chiasm
  • If the issue affects both eyes, it is behind the chiasm
    Vision and Human Performance
• Vision is the most valued sense among humans 
  • Most people would be least willing to give up their sense of sight
  • A large part of the brain is devoted to vision
• Vision is important in various fields, such as sports 
  • Major League Baseball players rely on their vision to see the laces on the ball
  • Some athletes undergo laser vision correction to improve their vision beyond 20/​​20
• The theoretical limit of human vision is defined by the pixelation of the retina 
  • Varies from person to person, but is around 20/​​08
  • Achievable by removing optical irregularities and neutralizing them with glasses or laser vision correction

Contact Lenses vs. Laser Vision Correction

• Contact lenses can provide good vision, but not superhuman performance 
  • Body regards contact lenses as foreign objects and attacks them
  • Susceptible to pollen, dust, and other debris
  • Orientation of lenses for astigmatism correction can be affected by blinking
• Laser vision correction can provide better optical performance than contact lenses 
  • Beneficial for athletes who need the best vision possible
  • Can achieve vision beyond 20/​​20

Vision and Evolution

• Humans have better vision than many animals, especially in low light conditions 
  • Possibly due to evolving as both hunters and hunted
• Humans have a poor sense of smell compared to animals 
  • Unclear why evolution did not push for a better sense of smell
• Vision is important for survival and functioning in the world 
  • Loss of vision due to trauma is a significant concern, especially for young people
  • Blunt trauma is a common cause of vision loss in young people
    Astigmatism and Vision
• Astigmatism: when the eye is shaped like a football instead of a basketball 
  • Typically occurs in the cornea (front part of the eye)
  • Cornea is about 550 microns thick (half a millimeter)
• Astigmatism prevalence: around 60% of patients with glasses prescription have some degree of astigmatism
• Nearsightedness (myopia) and farsightedness (hyperopia) can be influenced by the length of the eyeball (anterior-​​posterior axis) 
  • Nearsightedness: long eyeball, difficulty seeing far away objects
  • Farsightedness: short eyeball, difficulty seeing close objects

Environmental Factors in Vision Development

• Deprivation from outdoor light and near work can contribute to nearsightedness 
  • Studies show that children who spend more time outside have a lower risk of developing nearsightedness
  • Outdoor light, especially during midday, is important for preventing myopia
• Blue light is critical for wakefulness, attention, and potentially preventing myopia
• Genetic factors may also play a role in vision development, but environmental factors seem to be more powerful

Implications for Children’s Vision

• Encouraging outdoor activities and exposure to natural light can help prevent nearsightedness in children
• Spending too much time indoors, especially in dimly lit rooms, can increase the risk of nearsightedness
• Myopia is not just an inconvenience; it can also lead to other eye-​​related health issues such as cataracts, myopic macular degeneration, glaucoma, and retinal tears and detachments
  Children’s Outdoor Time and Vision Development
• Importance of good illumination for children’s vision development 
• Balance between outdoor time and indoor near activities (e.g., Legos, trains, trucks)
• Hunter-​​gatherer societies have well-​​tuned distance vision, no nearsightedness

Cataracts and Aging

• Cataracts are inevitable in aging, usually forming in the 70s
• Early signs: changes in night vision, glare, halos, streaks around lights, problems with contrast sensitivity
• Factors contributing to cataract formation: lens proteins degrading, UV light exposure, glucose in the lens, corticosteroid use, trauma

Cataract Surgery and Intraocular Lenses

• Cataract surgery involves removing the cataract and replacing it with an artificial lens
• Intraocular lenses have advanced to correct near vision, distance vision, astigmatism, nearsightedness, farsightedness, and presbyopia
• Cataract surgery is typically a once-​​in-​​a-​​lifetime procedure

History of Cataract Treatment

• Ancient world: “couching” procedure involved poking the lens of the eye backward, allowing unfocused light to enter
• Post-​​WWII: Harold Ridley discovered that plexiglass (polymethyl methacrylate) could be placed in the eye without an immune response
• Ridley’s idea led to the development of intraocular lenses, which have evolved and improved over time
  Cataract Surgery and Implant Lenses
• Tibial plateau made of polymethyl methacrylate, no longer used due to stiffness 
• Cataract removal through tiny incisions, using ultrasound or femtosecond laser 
  • Implant lenses can be folded and inserted through small incisions
  • Small incisions reduce healing time and astigmatism
• Implant lenses do not regrow the coating 
  • Can opacify after surgery, treatable with laser
• Cataract surgery can improve vision significantly 
  • Implant lenses can correct near and distance vision

Implant Lens Technology

• Different lenses for different patients 
  • More expensive lenses provide more spectacle independence
• Lenses can correct other visual defects 
  • Can be tuned for specific vision preferences (e.g., nearsightedness)
• Measurements needed for implant lenses 
  • Ensure cornea surface is pristine
  • Measure length of the eye, curvature of the cornea, and index of refraction
  • Calculate implant lens power and placement

Future of Implant Lenses

• Mid-​​2000s: development of zoom-​​focus implant lenses 
  • Lenses that could move or change shape
  • Surpassed by bifocal and trifocal implants in capability
• Potential game-​​changer: a lens that can change shape or position and zoom focus seamlessly from near to far
• Implanting lenses from deceased individuals not feasible, unlike corneas
  Corneal Pathology and Dry Eye
• Corneal abrasions: common issue caused by lack of lubrication or dry eye 
• Dry eye: caused by various factors 
  • Medications with anticholinergic side effects
  • Antihistamines
  • Hormonal influences (e.g., lack of testosterone)
  • Autoimmune conditions (e.g., Sjogren’s, rheumatoid arthritis)
  • Thyroid metabolism issues
• Treatment for dry eye 
  • Artificial tears (eye drops)
  • Omega‑3 fatty acid supplementation
  • Omega‑6 fatty acid supplementation (e.g., gamma-​​linolenic acid)

Light Exposure and Eye Health

• Balance between too much and too little light exposure
• Sunglasses recommended for protection against: 
  • Skin cancer on lower eyelid
  • Photo aging of the lens (delaying cataract onset)
  • Retinal damage (reducing risk of age-​​related macular degeneration)
• Light-​​eyed patients more susceptible to UV damage due to less pigment
• Wearing sunglasses when outside during daylight hours is advised for eye protection and longevity
  Sunglasses and Eye Protection
• Importance of wearing sunglasses even on overcast days 
  • Protects from damaging light
  • UV filter is the key for eye health protection, not the tint
• Polarized lenses
  • Blocks light in one meridian, letting all light through in another
  • Helpful for reducing glare on water or highways
  • No evidence that polarization is better for eye health than non-​​polarized lenses

Glasses vs. Contact Lenses

• Safest option is glasses (spectacles)
  • No risk associated with them
• Debate between long-​​term contact lens wear and laser vision correction 
  • Laser vision correction may be recommended if contacts are inconvenient or cause infections

Laser Eye Surgery

• PRK (Photorefractive Keratectomy) came before LASIK 
  • FDA approved in the mid-1990s
  • First procedure done in New Orleans by Dr. Margaret McDonald
• PRK and LASIK use excimer lasers 
  • Originally used to etch microchips
  • Can make cuts in human tissue without generating heat or immune response
• PRK changes the curvature of the cornea to improve vision 
  • Cannot change the length of the eye, which also affects vision
  • Only a small change in curvature is needed to focus light on the retina
    Laser Vision Correction: PRK
• PRK (Photorefractive Keratectomy) is a type of laser vision correction 
• Procedure:
• Eye is anesthetized
• Alcohol solution is applied to the cornea to remove the epithelial layer (about 50 microns thick)
• Laser is used to reshape the cornea by vaporizing tissue
• Laser moves around the cornea to avoid overheating tissue
• Procedure takes about 2–3 minutes per eye
• Recovery:
• Epithelial layer heals over in about 4 days
• Vision improves quickly, but full recovery takes several days
• A contact lens is used as a bandaid during the healing process
• PRK and LASIK have similar results 30 days after the procedure, but LASIK has a faster recovery time

Eye Tracking During Laser Vision Correction

• Patients’ eyes can move during the procedure
• Laser can track eye movement faster than the patient can move their eye
• Laser will not fire unless the eye is within its range of tracking
• Eye movement is not a significant concern during the procedure

Digital Mapping of the Eye

• Before laser vision correction, the eye is digitally mapped using a wafer sensing device
• A narrow beam of light is sent into the eye, and the distortion of the light as it bounces back is measured
• This information is used to determine the distortions in the eye and build a customized laser vision correction plan
• The technology was originally developed for telescopes to correct for atmospheric distortion
  LASIK and PRK Eye Surgery
• LASIK and PRK are two types of corrective eye surgery 
• LASIK involves creating a flap in the cornea and reshaping it 
  • Faster recovery time, less postoperative care
  • More common, about 80–85% of corrective eye surgeries
• PRK involves removing the epithelium and reshaping the cornea 
  • Slower recovery time, more postoperative care
  • Better for patients with thin corneas or preexisting dry eye
• Both procedures can result in temporary dry eye
• Night vision issues have been largely resolved with advancements in technology
• Costs for both procedures are similar, averaging around $4,000 per eye in North America
• Exclusion criteria for both procedures include: 
  • Unstable cornea
  • Irregular astigmatism
  • Autoimmune diseases
  • Other eye diseases (cataract, glaucoma, retinal pathology)
• Smile procedure is an alternative to LASIK and PRK 
  • Uses a single laser and a smaller incision
  • Designed to reduce dry eye and speed up recovery time
  • Not yet proven to be better or equal to LASIK or PRK
    Air Puff Telemetry and Glaucoma
• Air puff telemetry not considered gold standard for measuring pressure 
  • Blinking quickly and squeezing can cause false readings
• Glaucoma: damage to the optic nerve related to pressure 
  • Many different types of glaucoma, but all share this common pathway
  • Some people have normal pressures but still develop optic nerve damage
• Symptoms of glaucoma 
  • No symptoms until very end, when peripheral vision is damaged
  • As it progresses, can affect central vision and become symptomatic
• Glaucoma treatment
  • Pharmacological management has improved
  • Laser procedures and minimally invasive glaucoma procedures (MIGS) available
• 80% of glaucoma cases caused by chronic open-​​angle glaucoma 
  • Problem of overproduction of fluid inside the eye, causing high pressure
• Glaucoma screening
  • Annual eye exams check for glaucoma
  • Incidence increases with age, more important to pay attention to in 50s and beyond

UV Exposure and Eye Health

• Natural sunlight exposure important for eye health 
  • Wearing sunglasses can help protect eyes from UV damage
  • Hats can also provide some protection
• Nutritional supplements for eye health 
  • Vitamin C deficiency associated with elevated risk of cataracts
  • Antioxidants (A, C, E) have no effect on cataract formation
  • Lutein and zeaxanthine may have weak protective effects for cataracts and macular degeneration

Screen Use and Eye Health

• No evidence that screen use causes macular degeneration or cataracts 
  • Amount of UV radiation from screens is very low
• Blue light from screens can disrupt circadian rhythm 
  • Exposure to blue light at night can make it harder to sleep
  • Blue-​​blocking glasses may help with this issue
    Effects of Blue Light and Screen Time on Eyes
• Blue light from screens can disrupt circadian rhythms 
  • Not necessarily damaging to eyes, but can affect sleep
• Passive watching TV vs. active engagement with screens (e.g., checking email) 
  • Both may not be ideal, but active engagement can be more stimulating and disruptive to sleep
• Software like Flux can help reduce blue light exposure from screens

Contact Lenses and Eye Health

• Avoid sleeping in contact lenses to prevent infections 
  • Extended wear contact lenses not recommended by eye surgeons
• Daily disposable lenses are preferable if affordable
• Importance of eye protection and sunglasses

Cataract Surgery

• Not as daunting as it used to be 
  • Intraocular lenses have improved outcomes
• Can potentially correct other age-​​related visual changes
• Cataract surgery is typically a one-​​time procedure

Laser Eye Surgery

• Stability of prescription is important 
  • Length of the eye should be fixed
  • Cornea shape is fixed during surgery
• Prescription should not worsen with age unless cataract formation occurs

Eye Health as an Indicator of Metabolic Health

• Eye is a transparent organ, allowing direct observation of issues
• Diabetic retinopathy can be an early sign of diabetes 
  • Microvascular disease in the eye can indicate issues in other organs (e.g., kidneys, toes)
• Using eye health as a standard for metabolic health could provide a more accurate understanding of a person’s overall health 
  • Not a binary diagnosis, but rather a spectrum of health
    Glucose Migration and Lens Distortion
• Glucose migration into the lens can be an early indicator of metabolic issues 
• Lens distortion due to osmotic effect of glucose can be a canary in the coal mine for initial diagnosis and screening
• Technology to measure glucose in the lens is being studied, not commercially available yet
• Retinal vasculature can be imaged non-​​invasively with optical coherence tomography
• Diabetic patients with well-​​controlled sugar levels may still show signs of microvascular damage in their retina

Ophthalmology and Medicine Integration

• Ophthalmology should be more integrated into medicine
• Ophthalmologists can directly observe the brain and vascular tree, which can be helpful for systemic health
• More collaboration between ophthalmologists and other medical professionals can lead to better patient care and understanding of systemic health issues