Eye in Numbers

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Article initiated by:

Joobin Khadamy, MD, FEBO

All contributors:

Hoon Jung, MD, Joobin Khadamy, MD, FEBO, S. Grace Prakalapakorn, MD, MPH, Michael T Yen, MD

Assigned editor:

Michael T Yen, MD

Review:

Assigned status Up to Date

 by Michael T Yen, MD on July 2, 2024.

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Contributing Editors:	add

The significance of numbers in routine clinical practice has grown exponentially. They guide disease diagnoses, treatment choices (in terms of kind, dosage, and duration), aid in surgical precision, determine implant specifications, and even influence follow-up schedules. Daily clinic procedures involve various biometric assessments, generating essential numerical data. In the realm of ophthalmology, sometimes, the sole focus for specialists is a single numeric value, such as normal corneal power, acceptable residual stromal bed levels, or specific anatomical reference values. Despite the advancement of search engines, procuring normal value ranges and their clinical implications remains a cumbersome task. Therefore, there's a strong appreciation among clinicians for a centralized repository of reference values in ophthalmology. This initiative aims to collect and present the latest reference values and their clinical relevance across various ophthalmic conditions. The primary source for these numbers is The American Academy of Ophthalmology's Basic and Clinical Science Course™ book series. Continuous contributions from all members are vital to maintain the page's accuracy and relevance.

Eye in Numbers

Adult eye volume:

• ~6.5-7.0 milliliter.

Axial length (AL):

• Normal length in adults:
  • 23-25 mm
• High myopia (> − 6 D):
  • > 26 mm
• Pathologic myopia (> − 8 D):
  • 32.5 mm
• Microphthalmia:
  • < 21 mm in adults
  • < 19 mm at 1 year of age
• Nanophthalmos:
  • < 18 mm in a highly hyperopic eye
• Clinical pearls:The standard Morcher CTR comes in three sizes based on uncompressed diameter and used according to axial length(AL):
  • 12.3 mm (compresses to 10 mm, Morcher 14) : AL < 24 mm)
  • 13 mm (compresses to 11 mm, Morcher 14C): 24 mm < AL< 28 mm
  • 14.5 mm (compresses to 12 mm, Morcher 14A): AL > 28 mm
• Clinical pearls: Implant size can be calculated based on a simple algorithm:
  • axial length-2 mm = implant diameter
    • subtract 1 mm from implant diameter for evisceration and for hyperopia

Transverse diameter (i.e. at its widest point) of the globe:

• approximately 24 mm

Cornea:

• Corneal diameter:
  • In adults (reaches adult size by age 2 years):
    • Horizontal:
      • 12-12.5 mm
    • Clinical pearls: To calculate ACIOL size: horizontal white to white distance + 1 mm.
    • Vertical:
      • 11 mm
  • At birth:
    • 9.5-10.5 mm
  • Clinical pearls: Congenital glaucoma:
    • • >12 mm horizontally in the newborn
      • > 11.5 mm at birth
      • > 12.5 mm in 1-year-old children
      • > 13 mm in other children
    • Clinical pearls: Buphthalmos (“bull’s-eye”)
      • Horizontal corneal diameter > 13 mm
    • Clinical pearls: Megalocornea:
      • >13 mm
    • Clinical pearls:Microcornea:
      • <10 mm
• Consistency:
  • 70% of its dry weight: type I collagen
• Power:
  • Average 43 diopter (D) (air-tear interface)
  • Anterior: 48 (49) D
  • Post: -5.8 (6) D
  • Posterior corneal surface contributes approximately 0.4 D of against-the-rule astigmatism.
    • Clinical pearls: Values in various conditions:
      • Corneal plana:
        • < 43 D
      • Keratoconus:
        • Central K > 47.2
        • I-S difference: >1.4 D in 3 mm
        • Asymmetric K > 0.92 D
      • Risk for buttonhole with LASIK:
        • > 48 D
      • Risk for free flap with LASIK:
        • < 40 D
      • How to predict final K after LASIK:
        • Every 1 diopter myopic correction:
          • Flattening of 0.80 D for every diopter of myopia treated
          • Avoid final K after LASIK: < 35 or 36 D (e.g. 8-9 D < diopter correction with preoperative K: 43 D)
        • Every 1 diopter hyperopic correction:
          • Steepening of 1.00 D for every diopter of hyperopia correction.
          • Avoid final K after LASIK: 50 D< (e.g. 7 D < correction with preoperative K: 43 D)
      • Intacs in advanced cases of keratoconus:
        • K> 60.00 D has a lower likelihood of functional improvement of vision; a corneal transplant may be unavoidable.
      • Asphericity:
        • A normal cornea is prolate, with an asphericity Q value of –0.26.
• Corneal thickness:
  • Normal central corneal thickness (CCT):
    • 540 micron
  • Thickness near limbus:
    • 700 μm - 1.0 mm ( The "l" in the "limbus." looks like a 1)
  • Limbal relaxing incision (LRI depth):
    • 500-550 μm
• Epithelium thickness (important with crosslinking to subtract it from the thinnest point)
  • 10% of corneal thickness: 50 μm
• Bowman layer thickness:
  • 10 (8-14) μm
• Descemet thickness:
  • At birth: 3 μm
  • In adults: 10 - 12 μm
    • Clinical pearls: Risk for decompensation after intraocular surgery:
      • If CCT > 640 micron
    • Clinical pearls: Limbal/corneal relaxing incisions (LRI/CRI) depth using preset diamond knife:
      • 500–600 µm (90%) depth
    • Clinical pearls: Arcuate or straight incisions (AK) depth:
      • 99% depth (avoid: arcuate incisions > 90° due to decreased efficacy and increased instability)
    • Clinical pearls: Radial keratotomy depth:
      • 85-90% corneal thickness
    • Clinical pearls: Phototherapeutic keratectomy (PTK) depth:
      • To ablate corneal pathology limited to ⅓ anterior of the cornea ( about 180 μm)
    • Clinical pearls: Contraindication RSB LASIK depth: (RSB = CCT – Flap thickness – Ablation depth)
      • RSB thickness < 250 μm
      • Others do not accept the RSB to be less than 50% of the original CCT.
    • Clinical pearls: Contraindication thickness LASIK:
      • CCT < 480 μm, even if the calculated residual stromal bed (RSB) is thicker than 250 μm.
    • Clinical pearls: Intacs:
      • A lamellar channel at approximately 70% stromal depth (CCT - 50/60 micron)
    • Clinical pearls: Contraindication for ring/ICR:
      • Thickness <450 μm
    • Clinical pearls: The Raindrop Near Vision Inlay (Revision Optics, Lake Forest, CA): a hydrogel inlay with 2 mm in diameter and 32 μm thick centrally causes central corneal steepening)
      • Placed at a depth equal to or greater than 200 μm
    • Clinical pearls: Contraindication for CXL according to minimum thickness:
      • less than 400 μm (although some protocols may allow for treatment of corneas thicker than 300 μm)
  • LASIK flap thickness: 80-180 μm
    • Ultrathin:
      • 80–100 μm
    • Thin:
      • 120 μm
    • Standard:
      • 120–180 μm
    • Clinical pearls: Using the same microkeratome blade to create the flap in the fellow eye:
      • results in a flap that is 10–20 μm thinner than the flap in the first eye.
  • Automated therapeutic lamellar keratoplasty:
    • Clinical pearls: A microkeratome can be set for the depth of the cut (typically ranging from 130 to 450 um).
• Endothelial layer characteristics:
  • Endothelial cell density (ECD/Cell count): (4 - 3 -2 - 1 )
    • At birth:
      • 4000 cells/mm²
    • In young adults:
      • 3000 cells/mm²
    • In healthy 60 years old:
      • 2500-1500 cells/mm²
    • Clinical pearls: Not appropriate for donation:
      • 2000 /mm²
    • Clinical pearls: Risk for decompensation after intraocular operation:
      • 1000 cells/mm²
    • Clinical pearls: Contraindication for intraocular operation:
      • 500 cells/mm²
      • It decreases approximately linearly till the age of 60 but later humans lose cells at a lower rate than when young. Thus, a 70 and 80-year-old would have more cells than you would think.
  • Normal morphology and size of the endothelial cells:
    • Mean cell size or area:
      • 150-350 microns ²
  • Coefficient of variation (CV) index (CVI) (SD/mean cell area):
    • Normal < 0.40
    • Hexagonality/ 6A:
      • Normal > 50%
    • Clinical pearls: Risk for corneal decompensation after intraocular operation:
      • Polymeganthism:
        • CVI > 0.4
      • Pleomorphism:
    • Hexagonality <%50
    • Clinical pearls: The abovementioned parameters are important to be considered before intraocular surgery, as deviations from the normal ranges predict higher risk for corneal decompensation after surgery.

Conjunctiva:

• Limbus and germinal cells:
  • Approximately at least 25%–33% of the limbus must remain intact to ensure normal ocular resurfacing. This is important with chemical burns or ocular surface tumor surgeries)
• Giant papillae size:
  • >1 mm
• Margin of excision with squamous cell carcinoma (SCC) conjunctiva or cornea:
• Wide excision (4 mm margin)

Sclera:

Thickness:

• Thinnest location: immediately posterior to the insertion of the recti muscles
  • 0.3 mm
• Clinical pearls:Important with blunt trauma and scleral laceration.
• At the equator:
  • 0.4-0.5 mm
• Anterior to muscle insertions:
  • 0.6 mm
• Thickest (around the optic nerve head):
  • 1.0 mm
• Clinical pearls:Placements of sclerotomy with drainage of blood in suprachoroidal hemorrhage:
  • 5-6 mm posterior to the limbus (primarily at the inferotemporal quadrant)

Anterior chamber:

• Anterior chamber depth (ACD):
  • 3 mm
  • If ACD <2.0 mm:
    • Risk factors for angle closure.
  • If ACD < 3.2 mm:
    • Risk of endothelial and iris or angle trauma from placement of an anterior chamber, iris-fixated, or posterior chamber phakic IOL is increased.
• Angle:
  • The critical angle at which total internal reflection occurs at the air-tear interface is approximately 46 degrees.

Aqueous humor:

• Volume:
  • 260 microliter
• Production rate:
  • 2-3 microL/min (renews every 100 minutes)
  • At night has a lower turnover rate: about 1 microL/min: (renews every 200 minutes)
• Consistency:
  • Ascorbic acid (vitamin C) 10-50 times higher than in plasma.
• Anterior chamber (AC):
  • Volume:
    • 200 microliter
    • Clinical pearls: AC tap/paracentesis for anterior Chamber Specimen
      • Withdraw 0.05 to 0.1cc Use a 27 to 30G needle inserted near the limbus
• Posterior chamber (PC):
  • Volume:
    • 60 microliter.
• Phakic IOL:
  • Vault:
    • 250–750 μm, or 0.5–1.5 times the CCT
      • Clinical pearls: Vault < 90 microns:Increases the risk of anterior subcapsular cataract (ASC)

Intraocular pressure (IOP):

• Normal range:
  • Adults:
    • 10-21 mm Hg
  • At age 7 years old:
    • 14 mm Hg
  • In newborns:
    • 10-12 mm Hg
  • Glaucoma in children:
    • IOP > "normal" ranges from 10-15 mmHg.
  • Infants with primary congenital glaucoma often have IOPs in the 30 to 40 mmHg range, and may still have IOPs in the 20 mmHg range under general anesthesia.

Episcleral venous pressure (EVP)

• Normal EVP: 6 - 9 mm Hg

Pupil:

• The pupillary light reflex
  • Not reliably present until approximately 30 weeks’ gestational age.
• Size in adults:
  • 2 to 4 mm in diameter in bright light
  • 4 to 8 mm in the dark
• Diffraction-limited spot Airy-disk size
  • 1.2 mm
• Anisocoria:
  • > 1 mm difference between both eyes

Iris

• Thickness: 0.35-0.45 mm
  • Clinical pearl: iris thickness exceeding 0.7 mm considered increased based on normative values.

• • Clinical pearl: Proper iridotomy size:
    • at least 150-200 microns
    • ideally 500 micron

Lens:

• Refractive index:
  • 1.4
• Refractive power:
  • 20 diopters
• Consistency:
  • Alpha-crystallins have the largest molecular weight (600-800 kD) and comprise about 1/3 of all lens proteins.
  • Beta-crystallins have molecular masses from 23-32 kD and constitute approximately 55% of the water-soluble proteins in the lens.
• Diameter:
  • Equatorial diameter:
    • At birth:
      • 6.5 mm
    • Adults:
      • 8.54 – 9.70 mm
• Clinical pearls: Optimal capsulorhexis size:
  • 5.5 - 6 mm
• Capsule thickness:
  • Anterior capsule:
    • 14.0-15.5 microns
  • Thinnest point:
    • Posterior capsule:
      • 2.8-4.0 microns
  • Thickest point:
    • Posterior pre-equatorial area:
      • 23 microns
• Clinical pearls: Piggy back IOL power estimation:
  • IOL power in myopic refractive error (RE): 1.2 × RE
  • IOL power in hyperopic refractive error (RE): 1.5 × RE

Ciliary processes of the ciliary body:

• Ciliary processes Count:
  • 70 processes

Pars plana:

• Clinical pearls: Site of intravitreal injections between the horizontal and vertical rectus muscles:
  • Phakic eyes:
    • 3.5 to 4 mm posterior to the limbus
  • Pseudophakic or aphakic eyes
    • 3 to 3.5 mm posterior to the limbus
  • 1- 6 months:
    • 1.5 mm
  • 6 months - 1-year-old
    • 2 mm
  • 1- 2-year-old
    • 2.5 mm
  • 2-6-year-old
    • 3 mm

Ora serrata (the boundary between the pars plana and the retina):

• Distance from limbus/Schwalbe’s line:
  • Nasally:
    • 5.75 mm
  • Temporally:
    • 6.50 mm
    • Clinical pearls: Intravitreal injection is safer in temporal quadrant.
• Retina reaches ora / fully vascularized:
  • Nasally:
    • 36 weeks
  • Temporally:
    • 40 weeks
• Mature vascularization of the retina:
  • 3 months after birth
• Vascularization of the choroid:
  • 16 weeks gestation
• Clinical pearls: examine the temporal retina first with ROP screening.

Vitreous:

• Volume
  • Vitreous cavity
    • 5-6 mL
  • Vitreous body:
    • 4 mL
• Clinical pearls: Vitreous sampling volume:
  • Via pars plana vitrectomy
    • 0.2-0.5 mL
  • Vitreous tap:
    • 0.1-0.3 mL
  • Consistence:
    • >99% water

Macula:

• Diameter:
• 5.5 mm
• If the distance between optic disc to the macula is > 3 disc diameter (DD) it can be a sign of optic nerve hypoplasia (ONH).

Macula, perifovea, parafovea, fovea, foveola.

Fovea:

These are important to localize visual field defects and find a corresponding pathology.

• Diameter:
  • 1.5 mm (5 degrees) in (i.e. the diameter of an average-sized optic disc).
  • Clinical pearls: Important in understanding Monovision syndrome as the deviation is 8 prism diopter.
  • Rhodopsin is most sensitive to the electromagnetic spectrum's 510 nm (green light) wavelength.
  • A photostress recovery time > 90 seconds clearly indicates a significant maculopathy.

• Foveal avascular zone (FAZ):

• • Diameter: 500 microns (1:40 degrees)
  • Clinical pearls: Should be avoided with laser therapies.

• Foveola:

• • Location:
    • 4.0-4.5 mm (15 degrees) temporal to the optic disc
    • 0.8 mm (2:10 degrees) inferior to the optic disc
  • Diameter:
    • 350 microns
  • Cells: all cones
• Umbo:
  • Diameter:
    • 150 microns

ParaFovea:

• Ring width: 0.5 mm
• Outer radius: 2.5 mm
• Inner radius: 1.5 mm

PeriFovea:

• Ring width: 1.5 mm wide
• Outer radius: 5.5 mm
• Inner radius: 2.5 mm

Optic nerve:

• Number of axons:
  • In adults:
    • 1.2-1.5 million axons
  • The largest number of axons achieved at 16 weeks gestation:
    • 3.7 million
  • Healthy adult: achieved at 33 weeks gestation
    • 1.1 million
• Optic nerve's (ON) diameter:
  • Optic nerve's head diameter
    • 1.5-2.2 mm
  • Anterior to the lamina cribrosa
    • Horizontally:
      • 1.5 mm
    • Vertical:
      • 1.75 mm
  • Behind the lamina cribrosa
    • 3 mm
• Cup-to-disc ratio:
  • Normal:
    • < 0.5
  • Clinical pearls: Crowded discs or "disc-at-risk" is the strongest risk factor for developing NAION. A disc-at-risk is characterized as ONH that has a small diameter and small cup-to-disc ratio, typically 0.2 or less.
• Optic nerve's length:
  • Total:
    • Approximately 50 mm
  • Intrascleral:
    • 1 mm
  • Intraorbital:
    • 25-30 mm (apex to sclera 18 mm)
  • Intracanalicular:
    • 10 mm
  • Intracranial:
    • 10 mm
• Clinical pearls: With enucleation in retinoblastoma: excise at least 10 mm of ON to prevent spread.
• Clinical pearls: Time from damage to clinical apparent atrophy of ON:
  • 6-week

Retinal pigment epithelium (RPE):

• Clinical pearls: RPE detachments (PED) greater than 600 μm in height has a risk for RPE tear following anti-VEGFtherapy.
• Clinical pearls: In EOG Arden ratio
  • Normal > 2
  • Abnormal (e.g. BEST disease) ≤ 1.5

Choroid:

Nevus with thickness > 2 mm have a greater risk for melanoma.

Short posterior ciliary arteries:

• Counts: 20 arteries

Short posterior ciliary nerves:

• Counts: 10 nerves

Long ciliary arteries/nerves:

• Counts: 2 arteries/nerves

Extraocular muscles (EOM):

• Active muscle portion length:
  • Medial rectus (MR), superior rectus (SR), lateral rectus (LR), inferior rectus (IR), levator:
    • 40 mm
  • Superior oblique (SO):
    • 32 mm (shortest)
  • Inferior oblique (IO):
    • 37 mm
• Longest tendon length:
  • SO:
    • 26 mm
  • Levator:
    • 14-20 mm
• Shortest tendon (I M SIL Live So):
  • IO:
    • 1 mm
  • MR:
    • 4.5 mm (shortest between rectus muscles)
  • SR:
    • 6 mm
  • IR:
    • 7 mm
  • LR:
    • 7 mm
• Overal length:
  • Longest: SO (58 mm) >Levator>others>Shortest: IO (38 mm)
• Insertion distance from limbus:
  • MR:
    • 5.5 mm
  • IR:
    • 6.5 mm
  • LR:
    • 6.9 mm
  • SR:
    • 7.7 mm
• Arc of contact:
  • IO:
    • 15 mm (Longest)
  • LR:
    • 12 mm
  • SO:
    • 7–8 mm
  • MR:
    • 7 mm (Shortest)
    • LR inserts 2 mm more superior than MR.
  • EOM penetrate the tenon capsule 10 mm posterior to their insertions.

Orbit:

• Volume:
  • Slightly less than 30 cm³/mL.
• Clinical pearls: Think to the volume with retrobulbar injecting.
• Width:
  • Maximum at 1 cm behind the anterior orbital margin
• The average distance from the posterior globe to the optic foramen in an adult is 18 mm
• Exophthalmometry:
  • Exophthalmos: a 2 mm or greater asymmetry
• Interpupillary distance (IPD)
  • 60-62 mm
• Hypertelorism: Interpupillary distance more than 2 SD above the mean for age, sex, and ethnicity.
  • Intercanthal distance:
• 30-31 mm
• Telecanthus or dystopia canthus: Intercanthal distance more than 2 SD above the mean for age, sex, and ethnicity.

Ciliary ganglion:

• Located approximately 1 cm in front of the annulus of Zinn.

Tear and tear-film:

• Tear lake:
  • 7- 10 µl
• Clinical pearls: only ~20% of the administered eyedrop (10 µl of 50 µl) is retained in the tear lake. So, it is rarely necessary to add a second drop since most of the first drop is already wasted.
• Clinical pearls: Usual volume of eyedrops bottles and eyedrops are as follow:
  • 1 bottle = 5 ml
  • 1 ml = 20 drops
  • 1 drop = 50 µl
    • For example, one drop of atropine 1%, contains 0.5 mg of atropine. Then 1 bottle = 5 ml = 100 drops = 5000 µl (all numbers you need is 1 and 5).
• First tears:
  • 20 days old
  • Clinical pearls: First signs of Nasolacrimal duct obstruction (NLDO) are apparent this age.
• Fully build Lacrimal glands:
  • 6 weeks after birth
• Tear consistence:
• Aqueous (middle layer): provides oxygen to the epithelium, produced by lacrimal and accessory lacrimal (exocrine) glands (Krause’s and Wolfring’s)
  • Consistency:
    • 98% water
    • 2% protein
    • lysozyme (antibacterial enzyme) constitutes 30% of total protein in tear film
    • Lactoferrin
    • IgA and IgG (not IgD)
    • Tear pH = 7.2
      • Clinical pearls: Artificial tears are better to be neutral or slightly alkaline.
    • Tear osmolarity ~ 302 mOsm/L
      • Clinical pearls: Artificial tears are better to be iso-/hypo-osmolar
    • Basal secretion rate = 2 μL/min
• Mucin: inner layer; reduces surface tension and allows the aqueous tear film to be spread evenly; helps structure the tear film
  • Production: 2–3 mL/day
• Dye disappearance test (DDT):
  • NLDO > 5 minutes
  • Dry eye signs:
    • Tear meniscus height; <0.2 mm ( 1.0 mm in height. Heights of 0.3 mm or less are considered abnormal and a sign of dry eye.)
    • Tear breakup time; < 10 seconds
    • Schirmer’s test (< 10 mm/5 min)
    • Phenol red thread test (<10 mm/15 seconds)
    • Increased tear osmolarity (> 316 mOsm/L vs. NL 302)
    • Increased matrix metalloproteinase-9 level (>40 ng/mL)

• Specific dry eye tests:
  • The basic secretion test (after instillation of a topical anesthetic and light blotting of residual fluid from the inferior fornix, some recommend that the eyes be closed to eliminate blinking)
    • <3 mm after 5 minutes: highly suggestive of aqueous tear deficiency (ATD)
    • 3–10 mm is equivocal

• • The Schirmer I test (Done without topical anesthetic, relatively specific but poor sensitivity (high false negative), measures both basic and reflex tearing:
    • < 5.5 mm after 5 minutes: diagnostic of ATD
  • The Schirmer II test: measures reflex secretion, with topical anesthetic, a cotton-tipped applicator is used to irritate the nasal mucosa
    • < 15 mm after 2 minutes is consistent with a defect in reflex secretion.

Eyelid:

• Tarsus:
  • Height
    • Upper tarsus:
      • 11 mm (3 times greater than that of the lower tarsus (4 mm))
  • Lower tarsus:
    • 4 mm
• The marginal arterial arcade:
  • Upper eyelid
    • 2 - 3 mm superior to the eyelid margin/the cilia (lashes)
  • anterior to the tarsal plate (between the orbicularis and tarsal plate) or within the tarsal plate
  • The superior peripheral arterial arcade lies within Muller's muscle or between the Muller's muscle and the levator aponeurosis, superior to the upper border of the tarsal plate.
• Palpebral fissure (PF):
  • Height normally 10 to 11 mm
    • Women:
      • 9–11 mm
    • Men:
      • 7–8 mm
• MRD1:
  • 3 mm (3–4 mm)
    • Clinical pearls: increase with lid retraction and decrease with ptosis.
• MRD2:
  • 5 mm
• Length:
  • 30 mm
• Upper eyelid crease: levator adhesion to the skin.
  • Distance:
  • 10 mm from eyebrow to crease
  • 6 - 10 mm from crease to eyelid margin
    • Women: 8–10 mm
    • Men (slightly lower): 6–8 mm
• Clinical pearls: no crease with congenital ptosis and higher crease with involutional/aponeurotic ptosis.
  • Levator function (LF): distance of upper lid excursion while frontalis is immobilized;
    • Normal: around 15 mm
    • Normal: > 12 mm
    • Fair: 6 - 11 mm
• Clinical pearls: With ptosis correction if:
  • LF > 4 mm: Levator resection

Meibomian glands:

• Upper eyelid
  • 25 - 40 meibomian glands
• Lower eyelid:
  • 20 - 30 meibomian glands

Biopsy sizes:

• Biopsy size and width of margins should be based on clinical presentation, level of suspicion, and risk factor analysis.

Instruments:

• The Goldmann applanation tonometer measures the force necessary to flatten a corneal area of 3.06 mm diameter.

Instrument’s sensitivities, power, etc:

• A canister mask will filter these particles down to 0.1 µm.
  • Clinical pearls: The average particles produced in the LASIK plum are 0.22 µm.
• Measure the length of slit beam correction factors when using lenses:
  • Volk 60D – x 1.0
  • Volk 78D – x 1.1
  • Volk 90D – x 1.3
  • Clinical pearls: Using a 60 lens with a slit lamp, the length of the slit beam can correspond to the length of the papilla when the slit lamp is properly focused on the optic nerve head. This allows for a more detailed examination of the optic nerve head and facilitates measurements such as papillary length.

Visual acuity and visual acuity testing:

• A pinhole:
  • Correct up to 3 D of refractive error
  • The optimal size of a pinhole is 1.2 mm; smaller hole limits visual acuity due to increased diffraction.
• Visual estimation based on kind of nystagmus:
  • If vertical rotation of an optokinetic drum elicits a vertical nystagmus superimposed on the child’s underlying nystagmus:
    • usually 20/400 or better.
  • Searching nystagmus:
    • worse than 20/200.
  • Pendular nystagmus:
    • better than 20/200 in at least 1 eye.
  • Jerk nystagmus:
    • between 20/60 and 20/100.
• Monocular visual testing results with HOVT chart in preschool ages:
  • 2.5y:
    • 20/63 - 20/30 (0.33-0.66)
  • 3y:
    • 20/50 - 20/30 (0.4-0.66)
  • 4y:
    • 20/40 - 20/25 (0.5-0.8)
  • 5y:
    • 20/30 - 20/20 (0.66-1.0)
• The commercial filters used in the duochrome test produce a chromatic interval of about 0.50 diopters between the red and the green.
  • But the chromatic aberration of human eye is estimated 1.5 to 3 diopters (Fraunhofer found a chromatic aberration of from 1.5 to 3 diopters, and Helmholtz of 1.8 diopters).

Importance of time:

Time to add, or to do, onset/duration:

• Door to balloon in MI, stroke /thrombolysis/CRAO:
  • 90 min
• To reduce the chance of haze after PRK:
  • Oral vitamin C 1000 mg/day for 1 week before surgery and 2 weeks postoperatively,
  • avoidance of UV exposure
• Re-treatment after LASIK generally:
  • Not sooner than 3 months (once the refraction has stabilized)
• Repeating surface ablation
  • Wait at least 6–12 months before repeating surface ablation; most central islands diminish over time (especially after surface ablation)
• Haze after PRK can improve spontaneously:
  • wait at least 6–12 months before repeating surface ablation.
• Surgery after nerve palsy:
  • Wait at least 9-12 months; if the remaining deviation is still unacceptable and is too large to be corrected with prisms, surgical corrective options should be discussed with the patient.
• Corneal sensation recovery to preoperative levels after LASIK regardless of hinge type:
  • within 6–12 months after surgery.
• Pregnancy and breastfeeding:
  • Refractive surgery evaluation and procedure at least
    • 3 months after delivery and cessation of breastfeeding
• Corticosteroid:
  • approximately 5% of patients will develop an IOP > 31 mmHg after 6 weeks of treatment with topical dexamethasone.
  • The minimum length of time required for a steroid-response in IOP is highly variable, but it rarely occurs if the steroid is used for less than 2 weeks.
  • Permanent IOP elevations frequently occur if the steroid is used for ≥18 months.
• When to start systemic immunosuppressive:
  • Patients requiring long-term high dose systemic corticosteroids
    • greater than 7.5 mg daily for more than three months
  • If the patient takes eyedrops more than 3 times a day, systemic treatment should be considered.
• Absolute alcohol 20%:
  • loosen the epithelium after 10–45 seconds
• Mitomycin C (usually 0.02% or 0.2 mg/mL) can be placed on the ablated surface for approximately 12 seconds to 2 minutes.
• MG testings
  • Tensilon (edrophonium) is an acetylcholinesterase inhibitor.
    • Doses of 2 mg, 4 mg, and 4 mg are sequentially given until the patient has improvement in signs (e.g. raising of a ptotic eyelid).
    • Pretreating with atropine can lessen the cholinergic side effects (e.g. nausea, vomiting).
  • The neostigmine methylsulfate (Prostigmin) test is a long-acting acetylcholinesterase inhibitor (it is injected concurrently with atropine)
    • MG symptoms improve in 30-45 minutes.
• The sleep test involves taking eyelid height measurements
  • Patient sleeps for 30 minutes: Improvement in eyelid height supports a diagnosis of MG.
• The ice pack test involves placing an ice pack over the ptotic eyelid
  • For 2 minutes: Improvement in eyelid height also supports a diagnosis of MG.
• Sympathetic ophthalmia risk:
  • Latent period between the initial injury of one eye ("exciting eye") and the onset of inflammation in the non-traumatized eye ("sympathizing eye") is 4 to 8 weeks but 65% within 2-8 w and 90% 1 year.
• Hyphema surgical management:
  • A total hyphema persists for 4–5 days in a child, due to the difficulty of detecting early corneal blood staining in a child and the consequent risk of severe deprivation amblyopia.
  • In children with sickle cell trait or disease, even earlier if IOP >25 mm Hg for over 24 hours.
• Implantation of an artificial iris is not recommended for children younger than 16 years.
• Vitrectomy after trauma:
  • Recommended 5 (2- 14) days post perforating trauma not later than 14 d due to PVR.
• Congenital Cataract surgery:
  • Unilateral cases
    • before 6 weeks of age
  • Bilateral cases
    • before 8-10 weeks of age
    • The second intervention must be performed soon after the first to prevent amblyopia as sensory deprivation nystagmus develops if vision is not restored within 6-12 weeks of birth. The recommended maximal interval for children is
      • Under 2 years old: <2 weeks
      • Older than 2 years: <4 weeks
• Toxic Anterior Segment Syndrome (TASS) can occur within the first 24 hours after surgery but acute endophthalmitis generally develops 3-5 days after cataract surgery. The majority of cases of acute infecious endophthalmitis in the EVS (Endophthalmitis Vitrectomy Study) appeared within 3-10 days after cataract surgery, with a median of 6 days.
• Retained lens particles:
  • You can leave them inside the eye up to 3 weeks before vitrectomy.
• Postoperative Cystic macular edema (CME) maximum incidence:
  • 6-10 weeks after surgery.
• Tetracaine eyedrops:
  • The maximum effect is achieved within 10–20 seconds after instillation
  • efficacy lasting 10–20 minutes
• Retrobulbar block by Lidocaine (amide local anesthetic 0.5%, 1%, and 2%):
  • Ocular anesthesia and akinesia within 5-minutes
  • Lasts for approximately 1-2 hours
• Marijuana (Delta-9-tetrahydrocannabinol) intraocular pressure (IOP) lowering effects:
  • Short-lived: 3-to-4 hours and it is often quoted that one would need to smoke marijuana every 3-to-4 hours to maintain 24-hour IOP control.
• The duration of action of mydriatics/cycloplegics is as follows: (Atropine Still Holds Cycloegia To Pupils/ASH-CT)
  • Atropine - 7-14 days
  • Scopolamine - 4-7 days
  • Homatropine - 3 days
  • Cyclopentolate - 2 days
  • Tropicamide - 4-6 hours
  • Phenylephrine - 3 to 5 hours
• Full cycloplegia is achieved:
  • At least 30 minutes after tropicamide, 1%
  • At least 60 minutes after cyclopentolate, 1%
• Avoid sun exposure after photodynamic therapy (PDT), at least for 5 days.
• In retrobulbar optic neuritis acccording to the Optic Neuritis Treatment Trial (ONTT), if the MRI is positive, consider systemic steroids:
  • methylprednisolone 250 mg IV q6h for 3 days, followed by prednisone 1 mg/kg/day for 11 days and rapid taper 20 mg/day on day 12 and 10 mg/day on days 13–15.
• Giant cell arteritis and AION:
  • Emergent treatment with high-dose steroids should not be delayed while waiting for the temporal artery biopsy:
    • prednisone 60–120 mg orally
    • consider IV initially 1 g qd for 3 days
  • Some physicians routinely obtain a temporal artery biopsy (sometimes bilateral) on all patients, which should be performed:
    • within 2 weeks of initiating steroid treatment. Because of skip lesions, the biopsy specimen should be at least 2-3 cm in length.
• Injury to apparent optic atrophy:
  • 6 weeks
• Uveitis definitions:
  • Acute uveitis duration: < 3 months episode
  • Recurrent: acute episodes with more than 3 months inactivity intervals
  • Chronic uveitis duration: >3 months each episode
• Initial diabetic retinopathy screening time based on recent guidelines by the AAO Diabetic Retinopathy Preferred Practice Pattern:
  • Type 1 DM: 1st Retinal exam 3-5 years after diagnosis
  • Type 2 DM: 1st Retinal exam at the time of diagnosis
  • Pregnancy (with type 1 or type 2): 1st Retinal exam soon after conception and early in the 1st trimester of pregnancy
• Possible effective tamponade duration of the gases:
  • SF6:
    • 6 days
  • C2F6:
    • 15 days
  • C3F8:
    • 30 days
• Possible retention time ot the gases:
  • SF6:
    • 13 days ( 2-3 weeks)
  • C2F6:
    • 35 days ( 3-4 weeks)
  • C3F8:
    • 65 days ( 6-8 weeks)
• When different antiplatelets or anticoagulants should be paused before various intraocular or oculoplastic surgeries:

Timing of Pausing Antiplatelets and Anticoagulants Before Intraocular or Oculoplastic Surgery

Medication	Intraocular Surgery (e.g., Cataract, Glaucoma, Vitrectomy)	Oculoplastic Surgery (e.g., Blepharoplasty, Ptosis repair)	Comments
Aspirin	7-10 days before	7-10 days before	May continue in minor surgeries if risk of thromboembolism is high.
Clopidogrel (Plavix)	5-7 days before	5-7 days before	Consider bridging with low-dose aspirin if thromboembolic risk is high.
Ticagrelor (Brilinta)	5-7 days before	5-7 days before	Bridging therapy might be considered depending on the thromboembolic risk.
Prasugrel (Effient)	7-10 days before	7-10 days before	Typically requires longer cessation than clopidogrel due to higher potency.
Warfarin (Coumadin)	3-5 days before	3-5 days before	INR should be normalized (<1.5); consider bridging with LMWH if high risk.
Dabigatran (Pradaxa)	2-3 days before	2-3 days before	Consider longer cessation (4-5 days) in patients with renal impairment.
Rivaroxaban (Xarelto)	2-3 days before	2-3 days before	Discontinue 2 days before surgery for normal renal function; may require more if renal function is impaired.
Apixaban (Eliquis)	2-3 days before	2-3 days before	May consider 48-hour cessation, longer if impaired renal function.
Edoxaban (Savaysa)	2-3 days before	2-3 days before	Similar considerations as for other direct oral anticoagulants.
Heparin (Unfractionated)	4-6 hours before	4-6 hours before	Short-acting; can be paused closer to the surgery.
Low Molecular Weight Heparin (LMWH)	24 hours before	24 hours before	Enoxaparin typically paused 24 hours prior; consider renal function.
NSAIDs (e.g., Ibuprofen)	48-72 hours before	48-72 hours before	Avoid in cases where bleeding risk is significant.

Important doses:

• Hydroxychloroquine dosage of 5.0 mg/kg/day and a chloroquine dosage of 2.3 mg/kg/day based on the patient’s real body weight may be safer across all body mass indexes.
  • Cumulative total doses greater than 1000 g of hydroxychloroquine and 460 g of place patients at high risk of toxicity.
  • Additional risk factors include duration of use (>5 years).
• Toxoplasmic retinochoroiditis
  • Prevention of recurrences of toxoplasmic retinochoroiditis (paramacular toxoplasmosis)
    
    • Long-term intermittent trimethoprim/sulfamethoxazole prophylactic treatment: sulfamethoxazole/trimethoprim 800/160 mg 1 tablet every 3 days.
  • Prevention of recurrences of toxoplasmic retinochoroiditis following LASIK and phacoemulsification
    • Prophylactic treatment be given to patients 2 days prior to surgery and to be continued for a period of 1 week.
  • Treatment of toxoplasmic retinochoroiditis regimen (Adult)
    • Pyrimethamine 200 mg orally on day 1, followed by 50 mg orally daily for 4 weeks.
    • Sulfadiazine 2 g orally as a loading dose, followed by 1 g orally 4 times daily for 4 weeks.
    • Folinic acid 15 mg orally twice a week. Force fluids and give sodium bicarbonate.
  • Alternate Regimen (Adult)
    • Azithromycin, 500 mg orally daily for 4 weeks, or clindamycin 300-450 mg orally q 6 hrs for 4 weeks.
    • Trimethoprim, 160 mg/sulfamethoxazole 800 mg twice daily for 4 weeks.
      • Vision-threatening Lesions
        • Corticosteroids to be used only when vision is threatened: prednisone, 1 mg to 1.5 mg/kg/day, gradually tapered over a period of 4 weeks, or periocular injection of triamcinolone acetonide 40 mg once.
          • Give corticosteroids 3 days after initiation of antimicrobial agents.
  • Congenital Toxoplasmosis
    • Pyrimethamine, 1 mg/kg/day orally once every 3 days, and sulfadiazine, 50 mg to 100 mg/kg/day orally in 2 divided doses for 3 weeks.
      • Corticosteroids for vision-threatening lesions: 1 mg/kg/day orally in 2 divided doses. The dosage should be tapered progressively and later discontinued.
      • Folinic acid, 3 mg twice weekly during treatment with pyrimethamine.
  • Seronegative women who acquire toxoplasmosis during pregnancy may be treated with spiramycin 1 g orally every 8 hours.
• Herpes simplex:
  • Appropriate doses of systemic antiviral agents for treating active ocular disease are:
    • Acyclovir, 400 mg five times per day
    • Valacyclovir, 1000 mg three times per day
    • Famciclovir 250 mg three times per day
  • Appropriate Oral doses for prophylaxis for ocular herpes simplex disease are:
    • Acyclovir, 400 mg twice per day
    • Valacyclovir, 500-1000 mg per day
• Herpes zoster uveitis treatment:
  • Topical steroids and oral antiviral agents
    • Acyclovir 800 mg five times daily, for 10 to 14 days.
    • Valacyclovir 1 g three times daily, for 10 to 14 days.
    • Famciclovir 500 mg three times daily for 10 to 14 days.
    • Patients with recurrent disease can benefit from an extended duration of anti-viral therapy.

Intracameral drugs doses:

• Intracameral cefuroxime: 1 mg in 0.1 ml
• Intracameral moxifloxacin (Vigamox): 150 µg/0.1 mL
  • Clinical pearls:A full 3-mL bottle of moxifloxacin (Vigamox) diluted with 7 mL of BSS to achieve a concentration of 150 mcg/0.1mL, of which 0.3 to 0.4 mL is injected into the anterior chamber as the last step of surgery.

Intravitreal drugs doses:

• Bevacizumab (Avastin, off-label) 1.25mg/0.05mL (0.675mg/0.03mL if considering using for treatment of Zone I+ ROP in an infant)
• Ranibizumab (Lucentis): 0.5mg/0.05mL (for neovascular AMD, RVO, myopic CNVM) or 0.3mg/0.05mL (for diabetic retinopathy/DME)
• Aflibercept (Eylea): 2.0 mg /0.05 mL
• Brolucizumab (Beovu): 6 mg/0.05 mL
• Faricimab (Vabysmo): 6 mg/0.05 mL
• Triamcinolone acetonide (Kenalog, off-label): 2mg/0.05mL or 4mg/0.1mL (Triesence/ Trivaris is alcohol-free preparation that is FDA-approved for intraocular use)
• Ganciclovir: 4mg/0.1mL - administer 2 mg in 0.05 mL (twice weekly for cytomegalovirus retinitis for 14 days for induction)‪
• Clindamycin: 1mg/0.1mL
• Foscarnet: 2.4mg/0.1mL ‬‪- administer 1.2 mg in 0.05 mL
• Fomivirsen: 330 micrograms/0.05mL
• Methotrexate: 400 micrograms/0.1mL
• Vancomycin: 1mg/0.1mL
• Ceftazidime: 2.25mg/0.1mL
• Amikacin: 0.4mg/0.1mL
• Amphotericin B: 5 micrograms/0.1mL
• Voriconazole: 50-100 micrograms/0.1mL
• Dexamethasone: 0.4mg/0.1mL

Fortified eye drops:

• Bacitracin: 10,000 IU
• Cefazolin: 50 mg/ml
• Fortified ceftriaxone: 50 mg/mL
• Fortified ceftazidime: 50 mg/mL (5%)
• Vancomycin: 25 or 50 mg/ml - 50 mg/ ml (5%)
• Topical linezolid: 2 mg/ml (0.2%)
• Fortified gentamicin: 14 mg/mL (1.4%)
• Fortified tobramycin: 14 mg/mL (1.4%)
• Fortified amikacin eyedrops: 40mg/ml
• Clarithromycin: 10 mg/mL
• Azithromycin: 10 mg/mL
• Co‑trimoxazole (trimethoprim 16 mg/ml + sulfamethoxazole 80 mg/ml)

References:

1. 2022-2023 Basic and Clinical Science Course, Section 01: Update on General Medicine by Herbert J. Ingraham , ISBN: 9781681045412 , Publication Date: 2022-08-30

2. 2022-2023 Basic and Clinical Science Course, Section 02: Fundamentals and Principles of Ophthalmology by Vikram S. Brar Section 2 , ISBN: 9781681045429, Publication Date: 2022-08-30

3. 022-2023 Basic and Clinical Science Course, Section 03: Clinical Optics and Vision Rehabilitation by Scott E. Brodie , ISBN: 9781681045436, Publication Date: 2022-06-20

4. 2022-2023 Basic and Clinical Science Course, Section 04: Ophthalmic Pathology and Intraocular Tumors by Nasreen A. Syed ISBN: 9781681045443, Publication Date: 2022-06-20

5. 2022-2023 Basic and Clinical Science Course, Section 05: Neuro-Ophthalmology by M. Tariq Bhatti, ISBN: 9781681045450, Publication Date: 2022-06-20

6. 2022-2023 Basic and Clinical Science Course, Section 06: Pediatric Ophthalmology and Strabismus by Arif O. Khan, ISBN: 9781681045467, Publication Date: 2022-06-20

7. 2022-2023 Basic and Clinical Science Course, Section 07: Oculofacial Plastic and Orbital Surgery by Bobby S. Korn, ISBN: 9781681045474, Publication Date: 2022-06-20

8. 2022-2023 Basic and Clinical Science Course, Section 08: External Disease and Cornea by Robert W. Weisenthal, ISBN: 978168104548, Publication Date: 2022-06-20

9. 2022-2023 Basic and Clinical Science Course, Section 09: Uveitis and Ocular Inflammation by H. Nida Sen, ISBN: 9781681045498, Publication Date: 2022-06-20

10. 2022-2023 Basic and Clinical Science Course, Section 10: Glaucoma by Angelo P. Tanna, ISBN: 9781681045504, Publication Date: 2022-06-20

11. 2022-2023 Basic and Clinical Science Course, Section 11: Lens and Cataract by Linda M. Tsai, ISBN: 9781681045511, Publication Date: 2022-06-20

12. 2022-2023 Basic and Clinical Science Course, Section 12: Retina and Vitreous by Stephen J. Kim, ISBN: 9781681045528, Publication Date: 2022-06-20

13. 2022-2023 Basic and Clinical Science Course, Section 13: Refractive Surgery by M. Bowes Hamill Restricted Resource, ISBN: 9781681045535, Publication Date: 2022-06-20

14. Nixon HK. Preparation of fortified antimicrobial eye drops. Kerala J Ophthalmol [serial online] 2018 [cited 2022 Dec 23];30:152-4. Available from: http://www.kjophthal.com/text.asp?2018/30/2/152/239986

15. https://eyewiki.aao.org/Herpes_Simplex_Uveitis#Medical_therapy

16. https://www.aao.org/current-insight/management-of-ocular-toxoplasmosis