Periocular Skin
Ophthalmic Management of the Periocular Skin Leads to Better Patient Care
Why you need to know skin anatomy.
By Peter T. Pugliese, M.D., Reading, Pa. and Richard E. Castillo, D.O., O.D., Tulsa, Okla

The eyes are the most dynamic and complex surface structures of the body. We often forget that they consist of three components: the globes, the bony orbits and the periocular skin and its appendages (see illustration). Comprehensive eye care involves addressing the needs of all three components, of course, but here we'll focus on care of the periocular skin, which significantly contributes to the health and function of the eye and influences a patient's ability to see.

Never trivialize the importance of this skin to eye health; not only is it different from any other skin, but its influence is far greater than you perhaps realize. Here's what you and your patients need to know.

WHAT IT DOES AND WHY IT'S IMPORTANT

Aside from protecting the globe from the external environment, the periocular skin also acts as a barrier against evaporative tear loss. Eyelids are part of the lacrimal system, which distributes, drains and replenishes the precorneal tear film layer that's vital to both the physiology and optical properties of the cornea.

The delicate lid margins contain glandular elements vital to tear film composition. And finally, the bulbar face of the eyelids comprises the palpebral conjunctivas, which play a pivotal role in tear film physiology and in guarding against eye disease.

Never underestimate the importance of this relationship between the periocular skin and the eye. The eyelids are in direct contact with the eye some 15,000 times per day! Eyelid problems are involved in most infectious and inflammatory conditions of the adnexa and ocular surface, such as meibomian gland dysfunction, blepharitis, blepharoconjunctivitis, dry eye syndrome, peripheral corneal derangements and rosacea. It's therefore critical that you ensure that periocular skin is not only clean, but also healthy.

To best know how to do this, you need to understand the anatomy and physiology of normal skin. Along the way, you'll discover how periocular skin differs from other skin and why it should be an integral part of eye care. (See table below for more detail.)

ANATOMY OF THE SKIN

The skin is the largest organ of the body. It weighs slightly more than 3 kg (6.6 pounds) and covers nearly 2 square meters of area. It measures between 1.5-mm and
4-mm thick on average. It's thickest on the back and soles of the feet (4 mm). The scalp, forehead and wrist skin all measure less than 2 mm. The thinnest and most complex skin is the periocular skin (about .075 mm, or 75 µ).

Skin is dynamic; it constantly renews itself. It's also mosaic, meaning that the cells don't always grow at the same rate. Its primary functions are protection, sensory perception and as a guard against the passage of water, chemicals and microbes.

The skin has two surfaces -- an external surface (the epidermis) and an internal surface (the dermis).

THE EPIDERMIS

The epidermis is the keratinized outer skin layer. This tiny layer is our eyes' only real protection against the whole environmental world. (See figure)

Though it's thinner than the paper of this page, the epidermis is composed of four layers of cells. These include:

• The stratum corneum. The outer layer of the epidermis is called the stratum corneum and is composed of flat, hard and mostly "dried" cells. These cells are renewed every day.
  Within a 2-week period, all of the body's stratum corneum cells may have been entirely replaced by new cells. This "disposal" system allows the removal of waste products and toxins, which have accumulated in the corneocytes, from the body. The periocular epidermis and stratum corneum are replaced even faster (in 5 to 7 days), which is why it's so important to clean the skin regularly. Old skin flakes can be loaded with microbes and environmental toxins and can easily initiate or exacerbate infectious eye conditions if they fall into the eye.
  The stratum corneum of the eyelid contains fewer layers of cells than any other area of the body (10 or less, as opposed to 50 or more elsewhere), making each individual layer critically important.
  The inner three layers of the epidermis are the changing or differentiating layers from which various types of cells arise. Starting at the innermost layer, they are the basal layer, the spiny layer and the granular layer.
• The basal layer. This contains the living cells. They divide and differentiate to produce other layers of cells. This layer is firmly anchored to the layer beneath it by many fibrous bands.
  Four main types of skin cells exist: keratinocytes, melanocytes, Langerhans' cells and fibroblasts. The melanocytes control skin color and protect against sun damage. The Langerhans' cells are a key part of the cellular immune system. Fibroblasts synthesize critical proteins. For our purposes, the keratinocyte is most important.
  We believe that the state of the keratinocyte and its proteins indicate the skin's health. Keratinocytes originate in the basal layer and are full of moisture from the bloodstream. As they move upward, they flatten and dry out to help form the barrier layer and the stratum corneum. They also manufacture a protein called keratin (see the illustration ). About 90% to 95% of epidermal cells are keratinocytes.
• The spiny layer. The name "spiny" comes from the little bridge-like hairs that join the cells in this layer. These are the desmosomes, which are complex attachment sites between cells.
  As the cells move upward, these attachments diminish until they disappear at the stratum corneum. This allows cells to flake off and be washed away.
• The granular layer. This layer is composed mostly of keratin fiber cells and many lamellar bodies. The lamellar bodies are key structures in the skin, for they're the origin of the lipid barrier of the stratum corne-um. They measure 0.2 µ to 0.3 µ in diameter. This lipid barrier plays a critical role in the body's defense against the outside world, so it's very important. (See the figure)
  Lipids are water-insoluble compounds. The important forms are phospholipids and cholesterol (both are important in the constitution of cell membranes, the latter particularly in the stratum corneum) and also glycolipids.

Peter Elias, M.D., has shown that the intercellular space in the stratum corneum is the key to barrier function. He pictures the stratum corneum as bricks (the corneocytes) and mortar (the lipid-containing intercellular spaces).

Lamellar bodies fuse together with the plasma membrane and secrete their contents into the intercellular space. The intercellular space then expands until it comprises 10% to 40% of the total volume of the stratum corneum.

Dr. Elias also noted that the ability of the skin to resist permeation isn't related to the thickness of the skin, but rather to the amount of lipids present in it.

It's important to realize that "permeation" doesn't refer to water, but to pathogens and organic and industrial oil-soluble pollutants. The eyelids are ten times more permeable than other body areas. It's not only that they're thinner, but that the lipid content is much lower than in other body areas. Ophthalmic management of the periocular skin is therefore critical.

THE EPIDERMAL APPENDAGES

You need to know about three types of appendages. They are the hair follicles, the sebaceous glands and the sweat glands.

• The hair follicles. Hair growth is controlled by the dermal hair papillae at the bulbous base of the cylindrical hair follicle. During the active growth phase, melanocytes combine with hair matrix cells to produce the hair follicle.
  These histologic features are also common to the eyelashes, the fine vellus hairs and the eyebrow terminal hairs.
  The hair follicle is also called the "pilosebaceous apparatus," for each hair follicle consists of a system. Each hair begins as a bud or peg, and grows by division of cells from the hair bulb located in the dermis. Only the lower growing end is alive; the rest of the hair is a compact mass of keratin cells.
• The sebaceous glands. These glands are widely distributed over the body. Every hair is associated with a sebaceous gland, but not all sebaceous glands are associated with hair follicles. When they are, they're called sebaceous follicles.
  Many sebaceous glands exist on the body. You'd find about 100 of them per square centimeter on most areas of the body, but on the face and scalp you'd find as many as 400 to 900 per sq. cm.
  At the eyelid margin, the unilobar sebaceous glands, which serve the lashes, are known as the glands of Zeis (see the figure). The sebaceous glands produce an oily secretion. The oily products are expressed through the excretory ducts of the sebaceous lobule into the mid-portion of the hair follicle. If eye lashes and eyebrows aren't kept clean, conditions such as folluculitis can result if the sebaceous gland becomes infected, leading to abscesses and styes.
  Deep within the tarsus of the eyelid is a second network of sebaceous glands, the meibomian glands. Instead of nurturing the lashes, the ducts of the meibomian glands open directly at the skin surface so that the oily secretions lubricate the lids and form a part of the external or "oily" layer of the tear film, which retards evaporation. There are 20 to 30 meibomian glands in the upper plate and 15 to 20 in the lower plate. With age, their number and productivity diminish.
  Given the importance of these glands to patient comfort and the degree to which they're involved in infectious and inflammatory conditions, they must remain healthy. Insist that your patients cleanse their faces and their eyelids daily.
• The sweat glands. The eyelid skin contains many sweat glands. You should know of two distinct types.

  1. At the eyelid margin, the glands of Moll release apocrine secretions into the lash follicles above the sebaceous duct.
  2. Beyond the eyelid margin, the remainder of the eyelid skin relies on eccrine sweat glands, which are situated in the slender dermis.

These sweat glands help regulate body temperature and create perspiration. The heat that's required to change water from a liquid to a gas or vapor is taken from the body and used up in conversion. As a result, the body cools down as the sweat evaporates from the skin.
Sweat is composed mainly of water (99%) and minute amounts of dissolved substances including sodium chloride, urea, sulfates and phosphates. Sweat glands tend to become plugged. Every time a gland furnishes an opportunity to form an accumulation of secretion, it creates a ready, warm and moist environment for pathogens to fester.

• Other appendages. In the upper eyelid, in addition to the sebaceous and sweat glands are the glands of Krause, which are accessory lacrimal glands. Other small accessory glands, the tarsal lacrimal glands (of Wolfring), can be found in the connective tissue above the tarsal plate. All these glands and appendages underscore the complexity and importance to vision of the ultra-thin periocular skin. (See the illustration)
  The epidermis is joined to the dermis by an undulating membrane, or papilla, which forms ridges and grooves. In typical skin, these ridges help to anchor the epidermis to the dermis, particularly in areas of friction such as the soles and palms. In the skin of the eyelid, however, there aren't any ridges where the epidermis joins the dermis, although they reappear at the eyelid margins, helping to make the overall periocular skin most fragile.

THE DERMIS

The dermis is a tough but resilient structure that allows the skin to move, absorb shocks, and cool and warm the body. It also permits the passage of nutrients to the epidermis.

The dermis is composed of loose connective tissue bound with ground substance. Within it are nerves, lymphatics, blood vessels and the organs of the glands and hairs. The dermis of the periocular skin is less than 2-mm thick.

Ordinarily, the dermis lies between the epidermis and the subcutaneous fat layer, but in the eyelid, it lies between the epidermis and the orbicularis muscle. In fact, the eyelid is the place in the body site where striated muscle most closely approaches the skin surface. Without the cushion of subcutaneous fat, the periocular skin is more easily traumatized.

• Components of the dermis. The connective tissue consists of three types of fibers: collagen, elastin and reticulin. Each of these is chemically distinct from the other and has separate physical properties and functions.
  • Collagen is made of complex protein fibers arranged in long chains. It's tough and doesn't stretch easily. Collagen makes up 10% to 30% of the wet weight of the dermis. It gives the body structure and holds it together. If damaged by sun exposure, smoking, stress or soap, it causes the skin to droop.
  • Elastin is made of a material that's chemically different from collagen. Only about 1% to 3% of the dermis is elastin, but it's vital because it gives resilience to our skin so it snaps back when stretched. Like damaged collagen, damaged elastin causes flabby skin.
  • Reticulin, a type of collagen, is made of a fine network of cells, certain structures within cells or of connective tissue fibers between cells. It appears mainly in the papillary dermis.

HOW THE SKIN MAINTAINS ITSELF

After accommodating the critical appendages, the skin's other main function is to provide a protective barrier. Therefore, it's supple, yet strong and elastic. Also, it has the ability to repair itself when damaged by soap, sunlight or other environmental agents.

As we've seen, it takes about 30 days for skin to grow from the basal layer to the stratum corneum, except for periocular skin, where the growth period is much shorter.

The stratum corneum is constantly being lost to the environment, at the rate of about one layer per day. The rate of skin renewal depends on factors like the thickness of the skin, its location (the further from the heart, the slower it grows) and the person's age. There's even a growth variation between day and night.

The skin is most active at night. Therefore, patients should always clean the skin and apply treatment products twice a day, but especially at night.

OPTIMUM SKIN

Skin as unique, fragile and sensitive as periocular skin needs to be kept clean and healthy. Here are some guidelines to follow.

• Soft skin is healthy. Keeping the top layer of skin (the stratum corneum of the epidermis) supple is a key factor in skin health.
  Cracked skin is not only unattractive, but dangerous as well. Broken skin directly increases the risk of infections by allowing pathogens to enter all the way into the epidermis and beyond. (Consider a dry leaf: It will crack more easily than a moist leaf will.)
  When skin is damaged, holes are created in it. Thick skin has "reserve layers" that can endure this event, but the periocular skin allows much less room for error. Even a little dry skin here can prove to have dramatic consequences.
  Therefore, the body takes great pains to keep the top layer of skin intact. As in the military, once the perimeter is broken, all else is at risk. To prevent cracking, this skin must never be dehydrated.
  Therefore, moisturization is a critical step toward having healthy skin. Recall how soft and supple your elbows, knees, callouses and even fingernails look and feel when you've taken a bath or shower. Why? The water has plasticized, or softened, the protein in the skin.
  It's important to realize, however, that surface water will evaporate quickly and isn't materially effective in hydrating the skin.
• Surface water isn't enough to moisturize the skin for long. This is because water doesn't penetrate the skin in any great quantity due to the lipid barrier in the stratum corneum.
  Our skin needs only a little outside water to temporarily soften the protein that helps form the skin barrier. It's the surface barrier within the stratum corneum that helps keep within the skin the moisture that's "risen" upward from the bloodstream as part of the journey of the keratocyte.
  Key to moisturizing the skin, therefore, is optimizing the body's own barrier function.
• Many skin creams are useless. They give a temporary effect only. You need to recommend one with molecule-hydrating properties that stimulate the barrier layer.
• Drink lots of water! Each day, depending on the temperature and relative humidity, we lose about a half pint or more of our bodies' water. This normal water loss goes through the skin, where it binds to protein and makes it soft. But if the body becomes dehydrated, there's less moisture coming from the bloodstream. As in a spiral effect, less moisture results in a deficient barrier layer that can't hold any moisture, accelerating dehydration of the skin. Fluid intake is thus key to soft skin. This is why it's important to drink at least 6 to 8 glasses of water each day.
  Our bodies' water loss is usually fairly steady and even, except in low-humidity environments, which cause the water loss to increase.

  	The eyelid and its appendages. In direct contact with the eye some 15,000 times per day, this and other parts of the periocular skin significantly contribute to the normal physiology and function of the ocular surface and to visual function.

• Some soaps, shampoos and lid scrubs contribute to poor skin condition. You were probably taught that baby shampoo is safe to use. However, doctors too often generalize and believe any shampoo is safe and their patients risk burning their periocular skin and eyes. And even baby shampoo can disturb the stratum corneum.
  Soap is used to emulsify fat. Used on the face, it emulsifies the critical lipid barrier of the skin just as it emulsifies the grease in a frying pan. As we've seen, the periocular skin already has the lowest lipid content of any skin on the body. Once you break this barrier by emulsification, you let moisture out and bacteria in.
  Excessively using soap or the wrong type of any cleanser are the major causes of sensitive skin. The building blocks of proteins are amino acids, which are very sensitive to changes in pH (pH is a measure of hydrogen ion activity; the H stands for hydrogen).
  The pH values range from 1 to 14, with pH 7 being neutral. Above pH 7, alkalinity increases; below it, acidity increases. Each full unit of pH changes the acid content up or down by 10 fold.
  The pH of the outermost layer of the skin is 5.5. The reason it's acidic is that it represents the first line of defense against bacteria, which don't thrive in an acid pH.
  Most soaps and lid scrubs have a pH of 7.5 to 9, which isn't three times less acid but 1,000 to 10,000 more alkaline! Each time you wash your face or eyelids with a high-pH cleanser, you raise the pH, and your skin must bring it down again to the normal acid range.
  The reason such cleansers make the skin feel tight and dry is that they denature skin proteins by changing the pH. This is also called "stripping the skin." The stratum corneum, with its critical barrier layer, dries out, breaking the perimeter of defense and leading to greater risk of infections. Also, skin flakes are created that may enter into the tear film and cause infection.
• Carefully cleanse your skin every day. Daily cleansing is necessary because the periocular skin forms new layers faster than other skin and you want to avoid accumulation of skin flakes in a place where infections may fester. After all, there's often already debris on a patient's face from smoke, mascaras, dirt and dust. But tell patients to wash carefully, for as we've discussed, the periorbital skin is the thinnest and most permeable skin of the body. Avoid damaging it with emulsifying soaps.
  Once the skin is cleansed daily with a pH-sensitive cleanser, it's important to hydrate it to prevent cracking. A good moisturizer applied to the surface will slow the natural daily water loss, allowing more fluid to remain in the stratum corneum. Such a moisturizer will actually soften the skin, not wet it. As mentioned, it's most effective to apply moisturizers at night.
  Periocular skin is in constant motion. Not only do we blink 15,000 times per day with each eye, but we also wink, smile, squint and more. The key to the healthiest periocular skin is to optimize the structure that lies beneath the epidermis. You can have your patients do this by treating its key components (collagen and elastin, which give the skin its major support) or by stimulating their bodies' own rejuvenation system.

An effective skin care product must do the following:

• correct the underlying damage
• reduce the speed at which this damage occurs
• provide a means of helping the body restore the skin to normal by using its own repair systems.

WIDE RANGE OF BENEFITS

As you can see, your patients' health will benefit substantially from proper care of the periocular skin. Furthermore, skin that's well cared for has better density and elasticity. Patients will look younger as well as more vibrant.

Most patients not only like to see better, but look better. It's well documented that when we feel better, our body's composition and chemistry are different, healthier. So periocular skin care can potentially improve your patients' health on a very wide front! 

Peter T. Pugliese, M.D., has an international reputation as one of the world's most respected authorities in skin care research. Dr. Pugliese has more than 100 publications to his credit, has been the recipient of numerous prestigious awards and has speaking engagements from Paris to Tokyo. Dr. Pugliese holds seven patents. Many of his discoveries have influenced the decisions of leading cosmetic and pharmaceutical companies world wide.

Richard E. Castillo, D.O., O.D., is an associate clinical professor of ophthalmology at Northeastern State University College of Optometry, Okla. As medical director of a private eye and laser center in Tulsa, Dr. Castillo has more than 12 years of practical experience in the medical management of eye disease and oculoplastics , as well as anterior segment surgery, refractive procedures and laser surgery. Dr. Castillo has been a sought-after speaker at various continuing education programs nationwi