03 Apr 2018
Contact lenses are a suitable substitute for correcting vision in a number of scenarios. There are hundreds of different contact lens types out there in today’s market with the figure growing extensively every year. With the advancement of research and technology, manufactures are always attempting to better their own product lines to suit a variety of needs a person may have, whilst also attempting to 1-up their competitors.
The patient we are attempting to fit with lenses has never worn them before so as far as options go, we are open to explore different lens types and materials amounting to 100s of different combinations. She is a nurse who works long shifts in a hospital and desires fulltime CL wear of up to 12 hours a day, 7 days a week. To do this, we must assess each aspect of the test and result and cater lens choice to match intended wear time and to also correct her vision for both distance and near.
The prescription that we have been presented with is a high myopic prescription so we need to compensate for the change in distance as the contact lens will sit on the cornea and not 12mm away. The compensated contact lens prescription equates to:
Soft lenses come in many forms and for this patient, a silicone hydrogel (SiH) lens material would be the one to choose due to its high oxygen transmission (Dk/T) levels, much higher than hydrogel, like the SiH AirOptix Aqua, [Dk 138, 33% water, 8.6 base curve, 14.mm diameter, (AIR OPTIX® AQUA Contact Lens, no date)] lens vs. the Frequency 55, [Dk 21, 55% water, (Frequency 55 aspheric | CooperVision UK, no date)] hydrogel lens. The Dk/T should be at a level where enough oxygen is passing through to the cornea, avoiding hypoxic conditions and preventing neovascularisation and oedema of the cornea which can lead to permanent corneal damage.
SiH lenses however are not as comfortable as regular hydrogel materials due to the rubbery nature of the lens, and also the lenses hold less moisture compared to regular hydrogel. Silicone is not a wettable material so corneal hydration is an issue. (Sweeney, 2004, pp. 3 – 3). Manufacturers combat this by incorporating technology into the lens such as AquaGen found in Clarity 1 day toric [Dk 57, Water 56%, 8.6mm base curve, 14.3mm diameter (SAUFLON, no date)] .This allows the lens to stay hydrated and increase overall comfort wear-time, something extremely important for this nurse.
Soft lenses drape over the cornea and range between 13.8mm-14.5mm sizes in order to cater for the patient’s measurements. A well fitted soft lens will ensure that the lens has corneal coverage in all directions of gaze. The lens should have movement of at least 1/4mm when blinking, not more because of the variable vision it will cause, or less as it will cause discomfort and should also allow adequate exchange of tears behind the lens to allow debris removal (Gasson and Morris, 2010, pp. 227-227).
Rigid gas permeable (RGP) lenses are much more complex to fit than soft lenses They are tailor made to the patient’s prescription and measurements such as horizontal iris diameter (HVID) and pupil size. RGPs are smaller than soft lenses and smaller in diameter than the cornea itself, with diameters ranging from 8mm to 11mm. RGPs float on the tear film and can create a lens made out of tears.
(Gasson and Morris, 2010, pp. 137 – 139)
Practitioners need to take this tear lens into account as it can negate the need for toric lenses or require prescription adjustments through over-refraction (Gasson and Morris, 2010, pp. 137 – 139). RGPs offer superior clarity than their softer counterparts and are much more durable and longer lasting, however are mostly overlooked in modern times (outside of therapeutics) due to the patient’s impatience of adapting to the initial uncomfortable fitting. RGPs are also easier to lose as they can pop out of the eye much easier and are more difficult to completely cleanse, something important for this nurse considering her working environment.
Assessing her slit-lamp examination results such as her tear break up time (TBUT) and tear prism, I would be looking at a lens that plentiful hydration to the cornea. This is because her TBUT of less than 10 seconds at 7 seconds and her tear prism of 0.2 mm indicate that she suffers from dry eyes (Dryeyesmedical, no date). Having dry eyes and not addressing the issue will result in significantly reduced wear time due to great increase in discomfort. High water content lenses; whilst more comfortable than most other lenses at first, deteriorate in comfort as the day progresses due to evaporation (Efron, 2012, pp. 87 – 87). These lenses then proceed to draw water from the next available source being the tear film through osmosis will cause discomfort for this nurse as she does suffer from dry eyes, reducing wear time considerably. Her TBUT and tear prism will influence the lens choice as she does intend full time lens wear, such as a SiH lens like the Acuvue Oasys toric lens [Dk 147, Water 38%, 8.4mm base curve, 14.3mm diameter, (J&Jvisioncare, no date)] or a RGP lens.
The astigmatism present in her prescription will necessitate toric lenses which allow practitioners to correct astigmatism. Most popular toric lenses available on the market such as the Biofinity toric lens corrects astigmatism only up to a maximum of -2.25DC and the axis is only correctable to the nearest 10° meaning that contact lens practitioners must sometimes compromise the vision slightly when the prescription is unavailable in exact power and axis specifications such as this nurse (Ruben and editor., 1978, pp. 212 – 213), where an axis of 180° would need to be given for both lenses.
An ideal lens for this nurse such as the Clarity 1day toric employs prism ballast which places 1-1.5Δ of base down prism at the base of the lens for stability. Stability of the lens reduces lens rotation and ensures toric lenses stay on axis. This does increase lens thickness and causes a reduction of Dk/T at the base of the lens, increasing risk of hypoxia at the zone (Efron, 2012, pp. 221 – 221). Acuvue Oasys toric lenses employ peri ballast aka accelerated stabilisation designs which have 4 stability zones. This design is claimed to provide more rapid settling on the cornea; within 1 minute, and achieve correct orientation within 5° of the anticipated position in 90% of cases (Gasson and Morris, 2010, pp. 266 – 266)
Prism & Peri ballast designs (Methods of Stabilisation | Optometry by Catherine Care, no date)
RGP lenses would be a serious candidate due to her corneal astigmatism (K) readings gained from the keratometer. Her measurements gained were:
Every 0.05 of difference between the 2 readings gained by each eye corresponds to 0.25DC, so comparing her corneal astigmatism to prescription, we can deduce that the difference equates to -0.75DC in her right eye and -1.25DC in her left eye. This means that when the lens is fitted on the flattest K, the difference between the K readings will create a negative powered tear lens that will correct the astigmatism completely in both eyes for his nurse, negating the need for toric lenses (Gasson and Morris, 2010, pp. 137 – 139).
Multifocal contact lenses are an excellent way to correct presbyopia and exist both in soft and hard lens designs. Simultaneous designs such as concentric ring multifocals (MF) are fairly common such as the Oasys for presbyopia lens, [Dk 147, Water 38%, 8.4mm base curve, 14.3mm diameter, (J&Jvisioncare, no date)] which provides both distance and near vision in one lens. They do this based on pupil size and often are split up between centre distance (CD) lenses for the dominant eye in most cases and centre near (CN) lenses for the other eye. Depending on the level of illumination, a certain working distance will be favoured over the other as the concentric rings are positioned at intervals which the pupil size will coincide with. This MF design does increase the amount of glare experienced by the patient due to the rings and can also decrease contrast sensitivity due to superimposed retinal image sizes if CD and CN are given (Gasson and Morris, 2010, pp. 277 – 282). I would not recommend a MF soft lens for this patient as it will not correct her astigmatism.
Daily MF toric lenses do not currently exist, however monthly soft MF toric lenses do exist with one lens type being the Proclear multifocal, a hydrogel lens with low Dk and high water content [Dk 42, 62% water content, (Coopervision, no date)] something definitely less than ideal for our patient’s desired wear schedule. Bifocal RGP lenses exist providing excellent distance and near vision and use the lenses movement on the cornea. The lens moves up as the eye rotates down, bringing the segment into the pupil’s path and allowing the patient to read. As the eye rotates back up, the lens moves down and the segment moves out of the pupils path and distance vision is restored.
(Gasson and Morris, 2010, pp. 277 – 282)
RGP bifocals such as the Boston Multivison lens would be an excellent choice for this patient if she were to adapt to them due to correcting astigmatism through the tear lens, allowing her to see distance and reading in one package and allowing plenty of oxygen to pass through the lens.
Another successful form of CL correction for presbyopia is monovision (MV), in which one eye is optimally corrected for distance acuity and the other is corrected for near vision (Weissman, 2006, pp. 20 – 20). MV does not compromise lens fitting options and is a highly versatile option and is the least complicated method of dealing with. The distance prescription would be worn in the dominant eye and the reading prescription would be worn in the non-dominant eye, with the brain suppressing images from one eye depending on the working distance. The issue with MV however is that stereopsis is lost as binocular vision is not being utilised. This can be an issue for this nurse if she is required to carry out tasks that require accurate judgement of depth like administering an injection to a patient or driving. If the concept is thoroughly explained initially, there is a much higher chance of acceptance of MV and seeing that she hasn’t worn CLs before, she is very likely to adapt. (Gasson and Morris, 2010, pp. 277 – 282)
The other alternative to this would be just to correct her distance prescription with contact lenses and to give her a separate pair of +1.75DS reading spectacles which although a viable solution, can be inconvenient for her and defeats the purpose of replacing glasses with full time CL wear.
Some special advice for this patient would include managing her grade 1 blepharitis, which in its current state will not impact lens choice or length of wear if managed correctly. I would advise her to apply hot compresses to her lids and recommend a gel like Blephagel in order to accelerate debris clearance. I would advise her against using baby shampoo which is a surfactant, as it will break lipids in her tear film and will further detriment her dry eyes. I would advise her to administer artificial tears into her eyes which are CL compatible in order to maintain extended comfort all day. I would advise her to thoroughly clean her lenses daily if choosing a non daily lens by rubbing and rinsing in preservative free multipurpose solution, or alternatively recommend peroxide solution and let the lenses fully be cleansed without the need to rub and rinse.
My overall recommendation after all things considered would be to fit this patient with the soft bi-monthly Acuvue Oasys toric lens with HydraClear technology to permanently lock a high volume of wetting agent inside the contact lens (J&Jvisioncare, no date). I would utilise monovision with distance dominance to correct for presbyopia, thoroughly explaining to her the mechanics of monovision and what to expect, as not to be overwhelmed by loss of stereopsis and to increase the overall likelihood of acceptance. I’d also tell her to take precaution if driving. My reasoning for this is heavily based off her wearing schedule in tandem with her dry eyes and her working environment. In order to achieve the wear schedule that she desires, it is extremely important that the lens has a high Dk/T lens in order to prevent hypoxic conditions and a high wettability in order to maintain corneal hydration, minimising discomfort and thus allowing said wear schedule taking into account her dry eyes. She is a nurse so automatically this puts her at a higher risk of infection, hence a lens more frequently replaced would be ideal to prevent deposit build up from affecting her too much and overall decrease the risk of infection. I would recommend her the peroxide solution to further clean the lenses and to decrease the risk of infection and to apply artificial tears for extra comfort.
AIR OPTIX® AQUA Contact Lens(no date) Available at: http://www.airoptix.com/contact-lenses/aqua.shtml (Accessed: 28 April 2015)
CooperVision (no date)Proclear multifocal toric. Available at: http://coopervision.com/practitioner/our-products/proclear-family/proclear-multifocal-toric (Accessed: 25 April 2015)
Efron, N. (2012) Contact lens complications. Third edn. Edinburgh: Saunders (W.B.) Co
Frequency 55 aspheric | CooperVision UK(no date) Available at: http://coopervision.co.uk/contact-lenses/frequency-55-aspheric (Accessed: 28 April 2015)
Gasson, A. and Morris, J. (2010) The contact lens manual: a practical guide to fitting. Edinburgh: Elsevier Health Sciences
J&Jvisioncare (no date)ACUVUE® OASYS® for ASTIGMATISM. Available at: https://www.jnjvisioncare.co.uk/contact-lenses/all-acuvue-brand-contact-lenses/toric/acuvue-oasys-for-astigmatism (Accessed: 25 April 2015)
J&Jvisioncare (no date)ACUVUE® OASYS® for PRESBYOPIA | Johnson and Johnson Vision Care. Available at: https://www.jnjvisioncare.co.uk/contact-lenses/all-acuvue-brand-contact-lenses/multifocal/acuvue-oasys-for-presbyopia (Accessed: 25 April 2015)
MEDICAL, D. E. (no date) Diagnostic tests. Available at: http://www.dryeyesmedical.com/diagnosis/diagnostic-tests.html (Accessed: 25 April 2015)
Methods of Stabilisation | Optometry by Catherine Care (no date) Available at: http://optometry.catherinecaregroup.com/method-of-stabilisation/ (Accessed: 29 April 2015)
Ruben, M. and editor. (1978) Soft contact lenses: clinical and applied technology. New York: John Wiley
SAUFLON (no date)Clariti® 1day toric. Available at: http://www.sauflon.co.uk/eye-care-professionals/products/clariti-1day-toric (Accessed: 25 April 2015)
Sweeney, D. F. (2004) Silicone hydrogels: continuous-wear contact lenses. Oxford: Butterworth-Heinemann
Weissman, B. A. (2006) OPTOMETRIC CLINICAL PRACTICE GUIDELINE CARE OF THE CONTACT LENS PATIENT. 2nd edn. St. Louis, MO: American Optometric Association
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