Introduction
The concept of a protective eye bandage originated in the first-century ad when Celsus reportedly applied honey-soaked linen to the site of a pterygium removal to prevent symblepharon development ( ). The therapeutic use of contact lenses goes beyond visual improvement in irregular and distorted corneas or correction of refractive errors. The term ‘therapeutic contact lens’ has become synonymous, for many, with a soft plano ‘bandage’ lens; however, the therapeutic use of contact lenses is much more extensive.
Definitions
Recently, CLEAR proposed a clinical definition of therapeutic contact lenses, differentiating them from rehabilitative contact lenses. Both contact lens categories, therapeutic and rehabilitative, are considered medical contact lenses ( ):
Medical Contact Lenses are any type of contact lens that is worn for the primary purpose of treating an underlying disease state or complicated refractive status. Medical contact lenses may or may not correct refractive error. Medical contact lenses are prescribed for reasons other than the cosmetic purpose of eliminating the need for spectacles. There is no universally accepted definition for medical contact lenses, but some payers do set requirements as to condition or diagnosis (e.g., cornea ectasia, unilateral aphakia) or threshold value for refractive error (e.g. high myopia) before a coverage or reimbursement is granted. Requirements and definitions vary from nation to nation and by payer .
Medical contact lenses are subdivided into two different clinical categories:
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Therapeutic or Bandage Contact Lenses are contact lenses that are used for the treatment of ocular discomfort or to support the cornea during healing after surgery or when the cornea is being treated for an underlying disease state or to protect the cornea from the environment or mechanical interaction with the lids .
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Rehabilitative Contact Lenses are CLs that are prescribed for conditions that prevent a patient from achieving adequate visual function with spectacles because of high, irregular, or asymmetric refractive error .
Lens Types
It should be recalled that all types of contact lens have therapeutic uses.
Soft Hydrogel and Silicone Hydrogel Lenses
When considering the fitting of a bandage lens, it is necessary to define or predict its probable pattern of use. The relevant considerations are:
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whether extended wear is necessary,
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whether the patient (or, failing the patient, a relative or friend) can be taught to handle or at least to remove, the lens,
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the likely duration of therapeutic lens management,
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whether the patient lives within practical travelling distance of the clinic or hospital,
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whether the necessary topical medications are available nonpreserved and
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whether the risks of hypoxia, mechanical trauma and infection are outweighed by the perceived benefits of therapeutic lens wear.
In the past, clinics may have kept sets of bandage lenses – custom made from high-water-content materials – in various radii and diameters. These were superseded by commercially available frequent-replacement hydrogel lenses ( ), which in turn, have largely been replaced by lenses in silicone hydrogel materials.
Silicone hydrogel lenses have an important therapeutic role because of their very high gas permeability, which minimizes the induced hypoxic and hypercapnic stress ( ). Their relatively low water content is an advantage where hydration of the lens by the tear film is problematic, as occurs in aqueous tear deficiency. Soft bandage contact lenses have demonstrated positive results in managing dry eye in terms of comfort and visual acuity improvement since the 1970s ( ). Subsequent studies have confirmed these results. Comparison studies have been carried out between hydrogel and silicone hydrogel lenses in some therapeutic applications. For example, silicone hydrogel lenses have been shown to be a safe and effective alternative to conventional contact lenses for the treatment of bullous keratopathy ( ).
Silicone hydrogel lenses are widely used following photorefractive keratectomy and laser-assisted subepithelial keratomileusis (LASEK) ( Chapter 29 ). In one study, the corneal epithelial status was statistically better in the eyes with a silicone hydrogel bandage contact lens 5 days after surgery compared with when a hydrogel lens was worn ( ). Studies evaluating the relative performance of different silicone hydrogel lenses have shown little difference between them, except in terms of comfort ( ).
When fitting any soft lens, it is important for the lens to overlay all areas requiring cover and to aim for a minimal amount of movement on blinking. There must be no compression of the limbal vessels ( Fig. 28.1 ).
Corneal Lenses
Corneal lenses are frequently used for a combination of optical and therapeutic indications. Though they are usually smaller in diameter than the cornea, they may provide enough coverage to protect the cornea from abnormal lashes, keratinized lid margins and other hostile factors ( Fig. 28.2 ). Sometimes lenses of larger diameters are used ( Fig. 28.3 ).
Scleral Lenses
Scleral lenses have numerous therapeutic roles ( ). Their advantages include the following:
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there is no corneal contact whatsoever;
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any eye shape can be fitted;
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complete protection of the cornea and bulbar conjunctiva is provided;
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sealed fits are possible, using gas-permeable materials, which simplifies the fitting process and minimizes ‘settling’; and
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overnight wear is possible.
At one time, the fitting, and especially the ventilation, of scleral lenses required much practical experience. With the advent of gas-permeable scleral lenses, however, sealed fits have become the norm and less skill is required. So many rehabilitative and therapeutic indications have demonstrated that it can now be regarded as essential for specialist contact lens clinics to offer and fit scleral lenses (see Chapter 17 ).
Concurrent Medications
Nonpreserved unit-dose eye drops are indicated for concurrent use with soft and scleral lenses. Preserved eye drops are rarely used in this situation, because of concerns that preservatives such as benzalkonium chloride can accumulate in the soft lens or remain entrapped in the postscleral lens fluid reservoir and be toxic to the corneal epithelium. This effect is usually of no clinical importance when disposable lenses are used for short periods. Prescription medications, oily or viscous drops or ointment should not be used concurrently with contact lenses.
Scleral lenses may also be used as ocular drug delivery systems. It has been reported the use of nonpreserved antibiotics, anti-VEGF and stem cells with scleral lenses for ocular surface treatment ( ).
Indications
A contact lens may be fitted therapeutically for the relief of pain or discomfort or to assist in the healing of injured or diseased ocular tissue. Sometimes a therapeutic lens simultaneously addresses more than one clinical problem; it may additionally, be used to correct a refractive error and has the potential to deliver ophthalmic drugs to the ocular surface. The various indications for fitting therapeutic lenses are considered below.
Surgery
Soft bandage contact lenses increase comfort and enhance healing after penetrating keratoplasty, ptosis, pterygium, intracorneal ring segments and phacoemulsification (see Chapter 29 ).
Penetrating Keratoplasty
Bandage contact lenses are used after penetrating keratoplasty to promote re-epithelialization, prevent suture irritation and reduce irregularities in the wound margin ( ). Factors that influence the success of lens wear are the health status of donor and recipient corneas, surgical parameters and postoperative treatment ( ).
Ptosis
Soft bandage contact lenses are beneficial after ptosis surgery. have investigated the comfort of soft bandage contact lens wear after ptosis surgery. A soft contact lens was applied in only one eye; in the contralateral eye, no contact lens was applied. Patients reported significantly increased comfort in the eye where a contact lens was fitted. verified the efficacy of soft bandage contact lens wear in children after congenital blepharoptosis and found that patients wearing the lens experienced less ocular discomfort than the control group without contact lens use.
Pterygium
Studies on the use of a bandage contact lens after pterygium surgery are contradictory. Various studies have found that soft contact lens wear significantly reduced pain ( ) and enhanced epithelial healing ( ). In contrast to these findings, other studies did not find soft contact lens wear beneficial after pterygium surgery ( ). Interestingly, found worse pain levels in patients wearing contact lenses.
Intracorneal Ring Segments
Various reports described the successful use of soft bandage contact lenses after intracorneal ring segments for corneal recovery and comfort ( ).
Phacoemulsification
Bandage contact lenses may be used after cataract surgery to reduce symptoms of dry eye. Two different studies demonstrated significantly reduced dry eye symptoms in patients wearing soft contact lenses after phacoemulsification ( ).
Keratorefractive Procedures
Lens application has been shown to be important after keratorefractive procedures to attain optimal pain control and epithelial healing ( ) (see Chapter 29 ).
Photorefractive Keratectomy
found that after PRK, patients treated with two topical agents (anaesthetic and nonsteroidal antiinflammatory eye drops) and soft bandage contact lenses experienced less pain than patients treated only with topical agents, without bandage lenses. Soft bandage lenses are routinely used for 3–5 days for pain relief following refractive surgery procedures with epithelial removal ( ).
The results of studies comparing silicone hydrogel to hydrogel lenses after PRK are contradictory. Referring to the study by , a silicone hydrogel lens resulted in significantly faster corneal re-epithelialization and reduced patient discomfort compared to a hydrogel lens. did not find a difference in the rate of re-epithelialization. Although patients experienced a higher level of pain and greater prevalence of haze with the hydrogel lens, more infiltrates were observed with the silicone hydrogel lens ( ).
Laser-Assisted In Situ Keratomileusis
Soft bandage contact lenses may be used after laser-assisted in situ keratomileusis (LASIK) to reduce symptoms, promote wound healing and potentially prevent epithelial ingrowth. Therapeutic contact lenses, soft and scleral, are also beneficial to manage epithelial defects secondary to LASIK.
Two studies have evaluated the use of soft bandage contact lenses compared to no lens wear in patients who have undergone LASIK ( ). In the study by , contact lenses were removed one hour after the procedure in 29% of patients because of intolerance. The authors concluded that soft bandage lenses significantly reduced symptoms for up to four hours immediately after LASIK. Flap oedema and mucoid discharge at the lid margins were noted in overnight wear. In the prospective study by , patients experienced less pain and photophobia when wearing contact lenses compared to the control group without lens wear. However, when wearing contact lenses, patients complained of a foreign-body sensation. The authors also found that eyes wearing contact lenses had a less intense wound healing response at the flap margins compared to control eyes.
Studies evaluating the use of soft bandage contact lenses to prevent epithelial ingrowth are anecdotal. No difference was found in epithelial ingrowth in two retrospective studies ( ). Conversely, in a cohort study, only 3 eyes of 783 eyes who had undergone LASIK developed epithelial growth within the interface, with a minimum of 3 months of follow-up ( ). The authors of the latest study concluded that cleaning the stromal interface properly during surgery combined with a soft bandage contact lens may significantly reduce the incidence of epithelial growth within the interface.
Soft bandage contact lens use after LASIK may alter corneal topography in terms of asphericity and induce corneal oedema ( ). Asphericity changes were caused by soft contact lens mechanical pressure and corneal oedema.
Soft bandage contact lenses have been shown to be effective in managing complications after a LASIK procedure. Eyes with epithelial loosening ( ), epithelial defects ( ) and corneal flap dehiscence ( ) were effectively treated with therapeutic lenses.
Laser Epithelial Keratomileusis
evaluated a lotrafilcon A contact lens as a continuous wear bandage after LASEK, finding that it was effective and well-tolerated in patients undergoing this procedure. Two studies compared hydrogel and silicone hydrogel soft bandage contact lenses for continuous wear after LASEK. Silicone hydrogel was superior compared to hydrogel bandage contact lenses in both studies ( ). evaluated two generations of silicone hydrogel, Galyfilcon A and Balafilcon A, finding better comfort and deposit resistance on the lens surface with Galyfilcon A. The authors speculated that the score difference might be due to the mechanical characteristics of lens materials, modulus and thickness and deposit resistance. The tensile modulus of Balafilcon A is significantly greater than that of Galyfilcon A. Balafilcon A lenses are also thicker; this may have contributed to subjective lens discomfort, which was more significant in patients wearing Balafilcon A lenses. Deposit accumulation on Balafilcon A lenses may have contributed to blurred vision in the group wearing this lens material.
Phototherapeutic Keratectomy
Bandage contact lenses after phototherapeutic keratectomy (PTK) are beneficial. evaluated the use of soft bandage contact lenses after PTK in patients with recurrent corneal erosions secondary to bullous keratopathy. PTK with therapeutic soft contact lenses resulted in being an effective treatment with a reduced recurrence rate. investigated the efficacy of PTK and soft bandage contact lenses in children with dense superficial corneal opacities at risk for developing amblyopia. The treatment with PTK and therapeutic lenses, along with topical antibiotics, steroids and artificial tears, was successful. Best-corrected visual acuity was improved in four of five eyes.
Corneal Collagen Crosslinking
Soft bandage lenses are usually used in corneal collagen crosslinking (CXL) where the epithelium is removed (epi-off) to mitigate and promote re-epithelialization and reduce pain ( ). Two different contact lenses were investigated (Balafilcon A and hioxifilcon A), comparing their impact on corneal recovery and symptoms after CXL. Both lens materials allowed the epithelium to complete healing by day 3 with no significant difference in symptoms ( ).
Leakage Following Trauma or Surgery
A small aqueous leak following surgery ( Fig. 28.4 ) or trauma ( Fig. 28.5 ) can often be sealed with such a lens; if the anterior chamber is shallow or absent, then a slightly flat lens will be needed; this will have to be changed for a steeper lens as the chamber reforms and the cornea steepens.
Trabeculectomy
Bleb leaks following trabeculectomy may frequently occur in up to 56% of patients ( ). evaluated the safety and efficacy of soft bandage lenses after trabeculectomy. At 1-year follow-up, the rate of success in maintaining optimal intraocular pressure was higher in patients wearing contact lenses.
For optimal results, the contact lens should cover the superior conjunctiva with a minimum of two to three millimetres exceeding the limbus ( ). Contact lens diameter is also related to the corneal diameter, which may vary depending on race ( ). have successfully used a custom-made 17.5-mm diameter 78% water content bandage lens to arrest leakage from trabeculectomy filtration blebs. In a study by , lenses successfully fitted had a 20.5-mm diameter.
Wound Leaks
Corneal transplant complications such as loose sutures or slippage of the donor disc are usually best dealt with further surgery, for example, suture removal and/or resuturing. In such situations, contact lenses may be used to seal wound leaks. However, they are unlikely to have more than a temporary role (e.g. the relief of discomfort while arrangements are made for surgical intervention).
Sjögren Disease
Ocular surface disease (OSD) in Sjögren disease is a product of lacrimal functional unit dysfunction ( ). Ocular symptoms in patients with Sjögren disease include dryness, foreign-body sensation (which is constant and can affect their quality of life), photophobia, pain, stinging, burning, itch, epiphora and blurring or interrupted vision ( ). TFOS DEWS II proposed a management algorithm based on a sequence of four steps for the treatment of dry eye disease ( ). The more severe the condition, the more likely it is to jump to the next level, with the possibility to maintain the previous therapy. Tertiary treatment includes autologous/allogeneic serum eye drops and therapeutic contact lenses, including soft bandage contact lenses and scleral lenses.
examined the efficacy of silicone hydrogel and autologous serum eye drops and found that contact lenses were more effective in improving visual acuity, Ocular Surface Disease Index (OSDI) scores and corneal staining. However, soft contact lens wear in Sjögren syndrome may provoke adverse events, including microbial keratitis ( ).
Multiple studies have shown the efficacy of scleral lens use in managing ocular manifestations in Sjögren syndrome. The presence of a liquid reservoir between the lens and the ocular surface allows continuous hydration during lens wear, and the large lens diameter covers and protects an extensive area of the underlying ocular surface. The area not covered by a scleral lens may exhibit staining ( Fig. 28.6 ).
A study evaluated the impact of scleral lenses (16.00–17.50 mm) on dry eye and quality of life in 41 eyes, majorly with Stevens–Johnson syndrome (SJS) (53.7%) and Sjögren syndrome (26.8%) ( ). All patients reported improvement in visual acuity, dry eye symptoms, photophobia, foreign-body sensation and comfort. The mean amount of time of scleral lens wear was about 12 hours per day. Additionally, a significant decrease in tear osmolarity and staining were respectively observed at 6 and 12 months of scleral lens wear. The authors also reported enhanced quality of life of patients wearing scleral lenses.
A study compared lens comfort and dry eye symptoms of scleral lens wearers with dry eye fit with Tangible Hydra-PEG treated and untreated scleral lenses ( ). Tangible Hydra-PEG is a novel surface treatment comprised of a 90% water PEG-based polymer mixture that is permanently bonded to the surface of the contact lens made from the lubricant polyethylene glycol. PEG surface-treated scleral lenses provided improved comfort, reduced dry eye symptoms and reduced ocular surface compromise compared with untreated scleral lenses for those with dry eye.
Irradiation
illustrated overnight wear of scleral lenses in managing postradiotherapy keratopathy and lid scarring with trichiasis in a monocular patient. Initially, the patient was treated with lubricants, which failed to maintain comfort. A botulinum toxin-induced ptosis was used to ameliorate the ocular surface; this was not practicable since the eye treated was the only viable eye. Scleral lens wear showed optimal results regarding corneal protection from trichiasis, corneal hydration, visual clarity and comfort.
Chemical Injuries
Much has been written about the use of contact lenses in the management of chemical injuries, especially alkali burns ( Fig. 28.7 ). However, research into the role of the limbal stem cell origin of the corneal epithelium has shown that contact lens coverage of a chronic epithelial defect cannot prevent the colonization of the cornea by conjunctivally derived epithelial cells. There are, however, some situations in which a contact lens can assist healing, supported by topical medications, although very close supervision is required.
Tear Deficiency
Tear deficiency is usually managed using tear supplement drops and lubricating ointments, and sometimes the lacrimal puncta or canaliculi are deliberately blocked. Soft contact lenses are used less often. At one time it was thought that a high-water-content hydrogel lens could help to rehydrate a dry eye, but this is not possible as the lack of tears causes such a lens to dry and fall out of the eye. Silicone hydrogel (low-water-content) lenses are generally more successful in an abnormally dry ocular environment. The lens of choice is often a scleral lens, which covers the entire exposed surface of the eye, maintains a postscleral lens fluid reservoir and limits the evaporation of tears from the ocular surface.
Corneal Degenerations and Dystrophies
Corneal Dystrophies Involving the Epithelium
Epithelial basement membrane dystrophy is by far the most common epithelial dystrophy, but other dystrophies involving the corneal epithelium also cause pain or discomfort that can be relieved with soft lenses. They include Reis–Bücklers’ dystrophy, Meesman’s dystrophy, lattice dystrophy and Fuchs’ dystrophy. In Fuchs’ dystrophy, the failing corneal endothelium cannot prevent stromal oedema and bullous change in the epithelium ( ). Thygeson’s superficial punctate keratopathy is not recognized as a dystrophy but is appropriately considered here; this condition can sometimes be managed successfully with hydrogel lenses ( ), although a weak topical steroid is a more usual form of management. summarized the current knowledge for each corneal dystrophy and provided the methods and rationale for contact lens management. Patients with corneal dystrophies may benefit from the use of scleral lenses ( ).
Corneal Degenerations Involving the Epithelium
Conditions such as Salzmann’s nodular degeneration, rosacea keratopathy and atopic keratoconjunctivitis – with or without ectasia – can sometimes be so uncomfortable that a therapeutic contact lens is indicated. In such cases, a lens will probably also improve visual potential. Concurrent conjunctival disease and tear abnormality may benefit from the use of a scleral lens ( Fig. 28.8 ).
Corneal Degenerations Involving the Endothelium
Corneal trauma or surgery that has depleted endothelial functional reserves can lead to epithelial bullous keratopathy, the discomfort of which is often amenable to management with hydrogel or silicone hydrogel lenses. In some cases, a corneal transplant will subsequently provide a cure. Formerly this meant a full-thickness procedure, but recently a method of replacing the endothelium, Descemet’s stripping endothelial keratoplasty has been described and is gaining acceptance. A combination of PTK and therapeutic contact lens wear for a limited period has been proposed in cases of bullous keratopathy not suitable for corneal transplantation ( ).
Recurrent Erosion Syndrome
Corneal epithelial pain can be severe and disabling. A simple corneal abrasion usually heals quickly and needs no help from the clinician, but a persistent or recurrent epithelial failure may benefit from fitting a therapeutic lens, either soft or scleral, which acts as a mechanical barrier between the injured corneal surface and the lid.
The recurrent corneal erosion syndrome is a common condition involving the corneal epithelium and the epithelial basement membrane. Recurrent erosion syndrome is characterized by the repeated breakdown of epithelium and may cause moderate-to-severe pain, photophobia, lacrimation and corneal scarring compromising vision. Minor trauma to the cornea may predispose to this condition. Very often, corneal epithelial basement membrane dystrophy (such as Cogan’s microcystic dystrophy or map-dot-fingerprint dystrophy) is found to be present; this is a bilateral condition, so both eyes should always be carefully examined. The eye with the erosion often becomes acutely painful when the eyes are opened during the night or when waking, for at that time, tear production is minimal and friction maximal, so the lid margin pulls on the unstable patch of the epithelium, sometimes causing epithelial disruption. A contact lens interposed between the cornea and lid can reduce friction ( ). Anterior stromal puncture is a low-cost alternative; however, it carries the risk of corneal perforation.
Soft bandage contact lenses are usually used to alleviate pain and favour re-epithelialization. Three months of extended-wear bandage lens may be sufficient to avoid the recurrence of corneal erosions in the majority of cases ( ).
Recurrent erosion may also heal with scleral lenses. The use of scleral lenses in the management of recurrent corneal erosions associated with lattice and Avellino dystrophy ( ), anterior basement membrane dystrophy ( ) and Salzmann’s nodular degeneration ( ) has been described. If necessary, scleral lenses may be fitted in an overnight regimen.
Persistent Epithelial Defect
Corneal epithelial defects are considered persistent when there is a failure of the treatment to obtain corneal epithelialization within 2 weeks ( ). If not appropriately managed, persistent epithelial defect (PED) may lead to ulceration or scarring ( ). Therapeutic contact lenses help protect the corneal surface from mechanical trauma from the eyelids and promote epithelial healing.
Soft bandage contact lenses are considered standard therapy and are used in a conservative management protocol in combination with lubrication, punctal occlusion and epithelial debridement ( ). investigated the safety and efficacy of lotrafilcon A lenses for therapeutic purposes in different OSDs, including four eyes with PED. The lenses were used in a continuous wear regimen from 3 to 12 months. The authors found that more months of wear was especially advantageous as it decreased epithelial trauma, pain and infection risk associated with more frequent replacement of the lenses. demonstrated that combining silicone hydrogel lenses with serum eye drops may be effective in treating intractable PEDs.
Although soft bandage contact lenses are mostly used for the treatment of PED, several studies reported successful use of scleral lenses, even in cases that have failed with previous treatment ( ). showed a successful re-epithelization but outlined microbial keratitis development in 29% of eyes (four eyes). All the later studies reported a complete re-epithelialization in most eyes with no adverse events ( ). Of interest, the study by demonstrated successful treatment in all patients who had failed to heal wearing a silicone hydrogel bandage contact lens.
Amniotic Membranes
Various reports showed the efficacy of amniotic membranes to treat severe corneal epithelial defects, using soft bandage contact lenses as part of the treatment approach ( ). Soft bandage contact lenses were shown to be successful in 25% of patients maintaining membrane position ( ). investigated the use of amniotic membranes for several ocular surface problems including PEDs, limbal stem cell deficiency, conjunctival reconstruction, bullous keratopathy and chemical/thermal injuries, finding that the operative technique least associated with failure was the use of bandage contact lens at the end of the procedure; the necessity of a therapeutic contact lens after the initial postoperative period was highly associated with failure.
Graft-Versus-Host Disease
Graft-versus-host disease (GvHD) has several ocular implications including keratoconjunctivitis sicca, chronic blepharitis, meibomian gland atrophy and dysfunction, superior limbic keratoconjunctivitis, lid fibrosis and atrophy with keratinization, which may result in entropion and ectropion. In acute GvHD, chemosis, oedema and pseudo-membrane formation may occur ( ). The corneal epithelium is affected by the disease and may provoke punctate erosions, filamentary keratitis and epithelial defects. Several reports on the use of therapeutic contact lenses in GvHD were found in the literature, which is often combined with other treatments, including preservative-free artificial tears, autologous serum tears, punctual plugs, topical cyclosporine, topical steroids, topical tacrolimus, lid hygiene, hot compresses, intense pulse light therapy, oral tetracyclines and moisture chamber goggles ( ).
Two reports examined continuous wear of silicone hydrogel lenses in patients with moderate-to-severe dry eye from GvHD and found improved visual acuity and symptoms ( ). Soft bandage contact lenses also ameliorated subjective dry eye symptoms in patients with superior limbic keratoconjunctivitis secondary to GVHD ( ).
Several studies have reported the use of scleral lenses in patients with GvHD ( ) ( Fig. 28.9 ). were the first to report positive outcomes of gas-permeable scleral lenses fitted in GVHD to principally decrease pain and photophobia. The authors also reported improvement in comfort and vision, confirmed by later studies ( ). In addition to these benefits, found improvement in OSDI scores. The highest improvement level for quality of life was reported by more than two-thirds (73%) of patients with GvHD ( ).
Limbal Stem Cell Deficiency
The role of limbal stem cells is to maintain corneal epithelial integrity and act as a barrier to prevent conjunctival epithelial cells from migrating onto the corneal surface. Limbal stem cells reside in the palisades of Vogt, in the area of the corneo-scleral junction. If this cell population is absent or impaired, the corneal epithelium is not sufficiently renewed or repaired. Neovascularization occurs due to conjunctival epithelial cells that migrate onto the surface of the cornea ( Fig. 28.10 ). Subsequent corneal scarring or inflammation may cause loss of vision.
