Ayurvedic medicine for the eyes is not one thing. It is two, and they have almost nothing in common. Applied preparations sit on or in the eye and carry sterility and injury risk. Oral formulations are swallowed, carry contamination and drug interaction risk, and cannot reach the eye in any concentration that matters. Neither category has evidence supporting treatment of glaucoma, retinal disease, or cataract. Some of these products contain lead, mercury, or arsenic by design. Knowing which category you have been handed is the first safety decision, and most patients are never told there is a difference.
Complementary-care boundary: nothing on this page replaces prescribed eye medication or surgery. Pressure-lowering drops for glaucoma, intravitreal injections for wet macular degeneration or diabetic macular edema, antibiotic or antiviral treatment of ocular infection, topical steroids prescribed for uveitis, cataract surgery, and retinal laser or repair all have evidence behind them, and none of them has an Ayurvedic equivalent. If you are taking or scheduled for any of these, continue. Ayurvedic preparations are adjuncts to comfort, never substitutes for sight-preserving treatment.
An Integrative Approach to Ayurvedic Eye Preparations
Patients usually arrive with a bottle, a jar, or a foil strip of tablets, often bought online or brought back from a trip, and one question: is this safe to use and will it help. Answering that honestly means asking what is physically in it, how it is meant to be used, what has actually been tested in people, and what the product is legally allowed to contain in the United States. Those four questions rarely get asked, and each has an uncomfortable answer.
There is a version of Ayurvedic eye care that is defensible. It is narrow. It involves preparations of documented composition, used for surface comfort in a diagnosed patient whose eye disease is being managed by an eye doctor, alongside diet, sleep, screen habits, and stress, which genuinely influence how a dry, irritated eye feels. It contains no metal, no unlabeled import, and no promise about vision that cannot be measured.
This page sets out what each traditional preparation physically is, what the published literature supports and where it runs out, what the heavy-metal problem really looks like in the data, how these products are regulated in the US, and which of them we use at Netra Eye Institute and which we refuse.
Two Separate Categories, and Why Conflating Them Causes Harm
Applied Preparations Touch the Eye
Drops, washes, pastes, ointments, and ghee baths are placed on the ocular surface or on the lid. Whatever is in them reaches the cornea and conjunctiva directly, with no digestion, no liver, and no dilution. Dose is not the main question here. Sterility, pH, particle size, and what happens if the corneal surface is broken are the questions that matter.
Oral Formulations Never Reach the Eye in Quantity
Tablets, powders, and medicated ghee taken by mouth are absorbed through the gut, processed by the liver, and diluted across the whole body. The blood-retinal and blood-aqueous barriers then exclude most of what is left. This is why modern ophthalmology gives so few oral drugs for eye disease, and why an oral herbal product should be judged as a systemic medicine, not as an eye treatment.
The Risks Do Not Overlap
An applied preparation can cause corneal infection, chemical injury, and scarring within days. An oral formulation can cause lead poisoning, liver injury, or a bleeding complication through an interaction, usually over months and usually silently. A clinic that reassures you about one category using safety information from the other is not giving you an answer.
The Marketing Deliberately Blurs the Line
Product pages routinely describe an oral tablet as a treatment for a named eye disease, and describe an eye drop using systemic language about nourishing tissue. Both blur the fact that nothing has been measured. When a single brand sells a drop and a tablet under one disease heading, the implied evidence is doing work that no study has done.
Heavy Metals Are Overwhelmingly an Oral Problem
Bhasma preparations, made by repeatedly calcining metals or minerals, appear in oral formulations far more often than in applied ones. The notable exception is traditional eye cosmetics such as kajal and surma, which are applied and which have repeatedly been found to be largely lead. Both hazards are real; they occur in different products and need to be asked about separately.
What to Establish About Any Product
Before anything goes in or near your eye, establish which category it belongs to, the full ingredient list including any mineral or metal component, who manufactured it and where, whether it was tested for heavy metals, and how it is meant to be used. If any of those five cannot be answered, that is your answer.
The Applied Preparations, and What Each Physically Does
Aschyotana
Drops instilled into the open eye, usually a few drops at a time, in the shortest-contact procedure of the group. Functionally this is an eye drop: it wets the surface, dilutes irritants, and washes away debris. The risks are those of any drop, dominated by what it is dissolved in and whether the container has been contaminated between uses.
Seka
A stream of warm liquid poured over the eye from a height for several minutes, also called Parisheka. It combines irrigation with sustained warmth on the lids. Of all these procedures it maps most closely onto something conventional, the warm compress, and the warmth is the part with a plausible mechanism in evaporative dry eye.
Anjana
A paste, powder, or thickened preparation applied along the lid margin with a rod or fingertip. This is the traditional form nearest to kajal and surma, and it is the one we treat with most suspicion, because lid margin application of a mineral-containing powder is precisely the practice repeatedly linked to lead exposure, and because the lid margin is a poor place for particulate matter.
Tarpana
Warm medicated ghee held over the open eye inside a sealed dough ring for five to fifteen minutes. It has the longest contact time and, unsurprisingly, the most risk. It also has the only small body of human trial evidence in this group, all of it in dry eye and all of it unblinded and single-center.
Putapaka
A more concentrated retention procedure using a liquid prepared by wrapping and roasting herbal and sometimes animal material, then expressing the juice. It is traditionally used after Tarpana. There is no clinical trial evidence for it, and the preparation method makes microbiological quality harder to control rather than easier.
Vidalaka
A herbal paste applied to the outside of the closed lid and left in place, never entering the eye. It is the lowest-risk member of the group for that reason, and its effects are limited to skin contact, warmth, and the modest pressure of the paste. Contact dermatitis of the lid skin is the realistic adverse effect.
Contact Time Predicts Risk
Reading down that list, risk tracks one variable more than any other: how long a non-sterile substance stays against the ocular surface. A brief drop is recoverable; ten minutes of a warm pooled preparation over an eye with a break in its epithelium is how traditional eye remedies produce the corneal ulcers and scarring documented in reviews from regions where they are common.
The Oral Formulations and What They Are Claimed to Do
Triphala
A fixed combination of three dried fruits, amalaki, bibhitaki, and haritaki, taken as powder, tablet, or decoction. It is the most widely used Ayurvedic preparation associated with eye health and the most extensively studied, though almost entirely outside ophthalmology. Randomized trials exist for gut microbiota and for cholesterol. None demonstrates an effect on any eye disease.
Saptamrita Lauha
A classical formulation combining Triphala and licorice with Lauha Bhasma, an iron preparation. It is frequently recommended for eye complaints in traditional practice. The important fact about it is structural: it is a metal-containing preparation, and iron bhasma products vary widely in composition. We do not use it or recommend it.
Mahatriphala Ghrita
Ghee cooked with Triphala and several other herbs, taken orally by the spoonful rather than applied. It is positioned as a Rasayana for the eyes. The relevant limitations are that it is a fat-based preparation with meaningful caloric and lipid load, that its herbal content varies by manufacturer, and that no controlled trial has tested it for any ophthalmic endpoint.
Amalaki on Its Own
Indian gooseberry is used alone as well as within Triphala, usually justified by its vitamin C content and antioxidant activity in the laboratory. Systematic reviews of oral amla have examined lipids, glucose, and inflammatory markers. Antioxidant activity in a test tube is not a treatment effect, and there is no trial linking it to vision or to structural eye disease.
What Rasayana Claims Actually Mean
Rasayana is a traditional category meaning rejuvenative or restorative, and it is not a claim about any measurable ophthalmic outcome. When a product label translates it as restoring vision or regenerating the optic nerve, that is a translation error at best and a marketing decision at worst. No oral Ayurvedic preparation has been shown to regenerate retinal or optic nerve tissue.
Where Oral Therapy Can Legitimately Help
Indirectly, and modestly. Systemic health affects the eye: blood sugar control alters diabetic retinopathy risk, and general diet, hydration, and sleep influence how a dry eye feels day to day. Dietary advice and an unhurried consultation that addresses these things have genuine value. That value does not transfer to a specific pill for a specific eye disease.
Which Single Herbs Have Any Real Ophthalmic Data
A handful of botanicals have been tested in people with eye disease. Setting them out individually is more useful than any general statement about herbs, because the quality of the evidence differs sharply between them and it is thin even at its best.
Saffron in Macular Degeneration
Saffron has the most credible ophthalmic data of any of these. A randomized clinical trial in mild to moderate age-related macular degeneration reported small improvements in retinal function measures, and further work has examined longer-term use. The effects were modest, the studies small, and none tested whether saffron changes the outcome that matters, which is progression to sight loss.
Ginkgo Biloba in Normal-Tension Glaucoma
A randomized crossover trial in Chinese patients with normal-tension glaucoma examined effects on visual field and contrast sensitivity, and the literature that followed has been inconsistent. Ginkgo also inhibits platelet aggregation, which matters for anyone on an anticoagulant. It is not a substitute for pressure-lowering treatment in any form of glaucoma.
Bilberry and Night Vision
Bilberry anthocyanosides are among the most heavily marketed eye supplements, on the basis of a wartime story about pilots that has no documentary support. A systematic review of placebo-controlled trials found that the more rigorous studies were negative. This is the clearest example in the field of a reputation surviving its own evidence.
Triphala and Its Constituents
Laboratory work on chebulagic and chebulinic acid, two Triphala constituents, has shown effects on chorio-retinal endothelial cells in culture, which is a reasonable basis for further research and nothing more. Cell culture results are separated from patient benefit by many steps, most of which fail. No human ophthalmic trial of Triphala exists.
Curcumin and Other Anti-Inflammatory Botanicals
Curcumin is widely promoted for ocular inflammation on the strength of laboratory activity. Its oral bioavailability is poor, which is why commercial products add absorption enhancers, and the human ophthalmic literature consists of small studies of mixed-ingredient supplements from which no single component can be credited.
What Counts as a Useful Comparison
Contrast all of this with the AREDS2 formulation, where tens of thousands of person-years of randomized data define a specific micronutrient combination, a specific stage of macular degeneration, and a measured reduction in progression risk. That is what adequate evidence for a supplement looks like. Nothing in the Ayurvedic materia medica approaches it.
How to Read a Confident Claim
Ask which trial, in whom, compared with what, and measured how. A claim supported by laboratory work will not survive that question. Neither will one supported by a single uncontrolled series. Both are common, and both are usually presented as though the answer were settled.
What These Preparations Can and Cannot Do
Stripped of the language around them, the applied preparations do a small number of physical things to the surface of the eye: they wet it, warm it, coat it, and in some cases irritate it. The oral formulations deliver plant compounds into the general circulation, where dose, absorption, and the ocular barriers determine that very little arrives at the eye.
Judged on what is measurable rather than what is claimed, the honest list of what Ayurvedic eye preparations may contribute is short, and every item on it concerns comfort or general health rather than disease:
- Temporary relief of dryness, grittiness, and burning through lubrication and warmth
- Softening of thickened meibomian secretion when sustained warmth is part of the procedure
- Reduced friction between lid and ocular surface during blinking
- A structured reason to rest the eyes away from screens and near work
- Attention to diet, sleep, hydration, and stress, which influence how a dry eye feels
- A consultation long enough to review lid hygiene, blink habits, and drop technique properly
- Support for adherence to the conventional treatment a patient has already been prescribed
What they cannot do is equally definite. They do not lower intraocular pressure, halt or reverse glaucomatous field loss, clear a cataract, change refractive error, regenerate photoreceptors or optic nerve fibers, dissolve vitreous floaters, or treat retinal detachment, macular edema, or neovascular macular degeneration. Any product sold on one of those claims is being sold on a false premise, and the cost of believing it is measured in vision that does not come back.
What We Will and Will Not Use at Netra Eye Institute
Diagnosis Comes First, Always
Nothing is applied to or recommended for an eye that has not been examined and diagnosed by a clinician qualified to do so. Our practitioners are licensed in acupuncture and Oriental medicine and practice Ayurvedic therapy within that scope. They are not ophthalmologists, they do not diagnose or manage eye disease as ophthalmologists do, and they work with your eye doctor rather than in place of one.
Documented Composition Only
We use preparations whose full composition we can document, from manufacturers who can supply testing records. If we cannot establish what is in a product, it is not used, regardless of how long it has been in traditional use or how well a patient reports tolerating it elsewhere.
Applied Preparations, Narrowly
Warm applications and lubricating preparations are used for ocular surface complaints, principally evaporative dry eye and screen-related irritation, in eyes with an intact corneal surface and no active infection. The treatment plan sits alongside lid hygiene, artificial tears, and any prescribed therapy, and it is stopped if measured symptom scores do not improve.
Oral Formulations, Very Narrowly
Where an oral botanical is discussed at all, it is discussed as a systemic supplement with its own interaction profile, not as an eye treatment. We ask for a full list of prescribed medication first, and we do not recommend anything alongside anticoagulants, immunosuppressants, or a transplanted organ without the prescribing physician being involved.
Referral Is Not Optional
Sudden vision loss, a new shower of floaters or flashing lights, a curtain across the field, a red and painful eye, sudden double vision, or any unexplained drop in acuity produces an urgent referral the same day. Several of these are hours-to-days emergencies. No adjunctive therapy is offered in their place.
We Do Not Ask Anyone to Stop Treatment
We do not advise reducing or stopping glaucoma drops, postponing an injection, deferring surgery, or skipping a scheduled retinal review. If any practitioner in any setting suggests you do, treat that as a reason to leave. The most common serious harm in this field is not a toxic product; it is a delayed appointment.
What We Will Not Do
We do not use kajal, surma, or any traditional collyrium, all of which have repeatedly been shown to contain lead. We do not use or recommend bhasma preparations or any formulation with a metal or mineral component, including Saptamrita Lauha. We do not dispense unregulated imported products of unverifiable content, we do not recommend home-made eye washes of any kind, and we do not make claims about reversing, curing, or regenerating any structure in the eye.
The Heavy-Metal Problem, in Depth
Bhasma Is Not Contamination
This distinction is the one most often missed. A bhasma is a metal or mineral, repeatedly calcined and processed, that is included in a formulation on purpose. Lauha Bhasma is iron, Swarna Bhasma gold, Abhrak Bhasma mica, and there are lead and mercury preparations too. Analytical work shows that the metal content of these products varies substantially between samples.
The JAMA Internet-Purchase Study
In 2008, researchers bought Ayurvedic medicines from US and Indian websites and analyzed them. One in five contained detectable lead, mercury, or arsenic, and among the rasa shastra products, which are the ones meant to contain metals, the proportion was much higher. Some products contained enough lead that following the label dose would exceed regulatory limits many times over. This was ordinary online purchasing, not a search for counterfeits.
The Scoping Review That Followed
A later systematic scoping review of heavy metals in Indian traditional systems of medicine pulled together the analytical and case literature and reached the same conclusion from a wider base. The problem is not confined to one country of manufacture, one company, or one decade, and case reports of severe lead poisoning traced to Ayurvedic products continue to appear in the medical literature, including fatal ones.
Kajal, Surma, and Lead in the Eye Itself
Traditional eye cosmetics deserve separate emphasis because they are applied to the eye and are often used on infants. Analyses of kajal, surma, kohl, and tiro have repeatedly found products that are largely lead sulfide. Public health reports have documented infant lead poisoning traced directly to an imported eye cosmetic, and a recent review in the pediatric literature sets out these powders as an ongoing source of exposure in the United States.
What Lead Exposure Actually Costs
Lead has no safe level. In children it lowers cognitive function permanently, and no chelation reverses that. In adults it causes anemia, abdominal pain, peripheral neuropathy, kidney injury, hypertension, and reproductive harm, and it accumulates in bone over years. These effects are gradual and easy to attribute to something else, which is exactly why exposure so often continues.
Traditional Does Not Mean Tested
Long use establishes that a preparation was tolerated well enough to keep being made. It does not establish that it works, and it cannot detect harm that appears slowly or that looks like ordinary aging. Historical practice had no way to measure blood lead, liver enzymes, or kidney function. Appealing to centuries of use as evidence of safety asks a tradition to answer a question it never had the instruments to ask.
How These Products Are Regulated in the United States
They Are Sold as Dietary Supplements
Oral Ayurvedic formulations reach the US market as dietary supplements, not as drugs. Under the framework established by the Dietary Supplement Health and Education Act, a supplement does not need FDA approval before sale. The manufacturer is responsible for its safety, and the agency acts after a product is already being sold.
What That Means for the Bottle in Your Hand
No one verified before sale that the contents match the label, that the dose is consistent between batches, or that the product is free of lead, mercury, or arsenic. Good manufacturing practice rules exist and are enforced by inspection, but inspection reaches a fraction of products, and imported and online-only sellers are the hardest to reach.
The Structure-Function Loophole
A supplement may not claim to treat a disease, so labels say things like supports healthy vision or promotes eye comfort instead. These structure-function statements need no proof and carry a disclaimer in small print. When marketing elsewhere, in a video or a consultation, supplies the disease claim the label cannot, the regulatory line has been crossed in substance if not on paper.
Eye Drops Are a Different Category
Anything intended for instillation into the eye is a drug in US law, not a supplement, and is expected to be manufactured sterile under drug rules. Herbal eye drops sold as wellness products frequently sit outside that framework entirely. Recent contamination outbreaks involving marketed artificial tears are a reminder that sterility failures in eye products cause blindness, not inconvenience.
Ayurvedic Practice Is Not Separately Licensed
Most US states, New Jersey among them, do not license Ayurvedic practitioners as such. Practitioners work under another license where they hold one, most often acupuncture, or under none. There is no state board setting a scope of practice for Ayurveda, no protected title, and no disciplinary route specific to it. Asking what license someone actually holds is a reasonable question, and the answer varies enormously.
What Better Purchasing Looks Like
Prefer manufacturers who publish third-party heavy-metal testing by batch. Avoid any product containing bhasma or an unspecified mineral ingredient. Avoid anything whose label is not fully in English with a complete ingredient list. Avoid sellers who diagnose. If a product cannot tell you what is in it, no amount of tradition behind it fixes that.
Interactions With Prescribed Eye and Systemic Medication
Herbal products interact with prescribed drugs, and the interactions that matter most are the ones that are silent until something goes wrong. Tell your ophthalmologist and your primary care physician about everything you take, including things you think of as food. These are the specific situations to raise before starting anything.
- Warfarin and other anticoagulants: a systematic review documents numerous herbal and dietary supplement interactions affecting anticoagulation, and ginkgo additionally inhibits platelet aggregation
- Antiplatelet therapy before eye surgery, where bleeding risk and the timing of any pause belong entirely to your surgeon and physician
- Diabetes medication, where botanicals that lower blood glucose can push a controlled patient into hypoglycemia
- Blood pressure medication, where additive effects and interactions can cause symptomatic low pressure
- Thyroid replacement and any drug with a narrow therapeutic window, where absorption changes matter more than they appear to
- Immunosuppressants after corneal or other transplant, where an altered drug level threatens the graft
- Existing liver disease or any drug known to affect the liver, given that herbal and dietary supplements are a recognized and growing cause of drug-induced liver injury
- Kidney impairment, which reduces clearance of both herbal constituents and any metal contaminant present
- Pregnancy, breastfeeding, and use in children, where lead exposure in particular causes irreversible harm
- Oral iron or high-dose mineral supplements taken alongside a bhasma-containing formulation, compounding a metal load nobody has measured
One practical step covers most of this. Photograph every label, front and back, including the ingredient panel, and bring the photographs to every appointment. A pharmacist can screen the list against your prescriptions in a few minutes, and that short conversation prevents the majority of avoidable problems in this area.
Frequently Asked Questions on Ayurvedic Medicine for Eyes
No. A clouded lens is corrected surgically and nothing else clears it. Glaucoma is controlled only by lowering intraocular pressure with drops, laser, or surgery, and the field loss it causes does not come back. Using Ayurvedic preparations in place of either causes permanent vision loss, and in glaucoma that loss is painless and often unnoticed until it is severe.
Oral Triphala from a reputable manufacturer is generally well tolerated, with loose stools the common effect. There is no trial evidence that it improves any eye condition. Buy only from a manufacturer that publishes batch heavy-metal testing, check with a pharmacist if you take prescribed medication, and do not use a home-made Triphala decoction as an eye wash.
Look for the word bhasma, for any named metal such as lauha, swarna, rajata, naga, or vanga, and for rasa shastra products generally. If the label is incomplete or not in English, assume you cannot know. Manufacturers who test publish certificates of analysis by batch; those who do not, do not. If you have been taking a product like this, a blood lead test is inexpensive and worth doing.
In US law anything instilled into the eye is a drug and must be made sterile under drug manufacturing rules. Herbal eye drops sold as wellness products often sit outside that framework, and imported ones almost always do. Contaminated eye drops have caused vision loss and worse, so this is the category where informal sourcing is least defensible.
No. Homemade does not mean lead-free, and the pigments and vessels used are themselves common sources. Public health investigations have traced infant lead poisoning directly to imported eye cosmetics, and lead damages the developing brain permanently. This is the one recommendation on this page we make without any qualification: do not use it.
Selected References for Scientific Support
- Saper RB, Phillips RS, Sehgal A, et al. Lead, mercury, and arsenic in US- and Indian-manufactured Ayurvedic medicines sold via the Internet. JAMA. 2008. PubMed
- Mukhopadhyay S, Abraham SE, Holla B, et al. Heavy Metals in Indian Traditional Systems of Medicine: A Systematic Scoping Review and Recommendations for Integrative Medicine Practice. J Altern Complement Med. 2021. PubMed
- Liu J, Zhang F, Ravikanth V, et al. Chemical Compositions of Metals in Bhasmas and Tibetan Zuotai Are a Major Determinant of Their Therapeutic Effects and Toxicity. Evid Based Complement Alternat Med. 2019. PubMed
- Hore P, Sedlar S. Traditional Eye Cosmetics and Cultural Powders as a Source of Lead Exposure. Pediatrics. 2024. PubMed
- Centers for Disease Control and Prevention (CDC). Infant lead poisoning associated with use of tiro, an eye cosmetic from Nigeria - Boston, Massachusetts, 2011. MMWR Morb Mortal Wkly Rep. 2012. PubMed
- Cericola G, Puzik A, Salou S, et al. Case Report: Severe lead poisoning due to exposure to ayurvedic herbal medicine. Front Pediatr. 2025. PubMed
- Sahay P, Saluja G, Maharana PK, et al. Topical ayurvedic ointment-induced chemical injury presenting as bilateral acute keratitis. BMJ Case Rep. 2017. PubMed
- Tan CSS, Lee SWH. Warfarin and food, herbal or dietary supplement interactions: A systematic review. Br J Clin Pharmacol. 2021. PubMed
- Halegoua-DeMarzio D, Navarro V. Challenges in herbal-induced liver injury identification and prevention. Liver Int. 2025. PubMed
- Timmapur GM, Fiaz S. Efficacy of Triphala Ghrita and Goghrita Manda Tarpana in the management of Shushkakshipaka w.s.r. to dry eye syndrome: An open labelled randomized comparative clinical trial. Ayu. 2020. PubMed
- Vardhan P, Dhiman KS. Clinical study to assess the efficacy of Keshanjana and Netra Parisheka in the management of Shushkakshipaka (dry eye syndrome). Ayu. 2014. PubMed
- Ashwini BN, Sivabalaji K, Bhutada R, et al. Comparative efficacy of Shatavari Ghrita eye drops with Shatavari Ksheerapaka versus Triphala Ghrita eye drops with Shatavari Ksheerapaka in postmenopausal ocular surface disease: a randomized, single-blind trial. Front Med (Lausanne). 2026. PubMed
- Dhiman KS, Ahuja DK, Sharma SK. Clinical efficacy of Ayurvedic management in computer vision syndrome: A pilot study. Ayu. 2012. PubMed
- Dhiman KS, Shukla VJ, Bhalodia NR, et al. Quality control evaluation of Keshamasi, Keshanjana and Keshamasi eye ointment. Ayu. 2014. PubMed
- Peterson CT, Pourang A, Dhaliwal S, et al. Modulatory Effects of Triphala and Manjistha Dietary Supplementation on Human Gut Microbiota: A Double-Blind, Randomized, Placebo-Controlled Pilot Study. J Altern Complement Med. 2020. PubMed
- Shanmuganathan S, Angayarkanni N. Chebulagic acid and Chebulinic acid inhibit TGF-beta1 induced fibrotic changes in the chorio-retinal endothelial cells by inhibiting ERK phosphorylation. Microvasc Res. 2019. PubMed
- Broadhead GK, Grigg JR, McCluskey P, et al. Saffron therapy for the treatment of mild/moderate age-related macular degeneration: a randomised clinical trial. Graefes Arch Clin Exp Ophthalmol. 2019. PubMed
- Canter PH, Ernst E. Anthocyanosides of Vaccinium myrtillus (bilberry) for night vision: a systematic review of placebo-controlled trials. Surv Ophthalmol. 2004. PubMed
- Guo X, Kong X, Huang R, et al. Effect of Ginkgo biloba on visual field and contrast sensitivity in Chinese patients with normal tension glaucoma: a randomized, crossover clinical trial. Invest Ophthalmol Vis Sci. 2014. PubMed