Common problems

A 2010 study of 144,799 device-associated visits of children to emergency departments showed contact lenses to be the number 1 cause of adverse events (23%). Corneal abrasions, conjunctivitis, and hemorrhage were most frequent.

1.Corneal abrasions and edema are highlighted when fluorescein dye is placed in the eye and illuminated with the cobalt blue light. Areas of lost or damaged corneal epithelial cells take up the dye and appear brighter (Fig. 2.36).

2.The upper palpebral conjunctiva is the area most often irritated by contact lenses. Called papillary conjunctivitis (Fig. 2.37), it is often due to contact lens deposits, especially in allergic individuals. it responds well to more frequent replacements.

3.The bulbar conjunctiva surrounding the cornea reddens when the cornea is being compromised as with tight-fitting lenses. (Fig. 2.38).

4.Infected corneal ulcers (Figs 6.21 and 6.22) are the most serious complication and most threatening to vision.

Refractive surgery

The refractive power of the eye may be altered by surgically reshaping the cornea, thereby eliminating the need for distance correction (Fig. 2.39).

Fig. 2.36 Fluorescein staining of the cornea.

Fig. 2.37 Papillary conjunctivitis with characteristic whitish elevations of conjunctiva.

Fig. 2.38 Limbal injection from a tight-fitting lens.

Refractive surgery began twenty-five years ago in Russia with the radial keratotomy technique (Fig. 2.40). In this procedure, the cornea is flattened with 4–8 radial incisions through 90% of the corneal depth. It has lost popularity due to slow healing, the inability to accurately predict the amount of correction, variable vision throughout the day, glare, halos, infection, and corneal perforation with secondary cataract formation.

Three newer procedures, 1. LASIK, 2. PRK, and 3. epi-LASIK correct myopia, hyperopia, and astigmatism utilizing an excimer laser to remove corneal stroma. In order for the laser to effectively reach the stroma, the corneal epithelium must be gotten out of the way. These three techniques vary in the way this is done.

1. Laser in situ keratomileusis (LASIK— Figs 2.41–2.47) is the most frequently performed elective surgery done in the world with. Many millions have been done since its introduction in 1990. A flap of epithelium, Bowman’s membrane, and stroma is created with a blade or femtosecond laser. Then a different laser called an excimer is used to ablate the underlying stromal bed.

Fig. 2.43 Superficial corneal flap created with microkeratome. Courtesy of Chris Barry, Med Sci, J. Ophthal. Photography 1999, Vol 22, No. 1A.

Fig. 2.40 Rare instance of traumatic rupture of radial keratotomy wound. Courtesy of Leo Bores.

Excimer laser beam

Fig. 2.41 LASIK—Flap of epithelium, Bowman’s membrane, and stroma is created with blade or laser. Then, an excimer laser ablates the stroma.

Fig. 2.42 Sculpted cornea after LASIK with remaining Bowman’s membrane.

Fig. 2.44 LASIK surgery showing flap being lifted with spatula and laser beam on central cornea ablating stroma. Courtesy of Summit Technology, Inc.

A disadvantage of LASIK is a resulting decrease in ocular rigidity. This is due to loss of ablated stromal bed and decreased effectiveness of stroma remaining in the flap since it never completely heals. To minimize the loss of effective stroma, the goal has been to make the thinnest possible flap. Up to six years later, the flap can still be lifted with a forceps (2.46). In eyes with over 8 diopters of myopia that require a lot of stromal ablation, this combined thinning becomes excessive and could result in an ectasia (bulging) of the cornea. Rarely, it may necessitate a corneal transplant.

Because LASIK damages more corneal stroma due to the flap, there is more loss of nerve fibers and a consequential increase in dry eye complaints. Another flap complication is that corneal epithelial cells may grow under the flap and might have to be removed (Fig. 2.47). This occurs in about 1% of primary surgeries, but in up to 23% of cases when the flap has to be lifted for a second LASIK procedure to treat residual refractive error.

2.An alternative to LASIK is photorefractive keratectomy (PRK—Figs 2.48 and 2.49). It avoids creating a flap by mechanically creating a central corneal abrasion. The advantage is it leaves more functioning stroma. The disadvantage is pain from abrasion and slower return of vision.

3.The newest technique, called epi-LASIK (Fig. 2.50) creates an epithelial flap that includes no stroma.

Fig. 2.45 Excimer laser used to remove a layer of central corneal stroma. Courtesy of Summit Technology, Inc.

Fig. 2.46 Late dislocation of a LASIK flap by self-inflicted injury. Courtesy of C.K. Patel, BSC, FRC Ophth. and Arch. Ophth., Mar. 2001, Vol 119, p. 447. Copyright 2001, Amer. Med. Assoc. All rights reserved.

Excimer laser beam

Fig. 2.48 PRK laser ablation of Bowman’s membrane and stroma after mechanical debridement of epithelium.

As a consequence there will be more stroma remaining to contribute to ocular rigidity. However, the epithelial flap heals more slowly than the LASIK flap so that vision takes longer to recover. It heals faster and has less pain than PRK where there is a total corneal abrasion after surgery.

All three laser techniques usually yield good results, but may be complicated by infection, glare, halos, dry eye, overor under-correction of refractive error, and unknown long-term effects. Although LASIK is still by far the most popular technique because of its quick healing, there is a movement toward epiLASIK because it minimizes dry eye and stromal flap complications.

Intac is a less used technique for correcting small amounts of myopia and keratoconus. It involves the placement of a plastic ring in the peripheral cornea (Fig. 2.51). Proponents argue that unlike LASIK, it is safer because it doesn’t involve surgery on the central visual axis.

Large amounts of hyperopia (over 4 diopters) and myopia (over 8 diopters) are difficult to correct with reshaping the cornea because it becomes too thin and unstable. Intraocular lenses can be inserted inside the eye (Fig. 2.52) to correct these larger refractive errors, but have all the inherent risks associated with intraocular surgery. There has to be a safe space between the cornea and the patient's natural lens or corneal edema and/or cataract could occur.

Fig. 2.49 Sculpted cornea after PRK or epi-LASIK.

Fig. 2.50 Epi-LASIK. Creation of epithelial flap with blade followed by laser ablation of stroma.

Fig. 2.51 Intac ring. Courtesy of Dimitri Azar, MD.

Fig. 2.52 Phakic 6H2 anterior chamber intraocular lens to correct refractive errors. Courtesy of Oii Inc.