Spherical VS Aspheric. BC Flatten Faster creating extra force at RZ

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Gervais Dean
6 years ago
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1 Spherical VS Aspheric BC Flatten Faster creating extra force at RZ

2 Aspheric BOZ As Function Of Treatment Zone (Back Optical Zone) BC Radius Flatten Faster Towards Edge Of BOZ OZD=5.2 mm OZD=6.0 mm

Fitting/Reverse Curves RC divided into 2 zones to achieve tear equilibrium (apply to Pull-on/Push-off forces created by AZ & TZ) RC2 (Relieve Curve-1a) used to enhance the building-up mid-peripheral

3 Fitting/Reverse Curves RC divided into 2 zones to achieve tear equilibrium (apply to Pull-on/Push-off forces created by AZ & TZ) RC2 (Relieve Curve-1a) used to enhance the building-up mid-peripheral tissue (steepen) for OK effect (enhancement by surface tension) Zone connecting to AC 0.3 mm RC TLT Apply Capillary Force (surface Tension Force) 0.2mm RC2 used to balance pressure between RC1 & AC1(same function as pressure pot)

4 Spherical and aspheric multifocal design (FOZ) Larger diameter of lens (with larger Base OZ) will provide extra add (aspheric principle: BC flatten towards periphery creating more add power)

the voided area (space) between the lens and the corneal model If the model is off, then the entire

6 OrthoTool Tear Film Analysis Chart Controlled Clearance Diagram Shows the Exact Amount of Tear Volume under Lens Front Optical Zone, Anterior Bowl The tear film analysis chart shows us the voided area (space) between the lens and the corneal model If the model is off, then the entire lens and tear film is off There is a designated area/volume in each zone for different targets and conditions

Force Concept Represents True Tear Volume & Force Applied at Various Points of Interest 5 Curves 8 Curves Push-Off of the TZ (BC flatter than K+ Aspheric BOZ) Surface Tension Force Pull-On of

7 Force Concept Represents True Tear Volume & Force Applied at Various Points of Interest 5 Curves 8 Curves Push-Off of the TZ (BC flatter than K+ Aspheric BOZ) Surface Tension Force Pull-On of the AZ towards RZ (capillary attraction) Surface Tension Negative Force: Pull Positive Force: Push Small Capillary Force Optimum balanced design brings those opposing forces into proper equilibrium

Tight Fit FZ wide (vaulting) Tight Fit Flatten RC (increase RZ width by 0.1 mm, e.g. 0.5 to 0.6 mm) Reduce Relieve curve (1a curve) TLT, e.g. 0.005 to 0.

8 Tight Fit FZ wide (vaulting) Tight Fit Flatten RC (increase RZ width by 0.1 mm, e.g. 0.5 to 0.6 mm) Reduce Relieve curve (1a curve) TLT, e.g to Flatten AC Reduce FOZD (from 0.7 to 0.6 mm) Increase targeting to maintain Orhto-k effect (+reduce RC TLT, e.g. from 0.2 to <0.18 microns Reduce BOZ asphericity

9 Lateral Displacement Not enough RED, increase RC force (target extra + increase back asphericity Widen RC width (to 0.6 mm), RC TLT less Increase OAD If AC loose, tighten, if tight loosen up

10 Lateral Decentration Can be loose or tight fit Increase diameter Flatten/tighten AC depending on fluorescein pattern AC1 larger than AC2 (e.g. 1.0/0.6 mm) If tight fit (adhesion, insufficient movement) widen RZ & relief curve Reduce aspheric at apex Reduce FOZD (6.0 mm) Flatten PC Remember to maintain force at RZ When AC tighter than normal, increase RZ width or vice versa If loose fit, tighten AC & Relieve curve TLT

11 High Riding, Lens fitting Loose Increase AC TLT Increase RZ force (reduce width of RC & relieve curve) Reduce BOZD width Target extra & increase aspheric to maintain extra force to compensate for smaller OAD

aspheric at apex (lower SAG, more central applanation)

12 RESIDUAL ASTIGMATISM UNEVEN FORCES APPLIED ON DIFFERENT AREAS OF TORIC ASPHERIC CORNEA SAG adjustment Reduce aspheric at apex (lower SAG, more central applanation) Increase RC width Flatten 1a curve TLT Tighten AC Original Final

13 FAKE CENTRAL ISLAND UNEVEN FORCES APPLIED AT DIFFERENT AREAS OF LENS FAILED TO SATISFY SAGITTAL EQUIVALENCY OF TEAR FILM SAG adjustment strategy: Lower SAG by flattening RC Increase relieve curve TLT Reduce aspheric at apex

to loosen up fit Reduce aspheric to lower the SAG

14 Central Island Pattern Alignment curve too tight causing central vaulting (Sag Imbalance) Reduce OAD to loosen up fit Reduce aspheric to lower the SAG Target extra to maintain force Widen RC width to lower SAG

Low Riding (loosen up fit) Reduce OAD Flatten Reverse/Relieve Curve depending on maps Flatten AC depending on Fluorescein pattern Reduce FOZ diameter (from 0.7 to 0.

15 Low Riding (loosen up fit) Reduce OAD Flatten Reverse/Relieve Curve depending on maps Flatten AC depending on Fluorescein pattern Reduce FOZ diameter (from 0.7 to 0.6 mm, loosen up) AC1 & AC2 less difference (e.g. 0.8/0.7 mm) Target extra to maintain force Reduce aspheric at BOZ if necessary Widen RC width (when necessary to release pressure) Increase Tension Force

16 HIGH RIDING LENSES: WITH SMALL AMOUNT OF FAKE CENTRAL ISLANDS (SMILEY FACE) Mostly loose fit or tight upper lid Excessive TLT under AC Insufficient forces at RZ Imbalance force under lens Solution same as low riding

17 Increase AC TLT High Riding Increase RZ force (reduce width of RC & relieve curve) Reduce BOZD width Target extra & increase aspheric at apex to maintain extra force to compensate for smaller BOZD

18 Trial Lens Set Single Spherical Set for Targeting form Plano to -8.0 D

Plano = 20 microns of Apical Clearance +1.00 = 20 + 10 = approx. 30 microns +2.

19 Plano = 20 microns of Apical Clearance = = approx. 30 microns = = approx. 40 microns = = approx. 50 microns = = approx. 60 microns

Eccentricity Required to Accomplish the Desired Apical Clearance +1.00 D correction use an eccentricity of 1.60 +2.00 D correction use an eccentricity of 1.70 +3.

20 Eccentricity Required to Accomplish the Desired Apical Clearance D correction use an eccentricity of D correction use an eccentricity of D correction use an eccentricity of D correction use an eccentricity of D. correction eccentricity of microns D. correction eccentricity of microns

21 +2.00 D. Correction D. Correction

22 RC is going to be a radius between 7.20 to 7.50 (width 0.5mm) Radius of RC needs to be adjusted flatter and flatter until the first radius that lifts the lens in the periphery AC approximately 1.0D flatter than flattest K (width 0.8mm) PC should provide 110 to 120 microns of clearance

23 Design Format/Preference Void area (value 0.00) Standard values

24 Setting Parameters in Preference Page (5Curves Design) Jessen Factor Apical TLT= 5-10 microns, depending on targeting Depending on target. Wider width with higher targeting (including Jessen Factor) TLT end of AC2=zero PC (edge) TLT= 80 microns

25 Setting Parameters in Preference Page (6 curves) Maximum target. After that, use manually to change Apply higher e value with smaller BOZD Standard: 1.4 for BOZD 5.4 mm BOZD 5.0mm= e 1.5 or above BOZD 5.2 -> 5.4mm= e 1.4 BOZD 5.6mm= e 1.2 BOZD 5.8->6.0mm= e 1.0 or <1.0 Original Rx+Jessen Factor mm D (0.4 mm) 0.5 mm -4.0 D to < -6.0 D 0.6 mm = -6.0 to -7.0 D 0.7 mm = >-7.0 D to -8.0 D 0.8 to 1.0 mm -9.0 D Adjust width according to K reading (0.1mm flatter with steep K >44.0 & 0.1mm steeper with flat k <41.00) Standard 20 microns (0.02), reduce to for increase in force at RC (width 0.3 standard) Standard at 6 microns (0.006), can go down to or up to AC1 & 2 as close as possible unless displacement. AC1 > AC2 for lateral displacement. AC 1 = AC 2 for vertical displacement

Using Orthotool Software

Using Orthotool Software OrthoTool 101010 (2008) Original Design with 5 Curves. You can just use the new version 2013 Toric RC, AC & PC only with OT 2008 so far Hyperopic ortho-k GP lens design Aspheric