Abstract: OSDI and the post-menopausal dry eye...

Aha. An opportunity to preach a sermon on a favorite topic.

As many of you know I've long been a fan of the OSDI. It's a quick 12-question survey (technically, a scientifically validated instrument) that I encourage all patients to use regularly to 'quantify' their dry eye symptoms. Complete it and take it to doctor appointments, especially if you're seeing a new doctor for the first time. Also, score yourself before and a month and three months after commencing any new treatments. If you want meaningful data, school yourself not to change your routine or treatments during that time.

Patients, if you've ever had the uncomfortable experience of trying to communicate how much pain you're in to a doctor who is looking quizzically (or worse) at you after gazing at your apparently 'quiet' corneas under a slit-lamp, the OSDI is for you. Your doctor cannot brush it aside as irrelevant. If they do, they're basically also saying that Restasis should never have been approved.

Doctors, if you've ever been tempted to think your dry eye patients who don't have glaring clinical signs are whining malcontents, I dare you to make all your patients (not just the dry eye ones) complete this survey with no explanation and then tabulate the data.

Here's a link to download a PDF copy.

Some years ago when Restasis first came on the market, Allergan reps distributed tear-off pads with this survey so doctors could use it to measure how patients are doing before and after starting on the drug. Wish they hadn't left off, but maybe we can collectively re-popularize it.

Clinical signs and symptoms in post-menopausal females with symptoms of dry eye.
Srinivasan S, Joyce E, Senchyna M, Simpson T, Jones L.
Ophthalmic Physiol Opt. 2008 Jul;28(4):365-72

Purpose: To characterize clinical signs and symptoms in a group of post-menopausal (PM) females who present with and without symptoms of dry eye.
Methods: Eighty-three healthy PM females were categorized as being symptomatic or asymptomatic of dry eye based on their response to the Allergan Ocular Surface Disease Index((c)) (OSDI) questionnaire. Non-invasive tear breakup time (NITBUT) was evaluated using the ALCON Eyemap(R). Tear volume was assessed using the phenol red thread (PRT) test and bulbar conjunctival hyperaemia was measured using objective and subjective methods.
Results: The total OSDI score (TOS) and subscores for the non-dry eye (NDE; n = 39) and dry eye (DE; n = 44) groups were significantly different (TOS: NDE = 7.43 +/- 7.71 vs DE = 24.87 +/- 13.89; p < 0.001). The DE group exhibited a shorter NITBUT (5.3 +/- 1.7 s vs 7.0 +/- 2.7 s; p = 0.0012). Tear volume was lower for the DE group (19.3 +/- 5.1 mm vs 16.3 +/- 5.6 mm; p = 0.031). Bulbar hyperaemia was higher in the DE group for both subjective grading using a modified CCLRU scale (48.4 +/- 10.0 vs 40.6 +/- 10.4; p = 0.0011) and objective measurement by spectrophotometer (Commission Internationale de l'Eclairage u' value = 0.285 +/- 0.006 vs 0.282 +/- 0.006; p = 0.005).
Conclusions: OSDI can be used to separate PM females who demonstrate clinical signs of ocular dryness. PM women with dry eye symptoms demonstrate shorter NITBUT, lower tear volume and increased bulbar conjunctival hyperaemia than those who have no symptoms.

Abstract: ELF MF and dry eye

Help! Calling electricians and engineer types with dry eye. I am ignorant as a stone about this and need a brief education.

Percolating at the back of my brain somewhere is an evolving composite answer to the question of "Why we are dry" - epidemiologically speaking. Many, probably most of the pieces are known but I am always on the lookout for additional clues. And yes, I know this study is just 15 rats for 7 days but it's suggestive and I'd like to get some sense of the potential relevance.

My question: Where do normal people typically get exposure to ELF magnetic fields?

The effect of extremely low frequency magnetic field on the conjunctiva and goblet cells.
Keklikci U, Akpolat V, Ozekinci S, Unlu K, Celik MS.
Curr Eye Res. 2008 May;33(5):441-6.

PURPOSE: The aim of this study was to examine the effects of extremely low frequency magnetic field (ELF MF) on the conjunctiva and goblet cells density.
METHODS: Thirty adult female Spraque Dawley rats were assigned to one of two groups, each containing 15 rats. The experimental group received magnetic field 4 hr/day for 7 days. The second group received standard laboratory care and served as a control. The specimens were evaluated by light microscopy for goblet cell density, conjunctival edema, inflammation, and fibroblast proliferation.
RESULTS: In ELF MF exposure group rats, the number of goblet cells was less than the control group. We also observed a significant difference between ELF MF exposure group and control group in terms of goblet cell density (p = 0.010). The ELF MF exposure group manifested conjunctival edema and inflammation compared to the control group (p < 0.001 and p = 0.003). There was no statistical difference between the groups for fibroblast proliferation (p = 0.422).
CONCLUSION: This study suggests that ELF MF exposure leads to morphological alterations of the conjunctiva and reductions in the number of goblet cells. We believe that ELF MF may cause dry eye symptoms.

Abstract: Smartplugs & canaliculitis

Maybe I'm hypersensitive because of all the people I know personally with SmartPlug complications, but if I read one more report like this I'm going to be seriously tempted to start calling them DumbPlugs.

Incidentally... I never knew that there was a "relatively large number of [Mycobacterium chelonae] infections associated with laser-assisted in situ keratomileusis and other forms of refractive surgery". Hm.

Mycobacterium chelonae canaliculitis associated with SmartPlug use.
Fowler AM, Dutton JJ, Fowler WC, Gilligan P.
Ophthal Plast Reconstr Surg. 2008 May-Jun;24(3):241-3.

Mycobacterium chelonae is ubiquitous in the environment but is an uncommon cause of ocular and periocular infections. It is a pathogen that has been gaining increased attention in the ophthalmic literature because of the relatively large number of infections associated with laser-assisted in situ keratomileusis and other forms of refractive surgery. The authors present 3 patients who developed canaliculitis culture positive for M. chelonae more than a year after SmartPlug placement. These cases highlight some of the clinical scenarios that may be encountered in those who present with canaliculitis with a history of intracanalicular plug placement. Therapeutic considerations are also suggested.

Abstract: DIabetes and dry eye

Study of dry eye signs/symptoms in diabetics.

I get kind of suspicious when I see things like "A dry eye questionnaire" (without further identification) in the Methods. Seems to me that if it were a previously published, scientifically validated instrument they would say so.

Tear Film Function in Type 2 Diabetic Patients with Retinopathy.
Yu L, Chen X, Qin G, Xie H, Lv P
Ophthalmologica. 2008 Jun 18;222(4):284-291.

Purpose: To investigate whether diabetes mellitus is correlated with tear film dysfunction.
Methods: Tear film function tests including tear film breakup time (BUT), fluorescein staining, Schirmer I test, rose Bengal staining, total tear protein detection, tear sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and TMS-4 corneal topography were performed. A dry-eye questionnaire was used.
Results: Compared with the control group and nonproliferative diabetic retinopathy (NPDR) group, in the proliferative diabetic retinopathy (PDR) group, the BUT and the value of the Schirmer I test were reduced significantly (p < 0.01); corneal fluorescein staining scores, the positive rate of rose Bengal staining and the surface regularity index (SRI) and surface asymmetry index (SAI) were higher (p < 0.01); concentrations of lactoferrin and tear-specific prealbumin were lower (p < 0.01, p < 0.05, respectively). In diabetic patients, the SRI and SAI were positively correlated with fluorescein staining scores (r = 0.754, 0.480, p < 0.01, respectively), and the dry-eye symptoms were significantly related to an abnormal BUT and Schirmer I test (p < 0.01, respectively).
Conclusion: The declined tear film function is severer in the patients with PDR than in those with NPDR. Besides the traditional methods, tear SDS-PAGE and TMS corneal topographic indices contribute to the discovery of tear film dysfunction in diabetic patients. Copyright © 2008 S. Karger AG, Basel.

Abstract: Pipeline drug development

My main comment on this review of what's going on in drug development is:

Why have I never heard of gefarnate, and is there really any current research going on with it? I see abstracts 10 years older and more, but nothing current. Since there are other references in this abstract to dead ducks (e.g. rebamipide, which probably wasn't officially dead till after this article was complete and waiting for press) I'll assume for the moment that this is an out of date reference... unless anyone would care to enlighten me otherwise.

Incidentally, here's a link to our dry eye drug pipeline page.

Therapeutic targets in dry eye syndrome.
Peral A, Dominguez-Godinez CO, Carracedo G, Pintor J.
Drug News Perspect. 2008 Apr;21(3):166-76.

Dry eye is a multifactorial disease of the tears and the ocular surface that manifests with a wide variety of signs and symptoms. It is prevalent in about 33% of the population worldwide. Due to the importance of the pathology, new tests, drugs and technologies have been developed to assist the diagnosis, management and follow-up of the disease. Current available therapies try to alleviate symptoms and to reduce signs in order to restore the ocular surface. Depending on the etiology of the pathology it is possible to use lubricants, secretagogues, biological tear substitutes or antiinflammatory drugs, either independently or combined. Nowadays, the therapies under clinical trial are devoted to stimulating tear components (e.g., diquafosol, a P2Y receptor agonist), or mucin secretion (e.g., rebamipide, an amino acid analogue of quinolinone). Others include gefarnate, a water-insoluble terpene fatty acid that contributes to restoring mucins on the ocular surface, or cevimeline, an oral cholinergic agonist that reduces the symptoms associated with dry eye. Other potential compounds described in patents are in a lower phase of drug development. These compounds come from different families of therapies, and among others, can be found in the form of steroidal and nonsteroidal antiinflammatory agents, vitamins A and D, neurotransmitters and neuropeptides.

Journal: Musings about why we don't "get" dry eye

While trying to chase bugs and a mini-abrasion off my brain this morning I was pondering once again some of the reasons why I think good dry eye care is such a scarce commodity.

Western medicine has this annoying way of looking at things in nice neat boxes for ease of use.

Are we looking at a person, or a pair of eyes? Ophthalmology seems to want to box up the eye and isolate it from the rest of the body. Yet most of dry eye is attributable to side effects of medications and surgeries; auto-immune disease; hormones; skin disease; eyelid mechanics; unfriendly home and office environments full of dried out air and allergens; and lousy diet.

Eye surfaces and a sophisticated lubricating system, or a tear film? Similarly, the cornea folks want to box up the tear film ("Three layers... not enough oil... add oil...") and/or the ocular surface ("Inflammation Is The Enemy...Must Fight Inflammation...")

What's missing?

Well, the rest of the body, for one. We pay lip service to it by pushing fish oil supplements, or going on allergy hunts, and under certain circumstances we test for Sjogrens, and we think we've done our duty and can return to the much more comfortable business of suppressing surface inflammation medically.

Then there's the complex interworkings of the tear system. This is increasingly evident in scientific findings - the ones that bother to look for the connections. (Mess with my MGs? Guess what - my mucus will suffer too. Mess with my nerve endings? You'll screw up my aqueous production. Mess with my aqueous? You'll screw up my MGs. And on and on.)

And then there's the question of what's happening on the infamous ocular surfaces themselves. You see what you look for, which raises many interesting questions of emphasis. For example, is the problem an inadequate or imbalanced tear film - or the surface state that occurs as a result, such as the "de-wetting" or whatever it is that's causing excessive pain? But again, that idea would take us out of the medical box into another area of science altogether. Sorry, no can do!

Ponder ponder ponder. Off to start the day now.

Journal: Foreign body sensation

I woke up in the middle of the night convinced a bug had walked onto my eye.

Talk about foreign body sensation.

I couldn't feel it - not with my fingers, I mean - and I was so sleepy nothing could have dragged me out of bed to look in a mirror. Nevertheless, this idea of a bug on my cornea was on my brain the instant I woke up and I couldn't shake it. And I'm not talking spider - probably never would have felt something like that - I mean something with a nice hard scaly body that can really scratch.

My cornea hurt like heck. My drops weren't in their usual place by my bed. So, I just rubbed my eye a bit and tried to go back to sleep.

It's my left eye, normally the good one of the two. True, I wasn't wearing my usual moisture goggle or even a sleep mask. In fact I was so worn out I don't think I even put drops in last night. But I don't recall ever having any very memorable spontaneous abrasion in that eye, at least not in recent years. When I get into any serious trouble at night it's always my right eye that gets the worst of it.

When I finally got up, sure enough, the eye was a nice shade of pink and had lots of mucous strands as though it had been trying to push something out. I hunted around and couldn't find any sign of something in my eye, so if there ever was something there, I guess it got away. It's been awhile since I had that strong an FBS right in the middle of my cornea. I've been back to the mirror several times to see if I could find anything, you know, like a tiny little leg or something. Nope, nothing. I've been pouring in the Dwelle, and the pain's starting to go down at least. And the way I noticed that is about the time I started becoming aware of how much my right eye hurts. Nothing like one kind of pain out-shouting another.

Teacher, I need a blackboard to go write on...

I will take care of my eyes before bed.
I will take care of my eyes before bed.
I will take care of my eyes before bed.
........................................

Abstract: Dry eye and refractive surgery

Predictably:

1) I could live without the Restasis/plug/Intralase cheerleading, but never mind

2) I am pleased to see the first three sentences of the Conclusions stated so nicely and I just wish these could be lifted verbatim and placed in every Informed Consent form for laser surgery, with a required verbal explanation by the physician.

3) I am just as disgusted with the last sentence of the Conclusions as I always am at this kind of a conclusion. Why laser these people with pre-existing dry eye at all?

Postrefractive surgery dry eye.
Curr Opin Ophthalmol. 2008 Jul;19(4):335-41.
Quinto GG, Camacho W, Behrens A.
The Wilmer Ophthalmological Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-0005, USA.

PURPOSE OF REVIEW: To report the recently published literature on ocular surface changes after refractive surgery, as well as the outcomes of treatment modalities on postrefractive surgery dry eye.

RECENT FINDINGS: Cyclosporine, the first US Food and Drug Administration approved agent to treat the underlying pathological mechanism of chronic dry eye, has demonstrated promising results in dry eye patients. Further, there may be an additive effect of topical cyclosporine and punctal occlusion. Femtosecond lasers for corneal flaps in laser in-situ keratomileusis seem to induce fewer signs and symptoms of dry eye and may be attributed to the creation of thinner flaps.

SUMMARY: Dry eye is one of the most common complications after photorefractive keratectomy and laser in-situ keratomileusis. Keratorefractive surgery is known to cause damage to the corneal sensory nerves. Several studies have demonstrated a decrease in corneal sensation, tear secretion, and tear film stability several months after keratorefractive surgery. For patients with preoperative dry eye, the ocular surface must be treated accordingly prior to surgery.

Abstract: Review of recent published research

Dry eyes: etiology and management.
Curr Opin Ophthalmol. 2008 Jul;19(4):287-91.
Latkany R.

PURPOSE OF REVIEW: Until recently, the cause of dry eye syndrome was uncertain and the treatment was palliative. Since discovering that dry eyes are caused by inflammation, there has been an abundance of research focusing on anti-inflammatory therapies, other contributing causes, and better diagnostic testing. This review summarizes some of the interesting published research on ocular surface disease over the past year.

RECENT FINDINGS: The definition of dry eye now highlights the omnipresent symptom of blurry vision. The re-evaluation of ocular surface staining, tear meniscus height, and visual change will allow for a better diagnosis and understanding of dry eyes. Punctal plugs, and oral and topical anti-inflammatory use will strengthen our arsenal against ocular surface disease.

SUMMARY: Major progress has occurred in the past few years in gaining a better understanding of the etiology of dry eye syndrome, which will inevitably lead to more effective therapeutic options.

Abstract: Tear glands, tit for tat, and... is this interesting or is this interesting!

Well, kewl - someone's finally speaking my language (so to speak)!

OK so it's only rabbits but I found this extremely suggestive. Has it been all said and done long ago and I just never noticed? Seriously, maybe it's just leaky brain syndrome but I honestly don't remember coming across something like this before, simple as it is.

They cauterized shut the meibomian glands of one eye and observed the effects on the tear film. Aqueous tears (i.e. from the lacrimal glands) increased and goblet cell density (i.e. mucous-makers) DECREASED.

Just playing guessing games here as I'm only looking at an abstract not data but:

Let's agree to ignore the lacrimal gland increase on the basis that screwing with the rest of the tear system has left such a bad surface that the bunnies are getting lots of reflex tearing.

Now look at the goblet cells: We've just simulated severe MGD or MG atrophy, goblet cell density is down so presumably mucous production is down. I've always felt that the 'unexplained' element with some of the patients who have severe burning or other 'surface symptoms' (including the infamous 'menthol sensation), despite decent aqueous production and a relatively quiet LOOKING ocular surface, might have as a common factor poor mucus resulting in poor 'wetting' (in a feeble attempt to speak Dr. Holly's language). If so, this might explain why some of these patients can max out on antibiotics, heat treatment, bleph treatment etc and still be in symptomatic hell. Furthermore, it might also help explain why simply applying something that 'wets' better (like Dwelle) can seriously improve symptoms even if the MGs remain completely unproductive, something I was puzzling over in an earlier post using our DEZ member 'Rozjen''s remarkable experience as an example... So now what I really want to know is whether it just compensates for the absence of the substance that is normally responsible for tear adherence or, as suggested in earlier studies, also actually improves goblet cell density. In due course hopefully we'll actually nail this down. Oh for research dollars. It wouldn't really take all THAT much.

[Changes in lacrimal secretion in rabbits according to meibomian glands activity][Article in Romanian]
Oftalmologia. 2007;51(4):121-5.
Stan C, Visan O, Samoila O, Mogosan C, Craciun C, Mera M.

PURPOSE: The purpose of this issue is to create an experimental animal model of dry eye and study the alteration of lachrymal secretion in time.
MATERIALS AND METHODS: We used a group of 8 rabbits in which the Meibomian gland orifices of the right eye were individually closed by cauterization, the results being related to the sound left eye.
RESULTS: We studied: the quantitative alteration of the lachrymal secretion using Schirmer 1 test; the alteration of lachrymal film using rose-bengal and fluorescein staining; the variation in tear protein concentration and histopathological changes in conjunctiva.
CONCLUSIONS: We found histopatological changes in conjunctiva and in the lachrymal secretion consisting in conjunctival goblet-ceil density decrease and watery secretion increase, probably due to lachrymal viscousity decrease mechanism.

Abstract: Dry eye after cataract surgery

This is nothing more than a blurb... But there is so little out there on dry eye after cataract in mainstream peer reviewed journals that I'll take anything I can get. I would love to see the raw data to get any idea of the correlations between incision size, topical meds and severity/persistence of dry eye after surgery. (Any MD, or co-managing ODs out there that happen to have collected data to share?)

[Clinical correlations between dry eye and cataract surgery][Article in Romanian]
Nistor MC, Nistor C.
Oftalmologia. 2007;51(4):79-82.

Cataract procedure is sometimes followed by dry eye symptoms. The dimensions of the incisions, topical medication and other manoeuvres are responsible for these phenomena. I tried to objective them by break-up-time (BUT) and Schirmer test. The favourable outcomes of artificial tears confirm this theory.

BOTOX / Blepharospasm alert

As some of you know, BOTOX injections can be used to treat blepharospasm. Typically patients get injections every 3 months.

I have heard from two different patients quite recently who experienced sudden complications from an injection. In one case, the lid froze open, causing severe pain and great risk to the cornea. In another, there are less severe but still serious problems with lid closure.

I am very concerned about this. If I've personally heard of two in a row, make no doubt there's more of it happening out there somewhere. Furthermore, LID PARALYSIS AND INCOMPLETE LID CLOSURE ARE NOT LISTED AS RISKS anywhere that I can find. Allergan's site lists ptosis, dry eye and corneal inflammation as side effects. The FDA site lists 'droopy eyelid' lasting a few weeks. This is more serious than any of those, however.

DOCTORS, please be on the alert for this and by all means file a Medwatch report or make sure your rep does. If any of your patients experience this please make sure they learn about ALL available remedies including things like Tranquileyes moisture goggles which will help hold their lids closed at night. If that's not suitable for your patient for some reason we can help you find alternatives such as eyelid-friendly tapes or sleep masks.

PATIENTS, if any of you reading this have experienced this complication, please urge your doctor to report it to the FDA. Whether or not your doctor undertakes to do so, please also file a Medwatch report on your own.

Here is the link to the FDA site for adverse event reporting.

As we witnessed so recently with LASIK, failure to report adverse events associated with drugs and medical devices has serious repercussions:

(1) it cripples the FDA's ability to pursue post-market safety issues, and

(2) it prevents future patients from receiving accurate information about the risks they may be undertaking.

(Note that after it was widely reported that only 140 "consumer complaints" had been received by the FDA about LASIK in 8 years, more than 200 more complaints were filed in less than a month - uncomfortable testimony to the FDA's failure to make their reporting system known and to physicians' and/or manufacturers failures to report poor patient outcomes.)

As conscientious consumers and professionals let's do our part to make things safer for future patients!

Thanks everybody.

Abstract: BAK BAAAD

Hopefully you all know this. But, it doesn't hurt to have the world expert in BAK say so. If your doctor has you on a BAK-containing medication used multiple times daily and has NOT discussed the risks with you, bring him a copy of this and talk about it.

On the other hand, sigh, in light of the problems preservative free vials pose for the elderly (see recent post) solutions are not always obvious or readily at hand.

Detrimental effect of preservatives in eyedrops: implications for the treatment of glaucoma.
Baudouin C.
Acta Ophthalmol. 2008 Jun 3. [Epub ahead of print]

Antiglaucoma medications are often associated with ocular adverse reactions such as dry eye, and burning or stinging sensations. These undesirable effects may lead to treatment discontinuation and reduced quality of life in patients with glaucoma. Antiglaucoma medications usually contain benzalkonium chloride (BAK) as a preservative. Animal studies, in vitro studies and in vivo experiments have demonstrated various adverse effects of BAK. Clinical studies have also shown an increased incidence of adverse events with BAK and have demonstrated that the withdrawal of preservatives reduces these effects. Collectively, these data suggest that preservative-free antiglaucoma treatments have clinically relevant benefits for patients.

Abstract: Dry eye at high altitudes....

Jimminy crickets. These people are DRY. More than half of 40+year olds in Tibet are symptomatic and 25% have a Schirmer at or under 5.

Altitude, altitude, altitude. This is why when I get a phone call from an area code in Colorado or New Mexico, I know what I'm going to hear before the conversation starts.

Dry eye syndrome in elderly Tibetans at high altitude: a population-based study in China.
Lu P, Chen X, Liu X, Yu L, Kang Y, Xie Q, Ke L, Wei X.
Cornea. 2008 Jun;27(5):545-51.

PURPOSE: To determine the prevalence of dry eye syndrome, analyze the relationship between dry eye symptoms and signs, and identify associated risk factors for dry eye syndrome in an elderly Tibetan population at high altitude.

METHODS: A population-based survey was conducted from October 2006 to December 2006. A stratified, clustered, random sampling procedure was used to select 2632 native Tibetan people > or = 40 years of age. Symptoms of dry eye were assessed by using a 6-item validated questionnaire. Dry eye syndrome was diagnosed in those subjects having 1 or more symptoms often or all the time. Positive signs included a tear film breakup time of < or = 10 seconds in 1 or both eyes, a Schirmer test score of < or = 5 mm, or a fluorescein score of > or = 1. Correlations between symptoms and signs were analyzed.

RESULTS: Of a total of 2632 eligible subjects, 2229 (84.69%) were examined. The data of 1840 participants were analyzed. Of 1840 participants, 52.4% (95% confidence interval: 50.2-54.7) were symptomatic. The tear film breakup time of < or = 10 seconds was seen in 35.3% (95% confidence interval: 33.1-37.5), a Schirmer test score of < or = 5 mm was seen in 24.7% (95% confidence interval: 22.8-26.7), and a fluorescein score of > or = 1 was seen in 5.8% (95% confidence interval: 4.7-6.9). The correlations between dry eye symptoms and signs were statistically significant. Independent risk factors for dry eye syndrome were positive dry eye signs, increased age, low education level and socioeconomic status, and higher altitude.

CONCLUSIONS: This study shows a high prevalence rate of dry eye syndrome in elderly Tibetans, representing an important health problem.

Abstract: Do your eyes dry out between blinks?

To be honest I'm slightly puzzled as to why we need an "Index" to define this particular baby.

Seems like a sub 1.0 result is the equivalent of a cardiologist saying "Yes, indeed you have heart trouble" which, considering you went to his office complaining of chest pains, you probably already knew.

But hey, if having another number on the chart is helping in some way, fine.

The Ocular Protection Index.
Ousler GW 3rd, Hagberg KW, Schindelar M, Welch D, Abelson MB
Cornea. 2008 Jun;27(5):509-13

The interaction of the time between blinks, or the interblink interval (IBI), and tear film breakup time (TFBUT) helps to regulate the integrity of the ocular surface. A protected surface exists when the TFBUT matches or exceeds the IBI. In contrast, an unprotected surface exists when TFBUT is less than the IBI. This is clinically relevant because repeated intermittent exposure of a tear film-deficient cornea can lead to ocular discomfort and the development of clinical signs, such as keratitis and redness. The relationship between TFBUT and IBI has been quantified by the Ocular Protection Index (OPI), which is calculated by dividing TFBUT by IBI. If the OPI is <1.0, the patient has an exposed ocular surface, putting them at risk for the development of the signs and symptoms of dry eye, whereas if the OPI is >or=1.0, the patient's ocular surface is tear film protected. The OPI has proven to be useful in assessing the factors that may cause or exacerbate dry eye. This review discusses the development and use of the OPI model, its relationship to dry eye, and factors that are known to alter blink rate and tear film integrity.