Rigid lens fitting made easy

The fitting of rigid lenses and, in particular, front surface toric rigid lenses and bi-toric lenses are generally perceived as being complex to fit. This may be due to a reduction in demand and perhaps a reduced emphasis on rigid lenses during undergraduate education.  

Of course, this might also be partly due to patient demands, most of whom prefer the instant gratification of soft lenses rather than the gradual build of tolerance to rigid lenses. An acceptable level of comfort can be achieved almost immediately with soft lenses, with no adverse effects to the ocular surfaces.^{1, 2}  

However, there most certainly remains a place for rigid lenses in modern contact lens fitting, and the fitting process need not be too onerous for the practitioner.   

In this case report, we will detail how a ‘happy’ contact lens wearer was refitted with a front surface toric and was ultimately happier than he had previously been. 

Patient – Andy 

Age 74. 

Andy has worn rigid lenses for 50 years and rarely wears spectacles. He is a non-driver, though is a sprightly gentleman and very active, going to the gym daily, watching football and enjoys meeting his friends for coffee or a glass of wine. 

 At his 2022 aftercare, he commented that his distance vision could be better when he was watching his beloved Heart of Midlothian Football Club. We reduced the power to help him watch the football. However, he commented a few weeks later that he could not read as well with the new lenses.  

Between us, we concluded that he would wear his ‘football’ lenses when watching Hearts and his other lenses the rest of the time, which he accepted was the reality. He was happily going between the two pairs of lenses though occasionally would mix them up after a wild weekend celebrating a rare Hearts win.  

Of course, a simple check on the focimeter helped us determine which lenses were which – until the next time. One suggestion for such patients wearing rigid lenses is to have different coloured lenses for each pair, which allows easy identification without the need to consult their practitioner.    

Patient  – Andy, 74 

In the early days of contact lens wear, Andy says the only option was rigid lenses and his practitioner made some adjustments to ensure they did not fall out when he was playing football. 

Andy reports that he never lost a lens while playing football during his 20-year career as a goalkeeper and ace penalty kick taker. Both his existing pairs of lenses were slightly on the steep side, which may well have been the adjustments made to ensure they did not fall out so easily during active sport. This also had the benefit of providing a little more plus power, which helped in later years for reading near vision.  

We had the option of trying a Menicon lens, which was new to the UK, the Menicon Omni.  

Menicon Omni 

Menicon Omni spherical design has a spherical optic zone and an aspherical periphery. For all Menicon Omni designs the back optic zone diameter (BOZD) will vary with the total diameter (TD). For TD = 9.10mm, BOZD = 7.30mm For TD = 9.60mm, BOZD = 7.50mm For TD = 10.10mm, BOZD = 7.70mm. Power range -25.00 to +25.00 D (0.25D steps). Base Curves 6.00 to 9.95mm (0.05 steps).  

Material – Roflufocon 

Dk – 65 

Specific Gravity – 1.17 

Wetting Angle – 6 

The Menicon Omni lens is available in spherical, toric, multifocal, and multifocal toric designs. 

I had discussions with Josie Barlow at Menicon Professional Services regarding how we currently ordered lenses. Josie suggested I could consider utilising some of the innovative technology being used to design lenses. I was hugely sceptical though decided I would perhaps try it at the next available opportunity.  

This opportunity arose when Andy came in for his aftercare. He mentioned that it was becoming a little inconvenient having to think what lenses he would wear on any given day and was there anything I could do to help him.  

We decided to test the water with Menicon’s new ‘Easyfit’ technology and see what they would produce. I sent away the relevant information and eagerly awaited the lenses. On arrival, I inspected the lenses and much to my astonishment the right lens was a front surface toric lens. I could not recall the last time I had seen one. Upon questioning a few colleagues, most admitted to never having seen one, though they did talk about them during their contact lens exams.   

  ^{Figure 3 Proportion of rigid lens fits by lens design  (Graphic: Professor Phillip Morgan)}

Lens performance 

The computer assisted technology concluded in the right eye there would be 1.84D of residual astigmatism and as such this would need to be corrected with the appropriate power in the final contact lens. The BOZR aligned with current thinking in that it was suggested the curve should be 7.90; which was almost exactly on the flattest keratometery reading of 7.90mm.  

For the left eye, we had -0.84D of residual astigmatism. Given that figure was less than 1.00D, the Easyfit technology does not recommend that such a low level of residual astigmatism needs correcting. Like the right eye, the BOZR is exactly on the flattest keratometer reading. Total diameter is 9.10mm, which is standard for an average VID Horizontal Visible Iris Diameterof 11mm. 

With regards to the BVP, we omitted the addition as the lenses were to be primarily used for distance only. It was anticipated that by fully correcting the astigmatism and residual astigmatism  this would improve both the distance and near acuities.  

Menicon omni optimum comfort 

R. 7.90/9.10/+8.25/-1.75x 137 6/9+ 

Prism 1.50 x 270 

L. 7.90/9.10/+8.75 6/9 

Binocularly 6/7.5   N6 at 45cm 

Observation showed both lenses centred and moved well. There was full coverage of the pupils in all directions of gaze and the lenses displayed around 0.9mm of movement on blink. The fluorescein picture displayed an alignment fitting in both eyes with just a small hint of an astigmatic fitting on the cornea, as we would expect on corneas with a difference of around 0.15mm of corneal astigmatism.  

The measured visual acuity was better for distance than the previous distance lenses and the near acuity identical to the vision achieved with the general purpose/monovision. In real vision terms, our patient reported significantly better distance acuity with the near being no worse than the previous lenses used for reading. 

Menicon Omni FT  

Menicon Omni FT (front toric) has a sphero-aspheric back surface and a front toric surface. Three engraved dots are located at the 3, 6 and 9 o’clock positions. This design includes a stabilisation prism (standard prism 1.5∆). 

The lenses are engraved with the date of manufacture. The engraving is laser etched and has no impact on the surface quality of the lens. 

Discussion  

What is residual astigmatism? 

Residual astigmatism is described as the refractive error present when a contact lens is placed on the cornea to correct an existing ametropia. With a spherical GP lens in place on the eye, the residual astigmatism is approximately equal to the difference between the corneal astigmatism and the refractive or composite astigmatic error of the eye.³ 

In many cases, sadly, corneal keratometry measurements are not even taken prior to contact lens fitting these days. This is a combination of manual keratometers not being available and the belief that it makes no difference as most soft toric lenses only come in one base curve.  

Advice and guidelines from College of Optometrists and ABDO suggest a detailed assessment of the anterior eye, which might be affected by contact lens wear. This should require a slit-lamp examination, keratometry, the use of diagnostic stains and the assessment of tear film quality and quantity.^{4, 5}  

Keratometry readings should be taken for all first-time fits to help establish if there is any residual astigmatism and also to have a baseline measurement from where we can monitor any changes in corneal curvature.   

For most new fits, rigid lenses might not be considered unless suggested by the patient. This results in most astigmatic patients being fitted with soft toric lenses, although some may find they can achieve better vision with rigid corneal lenses or even rigid semi-scleral lenses.  

^{(Graphic: Professor Phillip Morgan)}

The graph above (figure 2) shows the number of rigid lenses fitted to be relatively stable at around 5% in the UK.⁶ Of course, it was famously predicted by the esteemed Professor Nathan Efron in 1998 that rigid lenses may become obsolete by 2010.  

Prof Efron argued in a CLAE Editorial titled ‘Obituary – rigid contact lenses’ that this was essentially correct as the number of new fits was around 2% in 2010.⁷ Efron speculates on the reasons for this demise in rigid fitting and includes the lack of rigid lens training opportunities.  

With the availability of software such as the Easyfit technology, any lack of training opportunities or fitting skills becomes almost irrelevant. However, fitting skills are still required when it comes to interpretation of the lens fit and, in particular, for problem solving.  

New lens fits over time 

If we look at the distribution between spherical and toric lenses (all types of toric lenses) we see that the number of spheres are declining and toric lenses are increasing. This would lead one to speculate that practitioners are increasingly looking to rigid lenses for more complex prescriptions.  

The use of rigid lenses in the UK remains low by comparison to other countries.⁶ The leading nation when it comes to percentage of rigid lenses is the Netherlands. Global contact lens prescribing for rigid lenses has increased from 10% to 15% according to practitioner surveys.⁹  

^{Figure 4: Rigid lenses by country    (Graphic: Professor Phillip Morgan)}

• Graeme Stevenson FBDO(Hons) Cl is a CL optician based at Boots Opticians in Glasgow and is also ABDO regional lead for Scotland.  

Acknowledgements 

Thanks to Josie Barlow, Abeeda Khatoon and Phil Morgan for their help in drafting this article.  

References  

1. Wolffsohn JS, Ghorbani-Mojarrad N, Vianya-Estopa M, Nagra M, Huntjens B, Terry L, Sweeney LE, Dutta D, Joshi MR, Wright D, Bruce H, Hallam E, Jolly L, Chung YB, En Tsen JR, Bishop A, Davison R, Maldonado-Codina C; members of the British and Irish University and College Contact Lens Educators (BUCCLE) group. Fast versus gradual adaptation of soft monthly contact lenses in neophyte wearers. Cont Lens Anterior Eye. 2022 Aug;45(4):101469. doi: 10.1016/j.clae.
2. Wolffsohn JS, Dhirajlal H, Vianya-Estopa M, Nagra M, Madden L, Sweeney LE, Goodyear AS, Kerr LV, Terry L, Sheikh S, Murphy O, Lloyd A, Maldonado-Codina C; members of the British and Irish University and College Contact Lens Educators (BUCCLE) group. Fast versus gradual adaptation of soft daily disposable contact lenses in neophyte wearers. Cont Lens Anterior Eye. 2020 Jun;43(3):268-273. doi: 10.1016/j.clae.2019.08.011. 
3. Bennett, Edward S  & Hom, Milton M. Manual of Gas Permeable Contact Lenses. 2nd Edition 2003.Butterworth-Heinemann. ISBN: 9780750673358
4. ABDO website. Contact Lenses. https://www.abdo.org.uk/regulation-and-policy/advice-and-guidelines/clinical/contact-lenses/  accessed 30/12/2024
5. https://college-optometrists.org/clinical-guidance/guidance/knowledge,-skills-and-performance/fitting-contact-lenses#Assessingpatients accessed 30/12/2024
6. Morgan PB. Trends in UK contact lens prescribing 2024. Optician 2024. October 3rd 2024.
7. Efron, Nathan. Obituary – Rigid contact lenses. Contact Lens Anterior Eye, Issue 5, 245 – 252.
8. Efron, N. Morgan, PB. Woods, C.A. International trends in rigid contact lens prescribing:2000 – 2023:an update. Contact lens Anterior Eye. 2024;47,102255. Vincent SJ, Cho P. Specialise for special eyes in 2025. Cont Lens Anterior Eye. 2025 Feb;48(1):102356. doi: 10.1016/j.clae.2024.102356.