Decoding Your Eyeglass Prescription in San Francisco: What Those Numbers Really Mean for Your Vision
You just finished your comprehensive eye exam at Eyes in Disguise in Cow Hollow. Dr. Blas hands you a prescription filled with mysterious numbers, plus signs, minus signs, and abbreviations that look like they belong in a calculus textbook rather than on something meant to help you see clearly.
-2.50 -1.25 x 180. What does that even mean?
You squint at the paper (ironically, because you need new glasses), trying to decode whether these numbers are good or bad, strong or weak, and why there are so many different measurements for something as seemingly simple as "I can't see clearly."
If you've ever felt bewildered by your eyeglass prescription, you're not alone. After thirty years of writing prescriptions for San Francisco patients at Eyes in Disguise, I've answered thousands of questions about what those numbers mean, why they matter, and how they translate into the clear, comfortable vision you experience when you put on properly made glasses.
Understanding your prescription isn't just academic curiosity. It empowers you to make informed decisions about your eyewear, communicate effectively with opticians, understand why certain lens options benefit your specific prescription, and recognize when something isn't quite right with your new glasses.
This comprehensive guide will demystify every component of your eyeglass prescription, explain what different measurements mean for your vision and lifestyle, and help you understand why precision matters when translating numbers on paper into lenses that transform how you see San Francisco's beautiful landscapes from Cow Hollow to the Presidio.
The Anatomy of Your Eyeglass Prescription: Breaking Down Every Component
An eyeglass prescription is essentially a precise mathematical formula that describes exactly how light needs to bend to focus perfectly on your retina. Each number, symbol, and abbreviation serves a specific purpose in creating your custom vision correction.
Sphere (SPH): Your Basic Refractive Error
The sphere measurement is the primary number on your prescription and indicates whether you're nearsighted or farsighted:
Minus Signs (-) Mean Nearsightedness (Myopia): If your prescription shows negative numbers like -2.50 or -4.75, you're nearsighted. This means you see nearby objects clearly but distant objects appear blurry. The higher the negative number, the stronger your nearsightedness. According to research from theAmerican Optometric Association, myopia affects approximately 42% of Americans and has been increasing significantly in urban areas like San Francisco AOA, 2024.
Plus Signs (+) Mean Farsightedness (Hyperopia): Positive numbers like +1.75 or +3.25 indicate farsightedness. You may struggle to see nearby objects clearly while distance vision remains relatively good (though high hyperopia affects both near and distance vision). Farsightedness is less common than myopia but often goes undetected in younger patients whose eye muscles compensate.
The Magnitude Matters: Prescriptions are measured in diopters. Here's how to interpret the strength:
0.25 to 2.00: Mild prescription
2.25 to 5.00: Moderate prescription
5.25 to 8.00: Strong prescription
8.25+: Very strong prescription
At Eyes in Disguise, I see many Pacific Heights professionals with mild to moderate myopia from years of close work, and Presidio retirees developing farsightedness as their natural lens loses flexibility with age.
Why It Changes: Your sphere measurement isn't fixed forever. Myopia often progresses during teenage years and early twenties. Farsightedness becomes more apparent after age 40 when presbyopia compounds the focusing challenge. This is why annual eye exams at Eyes in Disguise are crucial for San Francisco patients.
Cylinder (CYL) and Axis: Correcting Astigmatism
If your prescription includes cylinder and axis measurements, you have astigmatism—an extremely common condition affecting about one in three Americans.
What Astigmatism Really Means: Unlike the spherical curvature of nearsightedness or farsightedness, astigmatism means your cornea has an irregular shape—more like a football than a basketball. This causes light to focus at multiple points rather than a single point on your retina, resulting in blurred or distorted vision at all distances.
Cylinder Power: This number (always written with a minus sign in the system we use) indicates how much astigmatism correction you need. Like sphere measurements:
0.25 to 1.00: Mild astigmatism
1.25 to 2.50: Moderate astigmatism
2.75+: Strong astigmatism
Axis: The Orientation: Astigmatism isn't uniform—the irregular curvature occurs along a specific meridian of your cornea. The axis (a number between 1 and 180) indicates the orientation of your astigmatism. Think of it like the hands on a clock indicating the direction of the irregularity. This number must be precise—even a 10-degree error can cause blurred, uncomfortable vision.
Example Prescription: -2.50 -1.25 x 180 means you have 2.50 diopters of nearsightedness plus 1.25 diopters of astigmatism oriented at 180 degrees (horizontal).
Many San Francisco patients at Eyes in Disguise discover they have astigmatism during comprehensive exams, often explaining why they've struggled with eye strain despite having "corrected" vision with glasses addressing only sphere.
Add Power: For Reading and Close Work
If you're over 40, your prescription may include an "Add" measurement—this addresses presbyopia, the age-related loss of focusing flexibility that affects everyone eventually.
Why Add Power Exists: Your eye's natural lens must change shape to focus at different distances. After age 40, that lens loses flexibility, making near focus progressively more difficult. Add power provides additional magnification for reading and close work.
Typical Add Powers:
+0.75 to +1.25: Early presbyopia (40-45 years)
+1.50 to +2.00: Moderate presbyopia (45-55 years)
+2.25 to +2.50: Advanced presbyopia (55-65 years)
Progressive vs. Bifocal vs. Reading Glasses: Your add power determines whether you need progressive lenses (gradual transition from distance to near), lined bifocals or trifocals (distinct zones), or separate reading glasses. At Eyes in Disguise, many Cow Hollow and Pacific Heights professionals choose progressive lenses for seamless vision at all distances without visible lines.
Pupillary Distance (PD): The Crucial Measurement Often Overlooked
Your PD isn't technically part of your prescription, but it's absolutely critical for accurate glasses. This measurement (typically 54-68mm) indicates the distance between your pupils and ensures the optical centers of your lenses align perfectly with your eyes.
Why PD Matters: Even a 2-3mm error in PD can cause eye strain, headaches, and blurred vision because your eyes must work harder to compensate for misaligned optical centers. This is particularly problematic with higher prescriptions and progressive lenses.
At Eyes in Disguise, we measure PD with digital precision during your exam and include it with every prescription. If you're ordering glasses online, ensure your PD is measured professionally—smartphone apps and ruler measurements are notoriously inaccurate.
Prism: Specialized Correction for Eye Alignment
Some prescriptions include prism correction (measured in prism diopters with a direction like "base in" or "base out"). Prism helps with eye alignment issues where your eyes don't naturally work together perfectly.
Who Needs Prism: Patients with binocular vision problems, muscle imbalances, or who've experienced trauma may benefit from prism. It redirects light to compensate for eye misalignment, reducing double vision, eye strain, and headaches.
Prism prescriptions require careful measurement and often adjustment. At Eyes in Disguise, we evaluate binocular vision thoroughly during comprehensive exams and prescribe prism when it can significantly improve visual comfort.
Understanding Your Prescription Strength: What's Considered "Strong"?
Patients frequently ask whether their prescription is "strong" or "weak." While these terms are subjective, understanding where your prescription falls on the spectrum helps you anticipate lens thickness, weight, and which lens options benefit you most.
The Prescription Strength Spectrum
Low Prescriptions (-0.25 to -2.00 or +0.25 to +2.00):
Lenses are thin and lightweight in any material
Standard plastic lenses work well
Minimal distortion at lens edges
Frames have few limitations
Many people function without glasses for short periods
Moderate Prescriptions (-2.25 to -5.00 or +2.25 to +5.00):
Benefit significantly from high-index materials to reduce thickness
Anti-reflective coating becomes more important as reflections increase
Frame size and shape affect appearance and comfort
May notice mild distortion with peripheral vision
Glasses become essential for most activities
Strong Prescriptions (-5.25 to -8.00 or +5.25 to +8.00):
High-index materials crucial for acceptable thickness/weight
Frame selection significantly impacts appearance
Smaller frames reduce edge thickness substantially
Peripheral distortion more noticeable
Specialized lens designs improve visual quality
Very Strong Prescriptions (Beyond -8.00 or +8.00):
Require ultra high-index materials (1.74 or higher)
Frame choice dramatically affects final appearance
Custom lens designs optimize optics
May benefit from contact lenses for better peripheral vision
Weight becomes significant consideration
At Eyes in Disguise, we guide San Francisco patients through lens material selection based on prescription strength, lifestyle needs, and aesthetic preferences. Our boutique eyewear collection includes frames particularly flattering for higher prescriptions.
Why Prescription Strength Matters for Lens Selection
Lens Thickness and Weight: Higher prescriptions create thicker lenses, especially at edges for myopia and centers for hyperopia. High-index materials (1.67, 1.74) bend light more efficiently, achieving the same correction with thinner, lighter lenses.
Optical Quality: Higher prescriptions magnify optical aberrations in peripheral lens areas. Aspheric lens designs flatten the curve, reducing distortion and improving how you look to others (reducing the "bug eye" or "small eye" effect of strong lenses).
Visual Field: Stronger prescriptions create more peripheral distortion in standard lenses. Digital free-form lenses optimize the entire lens surface, expanding your clear visual field—particularly valuable for driving and sports.
Frame Compatibility: Higher prescriptions limit frame choices. Very large frames create excessively thick edges; rimless frames may not support weight safely. At Eyes in Disguise, we help you select frames that work beautifully with your specific prescription.
5 Reasons Why Your Prescription Numbers Change Over Time
Your eyeglass prescription isn't static. Understanding why it changes helps you recognize when updates are needed and removes anxiety about changing numbers.
1. Natural Eye Growth and Development
Children and Teenagers: Eyes continue growing through the late teens or early twenties. Myopia often progresses during this period as eyeballs lengthen. This is why annual exams are crucial for young patients—outdated prescriptions cause unnecessary strain and may accelerate myopia progression.
Young Adults: While growth stabilizes, lifestyle factors (extensive near work, screen time) can still influence prescription changes through the late twenties.
At Eyes in Disguise, we see many San Francisco university students and young professionals whose myopia has progressed 0.50-1.00 diopters over several years. This is normal, not cause for alarm.
2. Presbyopia: The Universal Age-Related Change
After age 40, everyone experiences presbyopia—loss of near focusing ability. This isn't technically a prescription change in your distance vision but an addition to address near vision needs.
The Presbyopia Progression:
Early 40s: First need for reading help, initially only for small print or tired eyes
Mid 40s to early 50s: Progressive increase in add power, reading glasses become essential
Late 50s to 60s: Add power stabilizes at maximum (around +2.50)
Many Pacific Heights and Cow Hollow patients at Eyes in Disguise transition through presbyopia during their professional peak years. We help navigate this change with lens solutions that maintain your sophisticated image while providing the vision you need.
3. Health Conditions Affecting Vision
Certain health conditions cause prescription changes:
Diabetes: Blood sugar fluctuations affect lens shape, causing temporary prescription swings. Patients may experience dramatically different vision from morning to evening. Managing blood sugar stabilizes vision, but prescriptions may need adjustment as control improves.
Cataracts: Progressive lens clouding changes how light focuses, typically shifting patients toward nearsightedness. Sudden prescription improvement in farsighted patients over 60 often signals cataract development.
Medications: Certain drugs affect focusing ability or lens shape. Steroids, antihistamines, antidepressants, and many others can impact vision temporarily or long-term.
Dry Eye: Severe dry eye causes fluctuating vision that may seem like prescription change but actually reflects unstable tear film. At Eyes in Disguise, we address underlying dry eye with advanced TearCare treatment before finalizing prescriptions.
4. Lifestyle and Environmental Factors
Digital Device Use: Extended near work—increasingly common in San Francisco's tech-heavy economy—can cause temporary or permanent myopia progression even in adults. Research suggests excessive accommodation (focusing effort) may stimulate eyeball elongation in susceptible individuals.
Outdoor Time: Studies demonstrate that children and young adults who spend more time outdoors have slower myopia progression. San Francisco's beautiful parks and Presidio trails offer natural vision protection.
Lighting Conditions: Working in dim lighting or with poor contrast increases eye strain and may contribute to prescription changes over time.
5. Measurement Precision and Technique Refinement
Sometimes prescription "changes" reflect improved measurement accuracy rather than actual vision change:
Better Technology: Advanced autorefractors and aberrometers at Eyes in Disguise provide more accurate baseline measurements than older equipment, sometimes revealing subtleties previous exams missed.
More Thorough Refraction: Comprehensive refraction technique—carefully comparing multiple lens options—may identify astigmatism axis or cylinder power that quick refractions missed.
Patient Experience: First-time glasses wearers sometimes accept slightly blurry vision during initial exams because they don't know how clear vision can be. Return visits with better comparison references allow more precise prescriptions.
This is why I spend 60-90 minutes on comprehensive eye exams at Eyes in Disguise rather than rushing through in 20 minutes. Precision requires time and patience.
7 Lens Options That Transform How Your Prescription Performs
Your prescription numbers are only the starting point. Modern lens technology dramatically affects visual quality, comfort, and appearance. Here's how different lens options optimize your specific prescription:
1. High-Index Materials: Thinner, Lighter, More Attractive
What They Are: High-index materials (1.67, 1.74, 1.9) bend light more efficiently than standard plastic (1.50) or polycarbonate (1.59), achieving the same correction with less material.
Who Benefits Most: Anyone with prescriptions beyond ±3.00 sees significant thickness reduction. For strong prescriptions (±6.00+), high-index materials are essential for acceptable aesthetics and comfort.
The Trade-Off: Higher index materials reflect more light, making anti-reflective coating non-negotiable. They're also slightly more expensive than standard materials.
At Eyes in Disguise, we guide San Francisco patients toward the optimal balance of thickness, weight, cost, and optical quality for their specific prescription and frame selection.
2. Aspheric Lens Design: Flatter, Clearer, More Flattering
What They Are: Unlike conventional spherical lenses with uniform curvature, aspheric lenses use complex curves that flatten the lens profile while maintaining optical power.
Benefits: Reduced lens thickness (especially center thickness for plus prescriptions), wider clear viewing area, less distortion, and dramatically better appearance—eliminating the magnified "bug eye" effect of strong plus lenses or minimized "small eye" effect of strong minus lenses.
Who Benefits Most: Anyone with prescriptions beyond ±2.00, progressive lens wearers, and anyone concerned with appearance.
3. Digital Free-Form Lenses: Custom-Crafted Precision
What They Are: Traditional lenses are manufactured in standard curves with limited customization. Digital free-form lenses are computer-designed and precisely surfaced for your exact prescription, frame dimensions, and visual needs.
Benefits: Wider clear vision zones (especially in progressives), sharper peripheral vision, optimization for your specific viewing behaviors, and reduced higher-order aberrations.
Who Benefits Most: Progressive lens wearers, high prescriptions (±4.00+), patients with significant astigmatism (1.50+ cylinder), and anyone dissatisfied with past glasses despite "correct" prescriptions.
The Investment: Digital free-form lenses cost more than standard lenses but deliver measurably superior vision. For San Francisco professionals who depend on visual acuity, the investment pays dividends in productivity and comfort.
4. Anti-Reflective (AR) Coating: Essential for Modern Life
What It Does: Eliminates reflections from lens surfaces—improving clarity, reducing glare from headlights and screens, and making your lenses virtually invisible.
Who Benefits Most: Everyone, but especially:
Drivers (eliminates distracting nighttime reflections)
Computer users (reduces screen glare and eye fatigue)
Anyone with higher prescriptions (higher index materials reflect more light)
People concerned with appearance (makes eyes visible rather than hidden behind reflective lenses)
Quality Matters: Budget AR coatings smudge easily and don't last. Premium coatings like ZEISS DuraVision include multiple layers for maximum clarity plus hydrophobic, oleophobic, and anti-static properties that keep lenses cleaner longer.
At Eyes in Disguise, we exclusively use premium coatings because we've seen too many patients frustrated by inferior coatings that create more problems than they solve.
5. Blue Light Filtering: Protecting Digital-Age Eyes
What It Does: Filters high-energy visible blue light emitted by digital screens, LED lighting, and sunlight—potentially reducing digital eye strain and protecting long-term retinal health.
The Controversy: Research on blue light's effects remains mixed. What we know: Blue light suppresses melatonin (affecting sleep), contributes to digital eye strain symptoms, and may accelerate macular degeneration risk over decades. According toReview of Optometry, filtering blue light may reduce eye strain symptoms for some patients, though the 20-20-20 rule (looking away every 20 minutes) remains the most effective prevention Review of Optometry, 2024.
Who Benefits Most: San Francisco's tech workers spending 8-12 hours daily on screens, people with macular degeneration family history, and anyone experiencing digital eye strain despite proper prescriptions.
At Eyes in Disguise, we offer blue light filtering as part of comprehensive digital eye strain management—including prescription optimization, ergonomic guidance, and dry eye treatment when needed.
6. Photochromic (Transitions) Lenses: Adaptive Convenience
What They Are: Lenses that darken automatically in sunlight, eliminating the need to switch between regular glasses and prescription sunglasses.
Who Benefits Most: Patients moving frequently between indoor and outdoor environments, anyone seeking convenience, people with light sensitivity, and those who forget to switch to sunglasses.
Considerations: They don't darken inside cars (windshields block UV that triggers darkening), take a few minutes to lighten when coming indoors, and may not get as dark as dedicated sunglasses in extreme brightness.
Many Cow Hollow and Marina District residents at Eyes in Disguise love photochromic lenses for San Francisco's variable weather—perfect for transitioning from foggy mornings to sunny afternoons during the same outing.
7. Progressive vs. Bifocal Design: Presbyopia Solutions
Bifocals and Trifocals: Distinct zones for different viewing distances with visible lines separating zones. They provide wide viewing areas for each distance but abrupt transitions between zones.
Progressive Lenses: Gradual transition from distance through intermediate to near vision with no visible lines. They provide vision at all distances but require a brief adaptation period and have narrower optimal viewing zones.
Who Benefits Most:
Bifocals: Budget-conscious patients, those adapting poorly to progressives, people with very specific fixed viewing distances
Progressives: Anyone concerned with appearance, people needing intermediate vision (computer distance), professionals in client-facing roles
At Eyes in Disguise, 85% of our presbyopic San Francisco patients choose progressive lenses for seamless vision and sophisticated appearance. We offer premium designs with wider viewing zones and faster adaptation than entry-level progressives.
Common Prescription Mistakes and How to Avoid Them
Even with an accurate prescription from your comprehensive exam at Eyes in Disguise, things can go wrong between prescription and final glasses. Here's how to ensure your investment delivers the vision you deserve:
1. Inaccurate Pupillary Distance (PD) Measurements
The Problem: Online retailers and some discount optical shops rely on patient-measured PD or estimates from photos. Even 2-3mm errors cause eye strain, headaches, and suboptimal vision.
The Solution: Insist on professional PD measurement with digital pupillometers. At Eyes in Disguise, we measure PD for both distance and near vision during your exam, documenting it on your prescription.
2. Frame Selection Incompatible with Prescription
The Problem: Oversized frames with strong prescriptions create excessively thick edges. Rimless frames may not structurally support heavier lenses. Narrow frames may not accommodate progressive lens corridors.
The Solution: Work with experienced opticians who understand how prescription strength, lens design, and frame parameters interact. At Eyes in Disguise, our team guides you toward frames that complement your prescription both optically and aesthetically.
3. Skipping Essential Lens Treatments
The Problem: Budget-conscious patients decline AR coating, scratch-resistant treatment, or high-index materials to save money—then struggle with glare, scratched lenses, or uncomfortably thick/heavy glasses.
The Solution: View lens quality as part of prescription execution, not an optional add-on. Premium lens materials and treatments are investments in visual comfort, durability, and satisfaction. We help San Francisco patients prioritize which enhancements deliver the most value for their specific prescriptions and lifestyles.
4. Not Allowing Adequate Adaptation Time
The Problem: New prescriptions—especially first progressives or significant prescription changes—require adaptation. Some patients declare glasses "wrong" within hours.
The Solution: Allow 1-2 weeks for adaptation to new prescriptions, longer for first progressives. Your visual system must adjust to corrected input. If discomfort persists beyond adaptation time, return for verification. At Eyes in Disguise, we guarantee all prescriptions and remakes glasses if verification reveals errors.
5. Using Outdated Prescriptions
The Problem: Patients delay updating prescriptions for years, then struggle with eye strain, headaches, and reduced productivity—often not recognizing the connection between symptoms and outdated correction.
The Solution: Annual comprehensive eye exams at Eyes in Disguise ensure your prescription remains current. Even small changes (0.50 diopters) significantly impact comfort and visual efficiency.
When to Question Your Prescription: Red Flags That Warrant Follow-Up
While most prescriptions work beautifully once you've adapted, certain symptoms suggest problems warranting return visits:
Persistent Issues Beyond Adaptation Period
Continued blurriness after 2 weeks (for new prescriptions) or immediately (for unchanged prescriptions)
Constant headaches throughout the day, especially around eyes and temples
Double vision at any distance
Distortion or warping of straight lines
Eye strain increasing rather than decreasing over time
Difficulty focusing when looking from one distance to another
Imbalance feeling or spatial disorientation (especially with first progressives)
At Eyes in Disguise, we encourage San Francisco patients to return if glasses don't feel right after reasonable adaptation time. We verify prescriptions, check lens accuracy, evaluate frame fit, and remake glasses when errors are detected. Your visual comfort is too important to tolerate problematic glasses.
How We Verify and Resolve Prescription Problems
When patients return with concerns, we systematically investigate:
Prescription Verification: Re-examining your eyes to confirm the prescription remains accurate and appropriate.
Lens Verification: Using lensmeter to verify manufactured lenses match prescribed specifications exactly.
Frame Measurements: Ensuring proper fitting height (especially critical for progressives), pantoscopic tilt, vertex distance, and PD alignment.
Quality Inspection: Checking for manufacturing defects, scratches, or coating problems affecting vision.
We remake glasses at no charge when verification reveals errors in prescription, manufacturing, or measurements—ensuring you receive the vision quality your prescription promises.
Why You Can't (and Shouldn't) Use Someone Else's Prescription
"My vision is about the same as my friend's—can I just use their prescription?"
No. Here's why prescriptions are unique to your eyes:
Individual Variations: Even similar prescriptions vary in subtle ways—axis orientation of astigmatism, precise sphere and cylinder powers, PD measurements. Those differences dramatically affect visual clarity and comfort.
Binocular Balance: Your prescription accounts for how your two eyes work together. One person's -2.50 and -2.75 differs functionally from another person's -2.50 and -2.50 even if numbers look similar.
Lens Design Integration: Modern digital lenses are optimized for specific prescriptions. Using someone else's prescription means wearing lenses optimized for their eyes, not yours.
Health Considerations: Your prescription reflects your ocular health. Using someone else's glasses means missing potential eye health issues your own exam would reveal.
Legal and Safety Issues: Driving or working with incorrect prescription creates safety hazards and legal liability.
At Eyes in Disguise, every prescription is written specifically for you after comprehensive examination. This precision is why properly prescribed glasses deliver such superior vision compared to reading glasses or borrowed eyewear.
The Eyes in Disguise Difference: Precision Prescriptions for San Francisco's Discerning Patients
Understanding your prescription empowers you to make informed decisions about your eyewear. But translating that prescription into exceptional vision requires expertise, precision equipment, and genuine commitment to your visual success.
Why San Francisco Patients Choose Eyes in Disguise for Prescriptions
Comprehensive Examination Time: I spend 60-90 minutes on eye exams, not 15-20 minutes. This unhurried approach allows meticulous refraction, thorough health evaluation, and patient education about prescriptions and options.
Advanced Diagnostic Technology: Our corneal topography, aberrometry, and digital refraction systems capture data impossible with basic equipment—ensuring prescriptions account for subtle irregularities other exams miss.
Three Decades of Experience: Prescription writing is both science and art. Experience taught me to recognize when unusual prescriptions signal health concerns, when lifestyle factors should modify standard prescriptions, and how to optimize prescriptions for San Francisco's unique lighting and visual demands.
Boutique Eyewear Selection: We curate frames that work beautifully across prescription ranges—understanding which styles flatter higher prescriptions, which constructions support heavier lenses, and which designs accommodate progressive corridors optimally.
Premium Lens Laboratory Partnerships: We work exclusively with premier lens manufacturers who share our commitment to precision. Every lens is verified before delivery to ensure perfect execution of your prescription.
Guaranteed Satisfaction: If your new glasses don't provide the vision and comfort you expected, we investigate thoroughly and remake them until they're right—at no additional cost. Your vision is too important to accept anything less than perfect.
Transform Your Prescription Into Clear, Comfortable Vision
Your eyeglass prescription is more than random numbers on paper—it's a precise formula describing your unique vision needs and the exact correction required to help you see San Francisco's beauty with crystal clarity. Understanding what those numbers mean empowers you to make informed decisions about frames, lenses, and lens enhancements that optimize your investment.
At Eyes in Disguise, we're passionate about both precise prescriptions and helping you understand them. Whether you're getting your first glasses, updating a prescription that's served you for years, or struggling with vision despite "correct" prescriptions, we provide the expertise, technology, and personal attention that transforms prescriptions into exceptional vision.
Schedule your comprehensive eye exam at Eyes in Disguise in Cow Hollow. Call (415) 474-5321 or visit us at 2133 Union Street, San Francisco, CA 94123. Let's decode your vision needs and craft the perfect prescription for how you see and live in San Francisco.
About the Author
Dr. Michelle Blas, OD, has provided comprehensive eye care and precision eyeglass prescriptions to San Francisco patients for over 30 years at Eyes in Disguise Optometry in Cow Hollow. Board-certified with extensive training in refractive error management, complex prescriptions, and progressive lens optimization, Dr. Blas combines advanced diagnostic technology with meticulous refraction technique to ensure every prescription delivers maximum visual clarity and comfort. Her commitment to patient education and unhurried examination approach has established Eyes in Disguise as San Francisco's destination for patients seeking both precise prescriptions and genuine understanding of their vision needs. She serves patients throughout San Francisco including Pacific Heights, Marina District, Cow Hollow, Fillmore, Russian Hill, and the Presidio.
FAQ: Understanding Your Eyeglass Prescription
1. What do the plus and minus signs mean on my eyeglass prescription?
Minus signs (-) indicate nearsightedness (myopia)—you see nearby objects clearly but distant objects appear blurry. Plus signs (+) indicate farsightedness (hyperopia)—you may struggle more with near vision though both near and distance can be affected. The number following the sign indicates prescription strength in diopters. At Eyes in Disguise in San Francisco, we explain exactly what your prescription numbers mean for your vision and which lens options optimize your specific correction during your comprehensive exam.
2. Is my eyeglass prescription considered strong or weak?
Prescriptions from 0.25 to 2.00 diopters (plus or minus) are considered mild, 2.25 to 5.00 moderate, 5.25 to 8.00 strong, and beyond 8.00 very strong. Prescription strength affects lens thickness, weight, and which materials and designs work best for you. At Eyes in Disguise, we guide San Francisco patients toward optimal lens materials and frame selections based on prescription strength—ensuring comfortable, attractive glasses regardless of your numbers.
3. Why does my eyeglass prescription have three numbers (sphere, cylinder, axis)?
The three numbers indicate you have astigmatism—an irregular corneal shape causing blurred vision at all distances. Sphere corrects your basic nearsightedness or farsightedness, cylinder indicates how much astigmatism correction you need, and axis (1-180) shows the orientation of that correction. About one in three people have astigmatism. At Eyes in Disguise, we precisely measure both the amount and orientation of astigmatism during comprehensive eye exams to ensure optimal vision correction.
4. Can my eyeglass prescription change even though my vision seems fine?
Yes—prescriptions change for many reasons including natural eye growth in younger patients, presbyopia development after age 40, health conditions like diabetes, lifestyle factors like extensive screen time, and improved measurement precision with advanced technology. Small changes (0.25-0.50 diopters) may not dramatically affect clarity but can cause eye strain, headaches, and reduced visual efficiency. This is why annual eye exams at Eyes in Disguise are essential for San Francisco patients—maintaining optimal prescriptions prevents unnecessary strain.
5. What is the "Add" on my prescription, and why do I suddenly need it?
"Add" addresses presbyopia—the universal age-related loss of near focusing ability affecting everyone after age 40. Your eye's natural lens loses flexibility, making reading and close work difficult without additional magnification. Add power (typically +0.75 to +2.50) provides this magnification through progressive lenses, bifocals, or reading glasses. At Eyes in Disguise, we help San Francisco patients navigate presbyopia with lens solutions that provide seamless vision at all distances while maintaining your sophisticated image.
6. Do I need high-index lenses for my prescription?
High-index lenses (1.67, 1.74) bend light more efficiently than standard plastic, creating thinner, lighter lenses. They significantly benefit anyone with prescriptions beyond ±3.00 and are essential for prescriptions beyond ±6.00. High-index materials dramatically improve both aesthetics and comfort for stronger prescriptions. At Eyes in Disguise, we evaluate your prescription strength, frame selection, and aesthetic goals to recommend optimal lens materials—balancing thickness, weight, cost, and optical quality specifically for you.
7. How precise does my eyeglass prescription need to be?
Extremely precise—even 0.25 diopter errors in sphere or cylinder, or 5-10 degree errors in axis orientation can cause blurred vision, eye strain, and headaches. Pupillary distance must be accurate within 1-2mm. This is why comprehensive refractions at Eyes in Disguise take time—we carefully compare multiple lens options rather than rushing through quick approximations. Our advanced diagnostic equipment and meticulous technique ensure prescriptions provide the clear, comfortable vision you deserve.
8. Can I use someone else's eyeglass prescription if our vision seems similar?
Absolutely not. Prescriptions are unique to your individual eyes—accounting for precise refractive error, astigmatism orientation, pupillary distance, and how your two eyes work together. Even seemingly similar prescriptions vary in subtle ways that dramatically affect visual clarity and comfort. Using someone else's glasses causes eye strain, headaches, and may mask underlying eye health issues. At Eyes in Disguise, every prescription is written specifically for you after comprehensive examination—this precision is why properly prescribed glasses deliver superior vision compared to borrowed eyewear.
