Toric lenses with built-in pigmentation supply people with corneal irregularity the chance to right their imaginative and prescient whereas additionally altering their eye coloration. These specialised lenses mix the corrective properties of toric lenses, designed to deal with astigmatism, with the aesthetic enhancement of coloured contacts. An instance could be a affected person with astigmatism selecting hazel-tinted toric lenses to sharpen their imaginative and prescient and alter their eye coloration concurrently.
The provision of those specialised lenses represents a big development in eye care. Beforehand, people with astigmatism typically had restricted selections in beauty contact lenses. This innovation offers a sensible resolution for these looking for each visible readability and beauty modification. The flexibility to deal with each refractive error and aesthetic preferences contributes to improved self-confidence and general high quality of life.
This text will delve additional into the assorted points of those specialised lenses, protecting subjects reminiscent of lens varieties, becoming procedures, correct care and upkeep, and potential issues for wearers. It would additionally discover the newest developments in lens know-how and talk about the way forward for imaginative and prescient correction and beauty enhancement for people with astigmatism.
1. Toric Lens Design
Toric lens design is key to the performance of coloration contact lenses for astigmatism. In contrast to spherical lenses that right nearsightedness or farsightedness, toric lenses deal with the asymmetrical curvature of the cornea, attribute of astigmatism. This asymmetry causes gentle to refract erratically, leading to blurred or distorted imaginative and prescient in any respect distances. The toric lens design incorporates various refractive energy throughout completely different meridians of the lens, compensating for the irregular corneal form and focusing gentle appropriately onto the retina. This specialised design is essential for reaching clear imaginative and prescient in people with astigmatism who select coloration contact lenses for beauty functions.
The mixing of coloration pigments inside a toric lens necessitates cautious design issues. The colour portion should not intervene with the toric parts chargeable for astigmatism correction. Sustaining exact alignment of the toric axis is crucial for optimum visible acuity. Instability or rotation of the lens can compromise the corrective impact and end in blurred imaginative and prescient. Superior manufacturing strategies and lens supplies contribute to lens stability, guaranteeing constant and predictable imaginative and prescient correction. As an example, prism ballasting and peri-ballasting are generally employed to stabilize toric lenses, minimizing rotation and sustaining optimum visible readability. Think about a affected person with excessive astigmatism and a need for green-colored lenses. The toric design should exactly right the astigmatism whereas the inexperienced pigment stays aesthetically pleasing with out disrupting the corrective properties.
In abstract, the success of coloration contact lenses for astigmatism hinges upon meticulous toric lens design. The complicated interaction between corrective properties and beauty enhancements requires subtle manufacturing processes and exact becoming procedures. Understanding the intricacies of toric lens design permits practitioners to offer optimum imaginative and prescient correction and beauty advantages for people with astigmatism, empowering them with clear, snug imaginative and prescient and enhanced look. Challenges stay in balancing lens stability, oxygen permeability, and coloration vibrancy, however ongoing developments in lens know-how proceed to enhance the choices out there for people looking for each visible readability and aesthetic expression.
2. Colour Pigments
Colour pigments are integral to the aesthetic perform of coloration contact lenses designed for astigmatism. These pigments, embedded throughout the lens materials, alter the looks of the attention by absorbing and reflecting particular wavelengths of sunshine. Cautious choice and software of those pigments are important, as they need to not compromise the optical properties or the consolation of the lens. The pigments are sometimes encapsulated throughout the lens materials to forestall direct contact with the ocular floor, guaranteeing biocompatibility and minimizing the danger of irritation or allergic reactions. For instance, a blue pigment displays blue gentle whereas absorbing different wavelengths, giving the lens its blue hue. The focus and distribution of the pigment affect the depth and saturation of the colour change. In lenses for astigmatism, the pigment placement requires cautious consideration to keep away from interference with the toric parts of the lens chargeable for correcting the astigmatism.
Several types of pigments exist, every with its personal traits relating to coloration vibrancy, lightfastness, and biocompatibility. Natural pigments supply a wider vary of coloration choices and are usually extra vibrant, however could also be much less lightfast than inorganic alternate options. Inorganic pigments, derived from metallic oxides, supply higher stability and longevity however could have a extra restricted coloration palette. The selection of pigment will depend on elements reminiscent of desired coloration depth, lens materials compatibility, and regulatory necessities. Think about a affected person looking for vibrant violet lenses: natural pigments is perhaps most popular for his or her coloration depth, whereas a affected person prioritizing long-lasting coloration would possibly go for lenses with inorganic pigments.
In conclusion, coloration pigments play a vital function within the aesthetic enchantment of coloration contact lenses designed for astigmatism. The choice, software, and sort of pigment considerably affect the ultimate coloration, sturdiness, and biocompatibility of the lens. Balancing aesthetic issues with the optical necessities of toric lenses stays a problem, however ongoing developments in pigment know-how and lens manufacturing proceed to develop the choices out there to people looking for each imaginative and prescient correction and beauty enhancement. Additional analysis and improvement deal with enhancing pigment stability, growing coloration vibrancy, and enhancing the long-term security and luxury of those specialised lenses.
3. Oxygen Permeability
Oxygen permeability is a important consider sustaining corneal well being for any contact lens wearer, particularly these with astigmatism utilizing coloration contact lenses. The cornea, avascular in nature, depends on atmospheric oxygen for its metabolic processes. Contact lenses, performing as a barrier, can impede this oxygen transmission, probably resulting in corneal hypoxia and associated issues. Ample oxygen permeability is subsequently paramount in guaranteeing the long-term well being and luxury of the cornea in people utilizing coloration contact lenses for astigmatism.
-
Materials Properties
The oxygen permeability of a contact lens is primarily decided by the fabric from which it’s manufactured. Silicone hydrogel supplies exhibit considerably larger oxygen transmissibility in comparison with conventional hydrogel supplies. This enhanced permeability permits for higher oxygen circulate to the cornea, decreasing the danger of hypoxia-related issues. For coloration contact lenses for astigmatism, silicone hydrogel supplies are typically most popular on account of their superior oxygen permeability, enabling longer and extra snug carrying instances. As an example, a silicone hydrogel lens with a Dk/t of 150 permits considerably extra oxygen to succeed in the cornea than a hydrogel lens with a Dk/t of 30.
-
Lens Thickness
Lens thickness immediately influences oxygen transmission. Thicker lenses, even when fabricated from extremely permeable supplies, can impede oxygen circulate. In toric lenses for astigmatism, sustaining ample oxygen permeability whereas accommodating the various thickness required for astigmatic correction presents a design problem. Minimizing the middle thickness of the lens whereas preserving the required corrective energy is essential for optimum oxygen supply to the cornea. For instance, a thinner lens on the heart, even with a barely decrease Dk/t worth, could present higher oxygen transmission than a thicker lens fabricated from a cloth with the next Dk/t.
-
Water Content material
Whereas water content material contributes to lens consolation, it doesn’t immediately correlate with oxygen permeability. In some instances, larger water content material may even hinder oxygen transmission, particularly in conventional hydrogel lenses. Silicone hydrogel lenses, nonetheless, can obtain excessive oxygen permeability even with decrease water content material, providing a steadiness between consolation and corneal well being. A lens with excessive water content material and low oxygen permeability can really result in corneal edema, whereas a silicone hydrogel lens with reasonable water content material and excessive oxygen permeability can preserve corneal well being even throughout prolonged put on.
-
Medical Significance
Sustaining ample corneal oxygenation is essential for stopping issues reminiscent of corneal neovascularization, edema, and microbial keratitis. These issues can result in discomfort, blurred imaginative and prescient, and probably critical long-term penalties for ocular well being. Correct lens becoming and adherence to prescribed carrying schedules are important in minimizing the danger of those issues. Common eye examinations and consultations with eye care professionals are important for monitoring corneal well being and guaranteeing the continued suitability of coloration contact lenses for astigmatism. Neglecting oxygen permeability can result in vital issues, underscoring the significance of contemplating this issue when deciding on and becoming these lenses.
In conclusion, oxygen permeability is a paramount consideration within the profitable use of coloration contact lenses for astigmatism. Materials properties, lens thickness, and water content material all work together to affect the quantity of oxygen reaching the cornea. Prioritizing lenses with excessive oxygen transmissibility, guaranteeing correct match, and adhering to really useful put on schedules are important for preserving corneal well being and maximizing the advantages of those specialised lenses. Ongoing developments in lens supplies and designs proceed to enhance oxygen permeability, providing people with astigmatism higher selections in coloration contact lenses whereas minimizing the dangers related to diminished oxygen transmission to the cornea.
4. Prescription Accuracy
Prescription accuracy is paramount for profitable coloration contact lens put on in people with astigmatism. An inaccurate prescription, whether or not for the spherical or cylindrical element, or an incorrect axis orientation, can compromise visible readability and luxury. The toric lens design depends on exact alignment with the astigmatic axis of the cornea to right the refractive error. An incorrect axis, even by just a few levels, can induce ghosting, blurring, and eye pressure. Equally, an inaccurate spherical element can under- or over-correct the myopia or hyperopia current, resulting in suboptimal visible acuity. As an example, a prescription with an axis off by 10 levels can considerably blur imaginative and prescient, whereas an incorrect spherical energy can exacerbate current refractive errors. Think about a affected person with -2.00 sphere and -1.50 cylinder at 90 levels. A lens prescribed with -2.00 sphere and -1.50 cylinder at 80 levels, whereas seemingly shut, will end in noticeable blurring as a result of axis misalignment.
Moreover, prescription accuracy influences lens match and stability. An incorrect prescription can result in a poorly becoming lens, growing the probability of lens rotation and decentration. This instability can additional compromise the corrective impact of the toric lens, exacerbating the visible distortions brought on by the wrong prescription. For instance, a lens with extreme motion can intermittently blur imaginative and prescient because the toric axis shifts away from the supposed orientation. This dynamic blurring can contribute to discomfort and visible fatigue. Past speedy visible penalties, an ill-fitting lens on account of prescription inaccuracies may also enhance the danger of corneal issues, reminiscent of abrasions or hypoxia, on account of altered tear alternate and oxygen permeability. Exact measurements and cautious becoming procedures are essential for optimizing lens stability and minimizing these dangers.
In abstract, prescription accuracy is non-negotiable for reaching optimum visible outcomes and guaranteeing corneal well being in people with astigmatism carrying coloration contact lenses. Even seemingly minor discrepancies within the prescription can considerably impression visible readability, consolation, and lens stability. Meticulous refraction strategies, exact lens manufacturing, and correct becoming protocols are important for maximizing the advantages of coloration contact lenses for astigmatism whereas mitigating the dangers related to inaccurate prescriptions. The interaction between prescription accuracy and lens efficiency underscores the significance of complete eye examinations and ongoing collaboration between eye care professionals and sufferers to realize profitable outcomes in managing astigmatism with coloration contact lenses.
5. Correct Becoming
Correct becoming is essential for profitable coloration contact lens put on, significantly for people with astigmatism. Toric lenses, designed to right astigmatism, require exact alignment with the corneal floor to perform successfully. A poorly becoming lens can rotate or decenter, misaligning the toric axis and compromising the supposed astigmatic correction. This misalignment can result in blurred imaginative and prescient, ghosting, and discomfort. For instance, a lens that rotates excessively could cause intermittent blurring because the toric axis shifts away from the right orientation, resulting in fluctuating visible acuity and potential eye pressure. Moreover, an improperly fitted lens can disrupt tear movie distribution, resulting in dryness, discomfort, and an elevated threat of issues reminiscent of corneal abrasions or infections. Think about a affected person with a steep cornea fitted with a flat lens; the lens could transfer excessively, whereas a flat cornea fitted with a steep lens could end in a good, uncomfortable match, probably proscribing oxygen circulate to the cornea.
A number of elements contribute to correct lens becoming, together with lens diameter, base curve, and, critically for toric lenses, rotational stability. The lens diameter should correspond to the horizontal seen iris diameter to make sure ample corneal protection with out impinging on the sclera or conjunctiva. The bottom curve, reflecting the curvature of the posterior lens floor, should conform to the corneal curvature to make sure correct centration and motion. Rotational stability, particular to toric lenses, refers back to the lens’s skill to take care of its supposed orientation on the attention. Varied lens design options, reminiscent of prism ballasting and peri-ballasting, affect rotational stability. A well-fitted toric lens will exhibit minimal rotation, guaranteeing constant alignment of the toric axis with the astigmatic axis of the cornea. As an example, a lens with good rotational stability will persistently return to its right orientation after blinking, whereas a poorly stabilized lens will exhibit extreme and unpredictable rotation, resulting in fluctuating imaginative and prescient.
In conclusion, correct becoming is crucial for maximizing the visible advantages and luxury of coloration contact lenses for astigmatism. Correct measurements of corneal curvature and diameter are important stipulations for profitable becoming. Lens choice ought to prioritize designs that promote rotational stability to make sure constant and predictable astigmatic correction. A well-fitted lens minimizes visible distortions, enhances consolation, and reduces the danger of issues. Collaboration between eye care professionals and sufferers is essential all through the becoming course of to realize optimum outcomes and guarantee long-term satisfaction with coloration contact lenses for astigmatism. Ongoing developments in lens design and becoming strategies proceed to refine the method, providing improved consolation, imaginative and prescient, and security for people with astigmatism looking for each visible correction and beauty enhancement.
6. Lens Care
Correct lens care is crucial for sustaining ocular well being and maximizing the lifespan of coloration contact lenses for astigmatism. Neglecting lens hygiene can result in microbial contamination, growing the danger of infections, irritation, and probably sight-threatening issues. Given the complicated design of toric lenses, meticulous care is especially necessary to protect their structural integrity and optical efficiency. Efficient lens care practices reduce protein and lipid deposits that may accumulate on the lens floor, compromising visible readability and luxury.
-
Cleansing
Thorough cleansing removes particles, cosmetics, and microbial contaminants from the lens floor. Really useful cleansing options, particularly formulated for contact lenses, must be used in line with the producer’s directions. Rubbing the lens gently between the fingertips, even with “no-rub” options, enhances the cleansing course of. Keep away from utilizing faucet water, saliva, or selfmade options, as these can introduce dangerous microorganisms or harm the lens materials. For instance, a multipurpose resolution can each clear and disinfect lenses, simplifying the care routine.
-
Rinsing
Rinsing removes residual cleansing resolution and any loosened particles from the lens floor. Sterile saline resolution is the really useful rinsing agent. Thorough rinsing is essential to reduce the danger of chemical irritation or allergic reactions brought on by residual cleansing resolution parts. Keep away from reusing saline resolution, as this will introduce contaminants. An instance of efficient rinsing includes directing a gradual stream of saline over each surfaces of the lens for a number of seconds.
-
Disinfection
Disinfection eliminates or neutralizes dangerous microorganisms that may adhere to the lens floor. Varied disinfection strategies exist, together with chemical disinfection utilizing multipurpose options or hydrogen peroxide programs, and thermal disinfection utilizing warmth. The chosen disinfection technique must be suitable with the lens materials and adjust to producer suggestions. Failure to correctly disinfect lenses considerably will increase the danger of microbial keratitis, a critical corneal an infection. For instance, a hydrogen peroxide system successfully disinfects lenses however requires a neutralization step earlier than insertion to forestall corneal harm.
-
Storage
Correct lens storage maintains lens hydration and prevents microbial progress. Lenses must be saved in a clear lens case stuffed with recent disinfecting resolution. The lens case must be changed recurrently, sometimes each three months, to reduce the danger of contamination. Keep away from topping off outdated resolution, as this will dilute the disinfectant and compromise its effectiveness. instance of correct storage includes putting cleaned and disinfected lenses in a clear case stuffed with recent resolution, guaranteeing the lenses are totally submerged.
In conclusion, meticulous lens care is crucial for people utilizing coloration contact lenses for astigmatism. Common cleansing, rinsing, disinfection, and correct storage are important for stopping infections, sustaining lens integrity, and guaranteeing optimum imaginative and prescient and luxury. Adhering to those practices extends lens lifespan and minimizes the danger of issues. Neglecting lens care can have critical penalties for ocular well being, emphasizing the significance of incorporating these practices into every day routines. By following really useful lens care procedures, people with astigmatism can safely and successfully benefit from the beauty and visible advantages of coloration contact lenses.
7. Potential Problems
Whereas coloration contact lenses for astigmatism supply vital advantages, potential issues can come up, significantly with out correct care and lens choice. Understanding these potential points permits wearers to make knowledgeable choices and take applicable preventative measures. Ignoring these potential issues can jeopardize ocular well being and compromise the advantages these specialised lenses present.
-
Large Papillary Conjunctivitis (GPC)
GPC, an allergic inflammatory response, can develop in response to contact lens put on. It includes the formation of enormous bumps on the underside of the eyelids, resulting in itching, discomfort, and mucus discharge. Within the context of coloration contact lenses for astigmatism, protein deposits on the lenses can exacerbate GPC. Correct lens care and protein elimination are important for minimizing this threat. For instance, a affected person neglecting common lens cleansing would possibly expertise elevated GPC signs, whereas enzymatic cleaners might help handle protein buildup, decreasing the probability of this complication.
-
Corneal Neovascularization
Corneal neovascularization is the irregular progress of blood vessels into the cornea. It may be triggered by persistent hypoxia, typically related to insufficient oxygen permeability of contact lenses. Colour contact lenses, particularly these with decrease oxygen permeability, can enhance this threat. Selecting lenses with excessive oxygen transmissibility and adhering to really useful carrying schedules are essential for minimizing the danger of corneal neovascularization. As an example, a affected person carrying lenses with low oxygen permeability for prolonged intervals would possibly develop corneal neovascularization, whereas switching to silicone hydrogel lenses can considerably cut back this threat.
-
Infectious Keratitis
Infectious keratitis, a critical corneal an infection, can happen on account of microbial contamination of contact lenses. Improper lens hygiene practices considerably enhance this threat. Colour contact lenses, like every other contact lenses, require meticulous care to forestall microbial progress and subsequent an infection. Thorough cleansing, disinfection, and correct storage are essential. For instance, reusing lens resolution or neglecting to wash the lens case can introduce pathogens, growing the danger of infectious keratitis. A affected person growing ache, redness, and light-weight sensitivity after utilizing improperly cleaned lenses might need contracted infectious keratitis, requiring speedy medical consideration.
-
Corneal Abrasions
Corneal abrasions, scratches on the corneal floor, can happen on account of numerous elements, together with improper lens insertion and elimination, overseas physique entrapment underneath the lens, or a poorly becoming lens. With coloration contact lenses for astigmatism, an improperly fitted lens could cause extreme friction on the cornea, growing the danger of abrasions. Cautious dealing with and guaranteeing a correct match are important for minimizing this threat. For instance, a lens that matches too tightly can rub in opposition to the cornea, growing the danger of abrasion. A affected person experiencing sudden ache, tearing, and overseas physique sensation after inserting a lens might need a corneal abrasion, necessitating lens elimination {and professional} analysis.
These potential issues underscore the significance of cautious lens choice, meticulous hygiene practices, and common eye examinations. Whereas coloration contact lenses for astigmatism present beauty and imaginative and prescient correction advantages, minimizing these dangers by correct care {and professional} steering is crucial for sustaining long-term ocular well being. Ignoring these potential issues can result in vital discomfort, imaginative and prescient impairment, and probably irreversible harm to the attention. Steady developments in lens supplies and designs attempt to mitigate these dangers, however particular person accountability in correct lens care and adherence to skilled suggestions stays paramount for secure and profitable coloration contact lens put on.
Often Requested Questions
This part addresses widespread inquiries relating to coloration contact lenses for astigmatism, offering concise and informative responses to facilitate knowledgeable decision-making and promote optimum lens put on practices.
Query 1: Are coloration contact lenses for astigmatism costlier than common contact lenses?
Typically, specialised lenses, together with these combining coloration enhancement and astigmatism correction, incur larger prices as a result of extra intricate manufacturing course of and specialised becoming necessities.
Query 2: Can people with excessive astigmatism put on coloration contact lenses?
Developments in lens know-how have expanded choices for people with larger ranges of astigmatism. Consulting an eye fixed care skilled is essential to find out suitability and out there choices.
Query 3: How lengthy can coloration contact lenses for astigmatism be worn every day?
Really useful every day put on time varies relying on particular person elements and lens sort. Following prescribed put on schedules and consulting an eye fixed care skilled is essential to make sure corneal well being.
Query 4: Do all eye colours obtain the identical vibrancy with coloration contact lenses?
The ultimate coloration look will depend on the person’s pure eye coloration and the opacity of the lens. Lighter eyes are likely to exhibit extra noticeable coloration change in comparison with darker eyes.
Query 5: Can coloration contact lenses for astigmatism right all varieties of astigmatism?
Whereas these specialised lenses deal with most typical types of corneal astigmatism, sure irregular astigmatisms could require various corrective options. Skilled session is really useful to find out applicable choices.
Query 6: Are there any particular cleansing options really useful for coloration contact lenses for astigmatism?
Compatibility between lens supplies and cleansing options is crucial. Consulting an eye fixed care skilled ensures applicable resolution choice and minimizes potential issues associated to lens deposits or chemical interactions.
Understanding the nuances of coloration contact lenses for astigmatism empowers knowledgeable choices and promotes secure and efficient lens put on. Consulting with an eye fixed care skilled is at all times really useful for personalised steering and addressing particular person wants.
This data offers a complete overview of coloration contact lenses for astigmatism. For additional inquiries or personalised steering, consulting an eye fixed care skilled is really useful.
Important Suggestions for Colour Contact Lens Wearers with Astigmatism
People with astigmatism looking for beauty enhancement by coloration contact lenses require specialised care and consideration. The next suggestions present sensible steering for secure and profitable lens put on, selling optimum imaginative and prescient and ocular well being.
Tip 1: Seek the advice of a Certified Eye Care Skilled: A complete eye examination is essential for correct astigmatism evaluation and applicable lens choice. Skilled steering ensures correct match, optimum imaginative and prescient correction, and minimizes potential issues.
Tip 2: Prioritize Oxygen Permeability: Ample oxygen transmission to the cornea is crucial for stopping hypoxia-related issues. Silicone hydrogel lenses, recognized for his or her excessive oxygen permeability, are typically really useful for prolonged put on consolation and corneal well being.
Tip 3: Emphasize Lens Stability: Toric lenses, designed for astigmatism correction, require stability on the attention. Focus on lens designs that reduce rotation and decentration with an eye fixed care skilled, guaranteeing constant and predictable imaginative and prescient correction.
Tip 4: Keep Meticulous Lens Hygiene: Correct cleansing, rinsing, and disinfection are essential for stopping infections and sustaining lens integrity. Adherence to really useful lens care practices minimizes the danger of issues and extends lens lifespan.
Tip 5: Comply with Prescribed Put on Schedules: Exceeding really useful put on instances will increase the danger of issues reminiscent of corneal hypoxia and infections. Adhering to prescribed put on schedules and permitting the eyes ample relaxation intervals promotes ocular well being.
Tip 6: Schedule Common Eye Examinations: Ongoing monitoring of ocular well being is crucial for detecting potential issues early. Common eye examinations allow well timed intervention and changes to lens sort or put on schedule as wanted.
Tip 7: Perceive Potential Problems: Consciousness of potential issues, reminiscent of big papillary conjunctivitis, corneal neovascularization, and infectious keratitis, empowers proactive administration and knowledgeable decision-making.
Tip 8: Take away Lenses Instantly if Discomfort Happens: Discomfort, redness, or blurry imaginative and prescient can point out a possible drawback. Immediate elimination of lenses and session with an eye fixed care skilled facilitates well timed intervention and prevents issues.
Adhering to those pointers promotes a optimistic expertise with coloration contact lenses for astigmatism, guaranteeing optimum imaginative and prescient correction, consolation, and long-term ocular well being.
By following the following pointers, people can successfully handle their astigmatism whereas having fun with the beauty advantages of coloration contact lenses, contributing to improved imaginative and prescient and enhanced self-confidence. The following conclusion will summarize the important thing takeaways and reinforce the significance of accountable lens put on.
Conclusion
Toric lenses with coloration pigmentation supply people with astigmatism a chance to deal with each visible correction wants and aesthetic preferences. This text explored important points of those specialised lenses, together with toric lens design, coloration pigment integration, oxygen permeability issues, prescription accuracy, correct becoming protocols, important lens care practices, and potential issues. Understanding the interaction of those elements is essential for profitable lens put on and sustaining long-term ocular well being. Emphasis on skilled steering all through the method, from preliminary session and lens choice to ongoing monitoring and care, is paramount.
Advances in lens know-how proceed to develop choices and enhance outcomes for people with astigmatism looking for beauty enhancement. Accountable lens put on, knowledgeable by complete information {and professional} steering, empowers people to realize optimum imaginative and prescient correction and aesthetic expression whereas safeguarding ocular well being. Continued analysis and improvement promise additional developments in lens supplies, designs, and care practices, enhancing the protection, efficacy, and accessibility of coloration contact lenses for astigmatism.
