Advanced Refractive Error Topics (Part I)

Myopic Shift

increase in the power of the cornea and/or lens, or axial length

Myopic Shift - Cornea

increased cornea thickness, steeper curvature

Myopic Shift - Lens

thicker, steeper curvature, anterior shift in position, increase in refractive index

Health-Related Myopic Shift

Diabetes, Age-Related Cataracts, Corneal Edema

Diabetes Myopic Shift

hyperglycemia can cause a myopic shift bilaterally, excess glucose in the AH moves into the lens and is converted to sorbitol, water is drawn in and lens swells, increasing power

T/F: Hyperopic shifts have also been reported with hyperglycemia

True

Systemic Symptoms of Diabetes

Excessive thirst, frequent urination, excessive hunger, weight loss, fatigue, slow wound healing, increased yeast infections

When does diabetic myopic shift reverse?

after glucose level under control within a few months

Age-Related Cataracts

clouding of the crystalline lens with age

Different Types of Cataracts

Nuclear (center), Cortical (outer), Subcapsular

Nuclear Sclerosis

most common, hardening/yellowing at center, myopic shift, gradual increase in lens power

Corneal Edema

CL overwear, trauma, herpes, corneal dystrophy, pregnancy

Surgically-Induced Myopic Shifts

refractive surgery, cataract implant, scleral buckle for retinal detachment repair

Drug-Induced Myopic Shift

acute transient myopic shift from drugs, bilateral, can occur within a day to weeks of starting new meds, most common are sulfa drugs

Most Common Drug-Induced Myopic Shift Drugs

Sulfonamides (antibiotics), Hydrochlorothiazide (Diuretic)

Mechanism of Drug-Induced Myopic Shift

ciliary body edema moves lens forward causing AC to shallow out, increasing the overall power of the front of the eye, can also cause bilateral angle-closure glaucoma

Management of Drug-Induced Myopic Shift

reassure clearance within 1-2 weeks after discontinued use

Night Myopia

refractive error shifts toward increased myopia in dim illumination, younger people more likely to be affected

Etiology of Night Myopia

tonic accommodation; in the absence of an adequate visual stimulus, accommodation adopts an intermediate resting position or dark focus

Would Night Myopia affect night driving?

driving with headlights was not dark enough to cause dark focus

What if night vision is getting worse?

need to rule out retinal degeneration, RP, cataracts, not being fully corrected, tinted lenses

Degenerative Myopia

pathological myopia, associated with high myopia (>-6.00), axial length (>26/27mm)

Prevalence of Degenerative Myopia

pre-teen to young adulthood, 0.2% to 0.4% U.S., Chinese, Japanese, Jewish, Arab, women more than men

Accommodative Spasm

unable to relax, associated with prolonged near work

Pseudomyopia

sudden appearance of myopia

Etiology of Pseudomyopia

accommodative spasm from prolonged near work, drugs, systemics, inflammation

Symptoms of Pseudomyopia

distance blue worse at end of day, eyestrain, headaches after reading, difficulty changing focus near to far

Signs of Pseudomyopia

decreased distance VA, pupillary constriction, esophoira, reduced NRA, cycloplegia refraction

Prevalence of Pseudomyopia

rare

Treatment for Pseudomyopia

vision therapy

Early Adult-Onset Myopia Range

20 to 40 years old

Late Adult-Onset Myopia Range

> 40 years old

T/F: Adult-Onset Myopia is less severe than juvenile-onset myopia

True

What is adult-onset myopia associated with?

intensive near work, less prevalent overall

Deprivation Myopia

altered visual input during critical period of ocular development affects emmetropization process, causes elongation of eye

Causes of Deprivation Myopia

congenital cataract, corneal opacification, hemangioma of the eyelid

Ortho-K

flatten cornea with GP CL during sleep, remove in morning, clear for one day

What is the brand of ortho-k?

Paragon CRT

How much myopia is Paragon CRT approved for?

up to 6D of myopia and up to 1.75D of astigmatism

What does PRK stand for?

photorefractive keratectomy

PRK

removing corneal epithelium, flattening cornea with a laser, covering with a soft CL bandage

What level of myopia is PRK approved for?

0.75D to 13D

Who is PRK best for?

large pupils, thin corneas

What does LASIK stand for?

Laser-Assisted In-Situ Keratomileusis

LASIK

cutting a flap of corneal tissue, flatten gin the cornea with a laser, then repositioning flap

Who is LASIK approved for?

0.50D to 15D

What are the common complications of LASIK?

dry eye, halos around lights at night

Who is not a good candidate for LASIK?

large pupils, thin corneas

Epi-LASIK

Ultra-thin flap (epithelium)

LASEK

Ultra-thin flap (epithelium), diluted alcohol used to loosen corneal epithelium

IOL

implanted intraocular lens in front or behind the iris