OPT506 - L06 - RGP selection 2024-25 PDF

History & Symptoms Specialist Optometry Skills OPT506 Dr. Asma Zahidi RGP Selection and assessment of fit Dr Asma Zahidi Type of astigmatism refresh With the rule (WTR) Against the rule (ATR) cornea more curved in the cor...

History & Symptoms Specialist Optometry Skills OPT506 Dr. Asma Zahidi RGP Selection and assessment of fit Dr Asma Zahidi Type of astigmatism refresh With the rule (WTR) Against the rule (ATR) cornea more curved in the cornea more curved in the horizontal vertical meridian meridian r1 r1 Flattest curvature Steepest curvature r2> r1 r2 r2 r1> r2 Steepest curvature Flattest curvature Astigmatism decreases over first few years of life and changes with age Astigmatism tends to be with the rule when young and against the rule when older Type of astigmatism refresh Oblique the steepest curve lies in between 120 and 150 degrees or 30 and 60 degrees Steepest curvature 120° 60° Steepest curvature 150° 30° RGP Series Patient selection Trial lens selection Application Fitting Removal Tear lens Over refraction Introduction – What is an RGP? Made of a material that allows oxygen to pass through and reach the cornea Rigid, small, durable Provide good vision correction Often work well with astigmatism Less expensive in long term! Patient Selection  Optimal anterior eye characteristics  High motivation  Moderate to high Rx  Corneal toricity: >0.25 D & 2.00DC, back surface toric lens required to fit cornea RGP Fitting RGP fitting Assessed with and without fluorescein 1. Dynamic fit (without fluorescein)  How the lens moves and centres on the eye  Centration, lid interaction, movement on blink 2. Static fit (with fluorescein)  How the back surface of the lens relates to the cornea  Fluorescein & cobalt blue / burton lamp  Allows visualisation of the tear lens Dynamic fit Examine with wide, dim beam (ideally diffuser), low mag What to look at:  Centration  Lid interaction  Edge position  Movement on blink Dynamic fit - Centration  Compare position of centre of the lens to the centre of the cornea Record on a fitting cross  Important optically Best optics through optical centre Px sees through the BOZD  Interference from lid geometry Dynamic fit – lid interaction Lid attached Interpalpebral Low riding Dynamic fit – edge position The settled lens should stay within the limbus at all times Lens crossing the limbus can cause discomfort & mechanical problems Record lens edge position on 4 excursions of gaze How to record:  Does not cross limbus in excursions  Touches inferior-nasal limbus in up gaze  Crosses temporal limbus in left gaze  Dynamic fit – movement on blink Amount Type Direction Smooth Vertical Vertical meridian Observe the inferior Apical rotation ‒CL moves straight ↑ & (6 o’clock) CL edge ‒ ‘swan’ dive ↓ Oblique Record amount (mm) ‒ can indicate a flat ‒patient has ATR corneal ‒ usually: 1.0 - 2.0 fitting CL astigmatism mm Rocky ‒CL moves tempero- ‒ range: 0.5 - 3.0 mm ‒ can indicate a steep nasal or naso-temporal fitting CL Diagonal (path does not pass through centre of cornea) Speed  Slow How to record:  Average Oblique, 2.0mm, Fast,  Fast Apical rotation Px looks straight ahead (Primary gaze)! Static fit  Fluorescein & cobalt blue / burton lamp  Allows visualisation of the tear lens  Allows interpretation of how the back surface of the lens relates to the cornea  Insert fluorescein onto superior bulbar conjunctiva whilst px looks down  Why? Fluorescein patterns The best indicator of a fit is the fluorescein pattern The other bits give you an idea only Can easily be confused by too much or too little fluorescein You may need to re-centre the lens for an accurate assessment Ask patient to look down, lift top lid Ask patient to look straight ahead and use the bottom lid to re-centre lens Use the Wratten Filter! Cobalt Wratten Wratten Static fit (Fluorescein pattern descriptions) The centre  Pooling - fluorescein under the centre of the lens  Touch - no fluorescein under the centre of the lens  Apical clearance – ideal amount of fluorescein under lens The mid periphery  Touch / pooling / alignment  Width  Boundaries The periphery  Edge clearance Mid Centre Periphery periphery  Width  Static fit Steep fit Flat fit Alignment fit Apical clearance Central pooling Central touch Even mid-peripheral touch Wide mid- Wide mid-peripheral peripheral touch pooling Reasonably undefined central to mid-periph Narrow edge Wide edge boundary clearance clearance Defined mid-periph to periph boundary Even edge clearance “Typical” fluorescein patterns Fit Centre Mid-periphery Periphery Central Very narrow edge Steep pooling Central touch clearance 0.5mm Fitting characteristics table Bring this with you to practical sessions SUMMARY  RGP lens selection  Sph RGP neutralises astigmatism if TA=CA and CA≤ -2.00DC  TA≠CA astigmatism not neutralised by sph RGP – use FS toric  BVP - Consider BVD if Rx ≥±4.00D  RGP fitting – allow lens to settle before assessing fit  Two ways of assessing RGP  Dynamic and Static Further reading Eye essentials- RGP fitting (Franklin) RGP fitting chapters in any of these  Essential CL practice (Veys)  CL fitting (Phillips & Speedwell)  CL practice (Efron)  The CL manual (Gasson & Morris) Questions?