However, the instances of that ability are rare.The name of the disorder emphasizes problems with attachment but the criteria include symptoms such as failure to thrive, a lack of developmentally appropriate social responsiveness, apathy, and onset before 8 months. Assessment tools
There is as yet no universally accepted diagnostic protocol for reactive attachment disorder. Often a range of measures is used in research and diagnosis. Recognized assessment methods of attachment styles, difficulties or disorders include the Strange Situation Procedure (devised by developmental psychologist Mary Ainsworth), the separation and reunion procedure and the Preschool Assessment of Attachment, the Observational Record of the Caregiving Environment, the Attachment Q-sort and a variety of narrative techniques using stem stories, puppets or pictures. For older children, actual interviews such as the Child Attachment Interview and the Autobiographical Emotional Events Dialogue can be used. Caregivers may also be assessed using procedures such as the Working Model of the Child Interview.More recent research also uses the Disturbances of Attachment Interview (DAI) developed by Smyke and Zeanah (1999). The DAI is a semi-structured interview designed to be administered by clinicians to caregivers. It covers 12 items, namely "having a discriminated, preferred adult", "seeking comfort when distressed", "responding to comfort when offered", "social and emotional reciprocity", "emotional regulation", "checking back after venturing away from the care giver", "reticence with unfamiliar adults", "willingness to go off with relative strangers", "self-endangering behavior", "excessive clinging", "vigilance/hypercompliance" and "role reversal".
From outer to innermost, the four layers of the sclera are:

episclera
stroma
lamina fusca
endotheliumThe sclera is opaque due to the irregularity of the Type I  collagen fibers, as opposed to the near-uniform thickness and parallel arrangement of the corneal collagen. Moreover, the cornea bears more mucopolysaccharide (a carbohydrate that has among its repeating units a nitrogenous sugar, hexosamine) to embed the fibrils. The cornea, unlike the sclera, has five layers. The middle, thickest layer is also called the stroma. The sclera, like the cornea, contains a basal endothelium, above which there is the lamina fusca, containing a high count of pigment cells.Sometimes, very small gray-blue spots can appear on the sclera, a harmless condition called scleral melanocytosis. Function
Human eyes are somewhat distinctive in the animal kingdom in that the sclera is very plainly visible whenever the eye is open. This is not just due to the white color of the human sclera, which many other species share, but also to the fact that the human iris is relatively small and comprises a significantly smaller portion of the exposed eye surface compared to other animals. It is theorized that this adaptation evolved because of our social nature as the eye became a useful communication tool in addition to a sensory organ. It is believed that the conspicuous sclera of the human eye makes it easier for one individual to identify where another individual is looking, increasing the efficacy of this particular form of nonverbal communication, called cooperative eye hypothesis.